WO2017164375A1 - 磁性材料とその製造方法 - Google Patents
磁性材料とその製造方法 Download PDFInfo
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Definitions
- the present invention relates to a soft magnetic material or a semi-hard magnetic material and a manufacturing method thereof.
- the former metallic magnetic materials include silicon steel (Fe—Si), which is a Si-containing crystalline material, which is a typical example of electromagnetic steel, and Sendust (Fe—Al—Si), which is an intermetallic compound containing Al. )
- Electromagnetic soft iron (Fe) which is pure iron with a low carbon content and low impurity content with a C content of 0.3% by mass or less, permalloy mainly composed of Fe-Ni, and Metograss (Fe-Si-B)
- nano means a size of 1 nm or more and less than 1 ⁇ m.
- the nanocrystalline soft magnetic material is a heterogeneous system including a crystalline phase, an amorphous phase, a Cu-enriched phase, and the like, and magnetization reversal is considered to be mainly due to magnetization rotation.
- oxide-based magnetic material examples include ferrite-based magnetic materials such as Mn—Zn ferrite and Ni—Zn ferrite.
- Silicon steel is the most widely used soft magnetic material to date in high performance soft magnetic material applications. It has a high magnetization and low coercivity with a saturation magnetization of 1.6 to 2.0 T and a coercive force of 3 to 130 A / m. Magnetic material with magnetic force. This material is obtained by adding up to about 4% by mass of Si to Fe, reducing the coercive force by reducing the magnetocrystalline anisotropy and the saturation magnetostriction constant without significantly impairing the large magnetization of Fe. is there. In order to improve the performance of this material, by appropriately combining hot and cold rolling and annealing of appropriately controlled materials, the foreign matter that obstructs the domain wall movement is removed while increasing the crystal grain size. It is necessary to.
- this material is a rolled material, it has a thickness of generally less than 0.5 mm, and since it is a homogeneous metal material, it has a low electrical resistance of approximately 0.5 ⁇ m.
- each silicon steel sheet surface is covered with an insulating film, It is punched with a mold and applied to large-scale equipment with a thickness while suppressing eddy current loss that occurs in high rotation applications such as for next-generation automobiles by lamination and welding. Therefore, process costs for punching and stacking and deterioration of magnetic characteristics are serious problems.
- Nanocrystalline soft magnetic materials such as Fe-Cu-Nb-Si-B are obtained by heat-treating an alloy that has become amorphous by quenching once at a temperature higher than the crystallization temperature. It is a soft magnetic material having a nanocrystalline structure with a random orientation having an amorphous grain boundary phase precipitated in an amorphous state.
- the coercive force of this material is as low as 0.6 to 6 A / m and the saturation magnetization is 1.2 to 1.7 T, which is higher than that of an amorphous material.
- This material is a relatively new material developed in 1988, and the principle of its magnetic properties is that the crystal grain size is made smaller than the ferromagnetic exchange length (also called exchange coupling length) and the randomly oriented main phase.
- ferromagnetic phases are ferromagnetically coupled through the amorphous interfacial phase, so that the magnetocrystalline anisotropy is averaged and a low coercive force is obtained.
- This mechanism is called a random magnetic anisotropy model or a random anisotropy model (see, for example, Non-Patent Document 1).
- the product thickness is about 0.02 to 0.025 mm, and it is insulated, cut, aligned, laminated,
- the welding and annealing processes are more complicated than silicon steel and have problems such as workability and thermal stability.
- the electrical resistivity is as small as 1.2 ⁇ m, and the problem of eddy current loss similar to other rolled materials and ribbons has been pointed out.
- ferrite-based oxide materials have the least eddy current loss problem in high-speed applications.
- the electrical resistivity of this material is 10 6 to 10 12 ⁇ m, and it can be easily bulked to 0.5 mm or more by sintering and formed into a molded body without eddy current loss. It is a suitable material.
- it since it is an oxide, it does not rust and has excellent magnetic property stability.
- the coercive force of this material is relatively high at 2 to 160 A / m, and the saturation magnetization is particularly small at 0.3 to 0.5 T, so that it is not suitable for, for example, a high-performance high-rotation motor for next-generation automobiles.
- metallic soft magnetic materials such as silicon steel are rolled materials and are used because they are thin and have a low thickness.
- they have low electrical resistance and cause eddy current loss for high-speed, high-performance motors.
- oxide-based soft magnetic materials such as ferrite have high electrical resistance and no problem with eddy current loss, but their saturation magnetization is as low as 0.5T or less, making them suitable for next-generation automotive high-performance motors. Absent.
- an oxide-based soft magnetic material is superior in stability and superior to a metal-based soft magnetic material.
- the upper limit of the thickness that can be used for the motor is estimated below.
- the skin depth s at which the intensity is 1 / e is as shown in the following relational expression (1).
- the skin depth is 0.14 mm when the number of poles of the next-generation automobile motor is 8 poles, the highest speed is 10,000 rpm, that is, f is 667 [Hz].
- the condition that does not significantly reduce the effective magnetization of the material is to make the particle size of the material not more than twice the skin depth. Therefore, for example, when a silicon steel plate is used at 667 Hz, the plate thickness must be about 0.3 mm. However, since the thickness of the next-generation automobile motor is, for example, 9 cm, a thin silicon such as 0.3 mm thickness is required. When steel plates are used, about 300 sheets must be insulated and laminated. The process of insulating, punching, aligning, welding, and annealing such a thin plate is complicated and expensive. In order to increase the thickness of the laminated plates as much as possible, it is necessary to increase the electrical resistivity of the material.
- soft magnetic materials that have higher electrical resistance than metallic silicon steel plates, saturation magnetization is higher than ferrite magnetic materials, and have physical properties to compensate for both problems, that is, high saturation magnetization of metal magnetic materials. And the appearance of soft magnetic materials that combine the advantages of both oxide-based magnetic materials with low eddy current loss, no lamination and complicated processes, and high oxidation resistance and good magnetic stability. It was rare.
- An object of the present invention is to provide a new magnetic material with high magnetic stability and a method for manufacturing the same, which can solve the above-mentioned problems such as eddy current loss because the electric resistivity is higher than that of a magnetic material. .
- an object is to provide a powder sintered magnetic material that can be reduced.
- the inventors of the present invention simultaneously satisfy the two points of contradictory characteristics, high magnetization, and high electrical resistivity that can solve the above-mentioned problem of eddy current loss in a conventional magnetic material, and also a lamination process and the like.
- the magnetic materials with excellent electromagnetic characteristics that combine the advantages of both metal-based magnetic materials and oxide-based magnetic materials, and magnetic materials with stable magnetic characteristics even in the air, are intensively studied. did.
- titanium ferrite in the present invention, "a completely different from a conventional crystalline or amorphous material, or a nanocrystalline soft magnetic material in which homogeneous nanocrystals are deposited in an amorphous state" (Also referred to as “Ti-ferrite”), by disproportionation during the reduction reaction, a magnetic material containing two or more kinds of crystal phases, or one crystal phase and an amorphous phase, was found, its composition and crystal structure, powder
- the present invention has been achieved by controlling the body particle diameter and crystal grain diameter, establishing a method for producing the magnetic material, and establishing a method for solidifying the magnetic material without stacking.
- the saturation magnetization is 0.3 T of ferrite, that is, the magnetic material of the present invention has a density close to that of a metal system, so that it is typically 30 emu / g as represented by the density of Fe.
- the saturation magnetization is preferably 100 emu / g or more, more preferably 150 emu / g or more when limited to soft magnetic materials.
- an electrical resistivity of 1.5 ⁇ m or more is required.
- the present invention is as follows.
- the first phase having a bcc structure crystal containing Fe and Ti, and the phase containing Ti, the Ti content when the sum of Fe and Ti contained in the phase is 100 atomic%
- a soft magnetic or semi-hard magnetic material comprising a second phase that is higher than the Ti content when the total amount of Fe and Ti contained in the first phase is 100 atomic%.
- the first phase has a composition represented by a composition formula of Fe 100-x Ti x (x is an atomic percentage of 0.001 ⁇ x ⁇ 33), according to (1) or (2) above Magnetic material.
- the first phase is Fe 100-x (Ti 100-y M y ) x / 100 (x and y are atomic percentages 0.001 ⁇ x ⁇ 33, 0.001 ⁇ y ⁇ 50, M is Zr, (1) to (3) having a composition represented by a composition formula of Hf, Mn, V, Nb, Ta, Cr, Mo, W, Ni, Co, Cu, Zn, and Si). ) Magnetic material according to any one of (5) A phase having a bcc structure crystal including Fe and Ti is included as the second phase, and the Ti content when the total of Fe and Ti included in the phase is 100 atomic% is included in the first phase.
- the above (1) which is an amount that is 2 times or more and 10 5 times or less and / or 2 atoms% or more and 100 atoms% or less with respect to the Ti content when the total of Fe and Ti is 100 atomic%.
- (6) The magnetic material according to any one of (1) to (5), wherein the second phase includes at least one of a Ti-ferrite phase and a wustite phase.
- At least the first phase has a bcc phase having a composition represented by a composition formula of Fe 100-x Ti x (where x is an atomic percentage of 0.001 ⁇ x ⁇ 1), and a crystallite size of the bcc phase
- a magnetic material in the form of powder which has an average powder particle size of 10 nm to 5 mm in the case of a soft magnetic material, and 10 nm to 10 ⁇ m in the case of a semi-hard magnetic material
- the magnetic material according to any one of the above (1) to (11) which has the following average powder particle size.
- a magnetic material having a high saturation magnetization and a small eddy current loss in particular, a soft magnetic material suitably used for a high-rotation motor, and various soft magnetic materials and semi-hard magnetic materials having high oxidation resistance.
- a soft magnetic material suitably used for a high-rotation motor, and various soft magnetic materials and semi-hard magnetic materials having high oxidation resistance.
- it can be used in the form of a powder material such as ferrite, it can be easily bulked by sintering or the like. Therefore, such as lamination by using an existing thin metal-based soft magnetic material. Problems such as complicated processes and resulting high costs can also be solved.
- X-ray diffraction pattern The figure which shows the reduction temperature dependence of saturation magnetization (emu / g) and coercive force (kA / m) in a Fe-Ti magnetic material (Examples 1-11).
- the “magnetic material” referred to in the present invention means a magnetic material called “soft magnetism” (ie, “soft magnetic material”) and a magnetic material called “semi-hard magnetism” (ie, “semi-hard magnetic material”). )).
- the “soft magnetic material” means a magnetic material having a coercive force of 800 A / m ( ⁇ 10 Oe) or less
- the “semi-hard magnetic material” means a coercive force exceeding 800 A / m and 40 kA / m ( ⁇ 500 Oe) or less magnetic material.
- a semi-hard magnetic material is required to have an appropriate coercive force according to the application and to have high saturation magnetization and residual magnetic flux density.
- a soft magnetic or semi-hard magnetic material for high frequency generates a large eddy current, so that the material has a high electrical resistivity, a small powder particle diameter, or a thickness of a thin plate or ribbon. It becomes important.
- ferromagnetic coupling refers to a state in which adjacent spins in a magnetic material are strongly linked by exchange interaction.
- two adjacent crystal grains and / or amorphous grains are used.
- the state in which the inner spin is strongly linked by exchange interaction across the crystal boundary. Since the exchange interaction is an interaction that only reaches the distance based on the short range order of the material, if there is a nonmagnetic phase at the crystal boundary, the exchange interaction does not work on the spins on both sides, and the crystal grains on both sides There is no ferromagnetic coupling between (and / or amorphous grains).
- the term “crystal grains” includes amorphous grains depending on circumstances. The characteristics of the magnetic curve of a material in which ferromagnetic coupling is made between different types of adjacent crystal grains having different magnetic characteristics will be described later.
- disproportionation means that two or more kinds of phases or crystal structures having different crystal structures are produced from a phase having a homogeneous composition by a chemical reaction. This results from the reduction reaction involving a reducing substance such as hydrogen in the phase. During this “disproportionation” reaction, water is often produced as a by-product.
- the meaning of “including Fe and Ti” means that the magnetic material of the present invention always contains Fe and Ti as its components, and optionally the Ti is another atom (specifically In particular, Zr, Hf, Mn, V, Nb, Ta, Cr, Mo, W, Ni, Co, Cu, Zn, or Si) may be replaced by a certain amount, and oxygen (O component) may be contained, and when O component or iron oxyoxide is present as a secondary phase, H may be mainly contained as an OH group, other inevitable impurities, derived from raw materials An alkali metal such as K or Cl may be contained. Alkali metals such as K are suitable components in that they may have an effect of promoting a reduction reaction.
- Magnetic powder generally refers to powder having magnetism, but in the present application, the powder of the magnetic material of the present invention is referred to as “magnetic material powder”. Therefore, “magnetic material powder” is included in “magnetic powder”.
- the present invention relates to a magnetic material including a phase containing titanium in an ⁇ -Fe phase (first phase) and a Ti-enriched phase (second phase) having a Ti content higher than that phase.
- the best form is a “powder” in which both phases are mixed and bonded at the nano level.
- These magnetic material powders are directly compressed or sintered and used in various devices. Further, depending on the application, it can be molded by blending an organic compound such as a resin, an inorganic compound such as glass or ceramic, or a composite material thereof.
- the composition of the first phase containing Fe and Ti, and the composition of the second phase enriched with Ti, the crystal structure and morphology, the crystal grain size and the powder grain size, and the production methods thereof Explains the method for producing nano-composite oxide powder that is the precursor of the magnetic material of the invention, the method for reducing the powder, the method for solidifying the reduced powder, and the method for annealing in each step of these production methods To do.
- the first phase is a crystal having a crystal structure of a cubic crystal (space group Im3m) having a bcc structure containing Fe and Ti.
- the Ti content of this phase is preferably 0.001 atomic percent or more and 33 atomic percent or less, assuming that the total sum (total content) of Fe and Ti contained in the phase is 100 atomic percent. That is, the composition of the first phase is expressed as Fe 100-x Ti x (x is 0.001 ⁇ x ⁇ 33 in atomic percentage) using the composition formula.
- the Ti content or the Fe content is the sum of Fe and Ti contained in each phase (in this application, the total content may be referred to as described above, or the total amount as described above).
- the value of the atomic ratio of Ti or Fe to In the present invention this may be expressed as an atomic percentage, where the total (total content) of Fe and Ti contained in the phase is 100 atomic%.
- the Ti content be 33 atomic% or less in order to suppress a decrease in magnetization. Moreover, it is more preferable that the Ti content is 20 atomic% or less because magnetization exceeding 1T can be realized depending on the manufacturing method and conditions. Furthermore, if it is 10 atomic% or less, a magnetic material having a saturation magnetization exceeding 1.6 T can be produced. Moreover, it is preferable to make it 0.001 atomic% or more from the point which enables adjustment of the magnetic characteristic in a soft magnetic area
- the particularly preferable range of Ti content is 0.01 atomic% or more and 10 atomic% or less, and in this region, a semi-hard magnetic material can be prepared from soft magnetic depending on manufacturing conditions, and more preferable electromagnetic characteristics can be obtained. It becomes the magnetic material which it has.
- the Ti content of the first phase is preferably 5 atomic% or less. Since the first phase of the Fe—Ti composition having the bcc structure has the same crystal symmetry as the ⁇ phase that is the room temperature phase of Fe, this is also referred to as an ⁇ - (Fe, Ti) phase in the present application.
- the Ti component content of the first phase of the present invention is 100% atomic%, 0.001 atomic% or more and less than 50 atomic% of the Ti is Zr, Hf, Mn, V, Nb, Ta, Cr, Mo. , W, Ni, Cu, Co, Zn, and Si can be substituted (in this application, these substitution elements are also referred to as “M components”). Therefore, in the present invention, when Ti contained in the first phase has a composition substituted by M component, the combination of Ti and M component in the composition corresponds to the above-mentioned “Ti component”
- the Ti component content (specifically, the sum of the Ti content and the M component content in the composition) is 100 atomic%.
- co-addition of many element species to the soft magnetic material of the present invention has an effect of reducing the coercive force.
- Mn, V, Cr, Mo is contained in an atomic percentage of 1 atomic% or more when the Ti component content of the first phase is 100 atomic%, it does not greatly depend on the cooling rate in the reduction treatment or annealing treatment, This is effective in that the nanocrystallites of the present invention can be easily produced.
- Zr, Hf, Mn, Cr, V, Ni, Co, and Si are preferable as components that coexist in the soft magnetic material of the present invention because they reduce the anisotropic magnetic field.
- Ni is added in an amount of approximately 5 atomic% or less and Co is added in an amount of approximately less than 50 atomic% because saturation magnetization is improved.
- Zr, Hf, Mn, V, Nb, Ta, Cr, Mo, W are atomic percentages when the Ti component content of the first phase is 100 atomic%, and even in addition of 1 atomic% or less, Mn, Ni, Co, Cu, and Zn are preferable in order to suppress “inappropriate grain growth” and improve oxidation resistance and formability.
- Mn is co-added to Ti, not only the above effects but also a unique synergistic effect that achieves both low coercivity and high magnetization is exhibited.
- a preferable substitution amount of Mn for Ti is 0.01 atomic% or more and 50 atomic% or less.
- a more preferable amount of M component is 0.1 atomic percent or more and 30 atomic percent or less in terms of substitution amount with respect to Ti, regardless of the element type. Therefore, for example, when the first phase has a composition formula of Fe 100-x Ti x (x is 0.001 ⁇ x ⁇ 33 in terms of atomic percentage), the Ti component is 0.01 atomic% or more depending on the M component.
- the composition formula is Fe 100-x (Ti 100-y M y ) x / 100 (x and y are atomic percentages 0.001 ⁇ x ⁇ 33, 0.001 ⁇ y ⁇ 50, M is represented by any one or more of Zr, Hf, Mn, V, Nb, Ta, Cr, Mo, W, Ni, Co, Cu, Zn, and Si).
- “inappropriate grain growth” means that the nano-fine structure of the magnetic material of the present invention collapses and crystals grow with a homogeneous crystal structure.
- “grain growth” suitable in the present invention is a disproportionation reaction after the powder particle diameter grows large while maintaining the nano-structure that is the feature of the present invention, or after the powder particle diameter grows large. , Either the nanostructure appears in the crystal due to phase separation or the like, or both.
- the term “grain growth” in the present invention refers to grain growth that is not inappropriate, and generally refers to grain growth that can be said to be appropriate. Note that, regardless of whether the grain growth is inappropriate or appropriate, the surface area of the magnetic material per unit mass or per unit volume is reduced, so that the oxidation resistance generally tends to be improved.
- any M component addition of 0.001 atomic% or more is preferable in terms of the atomic percentage when the Ti component content in the first phase is 100 atomic%, and addition of 50 atomic% or less Is preferable from the viewpoint of preventing inhibition of various effects of the Ti component in the magnetic material of the present invention.
- Ti component when expressed as “Ti component” or in a formula such as “ ⁇ - (Fe, Ti)” phase or in the context of discussing magnetic material composition, it is expressed as “Ti” or “titanium”. In this case, not only the case of Ti alone but also a composition in which 0.001 atomic% or more and less than 50 atomic% of the Ti content is replaced with an M component is included.
- alkali metals such as H, C, Al, Si, S, N, Li, K, and Na
- alkaline earths such as Mg, Ca, and Sr
- rare earths such as Mg, Ca, and Sr
- Inevitable impurities such as halogen such as Cl, F, Br, and I
- the content thereof is 5 atomic% or less, preferably 2 atomic% or less, more preferably 0.1 atomic% or less, particularly preferably 0, based on the whole (that is, the total of Fe and Ti contained in the first phase). 0.001 atomic% or less.
- the ⁇ -Fe phase not containing Ti is not included in the first phase or the second phase.
- the ⁇ -Fe phase not containing Ti is expected to have saturation magnetization similar to electromagnetic soft iron, but the ⁇ -Fe phase is a nano-region powder, This is because the material has little influence on electrical resistivity, poor oxidation resistance, and inferior machinability.
- the ⁇ -Fe phase not containing Ti may exist as a separate phase as long as the object of the present invention is not impaired.
- the present invention is a soft magnetic material
- the volume fraction of the ⁇ -Fe phase is preferably less than 50% by volume with respect to the entire magnetic material of the present invention.
- the volume fraction referred to here is the ratio of the volume occupied by the target component to the total volume of the magnetic material.
- the second phase is a phase in which the content of Ti with respect to the sum of Fe and Ti contained in the phase is larger than the content of Ti with respect to the sum of Fe and Ti contained in the first phase.
- the second phase is a phase in which the atomic percentage of Ti with respect to the sum of Fe and Ti contained in the phase is larger than the atomic percentage of Ti with respect to the sum of Fe and Ti contained in the first phase. is there.
- cubic ⁇ - (Fe 1-y Ti y ) phase space group Im3m, the same crystal phase as the first phase, but a phase having a higher Ti content than the first phase
- TiFe phase space group Pm3m
- ⁇ - (Fe, Ti ) phase space group Fm3m
- wustite phase typically composition (Fe 1-z Ti z) a O phase, a is usually 0.85 1
- this phase may be simply referred to as (Ti, Fe) O phase or (Fe, Ti) O phase)
- ⁇ -Ti phase (Fe may be up to 23 atomic% and O may be included up to 8 atomic%) Etc.
- Laves phase is hexagonal (typically composition TiFe 2 phase), such as alpha-Ti phase (sometimes contain O up to 24 atomic%)
- ilmenite phase is rhombohedral (typically composition TiFeO 3 phase)
- titanohematite phase typically composition is Fe 2 -u Ti u O 3 phase
- Orthodoxic pseudobroccite phase Ferous pseudobrookite phase, typical composition is Fe 1 + v Ti 2-v O 5 phase
- brookite-type TiO 2 phase Ti-Fe amorphous phase
- the amorphous phase, the eutectic point composition phase, and the eutectoid point composition phase (also referred to as “amorphous phase etc.” in the present application) vary depending on the Ti content and the reducing conditions, but when an amorphous phase exists.
- the existing nanocrystal-amorphous phase-separated material is isolated in the form of islands and is separated from the first phase without forming a fine structure that floats in the amorphous sea.
- the content of the amorphous phase or the like is between 0.001 and 10% by volume, and not more than this is preferable from the viewpoint of suppressing the decrease in magnetization, and more preferable for obtaining a highly magnetized magnetic material. Is 5% by volume or less.
- An amorphous phase or the like may be intentionally included in order to control the disproportionation reaction itself, but in this case, it is preferably 0.001% by volume from the viewpoint of exhibiting the reaction control effect.
- the second phase described above is inferior to the saturation magnetization as compared with the first phase, but due to the coexistence of these phases, the electrical resistivity greatly increases. Furthermore, in the present invention, when a semi-hard magnetic material is formed, the coercive force is improved. On the contrary, in the present invention, when a soft magnetic material is formed, a small coercive force can be realized by ferromagnetic coupling with a phase crystal structure, composition, microstructure, interface structure, and the like. Further, in the second phase, similarly to the first phase, less than 50 atomic% of the Ti content (however, the content of the Ti component in the second phase is set to 100 atomic%) can be replaced with the M component.
- the “Ti component” of the second phase also has a composition in which Ti contained in the second phase is replaced by the M component, like the “Ti component” of the first phase. Means a combination of Ti and M components in the composition.
- the electrical resistivity, oxidation resistance, sinterability, and electromagnetic characteristics of the semi-hard magnetic material of the present invention may be improved.
- a phase that does not contain a Ti component, such as a compound phase of the M component or an Fe compound phase, and a phase in which the content of the M component is greater than or equal to the content of the Ti element is referred to as a “sub-phase”.
- Phases other than the first phase and the second phase ie, a wustite phase not containing Ti, a magnetite phase (Fe 3 O 4 ), a maghemite phase ( ⁇ -Fe 2 O 3 ), and a hematite phase ( ⁇ -Fe 2 O 3 ) , ⁇ -Fe phase, ⁇ -Fe phase and other secondary phases, iron oxide oxyoxide phases such as goethite, acagenite, lipidocrosite, ferrooxyhite, ferrihydrite, green last, water with or without Ti content, water Hydroxides such as potassium oxide and sodium hydroxide, chlorides such as potassium chloride and sodium chloride, fluoride, carbide, nitride, hydride, sulfide, nitrate, carbonate, sulfate, silicate, phosphoric acid Salts and the like may also be included, but these volumes are used for the first phase in order for the magnetic material of the present invention to have high saturation magnetization and
- the content of the M component in all phases including the first phase, the second phase, and the subphase must not exceed the content of Ti contained in the first phase and the second phase with respect to the above all phases.
