JP2005120470A - Method for producing metallic fine particle, and metallic fine particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive coating method having superior mass productivity and imparting superior corrosion resistance, and to provide a metallic fine particle. <P>SOLUTION: This method for producing the fine particle of a metal M1 reduced by an element M2 comprises mixing an oxide powder of a metal M1 with a powder containing such an element M2 that the standard free energy of the formation of its oxide satisfies the relationship of ΔG<SB>M1-O</SB>>ΔG<SB>M2-O</SB>, and heat-treating the mixed powder in a non-oxidizing atmosphere. Then, the surface of the fine particle of the metal M1 is covered with at least one substance among M2, an alloy containing M2, the oxide of M2, and a nitride of M2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  For magnetic recording media such as magnetic tapes and magnetic recording disks, electronic devices such as radio wave absorbers, inductors and printed circuit boards (soft magnetic bodies such as yokes), as well as magnetic beads for nucleic acid extraction and raw materials for medical microspheres The present invention relates to magnetic metal particles used and a method for producing the same.

  As electronic devices become smaller and lighter, the raw materials that make up electronic devices themselves are also required to be nanosized. At the same time, device performance must be improved. For example, for the purpose of improving the magnetic recording density, it is required to simultaneously increase the nanosize and the magnetization of the magnetic particles applied to the magnetic tape.

The main method for producing nanomagnetic particles is a liquid phase synthesis method represented by a coprecipitation method or a hydrothermal synthesis method. The nanomagnetic particles obtained by the liquid phase method were oxide particles such as ferrite and magnetite. Recently, a technique using thermal decomposition of a metal organic material has been taken, and for example, there is one that synthesizes Fe nanoparticles from Fe (CO) ₅ .

Since magnetic particles of metal are larger in magnetization than oxides, there are high expectations for industrial use. For example, metallic Fe has the advantage that its saturation magnetization is 218 A · m ² / kg, which is much larger than that of iron oxide, has excellent magnetic field response, and has high signal intensity. However, since metal particles such as metal Fe are easily oxidized, the specific surface area is extremely increased especially when the particle size is 100 μm or less, and even 1 μm or less, and the particles violently oxidize and burn in the atmosphere. In other words, problems such as violent oxidation in an aqueous solution and degeneration, deterioration of magnetism, and the like have occurred, making it difficult to handle as dry particles. Therefore, oxide particles such as ferrite and magnetite have been widely used.

  Therefore, when the metal particles are handled as dry particles, it is indispensable to provide a coating on the particle surface so that the particles are not directly exposed to the atmosphere (oxygen) in order not to impair the metal function. However, the method of coating the surface with a metal oxide not a little causes oxidative degradation of the metal (Patent Document 1).

  Therefore, a technique for coating metal particles with graphite has been reported (Patent Document 2). However, in order to coat the metal particles with graphite according to this method, the metal particles must be heat-treated at an extremely high temperature of 1600 ° C. to 2800 ° C. in order to create a state in which the metal melts carbon. There is concern about the result. As a coating method that overcomes this problem, there is a method of coating metal particles with boron nitride (BN) (for example, Non-Patent Document 1). BN is a material used for “crucibles”, has a high melting point of 3000 ° C. and excellent thermal stability, and has low reactivity with metals. It also has an insulating property. The production method for applying a BN film to metal particles is as follows: (1) a mixed powder of metal and B is heated by arc discharge in a nitrogen atmosphere, or (2) a mixed powder of metal and B is mixed in a mixed atmosphere of hydrogen and ammonia. There are methods such as heating, or (3) heat-treating a mixture of metal nitrate, urea and boric acid in a hydrogen atmosphere. In particular, since the manufacturing methods (2) and (3) are heat-treated at a low temperature of 1000 ° C., the particle sintering is expected to be greatly suppressed as compared with the graphite coating.