- the M component is contained in excess of the Ti content, effects on the electromagnetic characteristics peculiar to Ti, such as reduction of magnetocrystalline anisotropy and improvement of electrical resistivity, and further improvement of oxidation resistance due to passivation of the powder surface, etc. This is because the unique features are lost.
- the Ti content of the first phase and / or the second phase refers to an amount including such an M component.
- the second phase may have the same crystal structure as the first phase, but it is important that the composition is sufficiently different from each other, for example, the second phase relative to the sum of Fe and Ti in the second phase.
- the Ti content of the first phase is larger than the Ti content of the first phase relative to the total of Fe and Ti in the first phase, and the difference is more than twice and / or Fe and Ti in the second phase. It is preferable that the Ti content of the second phase with respect to the sum of is 2 atomic% or more.
- the Ti component content of the second phase itself does not exceed 100 atomic%, and when the lower limit value of the Ti content of the first phase is 0.001 atomic%, the Ti content of the second phase is the first phase.
- the Ti content of the second phase is preferably 90 atomic percent or less of the Ti content of the first phase.
- the Ti content of the second phase is 9 ⁇ 10% of the Ti content of the first phase. This is because the thermal stability of the entire magnetic material of the present invention may be deteriorated if the ratio exceeds 4 .
- the Ti content of the second phase is “twice or more” of the first phase
- the Ti content of each phase is obtained with one significant digit, and then the Ti content of the second phase. It means that the content is at least twice the Ti content of the first phase.
- the present invention aims to reduce the coercive force using the above-mentioned random magnetic anisotropy model or the fluctuation of magnetic anisotropy according to the model, and is a first phase that is crystallographically independent. And the second phase are magnetically coupled by exchange coupling at the nano level, or the Ti content in the bcc phase including the first phase and the second phase has a spatial change at the nano scale. (This is sometimes referred to as “concentration fluctuation” in the present invention). However, if the Ti composition ratio of the two phases is too close, the crystal orientation of the crystal phase may be aligned in the same direction, and the magnitude of the magnetocrystalline anisotropy constant is often the second phase.
- the preferable Ti content of the second phase is 2 atomic% or more, more preferably 5 atomic% or more, based on the total of Fe and Ti in the second phase. In the latter case, the two-phase magnetocrystalline anisotropy is reduced to less than half compared to the case where Ti is not included. If the Ti content is 8 atomic% or more, the magnetocrystalline anisotropy is extremely small, which is more preferable.
- phase (first phase) in which the Ti content is lower than the Ti content of the entire magnetic material of the present invention the phase (second phase) in which the Ti content is higher than that of the magnetic material of the present invention is also the same magnetic material Will exist within. Therefore, if they are ferromagnetically coupled to achieve isotropic properties, the magnetic material of the present invention, specifically, the soft magnetic material is obtained, and the coercive force is appropriately interposed through the interface of the first phase. If it has a function of increasing the electric resistance as a range, the magnetic material of the present invention, specifically, a semi-hard magnetic material can be obtained.
- the magnetic material of the present invention whose coercive force is reduced by such a mechanism generally has a Ti content of 10 atomic% or less with respect to the total of Ti and Fe in the magnetic material.
- the above is a magnetic composition of the present invention that is not found in many existing soft magnetic materials such as magnetic steel sheets and sendust that are designed so that the heterogeneous phase is thoroughly removed and the domain wall motion is not hindered as a highly homogeneous composition. This is one of the characteristics of the material, and can be said to be a characteristic common to magnetic materials in which magnetization reversal occurs due to rotation of magnetization.
- the state in which only the first phase and only the second phase are magnetically coupled by exchange coupling at the nano level may be included. Even in this case, the crystal axis orientations of adjacent nanocrystals are not aligned. It is important that there is a spatial distribution of Ti content in the nanoscale in the bcc phase including the first and second phases, isotropic.
- a magnetic material composed only of the first phase microcrystals and a magnetic material composed only of the second phase microcrystals are not achieved, and even when such a structure is included, In the present invention, the first phase and the second phase always exist in the magnetic material.
- the nanocrystal generation itself is a ferrite powder containing titanium, which is used to produce the magnetic material of the present invention, and has a nanoscale size (in this application, “titanium ferrite”). This is because it is greatly involved in the disproportionation reaction in each step of the reduction process starting with the reduction of “nano powder” or “Ti-ferrite nano powder”.
- a ferrite powder having a nanoscale size is also referred to as “ferrite nanopowder”, and the nanoscale refers to a scale of 1 nm to less than 1 ⁇ m unless otherwise specified.
- the first phase is an ⁇ - (Fe, Ti) phase, and mainly ensures high saturation magnetization.
- the second phase is a phase in which the Ti content relative to the sum of Fe and Ti contained in the phase is larger than the Ti content relative to the sum of Fe and Ti contained in the first phase.
- the second phase may be an ⁇ - (Fe, Ti) phase that is higher than the Ti content of the entire magnetic material, or may be another crystalline phase, an amorphous phase, or a mixed phase thereof.
- the soft magnetic material of the present invention has an effect of keeping the coercive force low, and even if a semi-hard magnetic material is included, it has an effect of imparting oxidation resistance and improving electric resistivity. Therefore, since the second phase is a total of the phases having these effects, the magnetic material of the present invention can be used if the presence of any of the phases exemplified above having a higher Ti content than the first phase can be shown. I understand that. If such a second phase does not exist and is composed only of the first phase, any one of magnetic properties such as coercive force, oxidation resistance and electrical conductivity is inferior, or the workability is further reduced. Therefore, the magnetic material is inevitably complicated in the molding process.
- the first phase and Ti composition may change continuously.
- the Ti composition of the first phase and the second phase may be observed as changing continuously.
- the Ti content of the second phase is more than twice the Ti content of the first phase, or the Ti content of the first phase when the Ti content of the second phase is 2 atomic% or more. It is desirable that the Ti content in the second phase is 2 times or more than the Ti content in the first phase and at least 2 atomic%.
- the composition ratio of Fe and Ti is desirably 1: 1 or less.
- the Ti content with respect to the total amount of Fe and Ti is 0.01 atomic% or more and 50 atoms. % Or less is desirable.
- the content of Ti combined with the first phase and the second phase is preferably 50 atomic% or less in order to avoid a decrease in saturation magnetization, and being 0.01 atomic% or more means oxidation resistance, etc. This is preferable in order to avoid the effect of adding Ti to the surface and to prevent the coercive force from becoming so high that it does not correspond to the intended application. Furthermore, the content of Ti including the first phase and the second phase, which is preferable from the viewpoint of a good balance between oxidation resistance and magnetic properties, is 0.05 atomic percent or more and 33 atomic percent or less, of which a particularly preferable range is 0.1 atomic% or more and 25 atomic% or less.
- the volume ratio of the first phase and the second phase is arbitrary, but the first phase, the first phase, and the volume of the entire magnetic material of the present invention including the first phase, the second phase, and the subphase
- the total volume of the ⁇ - (Fe, Ti) phase in the second phase is preferably 5% by volume or more. Since the ⁇ - (Fe, Ti) phase bears the main magnetization of the magnetic material of the present invention, it is preferably 5% by volume or more in order to avoid a decrease in magnetization. Furthermore, it is preferably 25% by volume or more, more preferably 50% by volume or more. In order to achieve particularly high magnetization without significantly reducing the electrical resistivity, it is desirable that the total volume of the ⁇ - (Fe, Ti) phase is 75% by volume or more.
- the second phase of the soft magnetic material of the present invention it is preferable that there is a ferromagnetic or antiferromagnetic phase (in this application, weak magnetism is also included therein) because the first phase crystal magnetism This is because there is an effect of reducing anisotropy.
- the Ti content of the second phase relative to the sum of Fe and Ti in the second phase is the same as the Fe and Ti in the first phase. More Ti content than the first phase with respect to the total of, and preferably this Ti content is 0.1 atomic% or more and 20 atomic% or less with respect to the total of Fe and Ti in the second phase, more preferably Has an ⁇ - (Fe, Ti) phase of 2 to 15 atomic%, particularly preferably 5 to 10 atomic%.
- the first phase also has a low coercive force when the Ti content is 5 atomic% or more and 10 atomic% or less with respect to the total of Fe and Ti in the first phase, but the Ti content is large to this extent. Then, saturation magnetization close to 2T cannot be exhibited. Therefore, it is preferable to realize a magnetic material having a large saturation magnetization and a small coercive force by combining the first phase having a Ti content of less than 5 atomic% and the second phase having a Ti content of 5 atomic% or more. .
- the second phase include a Ti-ferrite phase and a wustite phase.
- the former is ferromagnetic and the latter is antiferromagnetic, but both can promote ferromagnetic coupling if they are between the first phase.
- These oxide phases may be nano-sized and have a very fine structure.
- the wustite phase has a thickness of several atomic layers and is finely dispersed in the bcc phase or layered between the bcc microcrystalline phases. Sometimes it exists. When such an oxide layer is present, the crystal orientation of the bcc phase may be uniform in the region of several hundred nm to several tens of ⁇ m.
- the coercive force is lowered by a mechanism slightly different from random anisotropy.
- the mechanism is assumed to be as follows. Disproportionation causes a difference between the Ti content of the first phase relative to the sum of Fe and Ti in the first phase and the Ti content of the second phase relative to the sum of Fe and Ti in the second phase. If there is a fluctuation in the concentration of fine Ti content on the nanoscale, spatial fluctuation of magnetic anisotropy occurs, and when an external magnetic field is applied (as if a resonance phenomenon occurred) It is included in the mechanism of magnetization reversal. The fluctuation of the concentration has the same effect of reducing the coercive force not only when the second phase is an oxide phase but also when it is an ⁇ - (Fe, Ti) phase.
- Patent Document 1 International Publication No. 2009/057742 (hereinafter referred to as “Patent Document 1”), N. Imaoka, Y. Koyama. , T. Nakao, S. Nakaoka, T. Yamaguchi, E. Kakimoto, M. Tada, T. Nakagawa, and M. Abe, J. Appl. Phys., Vol. (Referred to as non-patent document 3)), and in both cases, a ferrite phase exists between the Sm 2 Fe 17 N 3 phases of the hard magnetic material, and these phases are ferromagnetically coupled to constitute an exchange spring magnet. is there.
- the present invention relates to a soft magnetic material or a semi-hard magnetic material, and has a completely different function from the hard magnetic exchange spring magnet.
- the presence of the second phase which is a Ti-ferrite phase or a wustite phase mediates exchange interaction between the first phases, and if such a second phase exists so as to surround the first phase, High electrical resistance and reduced coercivity. Therefore, it is one of the very preferable second phases particularly in the soft magnetic material of the present invention.
- the nonmagnetic TiO 2 phase is present in the second phase because the electrical resistance is particularly improved. Even if it exists between the first phases, ferromagnetic coupling such as Ti-ferrite phase occurs and does not have a direct effect on the magnetic properties. The presence of TiO 2 not only improves electrical resistance and oxidation resistance, but may also have an effect of reducing the coercive force in some cases.
- the volume fraction of the mixed oxide phase is It is preferably 95% by volume or less of the whole material, more preferably 75% by volume or less, and still more preferably 50% by volume or less.
- the Ti-ferrite phase is ferromagnetic, it has a lower magnetization than the ⁇ - (Fe, Ti) phase, and the wustite phase is weak even though it is antiferromagnetic. Magnetization is lower than the phase.
- the TiO 2 phase is nonmagnetic.
- any combination of the above oxide phases exceeds 95 volume% of the entire magnetic material, so that the magnetization of the magnetic material of the present invention becomes extremely low.
- the following is preferable.
- the content of these three oxide phases exceeds 75% by volume, so the magnetization becomes low. In order to avoid this, 75% by volume of the entire magnetic material.
- the TiO 2 phase is the main component, the characteristics of the magnetic material of the present invention having high magnetization are lost when the volume exceeds 50% by volume. It is preferably 50% by volume or less.
- the oxide phase is preferably 25% by volume or less.
- the electrical resistivity increases when a TiO 2 phase or the like is present. Therefore, when the TiO 2 phase or the like is positively contained, the preferable volume fraction is 0.001% by volume or more, and the magnetization is particularly lowered. In the case where TiO 2 or the like is present without being accompanied, in order to effectively improve the electrical resistivity, 0.01% by volume or more is further preferable, and particularly preferably 0.1% by volume or more.
- the oxide phase is TiO 2 or a mixture of Ti-ferrite and wustite
- the preferable volume fraction ranges are the same.
- the second phase include the ⁇ - (Fe, Ti) phase, Ti-ferrite phase, wustite phase, and TiO 2 phase, which have a higher Ti content than the first phase.
- the three phases other than the TiO 2 phase are ferromagnetic or antiferromagnetic. Therefore, if these phases are separated without ferromagnetic coupling, the magnetic curves are additive, so the magnetic curves of these mixed materials are simply the sum of the respective magnetic curves, and the entire magnetic material A smooth step occurs on the magnetic curve.
- a 1/4 major loop (when sweeping from 7.2 MA / m to zero magnetic field) out of the magnetic curve of the entire magnetic material obtained by measuring magnetization in a wide magnetic field range of 0 to 7.2 MA / m of external magnetic field
- a smooth step due to the above-mentioned circumstances or an inflection point based on it is certain on the 1/4 major loop. I can guess.
- these dissimilar magnetic materials are integrated by ferromagnetic coupling, there is no smooth step or inflection point on the major loop in the range of 7.2 MA / m to zero magnetic field, and the monotonous increase. Exhibits a convex magnetic curve.
- the local composition analysis of the metal element of the magnetic material of the present invention is mainly performed by EDX (energy dispersive X-ray spectroscopy), and the composition analysis of the entire magnetic material is performed by XRF (fluorescent X-rays). Elemental analysis method).
- EDX energy dispersive X-ray spectroscopy
- XRF fluorescent X-rays
- Elemental analysis method the Ti content of the first phase and the second phase is measured by an EDX apparatus attached to an SEM (scanning electron microscope), FE-SEM, TEM (transmission electron microscope), etc.
- FE-SEM, etc. attached with FE may be referred to as FE-SEM / EDX).
- the crystal structure of the first phase and the second phase is a fine structure of 300 nm or less, accurate composition analysis cannot be performed by SEM or FE-SEM, but Ti of the magnetic material of the present invention can be used. If only the difference in the Fe component is detected, it can be used as an auxiliary. For example, in order to find a second phase with a Ti content of 5 atomic% or more and less than 300 nm, a certain point in the magnetic material is observed, and its quantitative value is 5 atomic% or more as the Ti content. As a result, a structure having a Ti content of 5 atomic% or more or a part of the structure exists within a range of 300 nm in diameter centering on one point.
- the composition distribution measurement method described above must be selected as appropriate to specify the compositional and structural characteristics of the magnetic material of the present invention, such as the composition of the first phase and the second phase and the crystal grain size.
- the composition of the ⁇ - (Fe, Ti) phase can also be determined by confirming the position of the diffraction peak with an XRD (X-ray diffractometer).
- the diffraction peak of the ⁇ - (Fe, Ti) phase generally tends to shift to a lower angle as the Ti content increases.
- the behavior of the peaks of (110) and (200) is observed,
- composition of the whole magnetic material in the present invention is such that the Fe component is 20 atomic% or more and 99.999 atomic% or less, the Ti component is 0.001 atomic% or more and 50 atomic% or less, and O ( (Oxygen) is preferably in the range of 0 atomic% to 55 atomic% and satisfying these simultaneously. Further, an alkali metal such as K may be contained in an amount of 0.0001 atomic% to 5 atomic%. It is desirable that the subphase including K or the like does not exceed 50% by volume of the whole.
- the range of 55 atomic% or less not only has a low saturation magnetization, but also the first phase and the second phase due to the reduction of the titanium ferrite nanopowder.
- the magnetic material of the present invention does not necessarily contain oxygen, but it is desirable to include even a small amount in order to obtain a magnetic material with remarkably high oxidation resistance and electrical resistivity.
- the surface of the metal powder reduced in the gradual oxidation step described later is passivated, or an oxide layer mainly centered on TiO 2 exists in a part of the crystal grain boundary of the solid magnetic material by the operation.
- composition range of the entire magnetic material of the present invention is as follows: Fe component is 20 atomic% or more and 99.998 atomic% or less, Ti component is 0.001 atomic% or more and 50 atomic% or less, and O is A range of 0.001 atomic% to 55 atomic% is desirable.
- More preferable composition of the magnetic material of the present invention is that Fe component is 50 atomic% or more and 99.98 atomic% or less, Ti component is 0.01 atomic% or more and 49.99 atomic% or less, and O is 0.01 atomic% or more and 49 or less. .99 atomic% or less, and the magnetic material of the present invention in this range has a good balance between saturation magnetization and oxidation resistance.
- the present invention has a composition range in which the Fe component is 66.95 atomic% to 99.9 atomic%, the Ti component is 0.05 atomic% to 33 atomic%, and O is 0.05 atomic% to 33 atomic%.
- the magnetic material of the invention is preferable in that it has excellent electromagnetic characteristics and excellent oxidation resistance.
- the Fe component when the magnetic material of the present invention is particularly excellent in performance with a magnetization of 1 T or more, the Fe component is 79.95 atomic% or more and 99.9 atomic% or less, and the Ti component is 0. It is preferable that the composition range be from 0.05 atomic% to 20 atomic% and O is from 0.05 atomic% to 20 atomic%.
- the semi-hard magnetic material tends to contain more oxygen than the soft magnetic material.
- One of the present inventions is a magnetic material having a coercive force of 800 A / m or less, which is suitable for soft magnetic applications, and a magnetic material having oxidation resistance. This will be described below.
- the “magnetic properties” referred to herein include material magnetization J (T), saturation magnetization J s (T), magnetic flux density (B), residual magnetic flux density B r (T), and exchange stiffness constant A (J / m). , Magnetocrystalline anisotropy magnetic field H a (A / m), magnetocrystalline anisotropy energy E a (J / m 3 ), magnetocrystalline anisotropy constant K 1 (J / m 3 ), coercive force H cB ( A / m), intrinsic coercive force H cJ (A / m), permeability ⁇ 0 , relative permeability ⁇ , complex permeability ⁇ r ⁇ 0 , complex relative permeability ⁇ r , its real term ⁇ ′, imaginary term ⁇ ”And at least one of the absolute values
- the unit of“ magnetic field ”in the present specification uses A / m of SI unit system and Oe of cgs Gauss unit system together.
- the unit of “saturation magnetization” and “residual magnetic flux density” in this specification uses both SI unit system T and cgs Gauss unit system emu / g.
- the saturation magnetization value M s in the SI unit system is 2.16T.
- the coercive force refers to the intrinsic coercive force HcJ .
- oxidation resistance refers to various oxidizing atmospheres such as room temperature in air. This is a change with time in the magnetic characteristics.
- magnetic characteristics and electrical characteristics are also referred to as “electromagnetic characteristics”.
- the magnetization, saturation magnetization, magnetic flux density, residual magnetic flux density, and electrical resistivity are preferably higher, and the saturation magnetization is preferably as high as 0.3 T or 30 emu / g, particularly soft magnetism.
- the saturation magnetization is preferably as high as 0.3 T or 30 emu / g, particularly soft magnetism.
- a height of 100 emu / g or more is desirable, and an electrical resistivity of 1.5 ⁇ m or more is desirable.
- Other magnetic properties of the present invention such as crystal magnetic anisotropy constant, coercive force, magnetic permeability, relative magnetic permeability, etc., are appropriate depending on the application, including whether to use a semi-hard magnetic material or a soft magnetic material. To control.
- permeability, relative permeability not always highly necessary for some applications, if kept low core loss and coercivity sufficiently low, for example, dare relative permeability from 10 0 10 4 out of size
- dare relative permeability from 10 0 10 4 out of size
- One of the features of the present invention is not a magnetization reversal by domain wall movement, but a magnetization reversal mechanism mainly by direct rotation of magnetization, so that coercive force is low and eddy current loss due to domain wall movement is small, and iron loss is kept low.
- the magnetic permeability can be reduced by causing some local magnetic anisotropy at the crystal boundary to suppress the magnetization rotation by the external magnetic field.
- the reason why such a magnetic permeability can be adjusted is that the magnetic material has a large electrical resistivity even if it is sintered as it is, so that the iron loss due to eddy current is small, so that the coercive force is sacrificed a little. This is because the total iron loss can still be kept small even if the hysteresis loss slightly increases by designing the material to suppress the magnetic permeability.
- the soft magnetic material of the present invention exhibits an electric resistivity of 1.5 ⁇ m or more, and a semi-hard magnetic material exhibits a higher electric resistivity.
- the saturation magnetization tends to decrease as the electrical resistivity increases. Therefore, it is necessary to determine the composition of the raw material and the degree of reduction according to the desired electromagnetic characteristics. There is. In particular, less than 1000 ⁇ m is preferable for obtaining the feature that the magnetic material of the present invention has high magnetization. Therefore, a preferable range of electrical resistivity is 1.5 ⁇ m or more and 1000 ⁇ m or less.
- ⁇ Crystal boundary> Whether the magnetic material of the present invention is soft magnetic or semi-hard magnetic depends on the coercive force as described above, and is particularly closely related to its fine structure.
- the ⁇ - (Fe, Ti) phase and Ti-enriched phase may be observed as a continuous phase at first glance, but include many heterogeneous interfaces and grain boundaries, and simple twins such as contact twins and intrusion twins. Twins and repetitive twins including repetitive twins such as crystals, concentrated twins, ring twins, and multiple twins (see, for example, FIG. 1; upper part is first phase, lower part is Ti-enriched phase; first phase)
- the crystal boundary is observed in a group of curved curves), body crystal (see, for example, Fig. 2.
- the first phase and the second phase start from the titanium ferrite nanopowder when the second phase is an ⁇ - (Fe, Ti) phase.
- the ⁇ - (Fe, Ti) phase, the first and second phases has a variety of microstructures such as crystals such as crystals, minerals such as pyrite, meteorite, and rock crystals. It is held in a scale-down form, and contains various phases and nanocrystals with various Ti contents.
- the structure that appears to be a grain boundary or intergrowth also has a difference in the Ti content depending on the observation location, and may be a heterogeneous interface.
- ⁇ Random magnetic anisotropy model and coercivity lowering mechanism peculiar to the present invention In the soft magnetic material of the present invention described by the random anisotropy model, it is important that the following three conditions are satisfied. (1) The crystal grain size of the ⁇ - (Fe, Ti) phase is small, (2) being ferromagnetically coupled by exchange interaction; (3) Random orientation. Regarding (3), particularly in the region where the Ti content of the bcc phase is 10 atomic% or less, it is not always essential, and in this case, the coercive force decrease is caused by a principle different from the random anisotropy model.
- the magnetic anisotropy fluctuation based on the fluctuation of the concentration of the nanoscale Ti content is generated by the interaction of one or more of the first phase, the second phase, the first homology, and the second homology.
- the magnetization reversal is promoted, and the coercive force is reduced.
- the magnetization reversal mechanism based on this mechanism is unique to the present invention and, as far as the present inventors can know, has been found for the first time by the present inventors. In the case of grain growth at the time of reduction, when the particles are not fused so that the ferromagnetic phase is continuous, or when phase separation that causes separation of the particles occurs, the magnetic material of the present invention is retained.
- the first phase and the second phase are bonded together directly or via a metal phase or an inorganic phase. And, it is desirable to make it a state in which the whole is in the form of a lump.
- the exchange interaction is an interaction or force that works within a short-range order of several nanometers.
- the second phase needs to be ferromagnetic or antiferromagnetic in order to transmit the exchange interaction. Even if a part of the first phase and / or the second phase is in the superparamagnetic region, the material itself is ferromagnetic or antiferromagnetic in the bulk state. If there is sufficient exchange coupling, there may be a phase where exchange interaction is transmitted.
- the solidification described above is necessary to obtain a semi-hard magnetic material having a high residual magnetic flux density, although not limited to the above.
- the average crystal grain size of the first phase or the second phase of the soft magnetic material of the present invention, or the average crystal grain size of the entire magnetic material is preferably 10 ⁇ m or less.
- the average crystal grain size of the entire magnetic material is 10 ⁇ m or less.
- either the first phase or the second phase is in the nano region.
- both the first phase and the second phase are ferromagnetic phases, both preferably have an average crystal grain size of 10 ⁇ m or less, and less than 1 ⁇ m realizes low coercivity based on a random magnetic anisotropy model.
- the thickness is preferably 500 nm or less, more preferably 200 nm or less, although it depends on the Ti content, and is particularly preferable because of the remarkable reduction effect of the coercive force due to the mechanism unique to the present invention.
- the case towards K 1 of the first phase is large is large, in particular, the first phase, 10 [mu] m or less, preferably 500nm or less, even more preferably as long as 200nm or less, the coercive force Becomes extremely small and becomes a soft magnetic material suitable for various transformers, motors and the like.
- the second phase When the second phase is not a ferromagnetic phase, the second phase does not participate in the coercive force reduction by the above-described random anisotropy model or the mechanism peculiar to the present invention. It is.
- the first phase in order to express the coercive force contrary to the above, is maintained at an average crystal grain size at the nano level, and an appropriate surface oxide layer is used as the second phase.
- An effective method is to provide the second phase with an average crystal grain size of several nanometers at the grain boundary of the first phase to maintain high magnetization while providing the coercive force of the semi-hard magnetic region and to impart oxidation resistance. It is.
- ⁇ Measurement of crystal grain size> In the measurement of the crystal grain size of the present invention, an image obtained by the SEM method, the TEM method or the metal microscope method is used. Within the observed range, not only the heterogeneous interface and the grain boundaries, but also all the crystal boundaries are observed, and the diameter of the crystal region surrounded by the boundaries is defined as the crystal grain size. If the crystal boundary is difficult to see, it is better to etch the crystal boundary using a wet method using a nital solution or the like, or a dry etching method. In principle, the average crystal grain size is selected from a representative portion and measured in a region containing at least 100 crystal grains.
- the average crystal grain size is obtained by photographing the observation region, defining an appropriate right-angled rectangular region on the photographic plane (enlarged projection surface on the subject photographing surface), and applying the Jeffry method to the inside. When observed with an SEM or metal microscope, the crystal boundary width may be too small to be observed with respect to the resolution. In this case, the measured value of the crystal grain size gives the upper limit of the actual crystal grain size. . Specifically, it is sufficient that the upper limit is a crystal grain size measurement value of 10 ⁇ m.
- the magnetic material falls below 1 nm, which is the lower limit of the crystal grain size, due to phenomena such as no clear diffraction peak on XRD and superparamagnetism confirmed on the magnetic curve. If indicated, the actual crystal grain size must be determined anew by TEM observation. In the present invention, it may be necessary to measure the crystal grain size irrespective of the crystal boundary. That is, when the crystal structure is finely modulated due to fluctuations in the Ti content concentration, the crystal grain size of the magnetic material of the present invention having such a fine structure is modulated by the Ti content. The width is the crystal grain size.
- This crystal grain size is often determined by TEM-EDX analysis or the like, but the size often corresponds to the crystallite size described in the next section.
- phase separation occurs due to the disproportionation reaction, and a composition width is generated in the Ti content of the bcc phase of the first phase and / or the second phase. Since the X-ray diffraction line peak position changes depending on the Ti content, for example, even if the line width of the diffraction line at (200) of the bcc phase is obtained, it does not make much sense to determine the crystallite size. .
- the crystallite refers to a small single crystal at a microscopic level that constitutes a crystal substance, and is smaller than individual crystals (so-called crystal grains) that constitute a polycrystal.
- the deviation of the diffraction line of (200) is about 0.07 ° (Co-K ⁇ line), so it is effective within the range of 1 nm to less than 100 nm. It is significant to measure the crystallite size of a single digit.
- the first phase has the phase (that is, only the first phase has the bcc phase and both the first phase and the second phase have the bcc phase)
- a preferable range of the crystallite size of the bcc phase is 1 nm or more and less than 100 nm. If it is less than 1 nm, it becomes superparamagnetic at room temperature, and the magnetization and permeability may become extremely small.
- the coercive force enters the soft magnetic region and becomes extremely small, which is preferable because it becomes a soft magnetic material suitable for various transformers, motors and the like.
- the thickness of 50 nm or less is a very preferable range because it is a region having a low Ti content, so that not only high magnetization exceeding 2T can be obtained, but also low coercive force can be achieved at the same time.
- the size of the powder of the soft magnetic material of the present invention is preferably 10 nm or more and 5 mm or less.
- the coercive force is not sufficiently reduced.
- the thickness exceeds 5 mm, a large strain is applied during sintering, and the coercive force is increased and warped without annealing after solidification. More preferably, they are 100 nm or more and 1 mm or less, Especially preferably, they are 0.5 micrometer or more and 500 micrometers or less. If the average powder particle size is within this region, a soft magnetic material having a low coercive force is obtained.
- the particle size distribution is sufficiently wide within each average powder particle size range defined above, high filling can be easily achieved with a relatively small pressure, and the magnetization per volume of the solidified molded body increases. preferable. If the particle size of the powder is too large, the domain wall movement may be excited. In the process of producing the soft magnetic material of the present invention, the domain wall movement is hindered by the heterogeneous phase formed by the disproportionation reaction. The magnetic force may increase. Therefore, when the soft magnetic material of the present invention is molded, it may be better that the surface of the magnetic material powder of the present invention having an appropriate powder particle size is oxidized.
- An alloy containing Ti forms a passive film of titanium oxide (mainly TiO 2 ) on the surface by oxidation, so that it has not only excellent oxidation resistance but also effects such as reduction of coercive force and improvement of electrical resistivity. There is. Appropriate gradual oxidation of the powder surface, handling of each process in air, solidification treatment in an inert gas atmosphere instead of a reducing atmosphere are also effective.
- the average powder particle size of the magnetic powder of the semi-hard magnetic material of the present invention is preferably in the range of 10 nm to 10 ⁇ m. When it is less than 10 nm, it is difficult to mold, and the dispersibility may be extremely poor even when dispersed in a synthetic resin or ceramic. Further, when the average particle diameter exceeds 10 ⁇ m, the coercive force reaches the soft magnetic region, and therefore belongs to the category of the soft magnetic material of the present invention.
- a more preferable average powder particle size is 10 nm or more and 1 ⁇ m or less, and if it is within this range, a semi-hard magnetic material in which both saturation magnetization and coercive force are balanced can be obtained.
- the powder particle diameter of the magnetic material of the present invention is evaluated based on the median diameter obtained from a distribution curve obtained by measuring a volume equivalent diameter distribution mainly using a laser diffraction particle size distribution meter.
- a representative portion is selected based on a photograph obtained by SEM or TEM of a powder, or a metal micrograph, and a minimum of 100 diameters are measured and determined. Although it may be less than this, in that case, it is required that there is a statistically sufficient portion representative of the whole and that the portion is measured.
- priority is given to a method using SEM or TEM.
- the numerical value R n is R / 2 ⁇ R n ⁇ 2R.
- the average powder particle diameter is determined with R being the geometric mean of the lower limit and the upper limit.
- the method for measuring the powder particle size of the magnetic material of the present invention is as follows: (1) When the measured value is 500 nm or more and 1 mm or less, the laser diffraction particle size distribution analyzer is given priority; (2) If it is less than 500 nm or exceeds 1 mm, the microscopic method is given priority. (3) When (1) and (2) are used together at 500 nm or more and 1 mm or less, the average powder particle size is determined with the above R.
- the powder particle diameter is represented by 1 to 2 significant digits in the case of (1) or (2), and is represented by 1 significant digit in the case of (3).
- the reason for using the particle size measurement method together is that when the particle size is just above 500 nm and below 1 mm, the method (1) may give an inaccurate value even with one significant figure, Since the method (2) requires time and effort to confirm that it is not local information, the value of the average powder particle size is first obtained by the method (1), and the value can be easily obtained by the method (2). This is because it is very reasonable to compare the two and determine the average powder particle size with the above R.
- the average particle size of the magnetic material powder of the present invention is determined by the above method. However, if (1) and (3) or (2) and (3) do not match with one significant digit, repeat the measurement with (1) or (2) again according to the average particle size range. , R must be determined.
- any one of the methods (1), (2), or (3) may be selected and adopted in a limited manner without depending on the above principle. In order to distinguish the magnetic material of the present invention from other magnetic materials, it is sufficient that the average powder particle size is determined by one significant digit.
- the macroscopic powder shape has a three-dimensional network shape including hollow portions that are many through holes, It may be a sponge shape. These are considered to be formed when grain growth proceeds by a reduction reaction and oxygen is released from the crystal lattice and a large volume reduction occurs.
- the powder particle size in this case is measured including the volume of the hollow portion inside.
- the magnetic material of the present invention is a magnetic material in a state in which the first phase and the second phase are continuously bonded directly or via a metal phase or an inorganic phase to form a lump as a whole (in this application, It can also be used as a “solid magnetic material”.
- the powder is made of an organic compound such as a resin, an inorganic compound such as glass or ceramic, or a composite material thereof. Can also be molded.
- the filling rate is not particularly limited as long as the object of the present invention can be achieved.
- the content is set to 60% by volume or more and 100% by volume or less. This is preferable because it is excellent from the viewpoint of the balance between resistivity and magnetization height.
- the filling rate here refers to the volume of the magnetic material of the present invention relative to the total volume of the magnetic material of the present invention including voids (that is, the magnetic material of the present invention, excluding portions that are not the magnetic material of the present invention such as voids and resins).
- the ratio of the volume occupied only by the material is expressed as a percentage.
- the further preferable range of the filling rate is 80% or more, and particularly preferably 90% or more.
- the magnetic material of the present invention originally has high oxidation resistance, but as the filling rate increases, the oxidation resistance further increases, and not only the application range is expanded, but also the saturation magnetization is improved and the performance is high. A magnetic material is obtained.
- the soft magnetic material of the present invention also brings about an effect that the combination of powders increases and the coercive force decreases.
- the magnetic material powder of the present invention is a sinterable powder material such as ferrite.
- Various solid magnetic materials having a thickness of 0.5 mm or more can be easily manufactured.
- various solid magnetic materials having a thickness of 1 mm or more and 5 mm or more can be manufactured relatively easily by sintering or the like if the thickness is 10 cm or less.
- one feature of the magnetic material of the present invention is that the electrical resistivity is large. Whereas other metal rolling materials and ribbon materials are made by a method that does not include grain boundaries, heterogeneous phases and defects, the magnetic material powder of the present invention contains many crystal boundaries and various phases.
- the surface oxide layer of the powder before solidification ie, TiO 2 , wustite, magnetite, Ti-ferrite, ilmenite present on the surface of the first phase or the second phase
- metal layers ie, Ti-rich metal layers
- at least one of TiO 2 , wustite, and Ti-ferrite can be given.
- the magnetic material of the present invention has the above-mentioned characteristics because the present invention is a magnetic material that is highly magnetized and formed by a method substantially different from other metal-based soft magnetic materials for high frequency applications, that is, titanium. Because we mainly reduce the ferrite nano-powder to produce metal powder with nano-crystallites and then mold it into solid magnetic material, we mainly provide build-up type bulk magnetic materials. is there.
- the electrical resistance is higher than that of existing metallic soft magnetic materials typified by silicon steel, so the lamination process that is normally required when manufacturing rotating equipment, for example, is considerably simplified. it can.
- the electrical resistivity of the magnetic material of the present invention is about 30 times that of silicon steel, the limit of the thickness at which eddy current does not occur is about 5 times based on the relational expression (1).
- the number of layers is also 1/5. For example, when it is applied to a stator of a motor having a high frequency of 667 Hz, the thickness is allowed to be 1.5 mm.
- the solid magnetic material of the present invention does not contain a binder such as a resin, has a high density, and can be easily processed into an arbitrary shape by a normal processing machine by cutting and / or plastic processing.
- a binder such as a resin
- one of the major features is that it can be easily processed into a shape such as a prismatic shape, a cylindrical shape, a ring shape, a disc shape, or a flat plate shape having high industrial utility value.
- a shape such as a prismatic shape, a cylindrical shape, a ring shape, a disc shape, or a flat plate shape having high industrial utility value.
- the cutting process mentioned here is a general metal material cutting process, which is machining by a saw, a lathe, a milling machine, a drilling machine, a grindstone, etc.
- a plastic process is a die cutting, forming, rolling, or explosion by a press. For example, molding.
- annealing can be performed in a range from room temperature to 1290 ° C. to remove strain after cold working.
- the method for producing the magnetic material of the present invention comprises: (1) Titanium ferrite nanopowder manufacturing process (2) Including both reduction processes, and if necessary, may include one or more of the following processes. (3) Slow oxidation step (4) Molding step (5) Annealing step Each step will be specifically described below.
- Titanium ferrite nanopowder manufacturing process (also referred to as “(1) process” in this application)
- a preferable manufacturing process of the nanomagnetic powder which is a raw material of the magnetic material of the present invention
- Known methods for producing ferrite fine powder include dry bead mill method, dry jet mill method, plasma jet method, arc method, ultrasonic spray method, iron carbonyl vapor phase decomposition method, etc. If the magnetic material of this invention is comprised, it is a preferable manufacturing method.
- Non-patent Document 4 the “ferrite plating method” described in Patent Document 1 is applied to the production process of titanium ferrite nanopowder used for producing the magnetic material of the present invention.
- the usual “ferrite plating method” is applied not only to powder surface plating but also to thin films, and its reaction mechanism has already been disclosed (for example, Masaki Abe, Journal of Japan Society of Applied Magnetics, 22 Vol. 9, No. (1998), page 1225 (hereinafter referred to as “Non-patent Document 4”) and International Publication No.
- Patent Document 2 2003/015109 (hereinafter referred to as “Patent Document 2”), in this manufacturing process.
- the powder surface as a base material for plating is not used.
- raw materials used for ferrite plating for example, titanium chloride and iron chloride
- this step (or method) is referred to as a “titanium ferrite nanopowder manufacturing step” (or “titanium ferrite nanopowder manufacturing method”).
- the “titanium ferrite nanopowder manufacturing process” having a spinel structure will be described below as an example.
- An appropriate amount of an aqueous solution adjusted in advance to an acidic region is placed in a container (also referred to as a reaction field in the present application), and the reaction is carried out in a room-temperature atmosphere under ultrasonic excitation or with mechanical stirring at an appropriate strength or rotation speed.
- a pH adjusting solution is dropped simultaneously with the solution to gradually change the solution pH from acidic to alkaline region, thereby generating titanium ferrite nanoparticles in the reaction field.
- the solution and the titanium ferrite nanopowder are separated and dried to obtain a titanium ferrite powder having an average powder particle diameter of 1 nm or more and less than 1000 nm (1 ⁇ m). Since the above method has a simple process, it is mentioned as an inexpensive method.
- the method for producing the titanium ferrite nanopowder used in the present invention is not limited to the above-mentioned production method, but the initial solution of the reaction field used in the production method before the start of the reaction (in this application, this is referred to as the reaction field). (Hereinafter also referred to as “liquid”), the reaction liquid, and the pH adjusting liquid will be described below.
- an acidic solution is preferable.
- inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid
- a hydrophilic solvent solution such as an aqueous solution of an organic acid (for example, acetic acid, oxalic acid, etc.), or a combination thereof can also be used.
- preparing the reaction solution in the reaction field in advance is effective for efficiently promoting the synthesis reaction of the titanium ferrite nanopowder.
- the pH is less than ⁇ 1, the material that provides the reaction field may be restricted, and inevitable contamination may be allowed. Therefore, it is desirable to control the pH between ⁇ 1 and less than 7. .
- a particularly preferred pH range is 0 or more and less than 7 in order to increase the reaction efficiency in the reaction field and to minimize elution and precipitation of unnecessary impurities.
- the pH range where the balance between reaction efficiency and yield is good is more preferably 1 or more and less than 6.5.
- the solvent for the reaction field a hydrophilic solvent among organic solvents can be used, but it is preferable that water is contained so that the inorganic salt can be sufficiently ionized.
- the reaction solution contains a chloride such as iron chloride or titanium chloride, a nitrate such as iron nitrate, or a nitrite, sulfate, phosphoric acid containing an Fe component and / or a Ti component (which may optionally include an M component).
- a solution mainly composed of water of an inorganic salt such as a salt or fluoride, or a solution mainly composed of a hydrophilic solvent such as water of an organic acid salt can be used if necessary. Also, a combination thereof may be used.
- the reaction solution contains iron ions and titanium ions.
- the iron ions in the reaction solution will be described either in the case of only divalent iron (Fe 2+ ) ions, in the case of a mixture of trivalent iron (Fe 3+ ) ions, or in the case of only trivalent iron ions. However, in the case of only Fe 3+ ions, it is necessary to include divalent or less divalent metal ions of the M component element.
- the valence of Ti ions in the reaction solution is typically divalent, trivalent, or tetravalent. In the reaction solution or reaction field solution, tetravalence is particularly excellent in terms of reaction homogeneity.
- the titanium chloride aqueous solution may use a commercially available aqueous solution in advance, but when preparing from an undiluted solution to obtain an aqueous solution of any concentration, there is a danger of reacting explosively when dissolved in water, A method of mixing while cooling the solution by ice cooling or the like is recommended. In addition, since it emits hydrogen chloride when exposed to the atmosphere, it is desirable to handle it in a glove box with reduced oxygen concentration. Furthermore, when the aqueous solution is acidified with hydrochloric acid, titanium hydroxide, oxychloride and the like are not precipitated, and a transparent aqueous solution is obtained.
- pH adjusting liquid examples include alkaline solutions such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, acidic solutions such as hydrochloric acid, and combinations thereof.
- alkaline solutions such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, acidic solutions such as hydrochloric acid, and combinations thereof.
- a pH buffer solution such as an acetic acid-sodium acetate mixed solution or addition of a chelate compound is also possible.
- the oxidizing agent is not necessarily essential, but is an essential component when only Fe 2+ ions are contained as Fe ions in the reaction field solution and the reaction solution.
- oxidants include nitrite, nitrate, hydrogen peroxide, chlorate, perchloric acid, hypochlorous acid, bromate, organic peroxide, dissolved oxygen water, and combinations thereof. It is done.
- an inert gas such as nitrogen gas or argon gas may be introduced continuously or temporarily by bubbling the reaction field to limit the effect of other oxidants by limiting the oxidizing action of oxygen.
- the reaction can be controlled stably.
- titanium ferrite nanoparticles In a typical titanium ferrite nanopowder manufacturing method, formation of titanium ferrite nanoparticles proceeds by the following reaction mechanism.
- the nuclei of the titanium ferrite nanoparticles are generated in the reaction solution via an intermediate product such as green last or directly.
- the reaction solution contains Fe 2+ ions, which are adsorbed on the already formed powder nuclei or OH groups on the surface of the powder that has grown to some extent, and release H + .
- an oxidation reaction is performed by oxygen in the air, an oxidant, an anode current (e + ), or the like, a part of the adsorbed Fe 2+ ions are oxidized to Fe 3+ ions.
- Fe 2+ ions or Fe 2+ and Ti 4+ ions (or Ti and M component ions) in the liquid are adsorbed again on the metal ions that have already been adsorbed and release H + while being hydrolyzed.
- a ferrite phase having a spinel structure is formed. Since OH groups are present on the surface of the ferrite phase, metal ions are adsorbed again, and the same process is repeated to grow into titanium ferrite nanoparticles.
- the pH is set so that the equilibrium curve in the Fe-potential diagram crosses the line separating Fe 2+ ions and ferrite. While adjusting the redox potential, the reaction system should be shifted (slowly) from the stable region of Fe 2+ ions to the region where ferrite precipitates. Except for special cases, Ti 4+ is a tetravalent state from the beginning of the reaction, and has almost no effect on the oxidation-reduction potential change. Progress).
- the reaction solution is adjusted on the acidic side, and the alkaline solution is added at once to make the reaction field a basic region. Often generated.
- the alkaline solution is added at once to make the reaction field a basic region. Often generated.
- titanium ferrite nanopowder it can be considered that due to the difference in solubility product between the Fe component and the Ti component, consideration has been given so as not to become non-uniform. Of course, it may be prepared by this method, and since very small nanoparticles can be produced, it can also be used as a ferrite raw material for the magnetic material of the present invention.
- the pH adjuster is also dropped at the same time to gradually change the pH from acidic to basic.
- the process is designed so that the Ti component is steadily incorporated into the Fe-ferrite structure.
- H + released when ferrite is generated by the mechanism as described above is increased by charging the pH adjusting liquid into the continuous reaction field. The generation and growth of titanium ferrite particles occur one after another.
- Dispersion is very important to prevent fine particles generated by titanium ferrite nanopowder synthesis reaction from agglomerating and inhibiting homogeneous reaction. Dispersion is very important. Depending on the purpose of reaction control, such as a method of conveying and circulating the liquid with a pump, a method of simply stirring with a stirring spring or a rotating drum, or a method of swinging or vibrating with an actuator, etc., any one of known methods, Or the combination is used.
- the reaction temperature is selected from 0 to 100 ° C. from the freezing point to the boiling point of water under atmospheric pressure because the titanium ferrite nanopowder production method used in the present invention is a reaction in the presence of water. It is.
- a method of synthesizing titanium ferrite nanopowder in a temperature range exceeding 100 ° C. by placing the entire system under a high pressure is a titanium ferrite nano exhibiting the effect of the present invention.
- the powder it belongs to the magnetic material of the present invention.
- reaction excitation method in addition to the above-mentioned temperature and ultrasonic waves, pressure and optical excitation may be effective.
- the titanium ferrite nanopowder manufacturing method when the titanium ferrite nanopowder manufacturing method is applied using an aqueous solution containing Fe 2+ as a reaction solution (particularly when the reaction is performed under the condition that Fe is mixed into the titanium ferrite nanoparticles as divalent ions). It is important that divalent ions of Fe are observed in the finally formed ferrite coating layer of the magnetic material of the present invention when the Ti content is less than 40 atomic%.
- the amount is preferably Fe1 / Fe3 + ratio and is 0.001 or more.
- an electron beam microanalyzer EPMA
- EMA electron beam microanalyzer
- the surface of the titanium ferrite nanoparticles is analyzed by EPMA, the X-ray spectrum of FeL ⁇ -FeL ⁇ is obtained, the difference between the above two materials is taken, and iron oxide containing Fe 2+ (eg, magnetite) And the amount of Fe 2+ ions in the titanium ferrite nanoparticles can be identified by comparing with the spectrum of a standard sample of iron oxide (eg, hematite or maghematite) containing only Fe 3+ .
- a standard sample of iron oxide eg, hematite or maghematite
- the measurement conditions of EPMA are an acceleration voltage of 7 kV, a measurement diameter of 50 ⁇ m, a beam current of 30 nA, and a measurement time of 1 second / step.
- Typical impurity phases of titanium ferrite nanopowders include oxides such as titanohematite, goethite, acagenite, lepidochrosite, ferrooxy height, ferrihydrite, green rust and other iron oxyoxides, potassium hydroxide
- hydroxides such as sodium hydroxide
- ferrihydrite phase and titanohematite phase form ⁇ - (Fe, Ti) phase and other second phases after reduction. Therefore, it is not always necessary to remove.
- ferrihydrite phase and titano hematite phase are observed as a plate-like structure having a thickness of several nm in SEM observation or the like.
- the volume fraction is smaller than that of nanopowder.
- the Ti ratio of the phase other than the titanium ferrite nanopowder centered on ferrihydrite and titanohematite is titanium ferrite.