JP 2000-30920 A (pages 9-11, FIG. 2) JP-A-9-143502 (pages 3-4, FIG. 5) “International Journal of Inorganic Materials 3 2001”, 2001, p. 597

  Although a technique for coating graphite on the surface of metal fine particles as disclosed in Patent Document 2 has been devised, there is a problem that production efficiency is low and practicality is poor. In addition, a method of coating metal nitride with boron nitride has been devised, but there is a problem that boron powder is very expensive and the raw material cost is high. Further, since graphite has a structure in which graphene sheets are laminated, lattice defects are always introduced when coating spherical particles. Similarly, since boron nitride has a laminated structure, it is difficult to obtain a completely crystalline coating layer. Therefore, the coating with these defects cannot be said to be satisfactory in applications requiring high corrosion resistance such as magnetic beads. Accordingly, there has been a demand for a metal fine particle having higher corrosion resistance and a production method excellent in industrial productivity that can provide it at low cost and in a simple manner.

  The inventor of the present invention has arrived at the present invention as a result of intensive studies to achieve the above object.

(1) In the method for producing metal fine particles of the present invention, an oxide powder of metal M1 is mixed with a powder containing element M2 in which the standard free energy of formation of oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O. Then, the surface of the metal fine particles of the metal M1 reduced by the element M2 is coated with at least one of M2, M2 oxide, and M2 nitride by heat-treating the mixed powder in a non-oxidizing atmosphere. It is characterized by. In the heat treatment, by using the powder containing the element M2 that satisfies such a relationship with the metal M1, the oxide powder of the metal M1 is reduced by the element M2, and at the same time, a coating such as an oxide of the element M2 is formed. The Therefore, since the generation of the metal particles and the formation of the coating are performed in the same process, the process is greatly simplified and contributes to the improvement of productivity, and oxidation deterioration of the metal fine particles can be prevented. The heat treatment temperature is preferably in the range of 900 ° C to 1500 ° C.

  (2) Still another manufacturing method of the present invention is the manufacturing method of metal fine particles according to (1), wherein the metal M1 is Fe, and the element M2 is Al, Mn, Nb, Ti, V It is at least one of these. Since these M2 elements have a lower standard generation energy of oxide than Fe, the oxide of Fe can be reduced efficiently and reliably. Therefore, magnetic metal fine particles having high saturation magnetization and excellent corrosion resistance can be provided.

(3) In the metal fine particles of the present invention, the surface of the metal fine particles of the metal M1 is an oxide of elements M2, M2 and M2 in which the standard free energy of formation of the oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O It is characterized by being covered with at least one of nitrides. By coating the metal fine particles with an M2 oxide or the like that satisfies the above relationship, metal fine particles having excellent corrosion resistance can be obtained.

(4) Furthermore, other metal fine particles of the present invention are oxides of M2 and M2 of element M2, in which the standard free energy of formation of the oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O with respect to metal M1, Two or more metal M1 particles are contained in the mother particle composed of at least one of M2 nitrides. By using the metal fine particles having such a structure, it is possible to obtain particles having excellent corrosion resistance and to control the specific gravity and dispersibility of the particles.

  (5) Further, another metal fine particle of the present invention is the metal fine particle according to the above (3) or (4), wherein the element M2, the oxide of M2, and the nitridation of M2 in the X-ray diffraction pattern of the metal fine particle Among the diffraction peaks of any of the objects, the peak with the highest intensity has a half-width of 0.3 ° or less, and the intensity ratio of the diffraction peak of metal M1 to the peak with the highest intensity is 0.001 or more. It is characterized by being. This configuration means that the crystallinity of the coating is good, and the particles having such a coating have high reliability and corrosion resistance.

  (6) Further, another metal fine particle of the present invention is the metal fine particle according to any one of (3) to (5), wherein the metal M1 is Fe, and the element M2 is Al, Mn, Nb. , Ti, or V. A structure in which the metal M1 is Fe, which is a magnetic element having a high saturation magnetization, and the M2 element is at least one of Al, Mn, Nb, Ti, and V, which have a low standard generation energy of oxide, makes it easy to obtain a dense coating. In addition, magnetic metal fine particles having high saturation magnetization and excellent corrosion resistance can be provided.