- the state of aggregation such as ferrihydrite phase (especially not to be unevenly distributed to about a few microns). Need attention. Regardless of the above, the content of the ferrihydrite phase and Ti-ferrite phase in which Ti can easily be incorporated in the total magnetic material is intentionally set to 0 so that the above-mentioned inappropriate subphase not containing Ti does not precipitate. It is also possible to coexist in a range of 0.01 volume% to 33 volume%. This is more industrially advantageous because it is not necessary to strictly maintain the control conditions for producing the ferrite nanopowder.
- the average particle size of the titanium ferrite nanopowder used as the raw material of the present invention is preferably 1 nm or more and less than 1 ⁇ m (1000 nm). More preferably, they are 1 nm or more and 100 nm or less. If it is less than 1 nm, the reaction during the reduction cannot be sufficiently controlled, resulting in poor reproducibility. If it exceeds 100 nm, inappropriate grain growth of the metal component reduced in the reduction step becomes remarkable, and in the case of a soft magnetic material, the coercive force may increase, and therefore, 100 nm or less is preferable.
- the thickness is 1 ⁇ m or more, the ⁇ -Fe phase is separated, and Ti is not taken into this phase, so that only the magnetic material having excellent electromagnetic characteristics and poor oxidation resistance of the present invention may be obtained. It is preferably less than 1 ⁇ m.
- the titanium ferrite nanopowder used in the present invention is produced mainly in an aqueous solution, decantation, centrifugation, filtration (especially suction filtration), membrane separation, distillation, vaporization, organic solvent substitution, Water is removed by solution separation by magnetic field recovery of powder, or a combination thereof. Thereafter, it is vacuum dried at room temperature or at a high temperature of 300 ° C. or lower, or dried in air.
- Hot air drying in air inert gas such as argon gas, helium gas, nitrogen gas (however, in the present invention, nitrogen gas may not become an inert gas depending on the temperature range during heat treatment) or hydrogen It can also be dried by heat treatment in a reducing gas such as a gas or a mixed gas thereof.
- (2) Reduction step (also referred to herein as “(2) step”) This is a step of reducing the titanium ferrite nanopowder produced by the above method to produce the magnetic material of the present invention.
- the method of reducing in the gas phase is most preferable, and the reducing atmosphere is a mixed gas of an organic compound gas such as hydrogen gas, carbon monoxide gas, ammonia gas or formic acid gas and an inert gas such as argon gas or helium gas.
- an organic compound gas such as hydrogen gas, carbon monoxide gas, ammonia gas or formic acid gas
- an inert gas such as argon gas or helium gas.
- low-temperature hydrogen plasma, supercooled atomic hydrogen, etc. and these can be circulated, refluxed, or sealed in horizontal and vertical tubular furnaces, rotary reactors, sealed reactors, etc. Examples thereof include a heating method, a heating method using infrared rays, microwaves, laser light, and the like.
- a method of reacting continuously by using a fluidized bed is also mentioned.
- a method of reducing with solid C (carbon) or Ca a method of mixing calcium chloride or the like and reducing in an inert gas or a reducing gas, and industrially, once Ti oxide is converted into chloride.
- a method of reducing with Mg if the magnetic material of the present invention is obtained, it falls within the category of the production method of the present invention.
- a preferable method in the production method of the present invention is a method of reducing in a hydrogen gas or a mixed gas of an inert gas as a reducing gas.
- reduction with C or Ca is too strong to control the reaction for constituting the soft magnetic material of the present invention.
- problems such as the generation of toxic CO after reduction and the presence of calcium oxide that must be washed away, but the reduction with hydrogen gas is consistently clean. This is because a reduction process can be performed.
- the Ti-ferrite of the present invention has a diameter of 1 nm or more and less than 1000 nm (1 ⁇ m), and Ti is dispersed atomically in a highly active nanopowder, and the affinity between Ti and Fe is high. Since it is high, it is alloyed as ⁇ - (Fe, Ti) under a hydrogen gas stream. Nano-domain powders are highly reactive, often contrary to thermodynamic expectations, leading to results beyond the norm in metallurgy. Conventionally, it is a Ti oxide that can be substantially reduced only in the presence of Ca, C, etc., but according to the method of the present invention, a part of the Ti component is contained in the first phase, the first phase, and the second phase.
- ⁇ - (Fe, Ti) phase of the phase it can be reduced to a metallic state and exist as an alloy.
- the present inventors presume that the coexistence of a trace amount of alkali metal such as K also affects the reaction promoting action.
- the higher the reduction temperature the more the ⁇ It cannot be said that the average Ti content in the-(Fe, Ti) phase increases.
- the Ti content in the ⁇ - (Fe, Ti) phase once becomes high when the reduction temperature is in the range of 450 ° C. or higher and 550 ° C. or lower. Until then, Ti content falls on the contrary, and Ti content increases with a raise of reduction temperature again after that.
- the oxygen content in the material of the present invention is generally determined by an inert gas melting method, but when the oxygen content before the reduction is known, the weight difference between before and after the reduction The oxygen in the material can be estimated. However, when a halogen element such as chlorine whose content easily changes before and after reduction, an alkali element such as K or Na, or a volatile component such as water or an organic component is contained in a large amount, The contents of these elements and components should be identified separately. This is because the oxygen content cannot be strictly estimated only by the weight change before and after the reduction reaction.
- the alkali metals derived from the raw materials for example, K begins to dissipate from the magnetic material by vaporization at 450 ° C., and most of it is removed at 900 ° C. or higher, depending on the Ti content and the reduction time. Therefore, in the initial stage of the reduction reaction, if the alkali metal derived from the raw material, which should be left in order to utilize its catalytic action, is not preferable in the product stage depending on the application, the reducing conditions are By appropriate selection, the alkali metal can be appropriately removed to a finally acceptable range.
- the range of the final content of alkali metals such as K that can be easily removed while providing an effective effect for reduction is a lower limit value of 0.0001 atomic% or more and an upper limit value of 5 atomic% or less.
- the upper limit value can be further controlled to 1 atomic% or less, and can be 0.01 atomic% when it is most precisely controlled.
- Halogen elements such as Cl (chlorine) remaining in the titanium ferrite nanopowder are released out of the material system mainly as hydrogen halides such as HCl in a reducing atmosphere. Residual Cl and the like begin to decrease significantly at a reduction temperature of 450 ° C. or higher, and depending on the Ti and K content, and further the content change in the reduction process, if a reduction temperature of approximately 700 ° C. or higher is selected, It can be removed almost completely from within the material.
- the weight reduction due to evaporation of O component mainly as H 2 O is caused by volatile components such as Ti content, M component content, oxygen content, subphase and impurity content, and water. Usually, it is between 0.1% by mass and 80% by mass although it depends on the amount or the reducing reaction conditions such as reducing gas species.
- the local oxygen content is obtained based on a photograph such as SEM or EDX, or the phase identified by XRD or the like is specified on a microscopic observation image. You can also. This is a method suitable for roughly estimating the oxygen content and distribution of the first phase and the second phase.
- the reduction temperature of the present invention refers to the highest temperature among the temperature at the time of switching from the temperature raising process to the temperature lowering process and the temperature in the process of maintaining the temperature for a certain time.
- the reduction temperature is generally 400 ° C. or higher and 1290 ° C. or lower depending on the Ti content. .
- the magnetic material being reduced may be dissolved depending on the Ti content.
- the reduction treatment can be performed by freely selecting from a temperature range of 400 ° C. to 1290 ° C.
- the Ti content exceeds 33 atomic% and reaches 50 atomic%
- a temperature of 400 ° C. or higher is preferable because the reduction rate is very slow and it is possible to avoid a reduction in productivity due to a long reduction time.
- a preferable reduction temperature range is 400 ° C. or more and 1290 ° C. or less, and a more preferable reduction temperature range is 800 ° C. or more and 1200 ° C. or less.
- the reduction reaction proceeds as the reduction time increases. Therefore, the longer the reduction time, the higher the saturation magnetization.
- the coercive force does not necessarily decrease the coercive force even if the reduction time is increased or the reduction temperature is increased.
- the reduction time is preferably selected as appropriate according to the desired magnetic properties.
- the reduction temperature is selected in the range of approximately 400 ° C. to 1290 ° C., depending on the Ti content. Is preferred. When the temperature is lower than 400 ° C., the reduction rate is very slow, the reduction time becomes long, and the productivity becomes poor. Conversely, when the temperature exceeds 1290 ° C., melting starts, the characteristics of the nanocrystal of the present invention are hindered, and the coercive force is not properly controlled.
- a more preferable range of the reduction temperature is about 450 ° C. or more and 850 ° C. or less, and a particularly preferable range is about 500 ° C. or more and 700 ° C. or less.
- the reduction temperature is preferably 400 ° C. or higher and 1290 ° C. or lower.
- the magnetic material of the present invention contains Ti, the reduction rate is extremely slow compared to Fe-ferrite, for example, an intermediate between magnetite and maghemite (see Patent Document 1 and Non-Patent Document 3).
- Fe-ferrite for example, an intermediate between magnetite and maghemite
- it is reduced to almost 100% by volume ⁇ -Fe just by reduction in hydrogen at 450 ° C. for 1 hour.
- the Fe-ferrite is reduced to such an extent that it is not observed by X-ray diffraction.
- the Ti-ferrite phase will not disappear unless it is reduced to 600 ° C. for 1 hour, and only the ⁇ - (Fe, Ti) phase on XRD. Don't be.
- the nano-fine structure becomes extremely coarse while containing Ti in the ⁇ -Fe phase.
- an aggregate of microcrystalline structures including the first phase and the second phase can be obtained by a disproportionation reaction.
- the first phase and the second phase are phase-separated at the nanoscale in the reduction process during the production.
- various Ti contents and phases of crystal structures are separated by a disproportionation reaction, and their orientation is random, or Mn content at the nanoscale It is necessary that the amount of concentration fluctuation is inherent, and furthermore, each crystal phase must be ferromagnetically coupled.
- the titanium ferrite nanoparticles grow, and at this time, depending on the reduction temperature, the first phase and the second phase of the generated crystal phase are caused by the Ti content of the original titanium ferrite nanoparticles.
- the crystal structure and Ti content of the material vary widely. In the temperature range of 400 ° C. or more and 1290 ° C. or less, generally, the higher the temperature at which the metal phase is reduced, the higher the Ti content of the first phase. Conversely, in the temperature range of 1290 ° C. or more and 1538 ° C. or less. If not melted, the Ti content of the first phase tends to be smaller than the Ti content of the first phase in the temperature range of 400 ° C. to 1290 ° C. Therefore, the structure of the crystal phase varies depending on the temperature increase rate during the temperature increase process and the temperature distribution in the reactor.
- ⁇ - (Fe, Ti) phase and a Ti-enriched phase of several nanometers begin to appear inside. Since this phase exists densely between ⁇ - (Fe, Ti) phase particles like fish eggs, this phase is called a spawn phase.
- the XRD peak corresponding to this phase is not detected, and it is said that it is an amorphized phase or a phase in which the lattice is considerably broken, but EDX enriches Ti with a significant difference from the ⁇ - (Fe, Ti) phase.
- EDX enriches Ti with a significant difference from the ⁇ - (Fe, Ti) phase.
- the Ti content of the raw material titanium ferrite nanopowder is 33 atomic%, it is enriched with about 8 atomic% Ti. This is because, due to the Ti content of the titanium ferrite nanopowder, when the phase is reduced to the ⁇ - (Fe, Ti) phase, Ti cannot be completely dissolved in the ⁇ - (Fe, Ti) phase. It is thought that it precipitated as a Ti-rich phase.
- the second phase of the magnetic material of the present invention is Ti-ferrite and this spawn phase.
- the coercive force is high in the powder state, and it is suitably used as the semi-hard magnetic material of the present invention. This is not the case when a solid magnetic material is obtained by sintering or the like.
- the metal phase grows and ⁇ - (Fe, Ti) of various compositions containing Ti Phases can be seen.
- ⁇ - (Fe, Ti) phase grows to several ⁇ m or more, but as the temperature decreases, the ⁇ - (Fe, Ti) phase
- the Ti-enriched phase which can no longer be completely dissolved, is phase-separated one after another by the disproportionation reaction and precipitates as the second phase.
- This Ti composition distribution in the ⁇ - (Fe, Ti) phase is caused by a kind of disproportionation reaction of homologous species having the same crystal structure, and this reaction mainly occurs in the temperature reduction process of the reduction process. I guess that. Therefore, the nano-scale ⁇ - (Fe, Ti) phases with different Ti contents generated during the above reduction process are integrated by ferromagnetic coupling, so that soft magnetism typical as the magnetic material of the present invention is obtained. I understand that the material is formed.
- Ti can form a solid solution up to nearly 10 atomic% in the ⁇ -Fe phase, but Ti hardly dissolves in the ⁇ -Fe phase at room temperature. .
- the Ti content in the ⁇ - (Fe, Ti) phase of the magnetic material of the present invention can exist far beyond the solid solution source having this equilibrium composition, these are naturally non-equilibrium phases. If the operation of lowering the temperature from the reduction temperature to room temperature over an infinite time (the temperature lowering rate is infinitely small) can be performed, Ti cannot coexist in the ⁇ -Fe phase. On the other hand, if it is possible to perform an operation of decreasing the temperature from 1290 ° C.
- the soft magnetic material of the present invention cannot be formed by any of the above manufacturing methods. That is, the microstructure of the soft magnetic material of the present invention can be controlled by appropriately selecting a temperature lowering rate that is not close to the above two limits (not super slow cooling or super rapid cooling). However, the magnetic material of the present invention has a completely different microstructure from existing bulk materials and does not have a composition distribution according to the equilibrium diagram at room temperature. In the magnetic material, there may be a homogeneous phase that spreads in the nano range and along the equilibrium diagram.
- temperature control including the temperature rising process is important for the microstructure.
- the temperature rising / lowering rate in the reduction step of the present invention varies depending on the intended electromagnetic characteristics and Ti content, but is usually appropriately between 0.1 ° C./min and 5000 ° C./min. It is desirable to choose.
- the softening material having a low coercive force can be obtained by increasing the temperature raising / lowering rate at a rate between 1 ° C / min and 500 ° C / min. This is preferable because the magnetic material can be adjusted.
- the magnetic material of the present invention may contain TiO 2 as the second phase.
- this phase When this phase is present at the grain boundary or the powder particle surface, it exerts a strong oxygen barrier effect, and the acid resistance of the magnetic material of the present invention. Greatly contributes to improvement in chemical conversion.
- the semi-hard magnetic material of the present invention not only makes the effect of oxidation resistance remarkable, but also exerts an effect on improving the coercive force.
- the reason why appropriate grain growth occurs while maintaining the nano-fine structure even in a high temperature region exceeding 800 ° C. is unclear.
- the raw material is titanium ferrite nanopowder, and it is reduced to hydrogen and becomes a metal state like the first phase, the original grain shape and composition distribution are completely microstructured if appropriate reduction conditions are selected. Inappropriate grain growth that does not reflect the above and the crystal grain size becomes coarse due to the structure having a homogeneous composition distribution has not occurred. Since grain growth occurs along with the reduction reaction in this way, disproportionation proceeds while leaving a structure resembling intergrowth and body crystals when combined with the fact that volume reduction due to reduction occurs up to 52% by volume. Can also be easily analogized.
- Phase separation due to the disproportionation reaction during the temperature lowering process occurs mainly in the ⁇ - (Fe, Ti) phase, and nanoparticles and nanostructures are precipitated. It is considered that a disproportionated structure is formed.
- the reduction rate in the oxide phase containing Ti such as Ti-ferrite phase, it is known that the higher the Ti content, the slower the reduction rate.
- the reduction reaction rate is not uniform within the material. I think this also works favorably to preserve nanostructures. The above series of considerations is supported by the fact that the magnetic material of the present invention should lose its characteristics when melted.
- step (3) Slow oxidation step (also referred to as “step (3)” in the present application) Since the magnetic material of the present invention after the reduction step contains nano metal particles, there is a possibility of spontaneous ignition and combustion when taken out into the atmosphere as it is. Therefore, although it is not an essential step, it is preferable to carry out a gradual oxidation treatment immediately after completion of the reduction reaction, if necessary.
- the gradual oxidation primarily to the surface of the metal nanoparticles after reduction and oxidation wustite, magnetite, Ti- ferrite, by passivating the like TiO 2, suppresses rapid oxidation of the internal magnetic material body That is.
- Ti is contained as a metal component in the first phase or the first phase and the second phase until the reduction step.
- this Ti component is deposited on the alloy surface by the gradual oxidation process to form a passive film, but it has much higher oxidation resistance than the Fe magnetic material not containing the Ti component.
- Slow oxidation is carried out in a gas containing an oxygen source such as oxygen gas, for example, in the vicinity of room temperature to 500 ° C., but a mixed gas containing an inert gas having a lower oxygen partial pressure than the atmosphere is often used.
- the magnetic material powder of the present invention having a large Ti content, a sufficiently low reduction temperature and time, and having grown grains, it does not go through this gradual oxidation step and is stable even if released into the atmosphere.
- a dynamic membrane may be formed, and in this case, a special slow oxidation step is not required. In this case, opening to the atmosphere itself can be regarded as a slow oxidation process.
- ferromagnetic coupling may be broken by the oxidized layer or passivated film layer. Is preferred. Otherwise, it is preferable to perform the next molding step without passing through the gradual oxidation step as described above, and it is desirable to continue the reduction step and the molding step by deoxygenation or a low oxygen process.
- the magnetic material of the present invention is a magnetic material in which the first phase and the second phase are continuously bonded directly or via a metal phase or an inorganic phase to form a lump as a whole (that is, a solid phase). It is used as a magnetic material.
- the magnetic material powder of the present invention is used for various applications by solidifying itself or molding it by adding a metal binder, other magnetic material, resin or the like.
- the first phase and the second phase are already continuously or directly through the metal phase or the inorganic phase. In this case, it functions as a solid magnetic material without going through the main forming step.
- a method of solidifying only the magnetic material of the present invention it is put into a mold and compacted in a cold state and used as it is, or subsequently formed by performing cold rolling, forging, shock wave compression molding or the like.
- sintering is performed while performing heat treatment at a temperature of 50 ° C. or higher.
- a method of sintering by performing heat treatment as it is without applying pressure is called atmospheric pressure sintering.
- the heat treatment atmosphere is preferably a non-oxidizing atmosphere, and the heat treatment may be performed in an inert gas such as a rare gas such as argon or helium or nitrogen gas, or in a reducing gas containing hydrogen gas. Temperature conditions of 500 ° C. or lower are possible even in the atmosphere. Further, not only when the pressure of the heat treatment atmosphere is normal pressure as in normal pressure sintering, sintering in a pressurized gas phase atmosphere of 200 MPa or less or further sintering in a vacuum may be used.
- the heat treatment temperature is preferably 50 ° C. or higher and 1400 ° C. or lower in pressure molding, and 400 ° C. or higher and 1400 ° C. or lower in normal pressure sintering, in addition to room temperature molding performed at less than 50 ° C. Since the material may melt at a temperature exceeding 1290 ° C., the most preferable range of the molding temperature is generally 50 ° C. or more and 1290 ° C. or less.
- This heat treatment can be performed at the same time as compacting, and can also be performed by a hot pressing method, a HIP (hot isostatic pressing) method, a pressure sintering method such as an electric current sintering method, an SPS (discharge plasma sintering) method, It is possible to mold the magnetic material of the present invention.
- the applied pressure in the heating and sintering process is within a range of 0.0001 GPa to 10 GPa. If it is less than 0.0001 GPa, the effect of pressurization is poor, and there is no change in atmospheric pressure sintering and electromagnetic characteristics. If the pressure exceeds 10 GPa, the pressurizing effect is saturated, so that productivity is only lowered even if the pressure is increased.
- a large pressurization imparts induced magnetic anisotropy to the magnetic material, and the magnetic permeability and coercive force may deviate from the range to be controlled. Therefore, a preferable range of the applied pressure is 0.001 GPa to 2 GPa, and more preferably 0.01 GPa to 1 GPa.
- the ultra-high pressure HP method in which the green compact is charged into a capsule that is plastically deformed and heat-pressed by heat treatment while applying a large pressure from the uniaxial to triaxial directions is unnecessary and excessive. It is possible to prevent oxygen contamination.
- hot pressing which uses a uniaxial compressor and pressurizes and heats in cemented carbide and carbon molds, materials with a pressure of 2 GPa or more that are difficult even with tungsten carbide cemented molds can be used without problems such as damage to the mold.
- the capsule is plastically deformed by pressure and the inside is sealed, molding can be performed without touching the atmosphere.
- coarse pulverization, fine pulverization, or classification can be performed using a known method.
- Coarse pulverization is a step performed before molding when the reduced powder is a lump of several mm or more, or a step performed when powdering again after molding.
- adjusting the particle size using a sieve, a vibration or sonic classifier, a cyclone, etc. is also effective for adjusting the density and formability during molding.
- annealing in an inert gas or hydrogen can remove structural defects and distortion, and is effective in some cases.
- the fine pulverization is performed when the magnetic material powder after reduction or the magnetic material after molding needs to be pulverized from submicron to several tens of ⁇ m.
- dry and wet fine pulverizers such as rotating ball mill, vibrating ball mill, planetary ball mill, wet mill, jet mill, cutter mill, pin mill, automatic mortar and the like A combination of these is used.
- titanium ferrite nanopowder is produced by the step (1), and subsequently reduced by the step (2), and then the step (3) ⁇ (4 ) Or only the step (4).
- titanium ferrite nanopowder is prepared by the wet method exemplified in the step (1) and then reduced by the method containing hydrogen gas shown in the step (2).
- the present solid magnetic material can be molded to a thickness of 0.5 mm or more, and can be processed into an arbitrary shape by cutting and / or plastic processing.
- Step (1) ⁇ Step (2), Step (1) ⁇ Step (2) ⁇ Step (3), Step (1) ⁇ Step (2) ⁇ Step (5) described later
- Step (1) ⁇ Step (2) ⁇ Step (3) ⁇ Magnetic material powder obtained in step (5) described later, or magnetic material powder obtained in the above step (4)
- the magnetic material powder obtained by pulverizing the magnetic material formed in the above step, the magnetic material powder obtained by annealing the magnetic material powder obtained in the above step in the step (5) described later, and the magnetic sheet for high frequency When it is applied to a composite material such as a resin, compression molding is performed after mixing with a thermosetting resin or a thermoplastic resin, injection molding is performed after kneading with a thermoplastic resin, and extrusion molding, rolls are further performed. Molding is performed by molding or calendar molding.
- the shape of the sheet when applied to an electromagnetic noise absorbing sheet, is a batch type sheet by roll forming, roll forming or calendar having a thickness of 5 ⁇ m to 10,000 ⁇ m, a width of 5 mm to 5000 mm, and a length of 0.005 mm to 1000 mm.
- Examples thereof include various roll-shaped sheets formed by molding and the like, and cutting or molded sheets having various sizes including A4 plate.
- the magnetic material of the present invention typically has a first phase and a second phase, and one or both of the crystal grain sizes are in the nano region.
- annealing for various purposes such as crystal distortion and defects generated in each step and stabilization of the non-oxidized active phase as long as the object of the present invention is not impaired.
- stable reduction is performed simultaneously with drying for the purpose of removing volatile components such as water content.
- a so-called preliminary heat treatment (annealing) in which a fine particle component of about several nanometers is heat-treated, may be performed for the purpose of removing the heat.
- the coercive force of the soft magnetic material of the present invention can be reduced by removing distortions and defects of crystal lattices and microcrystals caused by volume reduction due to grain growth and reduction.
- a pulverization step is sandwiched after this step or after this step. Later, when annealed under appropriate conditions, the electromagnetic properties may be improved.
- annealing may be useful for removing distortions and defects near the surface, interface, and boundary caused by surface oxidation.
- Annealing after the molding step (4) is the most effective, and removes crystal lattices, microstructure distortion, and defects caused by subsequent cutting and / or plastic processing such as preforming, compression molding and hot pressing. Therefore, an annealing process may be actively performed after this process. In this step, it can be expected that the accumulated strains and defects are alleviated at a stretch in the previous step. Furthermore, after the above-described cutting and / or plastic working, the steps (1) to (4), the steps (2) to (4), the steps (3) and (4), and the step (4) It is also possible to perform annealing by summing up the strains in the above or the integrated strains.