(7) Furthermore, another metal fine particle of the present invention is the metal fine particle according to the above (6), wherein the saturation magnetization value is 100 to 180 A · m ² / kg. Such a saturation magnetization range can be realized by controlling the thickness of the coating and removing the nonmagnetic particles, and can provide metal fine particles having both high saturation magnetization and high corrosion resistance.

  (8) Further, another metal fine particle of the present invention is the metal fine particle according to (7), wherein 1 part by mass of the metal fine particle is added to 100 parts by mass of pure water and held for 1 hour. The elution amount of Fe into the pure water is 0.10 ppm or less. By using the metal fine particles of the present invention whose corrosion resistance has been improved by dense coating, it can be used for applications requiring high corrosion resistance.

  According to the present invention, an inexpensive coating method and metal fine particles excellent in mass productivity can be obtained. In addition, metal fine particles having excellent corrosion resistance can be provided.

The present invention (1) corresponds to a method for coating fine metal particles. That is, the oxide powder of the metal M1 that satisfies the relationship of ΔG _M1-O > ΔG _M2-O in which the standard free energy of formation of the oxide is mixed with the powder containing the element M2, and the mixed powder is mixed in a non-oxidizing atmosphere. By performing the heat treatment, the surface of the metal fine particles of the metal M1 reduced by the element M2 is covered with at least one of M2, M2 oxide, and M2 nitride. The particle size of the metal M1 oxide powder used in this production method can be freely selected according to the target particle size of the metal fine particles. The particle diameter of the metal M1 oxide powder is preferably selected from the range of 0.001 μm to 5 μm. Oxide particles having a particle size of less than 0.001 μm are not only large in “bulk” but also severely secondary agglomerated, making it difficult to handle in subsequent manufacturing processes. Moreover, the particle | grains exceeding 5 micrometers have a small specific surface area, and as a result, a reductive reaction becomes difficult to advance. Practically, the range of 1 to 1000 nm is preferable. The oxide powder of the metal M1 is selected from, for example, oxides of transition metals, noble metals, and rare earth metals M1. The element of the metal M1 is not particularly limited. For example, if it is a magnetic material, Fe, Co, Ni, or an alloy containing these is selected, and the oxide powder is Fe ₂ O ₃ , Fe ₃ O ₄ , CoO. , Co ₃ O ₄ , and NiO. Among these, Fe is particularly preferable as the metal M1 because of its high saturation magnetization.

In the powder containing the element M2, the M1 oxide can be reduced if the standard free energy of formation of the oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O . Here, ΔG _Mi-O represents a value of standard generation energy of Mi oxide (i is 1 or 2). For example, when considering the _Fe 2 _{O 3} as M1 oxide, ΔG _Fe2O3 = -740kJ / mol having a small .DELTA.G _M2-O than _{is, Al 2 O 3, As 2} O 5, CeO 2, Ce 2 O 3 , Co ₃ O ₄ , Cr ₂ O ₃ , Ga ₂ O ₃ , HfO ₂ , In ₂ O ₃ , Mn ₂ O ₃ , Mn ₃ O ₄ , Nb ₂ O ₅ , TiO ₂ , Ti ₂ O ₃ , Ti ₃ O ₅ , V ₂ O ₃ , V ₂ O ₅ , V ₃ O ₅ , ZrO ₂ , Sc ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , various rare earth element oxides, and the like. That is, the element M2 is preferably selected from Al, As, Ce, Co, Cr, Ga, Hf, In, Mn, Nb, Ti, V, Zr, Sc, Y, Ta, and each rare earth element, If it is a powder containing M2, Fe ₂ O ₃ can be reduced. As the powder containing M2, two or more kinds of powders containing different or the same kind of M2 may be used. Especially for Al, Mn, Nb, Ti, V, ΔG _{Fe2O3 of} Al ₂ O ₃ , Mn ₃ O ₄ , Nb ₂ O ₅ , Ti ₂ O ₃ , Ti ₃ O ₅ , V ₂ O ₅ , V ₃ O ₅ Is preferable as the M2 element because iron oxide is easy to reduce. Among these elements, Al and Ti are lighter elements than other elements, so using them for coating lowers the specific gravity of the coated fine metal particles, and is suitable for dispersion in liquids, such as for magnetic beads.