- any of vacuum, reduced pressure, normal pressure, and pressurization of 200 MPa or less is possible, and as a gas type, an inert gas typified by a rare gas such as argon, nitrogen gas, A reducing gas such as hydrogen gas, or an atmosphere containing an oxygen source such as in the air can be used.
- the annealing temperature is from normal temperature to 1290 ° C., and depending on the case, treatment at a low temperature from liquid nitrogen temperature to normal temperature is also possible.
- the apparatus for the annealing process is almost the same as the apparatus used in the reduction process and the molding process, and can be implemented by combining known apparatuses.
- the saturation magnetization was corrected with a 5N Ni standard sample, and obtained by the saturation asymptotic rule.
- the magnetic field shift in the low magnetic field region was corrected using a paramagnetic Pd standard sample.
- the “inflection point on the 1/4 major loop” is “ It was judged as “No”.
- the direction of the measurement magnetic field is the axial direction in the case of magnetic powder, and the radial direction in the case of a molded body.
- the saturation was converted into T (Tesla) units using the density.
- the relative magnetic permeability of the molded body was roughly estimated using a magnetic curve in which the demagnetizing factor was determined using a Ni standard sample having the same shape as the measurement sample and the demagnetizing field was corrected based on the value.
- (IV) Fe content, Ti content, oxygen content, ⁇ - (Fe, Ti) phase volume fraction The Fe and Ti contents in powder and bulk magnetic materials were quantified by fluorescent X-ray analysis. The Fe and Ti contents of the first phase and the second phase in the magnetic material were quantified by EDX attached thereto based on an image observed by FE-SEM. Further, the volume fraction of the ⁇ - (Fe, Ti) phase was quantified by image analysis in combination with the result of the XRD method and the above method using the FE-SEM. An oxygen characteristic X-ray surface distribution map using SEM-EDX was mainly used to distinguish whether the observed phase was an ⁇ - (Fe, Ti) phase or an oxide phase. Further, the validity of the ⁇ - (Fe, Ti) phase volume fraction value was also confirmed from the saturation magnetization value measured in (I).
- the oxygen content was basically determined by an inert gas melting method. Further, the amount of oxygen in the magnetic material after the reduction process was also confirmed by a decrease in weight after the reduction. Furthermore, image analysis by SEM-EDX was used for identification of each phase. The amount of K was quantified by fluorescent X-ray analysis.
- V Average powder particle diameter Magnetic powder was observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) to determine the powder particle diameter. A part that sufficiently represents the whole was selected, and the number of n was determined to be 100 or more with one significant digit.
- the volume equivalent diameter distribution was measured, and the median diameter ( ⁇ m) obtained from the distribution curve was evaluated.
- the obtained median diameter was 500 nm or more and less than 1 mm, the value was adopted, and it was confirmed that the powder particle diameter roughly estimated by a method using a microscope coincided with one significant digit.
- Example 1 and Comparative Example 1 An aqueous solution of TiCl 4 aqueous solution (titanium chloride aqueous solution) and FeCl 2 .4H 2 O (iron (II) chloride tetrahydrate) were separately prepared, and these were mixed to prepare TiCl 4 and FeCl 2 prepared to 50.3 mM.
- the mixed aqueous solution was put into a reactor to obtain a reaction field solution. Subsequently, while vigorously stirring in the atmosphere, a 660 mM aqueous potassium hydroxide solution (pH adjusting solution) is dropped, and the pH of the system is gradually increased from the acidic side to the alkaline side in the range of 2.26 to 12.80.
- reaction solution a mixed aqueous solution (reaction solution) of 168 mM FeCl 2 and TiCl 4 was dropped and reacted for 15 minutes, and then dropping of the pH adjustment solution and the reaction solution was stopped, followed by further stirring for 15 minutes. Operation continued. Thereafter, the solid components are precipitated by centrifugation, redispersed in purified water, and centrifuged repeatedly, so that the pH of the supernatant solution is 9.13, and finally the precipitate is dispersed in ethanol, followed by centrifugation. It was.
- This Ti-ferrite nanopowder was charged into an aluminum titanate crucible and heated in a hydrogen stream to 300 ° C. at a rate of 10 ° C./min, and from 300 ° C. to 1100 ° C. at a rate of 2 ° C./min. Thereafter, reduction treatment was performed at 1100 ° C. for 1 hour. Thereafter, the temperature was lowered to 400 ° C. at 95 ° C./min, and allowed to cool from 400 ° C. to room temperature over 40 minutes. Subsequently, a slow oxidation treatment was performed at 20 ° C.
- the Ti content in each phase of the magnetic material (the numerical value in the figure is the Ti content in each phase)
- the value of the atomic ratio of Ti with respect to the sum of Ti and Fe of each phase is expressed as a percentage) and is greatly disproportionately distributed in the range of 0.7 atomic% to 15.9 atomic%. I understood it.
- an infinite number of curved crystal boundaries curved at intervals of the order of 10 nm were also observed in a region considered as one phase (that is, a region of ⁇ - (Fe, Ti) phase). .
- the crystal phase observed in this region is a measurement result obtained by averaging the composition in the region between 100 nm and 150 nm in radius with respect to the Ti content, and the distribution is also 0.8 atom% to 2.4 atom It was found that a crystal phase having a Ti content of 2 atomic% or more exists.
- the average crystal grain size of the entire magnetic material was 200 nm.
- the former phase corresponds to the first phase and the latter corresponds to the second phase.
- the volume fraction of the bcc phase was estimated to be 97% by volume.
- the peak position of the (110) diffraction line of the first phase observed by X-ray diffraction is the same as described above except that the Ti component is not added and the reduction temperature is 450 ° C. when measured by CoK ⁇ ray. Compared to the ⁇ -Fe powder produced by the method, it was on the lower angle side of 0.138 °, and the half-value width was 0.26 °.
- the Ti content of the magnetic material of this example was also measured by using XRD, which is considered to be excellent in terms of capturing the macro characteristics of the entire material.
- XRD X-ray diffraction
- the Ti content can be estimated to be about 8 atomic% or less based on the diffraction line peak position, its line width, and literature values, and the Ti content at the diffraction line peak position is about 2 atomic% or more. It was confirmed that it was 3 atomic%.
- Example 2 The Ti-ferrite nanopowder having a composition of (Fe 0.951 Ti 0.049 ) 43 O 57 with an average powder particle size of 20 nm of Comparative Example 1 was charged into an aluminum titanate crucible, The temperature was raised to 300 ° C. at 10 ° C./min, the temperature was raised from 300 ° C. to 600 ° C. at 2 ° C./min, and reduction treatment was performed at 600 ° C. for 1 hour. Thereafter, the temperature was lowered to 400 ° C. at 45 ° C./min and allowed to cool from 400 ° C. to room temperature over 40 minutes. Subsequently, a slow oxidation treatment was performed at 20 ° C.
- the obtained magnetic material is measured by X-ray diffraction, only the ⁇ - (Fe, Ti) phase is clearly recognized.
- the ⁇ - (Fe, Ti) phase which is a bcc phase is the main component.
- the presence of the first phase was confirmed.
- the peak position of the (110) diffraction line of the ⁇ - (Fe, Ti) phase observed by X-ray diffraction is compared with the ⁇ -Fe phase prepared in Example 1 when measured by CoK ⁇ ray. It was on the 0.085 ° lower angle side, and the half width was 0.21 °.
- this soft magnetic material has an ⁇ - (Fe, Ti) phase of 10 nm to 500 nm and a spawn phase of several nm.
- the Ti content in each phase was in the range of 1.9 atomic% to 5.4 atomic%, 5.9 atomic% to 8.1 atomic%, respectively. Therefore, it was found that the spawn phase is richer in Ti than the ⁇ - (Fe, Ti) phase.
- the magnetic material of this example was measured in the same manner as in Example 1 by using XRD.
- the Ti content can be estimated to be approximately 5 atomic% or less, and the Ti content at the peak position that can be judged as the (110) diffraction line of the ⁇ - (Fe, Ti) phase is about 2 atomic%. I confirmed that there was.
- the above-mentioned result of X-ray diffraction (that is, only the ⁇ - (Fe, Ti) phase that is the bcc phase was clearly observed for the observed magnetic material) and the above-mentioned result of FE-SEM (that is, the observed magnetic property)
- the material has an ⁇ - (Fe, Ti) phase having a Ti content of 1.9 atomic% to 5.4 atomic% and a Ti content of 2 atomic% or more from 5.9 atomic% to 8.1 atomic%
- the result of XRD (the ⁇ - (Fe, Ti) phase also has an ⁇ - (Fe, Ti) phase with a Ti content of 2 atomic%).
- the observed magnetic material has an ⁇ - (Fe, Ti) phase and a spawn phase having a Ti content higher than that phase, and this ⁇ - (Fe, Ti) It can be seen that an ⁇ - (Fe, Ti) phase, which is distinguished by Ti content, is also formed in the phase.
- the ⁇ - (Fe, Ti) phase having a Ti content of 1.9 atomic% corresponds to the first phase, and 5.9 atomic%.
- a spawn phase having a Ti content of from 8.1 atomic% to ⁇ and an ⁇ - (Fe, Ti) phase having a Ti content of 2.0 atomic% to 5.4 atomic% correspond to the second phase.
- the volume fraction of the bcc phase is estimated to be 92% by volume (excluding the spawn phase).
- the average crystal grain size of the first phase not containing the spawn phase was 100 nm
- the average crystal grain size of the second phase containing the spawn phase was 50 nm. In this case, it is assumed that the crystal grain size of the crystal grains other than the spawn phase does not change greatly depending on the Ti content.
- Ferrite nanopowders were produced in the same manner as in Example 1 or 2 except that the Ti component (titanium chloride aqueous solution) was not added.
- the ferrite nanopowder was prepared in Example 1 except that the reduction conditions were 425 ° C. for 1 hour (Comparative Example 2), the same temperature for 4 hours (Comparative Example 3), and 450 ° C. for 1 hour (Comparative Example 4).
- Fe metal powder was prepared in the same manner as in 2. The measurement was performed in the same manner. Table 1 shows the measurement results of the particle size and magnetic properties. In addition, these metal powders have a property that magnetic properties are lowered at a stretch just by being left in the air at room temperature. Table 2 shows the change rate ⁇ s (%) of saturation magnetization of Comparative Examples 2 to 4.
- Examples 3 to 11 The reduction temperature is set to the temperature shown in Table 1 in the range of 450 to 1200 ° C., and the temperature decrease rate v (° C./min) up to 400 ° C. is the rate indicated by the following relational expression when the reduction temperature is T (° C.).
- a magnetic material of the present invention was produced in the same manner as in Example 1 except that. The measurement was also performed in the same manner as in Example 1. In all of the examples, the observed magnetic material is formed with an ⁇ - (Fe, Ti) phase (first phase) and a phase (second phase) having a higher Ti content than that phase. I confirmed.
- the observed magnetic material includes a first phase of ⁇ - (Fe, Ti) phase and less than 2 atomic%, but more than twice and less than 10 5 times Ti than that phase.
- the second phase including the content (specifically, the titanomagnetite phase and the wustite phase) is formed.
- the observed magnetic material includes an ⁇ - (Fe, Ti) phase. a first phase, 2 albeit less than atomic%, the second phase (specifically containing Ti content of 10 5 times or less in 2 times more than its phase, titanosilicate hematite phase and titanomagnetites phase
- the observed magnetic material includes a first phase of ⁇ - (Fe, Ti) phase and less than 2 atomic%, but more than twice that phase. in (specifically, alpha-(Fe, Ti) phase) second phase comprising 10 5 times or less of the Ti content is formed I was sure that.
- Table 1 The measurement results of these phases, composition, particle size, and magnetic properties are summarized in Table 1.
- Example 6 shows Comparative Example 4 ( ⁇ -Fe powder), Example 2 (reduction at 600 ° C.), Example 3 (reduction at 450 ° C.), Example 9 (reduction at 900 ° C.), and Example 11 (reduction at 1200 ° C.).
- FIG. Within the range of this figure, it was confirmed that the diffraction peak of the (110) plane of the bcc phase shifted to a low angle as the reduction temperature increased. In particular, at 900 ° C. or higher, two types of bcc phases were observed, and the presence of the bcc phase as the first phase and the “bcc phase enriched with Ti” as the second phase was clearly distinguished.
- the shoulder structure on the high angle side is a diffraction peak due to the K ⁇ 2 line of the Co radiation source.
- the actual diffraction line position the generally subtracting the absorption of the K [alpha 2-wire shift to low angle side.
- the presence of Ti in the bcc phase is confirmed by comparison with the magnetic material not containing the Ti component of Comparative Example 4, or the average Ti content of the bcc phase based on the low-angle shift amount and literature values. Although the values are or determined by one significant figure, in the low-angle shift amount at this time, the influence by the absorption of K [alpha 2-wire is obtained by assuming that generally are canceled.
- the change in diffraction position due to being a nanocrystal is also offset by the subtraction when calculating the low angle shift amount in the above comparison, and further the measurement error due to the stability of the XRD apparatus used in this example is also present.
- the samples to be compared on the same day are continuously measured, and the diffraction peak position of the Si standard sample does not change before and after the measurement, thereby guaranteeing the validity of the above comparison.
- “(110) Ti content of bcc phase estimated by low angle shift amount” shown in the table is the maximum of the diffraction peak observed at the lowest angle. Calculation was based on the diffraction angle in the value.
- the other (110) diffraction peaks that is, diffraction peaks other than the “diffracted peak observed at the lowest angle”, are shifted by a low angle by containing Ti.
- the content of K in the entire magnetic material including Ti, Fe, O, and K is 0.04 atomic% to 1.4 atomic% at a reduction temperature of 450 ° C. to 700 ° C., and 0 atomic% at a reduction temperature of 800 ° C. or higher. (Examples 8 to 11).
- the TiO 2 phase was in the region of 0.1-4% by volume in all examples.
- FIG. 7 summarizes the measurement results of saturation magnetization and coercive force of Examples 1 to 11.
- Table 2 shows the saturation magnetization change rate ⁇ s (%) of Examples 1 and 11. The fact that ⁇ s shows a negative value indicates that the saturation magnetization of each magnetic powder is improved after standing at room temperature as compared to immediately after the production. From the result of this table
- surface, it turned out that the oxidation resistance of the metal powder of a present Example is favorable in t 60 or 120.
- Example 12 An Fe—Ti metal powder was prepared in the same manner as in Example 5 except that the reducing conditions were 550 ° C. and 4 hours. The measurement was also performed in the same manner as in Example 1. In the reduction time of 1 hour at 550 ° C., the reduction reaction proceeded and disappeared in the reduction time of 4 hours for the titanohematite phase and titanomagnetite phase that had not disappeared on XRD. From the results of SEM observation, it was found that the magnetic material of this example was a mixed phase of ⁇ - (Fe, Ti) phase and spawn phase. In this example, the observed magnetic material is formed with an ⁇ - (Fe, Ti) phase (first phase) and a phase (second phase) having a Ti content higher than that phase. Also confirmed. The measurement results of the phase, composition, particle size, and magnetic properties of this example are summarized in Table 1.
- This Ti-ferrite nanopowder was charged into an aluminum titanate crucible and heated in a hydrogen stream to 300 ° C. at a rate of 10 ° C./min, and from 300 ° C. to 1100 ° C. at a rate of 2 ° C./min. Thereafter, reduction treatment was performed at 1100 ° C. for 1 hour. Thereafter, the temperature was lowered to 400 ° C. at 95 ° C./min, and allowed to cool from 400 ° C. to room temperature over 40 minutes. Subsequently, a slow oxidation treatment is performed at 20 ° C.
- FIG. 9 shows the result of observation of this magnetic material by the FE-SEM / EDX method.
- a dark blackish crystal phase generally has a high Ti content
- a light and whitish crystal phase generally has a low Ti content.
- crystal phases having different color densities are phase-separated by a disproportionation reaction, and there are portions where aggregates are formed while maintaining chemical bonds.
- the Ti content in each phase of the magnetic material was highly disproportionately distributed at 2.7 to 99.6 atomic%.
- the peak position of the (110) diffraction line of the first phase observed by X-ray diffraction is 0.198 ° lower angle side than the ⁇ -Fe powder of Comparative Example 4 when measured by CoK ⁇ ray.
- the full width at half maximum was 0.21 °. From the result of the X-ray diffraction, it was found that the Ti content of the first phase which is the bcc phase was close to 20 atomic%. Therefore, in the measurement range of FIG. 9, the ⁇ content of 5.4 atomic% to 19.2 atomic% satisfying the condition that the Ti content as the second phase is at least twice 2.7 atomic% of the first phase.
- the second phase (Fe, Ti) is considered to be present, and in addition to the mixed phase, it was found that this phase can also be the second phase of the magnetic material of the present invention.
- the volume fraction of the entire bcc phase including these second phases was estimated to be about 63% by volume.
- the amount of TiO 2 phase present was also found to be at least 2.2% by volume, as observed by FE-SEM / EDX.
- the saturation magnetization of this magnetic material was 129.6 emu / g, the coercive force was 8 A / m, and there was no inflection point on the quarter major loop. Since the magnetic material of Example 13 had a coercive force of 800 A / m or less, it was confirmed to be a soft magnetic material.
- Example 14 The Ti-ferrite nanopowder having a composition of (Fe 0.730 Ti 0.270 ) 43 O 57 with an average powder particle diameter of 20 nm of Comparative Example 5 was charged into an aluminum titanate crucible and heated in a hydrogen stream at 300 The temperature was raised to 10 ° C./min at 10 ° C./min, the temperature was raised from 300 ° C. to 600 ° C. at 2 ° C./min, and reduction treatment was performed at 600 ° C. for 1 hour. Thereafter, the temperature was lowered to 400 ° C. at 45 ° C./min, and the mixture was allowed to cool from 400 ° C. to room temperature over 40 minutes.
- a slow oxidation treatment was performed in an argon atmosphere with an oxygen partial pressure of 1 vol% for 1 hour to obtain a magnetic material having a composition ratio of titanium and iron of Fe 71.4 Ti 28.6 .
- the O content with respect to the entire magnetic material including Ti, Fe, O, and K was 32 atomic%, and the K content was 4.2 atomic%.
- the average powder particle size of this Fe—Ti magnetic material was 30 nm. This magnetic material was analyzed by the following method, and this magnetic material was determined as Example 14.
- the ⁇ - (Fe, Ti) phase which is a bcc phase was the main component. Further, a slight TiO 2 phase (rutile phase), a Laves phase (Ti content of about 27 to 40 atomic%), and a ⁇ -Ti phase (Ti content of 69 atomic% or more) (these phases are combined In the examples, it was confirmed that the mixed phase had a higher Ti content than the ⁇ - (Fe, Ti) phase. Therefore, when this is applied to the definitions of the first phase and the second phase described above, the former ⁇ - (Fe, Ti) phase corresponds to the first phase and the latter mixed phase corresponds to the second phase.
- the magnetic material has an ⁇ - (Fe, Ti) phase of 10 nm to 200 nm and a spawn phase of several nm, as shown in FIG.
- the Ti content in each phase was in the range of 16.6 atomic% to 26.6 atomic% and 19.9 atomic% to 39.3 atomic%, respectively. Therefore, on average, the spawn phase was found to be richer in Ti than the ⁇ - (Fe, Ti) phase.
- the peak position of the (110) diffraction line of the first phase observed by X-ray diffraction is compared with the ⁇ -Fe magnetic powder prepared for comparison with Example 1 when measured by CoK ⁇ ray. 0.127 ° on the lower angle side, and the full width at half maximum was 0.23 °.
- the Ti content can be estimated to be approximately 0 to 20 atomic%. It was found that the Ti content of was about 3 atomic%, which is 2 atomic% or more. Therefore, based on the X-ray diffraction results, it has been clarified that the ⁇ - (Fe, Ti) phase includes the second phase.
- the other second phase is included in the spawn phase. That is, for example, when the spawn phase is referred to as the second phase and the TiO 2 phase is referred to as the second phase, these may indicate the same phase.
- the volume fraction of the bcc phase was estimated to be 55% by volume (excluding the spawn phase).
- the overall average crystal grain size is 30 nm
- the average crystal grain size of the first phase not including the spawn phase is 100 nm
- the average crystal grain size of the second phase including the spawn phase is 30 nm.
- the amount of TiO 2 phase present was found to be at least 2% by volume or more by FE-SEM / EDX observation.
- the saturation magnetization of this magnetic material was 115.5 emu / g, the coercive force was 25.8 kA / m, and there was no inflection point on the quarter major loop. Therefore, it was confirmed that the magnetic material of Example 14 is a semi-hard magnetic material because the coercive force exceeds 800 A / m and is 40 kA / m or less.
- Table 3 The results of measurement of the phase, composition, particle size, and magnetic properties of this example are summarized in Table 3.
- Example 15 to 23 The reduction temperature is set to the temperature shown in Table 3 in the range of 450 to 1200 ° C., and the temperature drop rate v (° C./min) up to 400 ° C. is expressed by the relational expression (2) when the reduction temperature is T (° C.).
- a magnetic material of the present invention was produced in the same manner as in Example 13 except that the speed was used. In all of the examples, the observed magnetic material is formed with an ⁇ - (Fe, Ti) phase (first phase) and a phase (second phase) having a higher Ti content than that phase. I also confirmed.
- Table 3 The results of measurement of the phase, composition, particle size, and magnetic properties of this example are summarized in Table 3.
- Example 11 summarizes the results of saturation magnetization and coercive force of Examples 13 to 23.
- the K content in the entire magnetic material including Ti, Fe, O, and K is 2.8 atomic% to 4.2 atomic% at a reduction temperature of 450 ° C. to 700 ° C., and is 800 ° C. or higher.
- 0 atomic% Examples 8 to 11.
- the TiO 2 phase was in the region of 0.1-4% by volume in all examples.
- Example 24 to 26 A magnetic material of the present invention was produced in the same manner as in Example 1 except that the Ti content, the reduction temperature, and the reduction time were set to the values shown in Table 4 and the rate of temperature increase and the rate of temperature decrease were as shown in Table 4. .
- the observed magnetic material is formed with an ⁇ - (Fe, Ti) phase (first phase) and a phase (second phase) having a higher Ti content than that phase. I also confirmed.
- Table 4 shows the measurement results of the phase, composition, particle size, and magnetic properties of the magnetic material of this example.
- Example 24 is the same as that of Example 5 or 17.
- the “fast” and “slow” conditions of the temperature rising / falling speed shown in Table 4 are as follows. (Temperature increase rate) “Fast”: The temperature is raised to a predetermined reduction temperature at 10 ° C./min. (However, in Examples 25 and 26, when 300 ° C. is reached, annealing is performed with a constant temperature holding process for 15 minutes) “Slow”: The temperature is increased to 10 ° C./min up to 300 ° C., and the temperature is increased at 2 ° C./min from 300 ° C. to a predetermined reduction temperature.
- Example 27 and 28 The magnetic material of the present invention was set in the same manner as in Example 22 except that the temperature increase / decrease rate was set by combining the “fast” and “slow” conditions described in Examples 24 to 26 as shown in Table 4. Produced. In all of the examples, the observed magnetic material is formed with an ⁇ - (Fe, Ti) phase (first phase) and a phase (second phase) having a higher Ti content than that phase. I also confirmed. Table 4 shows the measurement results of the phase, composition, particle size, and magnetic properties of the magnetic material of this example.
- the coercive force is lowered by slowing any of the ascending / descending speeds.
- the coercive force reaches 630 A / m, which is an area of a soft magnetic material.
- Example 29 The magnetic material powder of Example 10 was charged into a 3 ⁇ tungsten carbide carbide mold and cold compression molded in the atmosphere at room temperature and 1 GPa to obtain a green compact. Next, this green compact was sintered under normal pressure in hydrogen at 1000 ° C. for 1 hour to produce a solid magnetic material. The above-mentioned “slow” condition was selected for the temperature rising rate, and the above “fast” condition was selected for the temperature-decreasing rate.