When the oxide of the metal M1 is iron oxide and the M2 element is Ti, Ti for reducing the iron oxide is not limited to Ti alone, and Ti—Al, Ti—X ₁ (X ₁ : Ag, Au, Bi) Ti compounds such as C, Cu, Cs, Cd, Ge, Ga, Hg, K, N, Na, Pd, Pt, Rb, Rh, S, Sn, Tl, Te, Zn), or the like It may be a mixture of Reasons for limiting the X ₁ is standard free energy _{F X-O} of the oxide formation of the X ₁ is larger material than the product of the TiO standard free energy _{F TiO (= -490kJ / mol)} . If the X ₁ element of F _X-O <F _TiO is selected, the element X ₁ acts as a reducing agent and no Ti oxide is generated. The content of X ₁ is not particularly limited as long as Ti is sufficient to reduce iron oxide. On the other hand, when the oxide of the metal M1 is iron oxide and the M2 element is Al, the Al that reduces the iron oxide is not limited to Al alone, and Al—Ti, Al—X ₂ (X ₂ : Ag, Am As, Au, Ba, Be, Bi, C, Ca, Cd, Cr, Cs, Cu, Ga, Gd, Ge, Hg, In, Ir, K, Li, Lu, Mg, Mn, Mo, N, Na Al compound such as Os, Pb, Pd, Pt, Rb, Rh, Re, S, Sb, Sc, Si, Sn, Sr, Tc, Te, Tl, V, W, Zn, Zr) Alternatively, these compounds may be used. Reasons for limiting the X ₂ is greater substance than standard free energy of formation oxide X _{2 F X-O} is generated standard _Al 2 _{O 3} free energy _{F Al2O3 (= -1580kJ / mol)} . If the X ₂ element _satisfying F _X-O <F _{Al 2 O 3} is selected, X ₂ acts as a reducing agent and no Al oxide is generated. The content of X ₂ is not particularly limited as long as it contains Al sufficient to reduce iron oxide.

  The particle size of the M2-containing powder is preferably in the range of 1 nm to 1 mm, and in order to perform the reduction reaction more efficiently, the range of 1 nm to 0.1 mm is preferable. When the particle diameter exceeds 0.1 mm, the reduction reaction temperature becomes high, and it takes time to raise and lower the temperature, so the heat treatment cycle becomes long and the efficiency decreases, or a heat-resistant product must be used as a member of the furnace itself, Disadvantages such as increased equipment costs become significant. More preferably, it is the range of 0.01 micrometer-20 micrometers, Most preferably, it is 0.1 micrometer-5 micrometers. When the particle diameter is less than 0.01 μm, oxidation in the air becomes remarkable and it becomes difficult to function as a reducing agent. If it exceeds 20 μm, the specific surface area is small and the reduction reaction does not proceed sufficiently. In particular, when the thickness is in the range of 0.1 μm to 5 μm, the reduction reaction can proceed sufficiently while suppressing oxidation in the atmosphere.