- FIG. 12 is an SEM image obtained by observing the atmospheric pressure sintered body surface of this example. It was observed that there were many crystal boundaries in the sintered continuous layer.
- FIG. 13 is an observation of the polished surface of the surface of the atmospheric pressure sintered body of this example by FE-SEM / EDX.
- the observation area is mostly bcc phase of Fe-Ti metal (total bcc volume fraction is 97% by volume), and the crystal phase is divided into tens to hundreds of nanometers by disproportionation phase separation. Was observed. Further, the Ti content is widely distributed from 0.7 atomic% to 17.7 atomic%, and it has been found that a large Ti composition distribution is exhibited even within one crystal phase due to the disproportionation reaction. .
- Table 5 shows the measurement results of the phase, composition, particle size, magnetic properties, and electrical resistivity of this solid magnetic material.
- the solid magnetic material has a coercive force of 560 A / m and is a soft magnetic material.
- the coercive force is 980 A / m as described in Example 10 above. It was confirmed to be a semi-hard magnetic material.
- the coercive force is reduced because the powder is solidified by being connected by ferromagnetic coupling by sintering.
- Example 30 The magnetic material powder of Example 2 was charged into a 3 ⁇ tungsten carbide carbide mold, and a sintered body was obtained by an electric current sintering method in vacuum at 300 ° C. and 1.4 GPa. Table 5 shows the measurement results of the phase, composition, particle size, magnetic properties, and electrical resistivity of the solid magnetic material, which was the current-sintered body.
- FIG. 14 is an SEM image obtained by observing the surface of the current-sintered body of this example. Many spawn phases exist in the grain boundary of the crystal phase, and the crystal homology of the first phase of 100 nm, or the state where these and the second spawn phase are combined can be observed.
- the solid magnetic material has a coercive force of 560 A / m and is a soft magnetic material.
- the semi-hard material has a coercive force of 12400 A / m. It was confirmed to be a magnetic material.
- the coercive force is greatly reduced because the powder is solidified by being connected by ferromagnetic coupling by sintering.
- Example 31 The magnetic material powder of Example 22 was charged into a 3 ⁇ tungsten carbide super hard die and sintered by an electric current sintering method in vacuum at 300 ° C. and 1 GPa. The obtained solid magnetic material, which is an electric current sintered body, was annealed in hydrogen at 1000 ° C. for 1 hour. For the temperature increase rate, the “slow” condition in the description of Examples 24 to 26 above was selected, and for the temperature decrease rate, the “fast” condition was selected. Table 5 shows the measurement results of the phase, composition, particle size, magnetic properties, and electrical resistivity of this solid magnetic material.
- This solid magnetic material has a coercive force of 620 A / m, which is the soft magnetic material of the present invention.
- the semi-hard material has a coercive force of 850 A / m. It is a magnetic material.
- the coercive force is reduced because the powder is solidified by being connected by ferromagnetic coupling by sintering. From the analysis of the magnetic curve, it was found that the relative magnetic permeability of the solid magnetic materials of Examples 29 to 31 was on the order of 10 3 to 10 4 .
- Comparative Example 6 The powder of Comparative Example 3 was charged into a tungsten carbide cemented carbide die, and sintered by an electric current sintering method in vacuum at 315 ° C. and 1.4 GPa. The electrical resistivity of this material was 1.8 ⁇ m. Table 5 shows the measurement results of the particle size, magnetic characteristics, and electrical resistivity of these solid magnetic materials.
- the solid magnetic material of the present invention described in Examples 29 to 31 has a single-digit electrical conductivity higher than that of the solid magnetic material not containing Ti, and is an existing material such as 0.1 ⁇ m of pure iron. It was found that the electrical resistivity was about two orders of magnitude higher than 0.5 ⁇ m of the electrical steel sheet.
- Example 32 Using the same method as in Example 1, a Ti-ferrite nanopowder having an (Fe 0.996 Ti 0.004 ) 43 O 57 composition with an average powder particle size of 20 nm was obtained. As a result of analyzing the nanopowder by X-ray diffraction, it was found that a cubic Ti-ferrite phase was the main phase and a rhombohedral ferrihydrite phase was slightly contained as an impurity phase. . This Ti-ferrite nanopowder was charged into an alumina crucible, heated to 300 ° C. at a rate of 10 ° C./min in a hydrogen stream, held at 300 ° C. for 15 minutes, and then heated from 300 ° C.
- the average powder particle size of this Fe—Ti magnetic material was 100 ⁇ m.
- This magnetic material was analyzed by the following method. As a result of observing this magnetic material powder by an X-ray diffraction method, it was confirmed that the ⁇ - (Fe, Ti) phase which is a bcc phase is a main component. In addition, the presence of a TiO 2 phase having a higher Ti content than this phase was also confirmed. As a result, it was confirmed that the ⁇ - (Fe, Ti) phase of the bcc phase corresponds to the first phase, and the TiO 2 phase corresponds to the second phase.
- the Ti content calculated from the maximum value of the low angle shift amount at which the diffraction line intensity of (110) was a maximum value was about 1 atomic%.
- the crystallite size calculated from the diffraction line width of (200) was about 30 nm.
- the composition of the crystal phase in the region between the radius of 100 nm and 150 nm is the measurement result averaged with respect to the Ti content, and the distribution of the averaged composition is also 0.01 atom. % To 2.10 atomic%, and it was found that they differ greatly depending on the location.
- the average value of Ti content determined by SEM-EDX was about 0.04 atomic%. Therefore, even in the ⁇ - (Fe, Ti) phase region, the phase can be distinguished by the Ti content, for example, the ⁇ - (Fe, Ti) phase having a Ti content of 0.01 atomic%.
- the volume fraction of the entire bcc phase including these second phases was estimated to be about 99.9% by volume.
- the average crystal grain size of the entire magnetic material of this example was about 300 nm.
- the crystal grain sizes of the first phase and the second phase were each about 300 nm.
- the concentration of Ti content of about 1 nm to 40 nm in the bcc phase including the first phase and the second phase was found that there were fluctuations (contained within a Ti content of 0 atomic percent to 8.5 atomic percent).
- This size corresponds to the size of the crystallite size by XRD measurement.
- the saturation magnetization of the magnetic material of this example was 205.1 emu / g, the coercive force was 80 A / m, and there was no inflection point on the quarter major loop. Since the magnetic material of this example has a coercive force of 800 A / m or less, it was confirmed to be a soft magnetic material.
- the conventional magnetic material has contradictory characteristics, high saturation magnetization, and high electrical resistivity, which can solve the problem of eddy current loss, and requires complicated processes such as a lamination process.
- the present invention is mainly used for power equipment, transformers and information communication equipment, and includes various transformers, heads, inductors, reactors, cores (magnetic cores), yokes, magnet switches, choke coils, noise filters, ballasts, and other various actuators.
- Motors for rotating machines such as voice coil motors, induction motors, reactance motors and linear motors, especially motors for driving automobiles exceeding 400 rpm and generators, machine tools, various generators, various pumps, etc.
- the present invention relates to soft magnetic materials used for rotors, stators, etc., such as motors for household electrical products such as motors, air conditioners, refrigerators, and vacuum cleaners.
- the present invention relates to a soft magnetic material used for sensors via a magnetic field such as an antenna, a microwave element, a magnetostrictive element, a magnetoacoustic element, a Hall element, a magnetic sensor, a current sensor, a rotation sensor, and an electronic compass.
- a magnetic field such as an antenna, a microwave element, a magnetostrictive element, a magnetoacoustic element, a Hall element, a magnetic sensor, a current sensor, a rotation sensor, and an electronic compass.
- the present invention relates to a semi-hard magnetic material used for magnetic recording media and elements such as sensors, magnetic tags and biases such as spin valve elements, tape recorders, VTRs, and hard disks.
- electromagnetic noise absorbing materials electromagnetic materials such as electromagnetic absorbing materials and magnetic shielding materials, magnetic materials that suppress interference caused by unnecessary electromagnetic interference, inductor element materials such as noise removing inductors, RFID ( Radio Frequency Identification) Used for high-frequency soft magnetic and semi-hard magnetic materials such as tag materials and noise filter materials.
- electromagnetic materials such as electromagnetic absorbing materials and magnetic shielding materials
- magnetic materials that suppress interference caused by unnecessary electromagnetic interference inductor element materials such as noise removing inductors
- RFID Radio Frequency Identification Used for high-frequency soft magnetic and semi-hard magnetic materials such as tag materials and noise filter materials.
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Abstract
Description
(1)FeとTiを含むbcc構造の結晶を有する第1相と、Tiを含む相であって、その相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量が、第1相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量よりも多い第2相とを含む、軟磁性又は半硬磁性の磁性材料。
(2)磁性材料が軟磁性である、上記(1)に記載の磁性材料。
(3)第1相が、Fe100-xTix(xは原子百分率で0.001≦x≦33)の組成式で表される組成を有する、上記(1)または(2)に記載の磁性材料。
(4)第1相がFe100-x(Ti100-yMy)x/100(x、yは原子百分率で0.001≦x≦33、0.001≦y<50、MはZr、Hf、Mn、V、Nb、Ta、Cr、Mo、W、Ni、Co、Cu、Zn、Siのいずれか1種以上)の組成式で表される組成を有する、上記(1)~(3)のいずれか一つに記載の磁性材料。
(5)FeとTiを含むbcc構造の結晶を有する相を第2相として含み、その相に含まれるFeとTiの総和を100原子%とした場合のTi含有量が、第1相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量に対して2倍以上105倍以下の量及び/又は2原子%以上100原子%以下の量である、上記(1)~(4)のいずれか一つに記載の磁性材料。
(6)第2相が、Ti-フェライト相或いはウスタイト相の何れか少なくとも1種を含む、上記(1)~(5)のいずれか一つに記載の磁性材料。
(7)第2相がTiO2相を含む、上記(1)~(6)のいずれか一つに記載の磁性材料。
(8)FeとTiを含むbcc構造の結晶を有する相の体積分率が磁性材料全体の5体積%以上である、上記(1)~(7)のいずれか一つに記載の磁性材料。
(9)磁性材料全体の組成に対して、Feが20原子%以上99.998原子%以下、Tiが0.001原子%以上50原子%以下、Oが0.001原子%以上55原子%以下の範囲の組成を有する、上記(6)又は(7)に記載の磁性材料。
(10)第1相若しくは第2相、或いは磁性材料全体の平均結晶粒径が1nm以上10μm未満である、上記(1)~(9)のいずれか一つに記載の磁性材料。
(11)少なくとも第1相がFe100-xTix(xは原子百分率で0.001≦x≦1)の組成式で表される組成のbcc相を有し、そのbcc相の結晶子サイズが1nm以上100nm以下である、上記(1)~(10)のいずれか一つに記載の磁性材料。
(12)粉体の形態の磁性材料であって、軟磁性の磁性材料の場合には10nm以上5mm以下の平均粉体粒径を有し、半硬磁性の磁性材料の場合には10nm以上10μm以下の平均粉体粒径を有する、上記(1)~(11)のいずれか一つに記載の磁性材料。
(13)少なくとも第1相及び第2相が隣り合う相と強磁性結合している、上記(1)~(12)のいずれか一つに記載の磁性材料。
(14)第1相と第2相が、直接、或いは金属相若しくは無機物相を介して連続的に結合し、磁性材料全体として塊状を成している状態である、上記(1)~(13)のいずれか一つに記載の磁性材料。
(15)平均粉体粒径が1nm以上1000nm未満のチタンフェライト粉体を、水素ガスを含む還元性ガス中で、還元温度400℃以上1290℃以下にて還元することによって上記(12)に記載の磁性材料を製造する方法。
(16)平均粉体粒径が1nm以上1000nm未満のチタンフェライト粉体を、水素ガスを含む還元性ガス中で還元し、不均化反応により第1相と第2相を生成させることによって、上記(1)~(13)のいずれか一つに記載の磁性材料を製造する方法。
(17)上記(15)または(16)に記載の製造方法によって製造される磁性材料を焼結することによって、上記(14)に記載の磁性材料を製造する方法。
(18)上記(15)に記載の製造方法における還元工程後に、或いは上記(16)に記載の製造方法における還元工程後若しくは生成工程後に、或いは上記(17)に記載の製造方法における焼結工程後に、最低1回の焼鈍を行う、軟磁性又は半硬磁性の磁性材料の製造方法。
本発明によれば、フェライトのように粉体材料の形態で使用できるので、焼結などにより容易にバルク化でき、そのため、既存の薄板である金属系軟磁性材料を使用することによる積層などの煩雑な工程やそれによるコスト高などの問題も解決することができる。
本発明で言う「磁性材料」とは、「軟磁性」と称される磁性材料(即ち、「軟磁性材料」)と「半硬磁性」と称される磁性材料(即ち、「半硬磁性材料」)のことである。ここで、「軟磁性材料」とは、保磁力が800A/m(≒10Oe)以下の磁性材料のことで、「半硬磁性材料」とは、保磁力が800A/mを超え40kA/m(≒500Oe)以下の磁性材料のことである。優れた軟磁性材料とするには、低い保磁力と高い飽和磁化或いは透磁率を有し、低鉄損であることが重要である。鉄損の原因には、主にヒステリシス損失と渦電流損失があるが、前者の低減には保磁力をより小さくすることが必要で、後者の低減には材料そのものの電気抵抗率を高くすることや実用に給する成形体全体の電気抵抗を高くすることが重要になる。半硬磁性材料では、用途に応じた適切な保磁力を有し、飽和磁化や残留磁束密度が高いことが要求される。中でも高周波用の軟磁性或いは半硬磁性材料では、大きな渦電流が生じるため、材料が高い電気抵抗率を有すること、また粉体粒子径を小さくすること、或いは板厚を薄板或いは薄帯の厚みとすることが重要になる。
「磁性粉体」は、一般に磁性を有する粉体を言うが、本願では、本発明の磁性材料の粉体を「磁性材料粉体」と言う。よって、「磁性材料粉体」は「磁性粉体」に含まれる。
本発明において、第1相は、FeとTiを含むbcc構造の立方晶(空間群Im3m)を結晶構造とする結晶である。この相のTi含有量は、その相中に含まれるFeとTiの総和(総含有量)を100原子%とすると、好ましくは0.001原子%以上33原子%以下である。即ち、第1相の組成は、組成式を用いると、Fe100-xTix(xは原子百分率で0.001≦x≦33)と表される。
このbcc構造を有するFe-Ti組成の第1相は、Feの室温相であるα相と結晶の対称性が同じであるので、本願では、これをα-(Fe,Ti)相とも称する。