  The mixing ratio of the M1 oxide powder and the element M2-containing powder is preferably in the vicinity of the stoichiometric ratio where M2 reduces the M1 oxide, and more preferably, M2 is excessive in comparison with the stoichiometric ratio. preferable. If M2 is insufficient, the M1 oxide powder is sintered during the heat treatment and eventually becomes bulky, which is not suitable. For example, when reducing iron oxide with Ti-containing powder or Al-containing powder, the Ti-containing powder or Al-containing powder is preferably 25 to 60 mass% of the entire mixed powder. If it is less than 25 mass%, the reduction is insufficient, and if it exceeds 60 mass%, the ratio of Fe is lowered, causing a decrease in magnetization, which is not suitable. More preferably, it is 30-50 mass%. The mixing of the M1 oxide powder and the element M2-containing powder can be selected from a mortar, a stirrer, a V-shaped mixer, a ball mill, a vibration mill, and other general stirrers.

When the mixed powder of the M1 oxide powder and the M2 containing powder is heat-treated in a non-oxidizing atmosphere, a reduction reaction starts at the contact portion between the M1 oxide powder and the M2 containing powder, and finally the oxides of M2 and M2 , M1 metal particles having a surface coated with at least one of M2 nitrides are formed. Here, M2 and M2 oxide, and M2 nitride M2 may be one type, but may be two or more types. Hereinafter, the metal M1 particles are referred to as M1 metal particles. The atmosphere during the heat treatment is preferably a non-oxidizing atmosphere. For example, an inert gas such as Ar or He, N ₂ , CO ₂ , NH _3, or the like can be used, but is not limited thereto. The heat treatment temperature and time are preferably conditions sufficient for the reduction reaction to proceed sufficiently. More specifically, the heat treatment temperature is preferably in the range of 900 ° C to 1500 ° C. By this heat treatment, oxygen in iron oxide is transferred to M2 element such as Ti and Al, and M2 oxide such as Ti oxide or Al oxide encloses and covers the reduced Fe particles. Become. If the heat treatment temperature is less than 900 ° C., the reduction reaction does not proceed sufficiently, and if it exceeds 1500 ° C., oxidation of M2 elements such as Ti or Al occurs violently, and the sample becomes molten due to heat generated by the oxidation reaction. It becomes bulky.

For example, when M2 is Ti, for example, the oxide of M2 encapsulating and covering the M1 metal particles is typically Ti ₂ O, TiO, Ti ₃ O ₅ , TiO ₂ or the like. However, a mixed phase thereof may be used, and a composition represented by TiO _x (x: 0.3 to 2) is preferable. When x is less than 0.3, TiO _x is chemically unstable, the oxidation activity is increased, and the corrosion resistance is lowered. Further, Ti—X ₁ (X ₁ : Ag, Au, Bi, C, Cu, Cs, Cd, Ge, Ga, Hg, K, N, Na, Pd, Pt, Rb, Rh, S, Sn, In the case of using at least one compound from Tl, Te, and Zn, X ₁ may be contained in the Ti oxide. For example, taking the case where M2 is Al as an example, the Al oxide encapsulating the metal particles is typically Al ₂ O _3, but is not limited thereto, and AlO _y (y: 1.0 to 1.0). The composition represented by 1.5) is preferred. When y is less than 1.0, AlO _y is chemically unstable, and the corrosion resistance is similarly lowered. _Al-X 2 in the starting material (X 2: Ag, Am, As, Au, Ba, Be, Bi, C, Ca, Cd, Cr, Cs, Cu, Ga, Gd, Ge, Hg, In, Ir, K Li, Lu, Mg, Mn, Mo, N, Na, Os, Pb, Pd, Pt, Rb, Rh, Re, S, Sb, Sc, Si, Sn, Sr, Tc, Te, Tl, V, W , Zn, in the case of using at least one) compound from Zr, X ₂ may be contained in the Al oxide.

  The coating material and the M1 metal particles do not necessarily have a core-shell structure, and two or more M1 metal particles are included in particles composed of at least one of M2, M2 oxide, and M2 nitride. A dispersed structure may be used. That is, the configuration in which two or more M1 metal particles are contained in the mother particles such as the M2 oxide is preferable for easily covering the M1 metal particles and improving the corrosion resistance. Further, the metal particle portion does not need to be completely covered with the oxide or the like, and may contain particles in which the metal particles are partially exposed on the surface.

  According to the above manufacturing method, the mixed powder of the M1 oxide powder and the element M2 containing powder is heat-treated in the non-oxidizing atmosphere under the above-described conditions, so that the fine particles of the metal M1 reduced by the element M2 are obtained. , Metal fine particles characterized by being coated with at least one of M2 oxide and M2 nitride. The particle size of the metal fine particles depends on the particle size of the M1 oxide powder. For example, in order to obtain high corrosion resistance and dispersibility, the average particle diameter of the metal fine particles is preferably 0.01 μm to 100 μm. If the thickness is less than 0.01 μm, a sufficient thickness of coating cannot be secured and the corrosion resistance is lowered. On the other hand, if it exceeds 100 μm, the dispersibility in the liquid decreases. More preferably, it is 0.1-10 micrometers. In addition, the average particle diameter used the value of d50 measured with the wet particle size measuring device by laser diffraction as a representative example.

  The thickness of the coating having at least one of M2, M2 oxide, and M2 nitride is preferably 1 to 800 nm. If the thickness is less than 1 nm, sufficient corrosion resistance cannot be obtained. On the other hand, if it exceeds 800 nm, the particle diameter of the whole particle becomes large and the dispersibility in the liquid decreases, and in the case of magnetic metal fine particles, the saturation magnetization decreases. More preferably, it is 5 to 500 nm. The thickness of the coating was calculated from a transmission electron microscope (TEM) photograph. When the thickness was not uniform, the average of the maximum thickness and the minimum thickness was taken as the coating thickness.

  Further, in the present invention, the generation of the M1 metal fine particles by the reduction of the metal M1 oxide and the formation of the coating of the M2 element oxide and the like are performed in the same heat treatment step. No M1 metal oxide layer is clearly identified between the part and the coating. Moreover, since the heat treatment heated to 900 ° C. or higher is performed, the coating has high crystallinity and exhibits higher corrosion resistance than an amorphous or low-crystalline coating obtained by a sol-gel method or the like. In the present invention, the full width at half maximum of the diffraction peak of any of the elements M2, M2 oxide, and M2 nitride in the X-ray diffraction pattern of the metal fine particles is 0.3 ° or less, In addition, the fact that the intensity ratio of the peak with respect to the peak having the highest intensity among the diffraction peaks of the metal M1 is 0.001 or more was used for determining the crystallinity. In the X-ray diffraction pattern of the metal fine particles, the metal fine particles in the range where the peak of M2 oxide or the like is applied have high crystallinity, and as a result, high corrosion resistance is also realized. In the case of an amorphous coating or a coating with poor crystallinity, no peak is observed or the peak becomes broad, so that the peak intensity ratio is reduced and the full width at half maximum is increased. The intensity ratio does not particularly require an upper limit in terms of crystallinity, but an increase in the intensity ratio means an increase in the proportion of the coating portion. When the ratio of the covering portion is excessively increased, the saturation magnetization is remarkably lowered. Therefore, the intensity ratio is preferably 3 or less. Here, the X-ray diffraction pattern was measured by a concentrated beam method, and was measured by an angle scanning method in which the angle of the incident line and the diffraction line with respect to the sample surface was 1: 2. As the radiation light source, for example, when Fe particles are mainly used, a CuKα ray source is used. The half-width is defined as the angle between two points giving half the intensity of the substantial diffraction peak, excluding unwanted background diffraction intensity.

When the metal fine particles are magnetic metal fine particles, the magnetic particles obtained by the above production method may contain an excessive amount of non-magnetic components such as oxides. It is preferable to perform a separation operation. By performing such magnetic separation operation, magnetic particle metal fine particles having a saturation magnetization of 100 A · m ² / kg or more (corresponding to containing 46% or more of metal Fe particles having a bcc structure) can be obtained. In order to obtain high saturation magnetization, the coating that is a non-magnetic part is preferably as thin as possible, but in order to obtain sufficient corrosion resistance, it is preferable to have a sufficient coating thickness, The magnetization is 180 A · m ² / kg or less.