したがって、例えば、第1相がFe100-xTix(xは原子百分率で0.001≦x≦33)の組成式を有する場合に、そのTi成分がM成分によって0.01原子%以上50原子%未満の範囲で置換されたとすると、その組成式は、Fe100-x(Ti100-yMy)x/100(x、yは原子百分率で0.001≦x≦33、0.001≦y<50、MはZr、Hf、Mn、V、Nb、Ta、Cr、Mo、W、Ni、Co、Cu、Zn、Siのいずれか1種以上)で表される。
本発明において、第2相は、該相に含まれるFeとTiの総和に対するTiの含有量が、第1相に含まれるFeとTiの総和に対するTiの含有量よりも多い相である。換言すると、本発明において、第2相は、該相に含まれるFeとTiの総和に対するTiの原子百分率が、第1相に含まれるFeとTiの総和に対するTiの原子百分率よりも大きい相である。第2相としては、立方晶である、α-(Fe1-yTiy)相(空間群Im3m、第1相と同じ結晶相であるが、第1相よりもTi含有量が多い相)、TiFe相(空間群Pm3m)、γ-(Fe,Ti)相(空間群Fm3m)、ウスタイト相(代表的組成は(Fe1-zTiz)aO相、aは通常0.85から1未満、本明細書では、この相を単に(Ti,Fe)O相、(Fe,Ti)O相と標記する場合もある)、Ti-フェライト相(代表的組成は(Fe1-wTiw)3O4相、式中のTiが他のM成分を持たないときにはチタノマグネタイト相という。また式中のTiが他のM成分を持たずW=1/3のときウルボスピネル相ともいう。)、β-Ti相(23原子%までのFeや8原子%までOが含まれる場合もある)など、六方晶であるラーベス相(代表的組成はTiFe2相)、α-Ti相(24原子%までのOが含まれる場合もある)など、菱面体晶であるイルメナイト相(代表的組成はTiFeO3相)、チタノヘマタイト相(代表的組成はFe2-uTiuO3相)など、正方晶であるTiO2相のうちアナターゼ相、ルチル相など、斜方晶である擬ブロッカイト相(ferrous pseudobrookite相、代表的組成はFe1+vTi2-vO5相)、ブルッカイト型TiO2相など、さらにTi-Feアモルファス相など、Ti70Fe30共晶点組成相(組成比は有効数字1桁で記載)、Ti90Fe10共析点組成相(組成比は有効数字1桁で記載)など、又はそれらの混合物が挙げられる。なお、アモルファス相、共晶点組成相及び共析点組成相(本願では、「アモルファス相など」とも呼ぶ)に関しては、Ti含有量や還元条件によって異なるが、アモルファス相などが存在する際には、前述した既存のナノ結晶-アモルファス相分離型材料のような微結晶が島状となってアモルファスの海に浮かぶような微細構造は取らずに、第1相と分離して島状に存在することが多い。アモルファス相などの含有量は0.001から10体積%の間であって、これよりも多くしないのが、磁化の低下抑制の観点から好ましく、さらに高磁化の磁性材料とするためには、好ましくは5体積%以下とする。アモルファス相などは、不均化反応自体を制御するために、敢えて含有させることもあるが、この場合、0.001体積%超とするのが、この反応制御効果の発揮という観点から好ましい。
FeもTiも含まず、M成分の化合物だけで混在する相は、第1相や第2相に含まれない。しかし、電気抵抗率、耐酸化性、焼結性、及び本発明の半硬磁性材料の電磁特性改善に寄与する場合がある。上記のM成分の化合物相やFe化合物相などTi成分を含まない相、及び、M成分の含有量がTi元素の含有量以上である相を本願では「副相」という。
第2相が第1相と同じ結晶構造を有してもよいが、組成には相互に十分に差があることが大切で、例えば、第2相中のFeとTiの総和に対する第2相のTi含有量は、第1相中のFeとTiの総和に対する第1相のTi含有量よりも多く、更に、その差が2倍以上であること及び/又は第2相中のFeとTiの総和に対する第2相のTi含有量が2原子%以上であることが好ましい。
第2相のTi成分含有量自体が100原子%を超えることはなく、また、第1相のTi含有量の下限値が0.001原子%では、第2相のTi含有量が第1相のTi含有量の105倍を超えることはない。第2相のTi含有量は、好ましくは、第1相のTi含有量の90原子%以下である。第2相が常温で第1相と同じ結晶構造を保ったまま、Ti含有量が90原子%を超えると(従って、第2相のTi含有量が第1相のTi含有量の9×104倍を超えると)、本発明の磁性材料全体の熱的安定性が悪くなることがあるためである。
以下に、第2相の特定の仕方について述べる。まず、上述の通り、第1相はα-(Fe,Ti)相であり、主に高い飽和磁化を保証する。第2相は、その相に含まれるFeとTiの総和に対するTiの含有量が第1相に含まれるFeとTiの総和に対するTiの含有量よりも多い相である。本発明では、第2相は、磁性材料全体のTi含有量よりも多いα-(Fe,Ti)相でもよく、他の結晶相或いはアモルファス相、又はそれらの混合相でもよい。いずれであっても、本発明の軟磁性材料においては、保磁力を低く保つ効果があり、半硬磁性材料を含めても、耐酸化性を付与し電気抵抗率を向上させる効果がある。従って、第2相はこれらの効果を有する相の総体であるため、Tiの含有量が第1相よりも高い、先に例示した何れかの相の存在を示すことができれば本発明の磁性材料であるとわかる。もし、このような第2相が存在せず、第1相のみで構成されていれば、保磁力などの磁気特性、耐酸化性及び電気伝導率のうち何れかが劣るか、さらに加工性に乏しく、成形工程が煩雑にならざるを得ない磁性材料となる。
本発明の磁性材料において、強磁性として好ましい第2相の代表例としては、まず、第2相中のFeとTiの総和に対する第2相のTi含有量が、第1相中のFeとTiの総和に対する第1相よりもTi含有量が多く、しかも、好ましくはこのTi含有量が第2相中のFeとTiの総和に対して、0.1原子%以上20原子%以下、さらに好ましくは2原子%以上15原子%以下、特に好ましくは5原子%以上10原子%以下であるα-(Fe,Ti)相がある。
不均化により、第1相中のFeとTiの総和に対する第1相のTi含有量と、第2相中のFeとTiの総和に対する第2相のTi含有量との間に差が生じていて、空間的にナノスケールの微細なTi含有量の濃度のゆらぎがあれば、磁気異方性の空間的なゆらぎが生じ、外部磁場が付与されたときに一気に(あたかも共鳴現象が起こったように)磁化反転していくようなメカニズムに含まれる。上記の濃度のゆらぎは第2相が酸化物相である場合だけでなく、α-(Fe,Ti)相であっても、同様な保磁力低減の効果がある。
本願の実施例において、本発明の磁性材料の金属元素の局所的な組成分析は、主にEDX(エネルギー分散型X線分光法)により行われ、磁性材料全体の組成分析はXRF(蛍光X線元素分析法)により行われた。一般に第1相と第2相のTi含有量は、SEM(走査型電子顕微鏡)、FE-SEM、或いはTEM(透過型電子顕微鏡)などに付属したEDX装置により測定する(本願においては、このEDXを付属したFE-SEMなどをFE-SEM/EDXなどと記載することがある)。装置の分解能にもよるが、第1相と第2相の結晶構造が300nm以下の微細な構造であれば、SEM或いはFE-SEMでは正確な組成分析はできないが、本発明の磁性材料のTiやFe成分の差のみを検出するためであれば、補助的に利用することができる。例えば、Ti含有量が5原子%以上で、300nm未満の第2相を見出すには、磁性材料中のある1点を観測して、その定量値がTi含有量として5原子%以上であることを確認すれば、その一点を中心として直径300nmの範囲内に、Ti含有量が5原子%以上の組織或いはその組織の一部が存在することになる。また、逆にTi含有量が2原子%以下の第1相を見出すためには、磁性材料中のある1点の観測をして、その定量値がTi含有量として2原子%以下であることを確認すれば、その一点を中心として直径300nmの範囲内に、Ti含有量2原子%以下の組織或いはその組織の一部が存在することになる。
TEMに付属したEDX装置を用いて組成の分析を行うときは、例えば電子ビームを0.2nmに絞ることも可能で、非常に微細な組成分析を行うことが可能である。しかし逆に、ある一定の領域を満遍なく調べ、本発明の材料の全体像を知るためには、例えば6万点などといった大量のデータを扱う必要性が生じる。
即ち、上記の組成分布測定法を適宜選択して、本発明の磁性材料の組成上、構造上の特徴、例えば第1相、第2相の組成や結晶粒径などを特定しなければならない。
本発明における磁性材料全体における各組成は、磁性材料全体の組成に対して、Fe成分が20原子%以上99.999原子%以下、Ti成分が0.001原子%以上50原子%以下、O(酸素)が0原子%以上55原子%以下の範囲とし、これらを同時に満たすものが好ましい。さらに、Kなどのアルカリ金属が0.0001原子%以上5原子%以下で含まれてもよい。Kなどを含めた副相は全体の50体積%を超えないのが望ましい。
本発明のひとつは、保磁力が800A/m以下である軟磁性用途に好適な磁気特性と電気特性、並びに耐酸化性を有する磁性材料であるが、この点について以下に説明する。
10μΩm以上の電気抵抗率を示す本発明の軟磁性材料では、電気抵抗率が増すにつれて飽和磁化が低下する傾向があるので、所望の電磁気特性に合わせて、原材料の組成や還元度合を決定する必要がある。特に1000μΩm未満が、本発明の磁性材料の磁化が高いという特徴を得るのに好ましい。よって、好ましい電気抵抗率の範囲は1.5μΩm以上1000μΩm以下である。
本発明の磁性材料が、軟磁性になるか半硬磁性になるかは、前述のように保磁力の大きさによって分かれるが、特にその微細構造と密接な関係がある。α-(Fe,Ti)相やTi富化相は一見連続相として観察される場合があるが、多くの異相界面や結晶粒界を含み、また、接触双晶、貫入双晶などの単純双晶や集辺双晶、輪座双晶、多重双晶などの反復双晶を含む双晶、連晶(例えば図1を参照。上部が第1相、下部がTi富化相。第1相中の結晶境界が大きく湾曲した曲線群で観察される)、骸晶(例えば図2を参照。画面中央の黒い色のTi富化相において、内部が窪んだ、四角い渦巻き状の組織が観測される。この組織から相分離したと思われる白い色の第1相がこの組織に結合しているのが見られ、さらにその第1相からまた別の微細なTi富化相が相分離しているなど複雑な不均化反応の過程で形成された構造が見られる)などが含まれており、場所によりTi含有量に大きな差が見られる。本発明では、異相界面、多結晶粒界だけでなく、上記の様々な晶癖、晶相、連晶組織、転位などにより、結晶が区分されている場合、それらの境界面を総称して「結晶境界」と呼んでいる。
ランダム異方性モデルで説明される本発明の軟磁性材料では、以下の3条件を充足していることが大切である。
(1)α-(Fe,Ti)相の結晶粒径が小さいこと、
(2)交換相互作用により強磁性結合していること、
(3)ランダムな配向をしていること。
(3)について、特にbcc相のTiの含有量が10原子%以下である領域では、必ずしも必須ではなく、この場合、保磁力の低下はランダム異方性モデルとは異なる原理で生じている。即ち、第1相と第2相、第1相同志、第2相同志の何れか1種以上の相互作用により、ナノスケールのTi含有量の濃度のゆらぎに基づく磁気異方性のゆらぎが生じて、磁化反転が促され、保磁力の低減がなされる。このメカニズムによる磁化反転機構は、本発明に特有のものであり、本発明者らが知りうる限り、本発明者らによって初めて見出されたものである。
還元時に粒成長や、強磁性相が連続するように粒子同士が融着していない場合や、粒子同士が分離してしまうような相分離が生じている場合に、本発明の磁性材料の保磁力を軟磁性領域に持っていくためには、その後に焼結などを施して固化、即ち、「第1相と第2相が、直接、或いは金属相若しくは無機物相を介して連続的に結合し、全体として塊状を成している状態」にするのが望ましい。
本発明の軟磁性材料の第1相、又は第2相の平均結晶粒径、或いは磁性材料全体の平均結晶粒径は、10μm以下であることが好ましい。第1相及び第2相の平均結晶粒径が10μm以下である場合、磁性材料全体の平均結晶粒径は10μm以下である。
本発明の結晶粒径の測定はSEM法、TEM法または金属顕微鏡法で得た像を用いる。観察した範囲内で、異相界面や結晶粒界だけでなく全ての結晶境界を観察し、それに囲まれた部分の結晶領域の径を結晶粒径とする。結晶境界が見えにくい場合は、ナイタール溶液などを用いた湿式法やドライエッチング法などを用いて結晶境界をエッチングする方がよい。平均結晶粒径は、代表的な部分を選び、最低100個の結晶粒が含まれている領域で計測することを原則とする。これより少なくてもよいが、その場合は、統計的に十分全体を代表する部分が存在していて、その部分を計測していることが求められる。平均結晶粒径は、観測領域を撮影して、その写真平面(対象の撮影面への拡大射影面)上に適当な直角四角形領域を定め、その内部にJeffry法を適用して求める。なお、SEMや金属顕微鏡で観察した場合は、分解能に対して結晶境界幅が小さすぎて観測されないこともあるが、その場合、結晶粒径の計測値は実際の結晶粒径の上限値を与える。具体的には、上限が10μmの結晶粒径測定値を有していればよい。但し、例えばXRD上で明確な回折ピークを持たない、超常磁性が磁気曲線上で確認されるなどの現象から、磁性材料の一部乃至全部が結晶粒径の下限である1nmを切る可能性が示された場合は、TEM観察により実際の結晶粒径を改めて決定しなければならない。また、本発明において結晶境界とは関わらない結晶粒径の測定が必要な場合がある。即ち、Ti含有量の濃度のゆらぎにより、微細に結晶組織が変調している場合などであって、そのような微細構造を有する本発明の磁性材料の結晶粒径は、そのTi含有量の変調幅を結晶粒径とする。この結晶粒径はTEM-EDX解析などで決定する場合が多いが、その大きさは、次の項で記載する結晶子サイズとほぼ対応している場合が多い。
<結晶子サイズの測定>
本発明では、不均化反応により相分離が生じ、第1相及び/又は第2相のbcc相のTi含有量に組成幅が生じる。Ti含有量により、X線の回折線ピーク位置は変化するので、例えばbcc相の(200)における回折線の線幅を求めても、これにより結晶子サイズを決定することには余り意味はない。ここで、結晶子とは、結晶物質を構成する顕微鏡的レベルでの小さな単結晶のことであり、多結晶を構成する個々の結晶(いわゆる結晶粒)よりも小さい。
他方、bcc相のTi含有量が1原子%までの場合、(200)の回折線のずれが約0.07°程度(Co-Kα線)であるので、1nm以上100nm未満の範囲で、有効数字1桁の結晶子サイズを測定することは有意である。
本発明において、結晶子サイズは、Kα2回折線の影響を除いた(200)回折線幅とシェラーの式を用い、無次元形状因子を0.9として、bcc相の結晶子サイズを求めた。
bcc相は、少なくとも第1相が当該相を有する場合(即ち、第1相のみがbcc相を有する場合と、第1相及び第2相の両方がbcc相を有する場合)があるが、その好ましいbcc相の結晶子サイズの範囲は1nm以上100nm未満である。
1nm未満となると、室温で超常磁性となり、磁化や透磁率が極端に小さくなる場合があるので、1nm以上とすることが好ましい。
bcc相の結晶子サイズが100nm未満とすると、保磁力は軟磁性領域に入って極めて小さくなり、各種トランス、モータ等に好適な軟磁性材料となるので好ましい。さらに、50nm以下は、Ti含有量の低い領域であるから2Tを超える高い磁化が得られるだけでなく、低い保磁力も同時に達成でき、非常に好ましい範囲である。
本発明の軟磁性材料の粉体の大きさは10nm以上5mm以下が好ましい。10nm未満であると、保磁力が十分小さくならず、5mmを超えると、焼結の際に大きな歪みがかかり、固化後の焼鈍処理が無いと保磁力が反って大きくなる。さらに好ましくは100nm以上1mm以下であり、特に好ましくは0.5μm以上500μm以下である。この領域に平均粉体粒径が収まれば、保磁力の低い軟磁性材料となる。また、上記で規定した各平均粉体粒径範囲内で粒径分布が十分広ければ、比較的小さな圧力で容易に高充填が達成され、固化した成形体の体積当たりの磁化が大きくなるため、好ましい。粉体粒径が大きすぎると磁壁の移動が励起される場合があり、本発明の軟磁性材料の製造過程における、不均化反応によって形成される異相により、その磁壁移動が妨げられ、むしろ保磁力が大きくなる場合もある。そのため、本発明の軟磁性材料の成形の際、適切な粉体粒径を有した本発明の磁性材料粉体の表面が酸化された状態であった方がよい場合がある。Tiを含む合金は、酸化により表面に酸化チタン(主にTiO2)の不働態膜を形成するため、耐酸化性が極めて優れるだけでなく、保磁力の低減、電気抵抗率の向上などの効果がある。粉体表面の適切な徐酸化、空気中での各工程ハンドリング、還元性雰囲気でなく、不活性ガス雰囲気などでの固化処理なども有効である。
本発明の半硬磁性材料の磁性粉体の平均粉体粒径は10nm以上10μm以下の範囲にあるのが好ましい。10nm未満であると成形しづらく、合成樹脂やセラミックに分散して利用する際も分散性が極めて悪いことがある。また10μmを超える平均粉体粒径では、保磁力が軟磁性領域に至るので、本発明の軟磁性材料の範疇に属する。さらに好ましい平均粉体粒径は10nm以上1μm以下で、この範囲であれば、飽和磁化と保磁力双方のバランスが取れた半硬磁性材料となる。
本発明の磁性材料の粉体粒径は、主としてレーザー回折式粒度分布計を用いて体積相当径分布を測定し、その分布曲線より求めたメジアン径によって評価する。または粉体のSEM法やTEM法で得た写真、または金属顕微鏡写真を元に代表的な部分を選び、最低100個の直径を計測して求める。これより少なくてもよいが、その場合は、統計的に十分全体を代表する部分が存在していて、その部分を計測していることが求められる。特に500nmを下回る粉体、1mmを超える粉体の粒径を計測するときは、SEMやTEMを用いる方法を優先する。又、N種類(N≦2)の測定法又は測定装置を併用し、合計n回の測定(N≦n)を行った場合、それらの数値Rnは、R/2≦Rn≦2Rの間にある必要があって、その場合、下限と上限の相乗平均であるRを持って平均粉体粒径を決定する。
本発明の磁性材料は、第1相と第2相が、直接、或いは、金属相若しくは無機物相を介して連続的に結合し、全体として塊状を成している状態の磁性材料(本願では、「固形磁性材料」とも称する。)として活用できる。また、前述したように、粉体の中に多くのナノ結晶がすでに結合されている場合には、その粉体を樹脂などの有機化合物、ガラスやセラミックなどの無機化合物、またそれらの複合材料などを配合して成形することもできる。
充填率について、本発明の目的を達成できる限り特に限定はないが、Ti成分の少ない本発明の磁性材料の場合は、60体積%以上100体積%以下とするのが、耐酸化性、及び電気抵抗率と磁化の高さのバランスの観点から優れているので好ましい。
本発明の磁性材料粉体は、フェライトのように、焼結可能な粉体材料であることが大きな特徴の一つである。0.5mm以上の厚みを持った各種固形磁性材料を容易に製造することができる。さらに1mm以上、そして5mm以上の厚みを持った各種固形磁性材料でも、10cm以下の厚みであれば、焼結などにより、比較的容易に製造可能である。
さらに、本発明の磁性材料の一つの特徴は、電気抵抗率が大きいことである。他の金属系圧延材料や薄帯材料が、結晶粒界、異相や欠陥を含まないような製法で作られるのに対し、本発明の磁性材料粉体は多くの結晶境界や多様な相を含んでおり、それ自体電気抵抗率を上昇させる効果がある。その上、粉体を固化する際には、特に固化前の粉体の表面酸化層(即ち、第1相や第2相の表面に存在するTiO2、ウスタイト、マグネタイト、Ti-フェライト、イルメナイト、チタノヘマタイト、アモルファスなどの酸素量が高い層、中でもTiを多く含む酸化物層)及び/又は金属層(即ち、Tiを多く含む金属層)が介在するので、バルク体の電気抵抗率も上昇する。
特に、電気抵抗率を上昇させる表面酸化層の好ましい構成化合物としては、TiO2、ウスタイト、Ti-フェライトのうち少なくとも1種が挙げられる。
本発明の磁性材料が上記の特徴を有するのは、本発明が、高磁化であって高周波用途の他の金属系軟磁性材料とは本質的に異なった方法で形成された磁性材料、即ちチタンフェライトナノ粉体を還元して、まずナノ微結晶を有する金属粉体を製造し、さらにそれを成形して固形磁性材料とする、ビルドアップ型のバルク磁性材料を主に提供しているからである。
次に本発明の磁性材料の製造方法について記載するが、特にこれらに限定されるものではない。
本発明の磁性材料の製造方法は、
(1)チタンフェライトナノ粉体製造工程
(2)還元工程
の両工程を含み、必要に応じて、さらに以下の工程のいずれか1工程以上を含んでもよい。
(3)徐酸化工程
(4)成形工程
(5)焼鈍工程
以下に、それぞれの工程について、具体的に述べる。
本発明の磁性材料の原料であるナノ磁性粉体の好ましい製造工程としては、湿式合成法を用いて全室温で合成する方法を備えるものがある。
公知のフェライト微粉体の製造方法としては、乾式ビーズミル法、乾式ジェットミル法、プラズマジェット法、アーク法、超音波噴霧法、鉄カルボニル気相分解法などがあり、これらの方法を用いても、本発明の磁性材料が構成されれば好ましい製造法である。但し、本発明の本質である、組成が不均化したナノ結晶を得るためには、主として水溶液を用いた湿式法を採用するのが最も工程が簡便で好ましい。
本製造工程は、特許文献1に記載されている「フェライトめっき法」を本発明の磁性材料を製造するために使用するチタンフェライトナノ粉体の製造工程に応用したものである。
通常の「フェライトめっき法」は、粉体表面めっきだけでなく、薄膜などにも応用され、また、その反応機構なども既に開示されているが(例えば、阿部正紀、日本応用磁気学会誌、22巻、9号(1998)1225頁(以後、「非特許文献4」と称する。)や国際公開第2003/015109号(以後、「特許文献2」と称する。)を参照)、本製造工程においては、このような「フェライトめっき法」とは異なり、めっきの基材となる粉体表面は利用しない。本製造工程においては、フェライトめっきに利用される原料など(例えば、塩化チタン及び塩化鉄)を100℃以下の溶液中で反応させて、強磁性で結晶性のチタンフェライトナノ粉体そのものを直接合成する。本願では、この工程(或いは方法)を「チタンフェライトナノ粉体製造工程」(或いは「チタンフェライトナノ粉体製造法」)と呼ぶ。
以下に、スピネル構造を有した「チタンフェライトナノ粉体製造工程」に関して例示して説明する。
一方、本発明の実施例では、反応液を滴下してチタンフェライトナノ粉体製造法における原料を反応場に供給しながら、pH調整剤も同時に滴下して、徐々にpHを酸性から塩基性へ変化させることにより、Ti成分を着実にFe-フェライト構造中に取り込んでいくように工程を設計している。この工程によれば、チタンフェライトナノ粒子を製造する段階で、上述のようなメカニズムでフェライトが生成される際に放出されるH+が、pH調整液の連続的な反応場への投入により中和されていき、次々にチタンフェライト粒子の生成や成長が生じる。また、反応初期には、グリーンラストが生じて反応場が緑色になる期間がある(反応場や反応液のpHなどの条件によっては黄色、黄緑色になる期間が前段にある)が、このグリーンラスト中にTi成分が混在することが重要であり、これが最終的にフェライトに転化した際、格子内にTiが取り込まれ、さらにこの後の還元反応において、第1相や第2相の中で、bcc構造を有するα-Fe相にTiが取り込まれていく。
上記方法で製造したチタンフェライトナノ粉体を還元して、本発明の磁性材料を製造する工程である。
よって、Ti-フェライトを水素ガスで還元した場合に、Ti-フェライト中の主なTiイオンであるTi4+イオンがTi金属の価数まで還元される事実は、今までのところ公知ではなく、今回、本発明者が初めて見出したものと考えている。その理由に関して、現時点では、以下のように考えている。
従って、昇温過程の昇温速度や反応炉内の温度分布により結晶相の構成が変化する。
従って、以上の還元工程中に生じる様々なTi含有量が異なるナノスケールのα-(Fe,Ti)相が、強磁性結合によって一体化することにより、本発明の磁性材料として典型的な軟磁性材料が形成されると理解している。
しかし、本発明の磁性材料は、バルクの既存材料とは全く異なった微細構造を有し、常温では平衡状態図に従った組成分布を有してはいないが、還元温度付近で、本発明の磁性材料内にナノ領域に広がる、平衡状態図に沿った均一相が生じていることがあり、その場合には、昇温過程も含めた昇降温の速度制御が、その微細構造にとって重要なことがある。かかる観点から、本発明の還元工程における昇降温速度としては、目的とする電磁気特性やTi含有量によって最適な条件は異なるが、通常、0.1℃/minから5000℃/minの間で適宜選択することが望ましい。
還元速度については、Ti-フェライト相などのTiを含む酸化物相では、Ti含有量が高いほど遅くなる傾向もわかっており、一度不均化が生じると還元反応速度が材料内で一律でなくなることもナノ構造を保持するのに好都合に働いていると考えている。
以上の一連の考察は、本発明の磁性材料は融解してしまうとその特徴を失うはずであることからも支持される。
上記還元工程後の本発明の磁性材料はナノ金属粒子を含むので、そのまま大気に取り出すと自然発火して燃焼する可能性が考えられる。従って必須の工程ではないが、必要に応じて、還元反応の終了後直ちに徐酸化処理を施すことが好ましい。
徐酸化とは、主に還元後のナノ金属粒子の表面を酸化してウスタイト、マグネタイト、Ti-フェライト、TiO2などとして不働態化することにより、内部の磁性材料本体の急激な酸化を抑制することである。本発明の製造方法によると、還元工程までで、第1相、又は、第1相及び第2相中にTiが金属成分として含まれる。本発明の磁性材料は、このTi成分が徐酸化工程により合金表面に析出して不動態膜となるが、Ti成分を含まないFe磁性材料に比べて格段の耐酸化性を備えることになる。徐酸化は、例えば常温付近~500℃内で、酸素ガスのような酸素源を含むガス中で行うが、大気より低酸素分圧の不活性ガスを含む混合ガスを使用する場合が多い。500℃を超えると、どのような低酸素分圧ガスを用いても、表面にnm程度の薄い酸化膜を制御して設けることが難しくなる。また、一旦真空に引いた後、反応炉を常温で徐々に開放して酸素濃度を上げていき、急激に大気に触れさせないようにする徐酸化方法もある。
本願では、以上のような操作を含む工程を「徐酸化工程」と称する。この工程を経ると次の工程である成形工程でのハンドリングが非常に簡便になる。
本発明の磁性材料は、第1相と第2相が、直接、或いは金属相若しくは無機物相を介して連続的に結合し、全体として塊状を成している状態である磁性材料(即ち、固形磁性材料)として利用される。本発明の磁性材料粉体は、そのもののみ固化するか、又は金属バインダや、他の磁性材料や、樹脂などを添加して成形するなどして、各種用途に用いる。なお、(2)の工程後、或いは更に(3)の工程後の磁性材料粉体の状態で、すでに第1相と第2相が、直接、或いは、金属相若しくは無機物相を介して連続的に結合されている場合があって、この場合は本成形工程を経ずとも固形磁性材料として機能する。
上記(1)の工程→(2)の工程、(1)の工程→(2)の工程→(3)の工程、(1)の工程→(2)の工程→後述の(5)の工程、(1)の工程→(2)の工程→(3)の工程→後述の(5)の工程で得た磁性材料粉体、または、以上の工程で得た磁性材料粉体を(4)の工程で成形した磁性材料を再び粉砕した磁性材料粉体、さらに、以上の工程で得た磁性材料粉体を後述の(5)の工程で焼鈍した磁性材料粉体を、高周波用の磁性シートなどの樹脂との複合材料に応用する場合には、熱硬化性樹脂や熱可塑性樹脂と混合した後に圧縮成形を行ったり、熱可塑性樹脂と共に混練した後に射出成形を行ったり、さらに押出成形、ロール成形やカレンダ成形などを行ったりすることにより成形する。
本発明の磁性材料は、第1相と第2相を有し、その一方或いは双方の結晶粒径がナノの領域にある場合が典型的である。
例えば、(1)のチタンフェライトナノ粉体製造工程後に、含有水分などの揮発成分の除去を目的とした乾燥と同時に安定した還元を行うため、後工程における不適切な粒成長の阻止や格子欠陥を除去するなどの目的で、数nm程度の微細粒子成分を熱処理する、いわゆる予備熱処理(焼鈍)が行われることがある。この場合、大気中、不活性ガス中や真空中で50℃から500℃程度で焼鈍することが好ましい。
また、(2)の還元工程後に、粒成長や還元による体積減少で生じた結晶格子や微結晶の歪みや欠陥を除去することで、本発明の軟磁性材料の保磁力を低減させることができる。この工程の後、粉体状のままで使用する用途、例えば粉体を樹脂やセラミックなどで固めて使用する圧粉磁心などの用途では、この工程後、或いはこの工程後に粉砕工程などを挟んだ後で、適切な条件で焼鈍すると電磁気特性を向上させることができることがある。