  In the metal fine particles of the present invention, the core metal M1 is Fe, and the element M2 contained in the coating is at least one of Al, Mn, Nb, Ti, and V, and the coating has high crystallinity, thereby providing high corrosion resistance. Can be realized. In this case, it is preferable that the elution amount of Fe into the pure water is 0.10 ppm or less when 1 part by mass of the metal fine particles is added to 100 parts by mass of pure water and held for 1 hour. In the present invention, ion-exchanged and distilled water was used as pure water, and the elution amount of Fe was analyzed by ICP of pure water from which Fe was eluted, and the Fe concentration was defined as the Fe elution amount. By setting the elution amount of Fe within the above range, the metal fine particles of the present invention can be suitably used for magnetic beads and the like that are required to have high corrosion resistance even when used in a solution. The smaller the elution amount of Fe, the better, and more preferably 0.05 ppm.

  Hereinafter, the present invention will be described by way of examples. However, the present invention is not necessarily limited by these examples.

(Example 1)
Α-Fe ₂ O ₃ powder having an average particle diameter of 0.03 μm and Ti powder having an average particle diameter of 17 μm were weighed so as to have a mass ratio of 1: 1 and mixed for 10 minutes with a V-shaped mixer. An appropriate amount of the obtained mixed powder was filled in an alumina boat, and heat treatment was performed at 1200 ° C. for 2 hours in nitrogen gas. After cooling to room temperature, the alumina boat was taken out and the heat-treated sample powder was collected.

The X-ray diffraction pattern of the sample powder is shown in FIG. When analyzed by Rigaku analysis software “Jade, ver. 5”, the diffraction pattern of FIG. 1 was identified as α-Fe, Ti ₃ O ₅ , and TiN. The horizontal axis of the graph in FIG. 1 corresponds to 2θ (°) of diffraction, and the vertical axis corresponds to the intensity of diffraction (relative value).

The standard generation energy of the oxide is ΔG _Ti3O5 = −2317 kJ / mol with respect to ΔG _Fe2O3 = −742 kJ / mol, and the standard generation energy of Ti ₃ O ₅ is smaller. That is, it is considered that α-Fe ₂ O ₃ is reduced by Ti to produce Ti ₃ O ₅ , and excess Ti that did not contribute to the reduction reacts with N atoms in the atmosphere to produce TiN.

The structure of the sample powder was observed with a high-resolution electron microscope (HRTEM). FIG. 2 is a HRTEM image of a cross section of a typical powder cut out by FIB processing. FIG. 3 shows a schematic view of the structure shown in FIG. When the composition of each phase of the structure is analyzed by EDX analysis, it can be seen that a plurality of Fe particles 1, 2, 3, 4 having a particle diameter of about 0.5 μm are coated with Ti ₃ O ₅ 5. The white part corresponds to the cavity 6. The horizontal bar in the figure represents a scale having a length of 500 nm.

Further, the magnetic properties of the sample powder were measured with a VSM (vibrating magnetometer). As a result of measuring the maximum applied magnetic field at 1.6 MA / m, the saturation magnetization Ms was 65.8 A · m ² / kg, and the coercive force iHc was 1.3 kA / m.

The full width at half maximum of the peak of Ti ₃ O _{5 having} the highest intensity other than α-Fe in FIG. 1 and the peak intensity ratio to the Fe (110) peak are shown in Table 2. The peak half-value width was as small as 0.3 or less, the peak intensity was 0.001 or more, and the crystallinity of the coating was good.