また、(3)の徐酸化工程では、焼鈍が、表面酸化により生じた表面、界面、境界付近の歪みや欠陥の除去に役立つことがある。
(4)の成形工程後における焼鈍が、最も効果的で、予備成形や圧縮成形、ホットプレスなど、その後の切削加工及び/又は塑性加工などで生じる結晶格子、微細構造の歪み、欠陥を除去するために積極的にこの工程後に焼鈍工程を実施することがある。この工程では、それよりも前にある工程で、積算された歪や欠陥などを一気に緩和させることも期待できる。さらには、前述した切削加工及び/又は塑性加工後に、(1)~(4)の工程、(2)~(4)の工程、(3)及び(4)の工程、さらに(4)の工程での歪などを、或いは積算された歪などをまとめて、焼鈍することもできる。
本発明の評価方法は以下の通りである。
磁性粉体の場合、ポリプロプレン製の円筒ケース(内径2.4mm、粉体層の厚みはほぼ1.5mm)に仕込み、成形体の場合は直径3mm、厚み約1mmの円盤上に成形し、振動試料型磁力計(VSM)を用いて外部磁場が-7.2MA/m以上7.2MA/m以下の領域で磁気曲線のフルループを描かせ、室温の飽和磁化(emu/g)及び保磁力(A/m)の値を得た。飽和磁化は5NのNi標準試料で補正し、飽和漸近則により求めた。保磁力は低磁場の領域の磁場のずれを、常磁性体のPd標準試料を用いて補正した。この測定において、7.2MA/mまで着磁した後、零磁場までの磁気曲線上に滑らかな段差、変曲点が見られない場合、「1/4メジャーループ上の変曲点」が「無」いと判断した。なお、測定磁場の方向は、磁性粉体の場合には軸方向、成形体の場合にはラジアル方向である。
常温、大気中に一定期間t(日)放置した磁性粉体の飽和磁化σst(emu/g)を上記の方法で測定し、初期の飽和磁化σs0(emu/g)と比較して、その低下率を、
Δσs(%)=100×(σs0-σst)/σs0の式
により評価した。Δσsの絶対値が0に近いほど高い耐酸化性能を有すると判断できる。本発明では、Δσsの絶対値が1%以下の磁性粉体を、期間t日において耐酸化性が良好と評価した。なお、本発明において、t(日)は60又は120である。
成形体をファン・デル・ポー(van der Pauw)法で測定した。
粉体やバルクの磁性材料におけるFe及びTi含有量は、蛍光X線分析法により定量した。磁性材料中の第1相や第2相のFe及びTi含有量は、FE-SEMで観察した像をもとに、それに付属するEDXにより定量した。また、α-(Fe,Ti)相の体積分率については、XRD法の結果とともに上記FE-SEMを用いた方法を組み合わせて画像解析により定量した。主として、観察された相が、α-(Fe,Ti)相と酸化物相のいずれであるかを区別するために、SEM-EDXを用いた酸素特性X線面分布図を使用した。さらに、(I)で測定した飽和磁化の値からも、α-(Fe,Ti)相体積分率の値の妥当性を確認した。
K量については、蛍光X線分析法により定量した。
磁性粉体を走査型電子顕微鏡(SEM)又は透過型電子顕微鏡(TEM)で観察して粉体粒径を決定した。十分全体を代表する部分を選定し、n数は100以上として、有効数字1桁で求めた。
磁性材料を走査型電子顕微鏡(SEM)で観察し、結晶境界で囲まれた部分の大きさを有効数字1桁で求めた。測定領域は十分全体を代表する部分を選定し、n数は100以上とした。結晶粒径は、全体の平均値、第1相及び第2相のみの平均値をそれぞれ別途計測して決定した。また、透過型電子顕微鏡(TEM)に付属するEDX装置を用いて、Ti含有量の差のある部分の大きさを調べ、微細なスケールの結晶粒径を見積もることも行った。Ti含有量の測定点数は65536点とした。
(VII) 結晶子サイズ
X線回折法により測定したbcc相の(200)回折線の線幅に対して、シェラーの式をあてはめ、無次元形状因子を0.9として、結晶子サイズを求めた。
TiCl4水溶液(塩化チタン水溶液)とFeCl2・4H2O(塩化鉄(II)四水和物)の水溶液を別途調製し、これらを混合して50.3mMに調製したTiCl4及びFeCl2の混合水溶液をリアクターに入れて反応場液とした。続いて、大気中にて激しく撹拌しながら、660mMの水酸化カリウム水溶液(pH調整液)を滴下して、系のpHを2.26以上12.80以下の範囲で酸性側からアルカリ性側に徐々に移行して調整し、同時に168mMのFeCl2とTiCl4の混合水溶液(反応液)を滴下して15分間反応させた後、pH調整液と反応液の滴下を中止して、さらに15分間撹拌操作を続けた。その後、遠心分離により固形成分を沈殿させ、精製水に再分散し遠心分離を繰り返すことにより、上澄み溶液のpHを9.13として、最後にエタノール中に沈殿物を分散した後、遠心分離を行った。
これらの画像解析、X線回折及び酸素含有量などにより、bcc相の体積分率は97体積%と見積もられた。なお、上記のように第2相を決定することにより、SEM像から第1相及び第2相の結晶粒径を決めることができ、画像解析の結果、それらの値はそれぞれ200nm及び400nmであった。
この磁性材料の飽和磁化は、202.8emu/g、保磁力は680A/mであり、4分の1メジャーループ上に変曲点はなかった。
従って、実施例1の磁性材料は保磁力が800A/m以下なので、本実施例の磁性材料が軟磁性材料であることも確認された。
本実施例の相、組成、粒径及び磁気特性の測定結果については表1に纏めて示した。
比較例1の平均粉体粒径が20nmの(Fe0.951Ti0.049)43O57組成を有したTi-フェライトナノ粉体を、チタン酸アルミニウム製のるつぼに仕込み、水素気流中、300℃までは10℃/minで昇温し、300℃℃から600℃までは2℃/minで昇温した後、600℃で1時間還元処理を行った。この後400℃までは45℃/minで降温し、400℃~室温までは40分をかけて放冷した。続いて20℃にて、酸素分圧1体積%のアルゴン雰囲気中で1時間徐酸化処理を行い、チタンと鉄の含有量比が、Fe94.4Ti5.6組成の磁性材料を得た。このときのTi、Fe、O、Kを含む全体の磁性材料に対するOの含有量は6.0原子%であり、Kの含有量は0.2原子%であった。また、このFe-Ti磁性材料の平均粉体粒径は50nmであった。この磁性材料に関する解析は以下の方法により行い、この磁性材料を実施例2とした。
これらの画像解析、X線回折及び酸素含有量などにより、bcc相の体積分率は92体積%(スポーン相を除く)と見積もられる。また、スポーン相を含まない第1相の平均結晶粒径は100nm、スポーン相を含む第2相の平均結晶粒径は50nmであることを確認した。この場合、Ti含有量により、スポーン相以外の結晶粒の結晶粒径は大きく変化しないと仮定している。
この磁性材料の飽和磁化は、194.1emu/g、保磁力は12.4kA/mであり、4分の1メジャーループ上に変曲点はなかった。
従って、実施例2の磁性材料は保磁力が800A/mを超え40kA/m以下なので、半硬磁性材料であることが確認された。
本実施例の相、組成、粒径及び磁気特性の測定結果は表1に纏めて示した。
Ti成分(塩化チタン水溶液)を添加しないこと以外は実施例1又は2と同様な方法で、フェライトナノ粉体を作製した。
このフェライトナノ粉体を、還元条件を425℃で1時間(比較例2)、同温度で4時間(比較例3)、450℃で1時間(比較例4)とする以外は、実施例1又は2と同様な方法でFe金属粉体を作製した。測定についても同様な方法で行った。
これら粒径及び磁気特性等の測定結果は表1に示した。
なお、これらの金属粉体は、室温大気中に放置するだけで、磁気特性が一気に低下する性質がある。表2に本比較例2~4の飽和磁化の変化率Δσs(%)を示した。
還元温度を450~1200℃の範囲で表1に示した温度とし、400℃までの降温速度v(℃/min)は、還元温度をT(℃)とした場合、以下の関係式で示す速度とする以外は実施例1と同様にして、本発明の磁性材料を作製した。
測定についても、実施例1と同様な方法で行った。そして、本実施例の全てにおいて、観測した磁性材料には、α-(Fe,Ti)相(第1相)と、その相よりもTi含有量の多い相(第2相)が形成されていることを確認した。なお、実施例3では、観測した磁性材料には、α-(Fe,Ti)相の第1相と、2原子%未満ではあるが、その相よりも2倍以上で105倍以下のTi含有量を含む第2相(具体的には、チタノマグネタイト相とウスタイト相)が形成されていること、また、実施例4では、観測した磁性材料には、α-(Fe,Ti)相の第1相と、2原子%未満ではあるが、その相よりも2倍以上で105倍以下のTi含有量を含む第2相(具体的には、チタノヘマタイト相とチタノマグネタイト相)が形成されていること、そして実施例8では、観測した磁性材料には、α-(Fe,Ti)相の第1相と、2原子%未満ではあるが、その相よりも2倍以上で105倍以下のTi含有量を含む第2相(具体的には、α-(Fe,Ti)相)が形成されていることを確認した。
これらの相、組成、粒径及び磁気特性の測定結果は表1に纏めて示した。
Ti、Fe、O、Kを含む全体の磁性材料に対するKの含有量は、還元温度450℃から700℃で0.04原子%以上1.4原子%以下、還元温度800℃以上で0原子%(実施例8~11)であった。TiO2相については全ての実施例で0.1~4体積%の領域にあった。
また、表2には実施例1及び11の飽和磁化の変化率Δσs(%)を示した。Δσsが負の値を示すのは、それぞれの磁性粉が作製直後に比べ、常温放置後、飽和磁化が向上していることを示す。この表の結果から、本実施例の金属粉体の耐酸化性は、t=60又は120において、良好であることがわかった。
還元条件を550℃、4時間とする以外は実施例5と同様にして、Fe-Ti金属粉体を作製した。測定についても、実施例1と同様な方法で行った。550℃において1時間の還元時間では、XRD上で消失していなかったチタノヘマタイト相やチタノマグネタイト相が4時間の還元時間では、還元反応が進み消失した。また、SEM観察の結果から、本実施例の磁性材料はα-(Fe,Ti)相とスポーン相の混合相であることがわかった。また、本実施例において、観測した磁性材料には、α-(Fe,Ti)相(第1相)と、その相よりもTi含有量の多い相(第2相)が形成されていることも確認した。
本実施例の相、組成、粒径及び磁気特性の測定結果は表1に纏めて示した。
TiCl4の原料を市販の四塩化チタン水溶液(Tiモル濃度=5.24M)に変更し、FeCl2の混合溶液との組成比を変える以外は実施例1と同様にして、平均粉体粒径20nmの(Fe0.730Ti0.270)43O57のTi-フェライトナノ粉体を作製した。ただし、反応系内のpHは、1.94から14.64まで変化し、遠心分離法で残存する溶液を洗浄する工程が終了した時点でのpHは10.65であった。図8には、このようにして作製したナノ粉体のSEM像を示した。平均粉体粒径は、約20nmである。またX線回折法により解析した結果、立方晶のTi-フェライト相(チタノマグネタイト相)が主な相であり、不純物相としてフェリヒドライト相が含有されていることがわかった。従って、このナノ粉体にはα-(Fe,Ti)相は含まれておらず、これを比較例5の粉体とし、その粒径、磁気特性などを表3に示した。
この磁性材料の飽和磁化は、129.6emu/g、保磁力は8A/mであり、4分の1メジャーループ上に変曲点はなかった。実施例13の磁性材料は保磁力が800A/m以下なので軟磁性材料であることが確認された。
本実施例の相、組成、粒径及び磁気特性の測定結果は表3に纏めて示した。
また、表2には実施例13の飽和磁化の変化率Δσs(%)も示した。この表の結果から、本実施例の金属粉体の耐酸化性は、t=120において、良好であることがわかる。
比較例5の平均粉体粒径20nmの(Fe0.730Ti0.270)43O57組成を有したTi-フェライトナノ粉体を、チタン酸アルミニウム製のるつぼに仕込み、水素気流中、300℃までは10℃/minで昇温し、300℃から600℃までは2℃/minで昇温したのち、600℃で1時間還元処理を行った。この後400℃までは45℃/minで降温し、400℃から室温までは40分をかけて放冷した。20℃にて、酸素分圧1体積%のアルゴン雰囲気中で1時間徐酸化処理を行い、チタンと鉄の含有量比が、Fe71.4Ti28.6組成である磁性材料を得た。このときのTi、Fe、O、Kを含めた全体の磁性材料に対するO含有量は32原子%であり、Kの含有量は4.2原子%であった。また、このFe-Ti磁性材料の平均粉体粒径は30nmであった。この磁性材料に関する解析は以下の方法により行い、この磁性材料を実施例14とした。
α-(Fe,Ti)相の(110)の回折線のピーク位置とその線幅及び文献値から、Ti含有量はほぼ0~20原子%と見積もることができ、上記回折線のピーク位置でのTi含有量は2原子%以上の約3原子%であることがわかった。従って、上記X線回折結果も踏まえると、このα-(Fe,Ti)相には第2相も含まれることが明らかになった。
画像解析、X線回折及び酸素含有量などにより、bcc相の体積分率は55体積%(スポーン相を除く)と見積もられた。また、全体の平均結晶粒径は30nm、スポーン相を含まない第1相の平均結晶粒径は100nm、スポーン相を含む第2相の平均結晶粒径は30nmである。
この磁性材料の飽和磁化は、115.5emu/g、保磁力は25.8kA/mであり、4分の1メジャーループ上に変曲点はなかった。
従って、実施例14の磁性材料は保磁力が800A/mを超え40kA/m以下なので半硬磁性材料であることが確認された。
本実施例の相、組成、粒径及び磁気特性の測定結果は表3に纏めて示した。
還元温度を450~1200℃の範囲で表3に示した温度とし、400℃までの降温速度v(℃/min)は、還元温度をT(℃)とした場合、関係式(2)で示す速度とする以外は実施例13と同様にして、本発明の磁性材料を作製した。また、本実施例の全てにおいて、観測した磁性材料には、α-(Fe,Ti)相(第1相)と、その相よりもTi含有量の多い相(第2相)が形成されていることも確認した。
本実施例の相、組成、粒径及び磁気特性の測定結果は表3に纏めて示した。
なお、図11は実施例13~23の飽和磁化と保磁力の結果をまとめたものである。
本実施例において、Ti、Fe、O、Kを含む全体の磁性材料に対するKの含有量は、還元温度450℃から700℃では2.8原子%から4.2原子%であり、800℃以上で0原子%(実施例8~11)であった。TiO2相については全ての実施例で0.1~4体積%の領域にあった。
Ti含有量、還元温度、還元時間を表4に示す値とし、また昇温速度、降温速度を表4の通りとする以外は、実施例1と同様にして、本発明の磁性材料を作製した。また、本実施例の全てにおいて、観測した磁性材料には、α-(Fe,Ti)相(第1相)と、その相よりもTi含有量の多い相(第2相)が形成されていることも確認した。
本実施例の磁性材料の相、組成、粒径及び磁気特性の測定結果を表4に示した。
表4に示された昇降温速度の「速」い条件と「遅」い条件は、以下のようである。
(昇温速度)
「速」い:所定の還元温度まで10℃/minで昇温する。(但し、実施例25及び26においては、300℃に達した時点で15分間の一定温度保持過程を挟んで焼鈍を行う)
「遅」い:300℃までは10℃/minで昇温し、300℃から所定の還元温度までは2℃/minで昇温する。
(降温速度)
「速」い:400℃までは関係式(2)で定める降温速度(40~95℃/min)で降温し、400℃から常温は40分間かけて放冷する。
「遅」い:300℃までは2℃/minで降温し、300℃から常温は30分かけて放冷する。
昇降温速度として、実施例24~26で記載した「速」い条件と「遅」い条件を表4のように組み合わせて設定する以外は、実施例22と同様にして本発明の磁性材料を作製した。また、本実施例の全てにおいて、観測した磁性材料には、α-(Fe,Ti)相(第1相)と、その相よりもTi含有量の多い相(第2相)が形成されていることも確認した。本実施例の磁性材料の相、組成、粒径及び磁気特性の測定結果を表4に示した。
実施例10の磁性材料粉体を3φのタングステンカーバイド製超硬金型に仕込み、大気中、常温、1GPaの条件で冷間圧縮成形を行い、圧粉体を得た。
次いで、この圧粉体を水素中、1000℃、1時間の条件で常圧焼結し、固形磁性材料を作製した。昇温速度は上記「遅」い条件、降温速度は上記「速」い条件を選択した。図12は、本実施例の常圧焼結体表面を観察したSEM像である。焼結された連続層の中に多くの結晶境界が存在しているのが観察された。
この固形磁性材料の相、組成、粒径、磁気特性及び電気抵抗率の測定結果を表5に示した。
実施例2の磁性材料粉体を3φのタングステンカーバイド製超硬金型に仕込み、通電焼結法により、真空中、300℃、1.4GPaの条件で焼結体を得た。得られた通電焼結体である固形磁性材料の相、組成、粒径、磁気特性及び電気抵抗率の測定結果を表5に示した。
実施例22の磁性材料粉体を3φのタングステンカーバイド製超硬金型に仕込み、通電焼結法により、真空中、300℃、1GPaの条件で焼結を行った。得られた通電焼結体である固形磁性材料を水素中、1000℃、1時間の条件で焼鈍した。昇温速度は上記実施例24~26の記載における「遅」い条件、降温速度は「速」い条件を選択した。
この固形磁性材料の相、組成、粒径、磁気特性及び電気抵抗率の測定結果を表5に示した。
なお、磁気曲線の解析から、実施例29~31の固形磁性材料の比透磁率は103~104のオーダーであることがわかった。
比較例3の粉体をタングステンカーバイド製超硬金型に仕込み、通電焼結法により、真空中、315℃、1.4GPaの条件で焼結を行った。この材料の電気抵抗率は、1.8μΩmであった。これらの固形磁性材料の粒径、磁気特性及び電気抵抗率の測定結果を表5に示した。
実施例1と同様な方法を用いて平均粉体粒径が20nmの(Fe0.996Ti0.004)43O57組成を有したTi-フェライトナノ粉体を得た。このナノ粉体をX線回折法により解析した結果、立方晶のTi-フェライト相が主な相であり、不純物相として菱面体晶のフェリヒドライト相が僅かに含有されていることがわかった。
このTi-フェライトナノ粉体を、アルミナ製のるつぼに仕込み、水素気流中、300℃までは10℃/minで昇温し、300℃で15分間温度保持したのち、300℃から1100℃まで10℃/minで昇温して、1100℃で1時間還元処理を行った。この後400℃までは95℃/minで降温し、400℃から室温までは40分をかけて放冷した。続いて20℃にて、酸素分圧1体積%のアルゴン雰囲気中で1時間徐酸化処理を行い、チタンと鉄の含有量比が、Fe99.6Ti0.4組成の磁性材料を得た。このときのTi、Fe、O、Kを含む磁性材料全体に対するO含有量は0.4原子%であり、K含有量は0であった。また、このFe-Ti磁性材料の平均粉体粒径は100μmであった。この磁性材料に関する解析は以下の方法により行った。
この磁性材料粉体をX線回折法で観測した結果、bcc相であるα-(Fe,Ti)相が主成分であることが確認された。また、この相よりもTi含有量の高いTiO2相の存在も僅かに確認された。これにより、上記bcc相のα-(Fe,Ti)相が第1相に相当し、上記TiO2相が第2相に相当することを確認した。
(110)の回折線強度が極大値となる低角シフト量の最大値から計算されるTi含有量は、約1原子%であった。
また、(200)の回折線幅から計算される結晶子サイズは約30nmであった。
本実施例の材料のSEM-EDX解析を代表的な場所を用いて行った結果、Ti含有量が0.01~2.43原子%と大きく不均化している結果を得た。Ti含有量が少ないbcc相と見られる領域の中にも10nmオーダーの間隔で湾曲した曲線状の無数の結晶境界が観察された。この領域内の結晶相に関して、半径100nmから150nmの間の領域での結晶相の組成がTiの含有量に関して平均化した測定結果であるが、その平均化された組成の分布も0.01原子%から2.10原子%と非常に幅広く、場所により大きく異なっていることがわかった。SEM-EDXによって求めたTi含有量の平均値は約0.04原子%であった。よって、α-(Fe,Ti)相の領域の中にも、Ti含有量で区別できる相、例えば、0.01原子%のTi含有量のα-(Fe,Ti)相に対してその相よりも2倍以上で105倍以下であり、Ti含有量が2原子%以上であるTi含有量2.10原子%のα-(Fe,Ti)相が存在していること、即ち、α-(Fe,Ti)相に関して、第1相以外に第2相に相当する相も存在していることが、この結果からも明らかになった。
これらの第2相を含め、全体のbcc相の体積分率を見積もると約99.9体積%であることがわかった。
本実施例の磁性材料全体の平均結晶粒径は、約300nmであった。第1相及び第2相の結晶粒径は、それぞれ約300nmであった。これらの結晶粒径が結晶子サイズ30nmより大きく測定される理由は、本実施例の平均結晶粒径の測定にSEM観察を用いていることにあり、SEMの分解能が低いため、或いはそもそもSEMでは観測できない結晶境界が存在しているため実際より大きめの値に計測されているからであると考えられる。しかし、本実施例の平均結晶粒径の測定にSEM観察を用いても、この大きさは10μm以下であって、本実施例の平均結晶粒径は、本発明の磁性材料の範囲内にあることが確認された。
また、75万倍の倍率で上記結晶境界付近の観察を行った結果、これらの結晶境界付近には異相が存在していないことを確認した。
さらに、粉体を厚さ100nmに切り出した板状試料に対して、TEM-EDX解析を行ったところ、第1相、第2相を含むbcc相内に約1nmから40nmのTi含有量の濃度ゆらぎ(0原子%から8.5原子%のTi含有量内に収まる)が存在することがわかった。この大きさはXRD測定による結晶子サイズの大きさに相当する。
本実施例の磁性材料の飽和磁化は、205.1emu/g、保磁力は80A/mであり、4分の1メジャーループ上に変曲点はなかった。本実施例の磁性材料は保磁力が800A/m以下なので、軟磁性材料であることが確認された。
Claims (18)
- FeとTiを含むbcc構造の結晶を有する第1相と、Tiを含む相であって、その相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量が、第1相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量よりも多い第2相を含む、磁性材料。
- 磁性材料が軟磁性である、請求項1に記載の磁性材料。
- 第1相が、Fe100-xTix(xは原子百分率で0.001≦x≦33)の組成式で表される組成を有する、請求項1または2に記載の磁性材料。
- 第1相がFe100-x(Ti100-yMy)x/100(x、yは原子百分率で0.001≦x≦33、0.001≦y<50、MはZr、Hf、Mn、V、Nb、Ta、Cr、Mo、W、Ni、Co、Cu、Zn、Siのいずれか1種以上)の組成式で表される組成を有する、請求項1~3のいずれか一項に記載の磁性材料。
- FeとTiを含むbcc構造の結晶を有する相を第2相として含み、その相に含まれるFeとTiの総和を100原子%とした場合のTi含有量が、第1相に含まれるFeとTiの総和を100原子%とした場合のTiの含有量に対して2倍以上105倍以下の量及び/又は2原子%以上100原子%以下の量である、請求項1~4のいずれか一項に記載の磁性材料。
- 第2相が、Ti-フェライト相或いはウスタイト相の何れか少なくとも1種を含む、請求項1~5のいずれか一項に記載の磁性材料。
- 第2相がTiO2相を含む、請求項1~6のいずれか一項に記載の磁性材料。
- FeとTiを含むbcc構造の結晶を有する相の体積分率が磁性材料全体の5体積%以上である、請求項1~7のいずれか一項に記載の磁性材料。
- 磁性材料全体の組成に対して、Feが20原子%以上99.998原子%以下、Tiが0.001原子%以上50原子%以下、Oが0.001原子%以上55原子%以下の範囲の組成を有する、請求項6又は7に記載の磁性材料。
- 第1相若しくは第2相、或いは磁性材料全体の平均結晶粒径が1nm以上10μm未満である、請求項1~9のいずれか一項に記載の磁性材料。
- 少なくとも第1相がFe100-xTix(xは原子百分率で0.001≦x≦1)の組成式で表される組成で表されるbcc相を有し、そのbcc相の結晶子サイズが1nm以上100nm以下である、請求項1~10のいずれか一項に記載の磁性材料。
- 粉体の形態の磁性材料であって、軟磁性の磁性材料の場合には10nm以上5mm以下の平均粉体粒径を有し、半硬磁性の磁性材料の場合には10nm以上10μm以下の平均粉体粒径を有する、請求項1~11のいずれか一項に記載の磁性材料。
- 少なくとも第1相及び第2相が隣り合う相と強磁性結合している、請求項1~12のいずれか一項に記載の磁性材料。
- 第1相と第2相が、直接、或いは金属相若しくは無機物相を介して連続的に結合し、磁性材料全体として塊状を成している状態である、請求項1~13のいずれか一項に記載の磁性材料。
- 平均粉体粒径が1nm以上1μm未満のチタンフェライト粉体を、水素ガスを含む還元性ガス中で、還元温度400℃以上1290℃以下にて還元することによって請求項12に記載の磁性材料を製造する方法。
- 平均粉体粒径が1nm以上1μm未満のチタンフェライト粉体を、水素ガスを含む還元性ガス中で還元し、不均化反応により第1相と第2相を生成させることによって、請求項1~13のいずれか一項に記載の磁性材料を製造する方法。
- 請求項15または16に記載の製造方法によって製造される磁性材料を焼結することによって、請求項14に記載の磁性材料を製造する方法。
- 請求項15に記載の製造方法における還元工程後に、或いは請求項16に記載の製造方法における還元工程後若しくは生成工程後に、或いは請求項17に記載の製造方法における焼結工程後に、最低1回の焼鈍を行う、軟磁性又は半硬磁性の磁性材料を製造する方法。
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WO2018155608A1 (ja) | 2017-02-24 | 2018-08-30 | 国立研究開発法人産業技術総合研究所 | 磁性材料とその製造法 |
US11331721B2 (en) | 2017-02-24 | 2022-05-17 | National Institute Of Advanced Industrial Science And Technology | Magnetic material and process for manufacturing same |
WO2019059256A1 (ja) | 2017-09-25 | 2019-03-28 | 国立研究開発法人産業技術総合研究所 | 磁性材料とその製造法 |
WO2019059259A1 (ja) | 2017-09-25 | 2019-03-28 | 国立研究開発法人産業技術総合研究所 | 磁性材料とその製造方法 |
US11459646B2 (en) | 2017-09-25 | 2022-10-04 | National Institute Of Advanced Industrial Science And Technology | Magnetic material and method for producing same |
US11732336B2 (en) | 2017-09-25 | 2023-08-22 | National Institute Of Advanced Industrial Science And Technology | Magnetic material and method for producing same |
JP2019087665A (ja) * | 2017-11-08 | 2019-06-06 | 国立研究開発法人産業技術総合研究所 | 磁性材料およびその製造方法 |
JP2019087664A (ja) * | 2017-11-08 | 2019-06-06 | 国立研究開発法人産業技術総合研究所 | 磁性材料およびその製造法 |
JP7001259B2 (ja) | 2017-11-08 | 2022-02-04 | 国立研究開発法人産業技術総合研究所 | 磁性材料およびその製造法 |
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JP6521415B2 (ja) | 2019-05-29 |
US10978228B2 (en) | 2021-04-13 |
CN110214355A (zh) | 2019-09-06 |
JPWO2017164375A1 (ja) | 2019-02-14 |
CN110214355B (zh) | 2021-08-24 |
EP3435386A4 (en) | 2020-02-19 |
US20190051436A1 (en) | 2019-02-14 |
EP3435386A1 (en) | 2019-01-30 |
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