  Further, in order to evaluate the corrosion resistance, 0.2 g of the produced powder was put into 20 g of pure water, and after 1 hour, only the supernatant was taken out and the Fe ion concentration in the solution was measured by ICP analysis. Pure water used was ion-exchanged and distilled. As a result, the elution amount of Fe was less than 0.01 ppm. Thus, it can be seen that the Fe particles encapsulated with Ti oxide or the like have little elution and are excellent in corrosion resistance.

(Example 2)
Α-Fe ₂ O ₃ powder having an average particle size of 0.03 μm and Si powder having an average particle size of 4.8 μm were weighed so as to have a mass ratio of 1: 1 and mixed for 10 minutes with a V-shaped mixer. An appropriate amount of the obtained mixed powder was filled in an alumina boat, and heat treatment was performed at 1200 ° C. for 2 hours in nitrogen gas. After cooling to room temperature, the alumina boat was taken out and the heat-treated sample powder was collected.

The X-ray diffraction pattern of the sample powder is shown in FIG. As a result of analysis in the same manner as in Example 1, the diffraction pattern in FIG. 4 was identified as α-Fe, SiO ₂ , and Si. The standard production energy of SiO ₂ is ΔG _{SiO 2} = −856 kJ / mol, which is smaller than the standard production energy of α-Fe ₂ O ₃ . That is, it is considered that Si acts as a reducing agent to reduce Fe ₂ O ₃ and generate SiO ₂ . The horizontal axis of the graph in FIG. 4 corresponds to 2θ (°) of diffraction, and the vertical axis corresponds to the intensity of diffraction (relative value).

FIG. 5 is an HRTEM image observed in the same manner as in Example 1. FIG. 6 is a schematic diagram for schematically explaining the structure of FIG. Fe particles 7 are covered with SiO ₂ 8. The horizontal bar in the figure represents a scale having a length of 500 nm. The values of the magnetic characteristics measured in the same manner as in Example 1 were the saturation magnetization Ms: 55.2 A · m ² / kg and the coercive force iHc: 1.5 kA / m.

  Table 2 shows the half-width of the Si peak having the highest intensity other than α-Fe and the peak intensity ratio to the Fe (110) peak in FIG. The peak half-value width was as small as 0.3 or less, the peak intensity was 0.001 or more, and the crystallinity of the coating was good.

(Example 3)
35 g of α-Fe 2 O 3 powder with an average particle size of 0.03 μm and 15 g of TiC powder with an average particle size of 1 μm (7: 3 by mass ratio) are put into a plastic container, and 500 g of zirconia balls are added, and the sealed plastic container is rotated. Stir and mix. An appropriate amount of the obtained mixed powder was filled into an alumina boat, and heat treatment was performed at 1200 ° C. for 2 hours in nitrogen gas using a tubular electric furnace. Thereafter, in order to purify the magnetic particles, only the magnetic particles were captured and separated using a permanent magnet in which the product was added and mixed and dispersed in an alcohol solvent. Thereafter, the purified powder was dried in a draft to obtain the magnetic particles of the present invention. FIG. 7 shows a result of observing the magnetic particles with a transmission electron microscope, and FIG. 8 shows a schematic diagram thereof. A particle having a diameter of about 1 μm in which TiO contained Fe particles having a particle diameter of about 350 nm was confirmed, and the thickness of the coating layer was 270 μm. The composition ratio of each phase was determined by EDX analysis (FIG. 9). Moreover, as a result of measuring the magnetization of this magnetic particle by VSM with a maximum applied magnetic field of 1.6 MA / m, a high value of 140 A · m ² / kg was obtained. Furthermore, as a result of measuring the particle size of the magnetic particles with a laser diffraction particle size distribution analyzer, d50 was 2.4 μm. In order to evaluate the corrosion resistance, 0.2 g of the above magnetic particles were put into 20 ml of pure water, and after 1 hour, only the supernatant was taken out, and the Fe ion concentration in the solution was measured by ICP analysis. As a result, it was less than 0.01 ppm. Further, when X-ray diffraction measurement was performed on the magnetic particles in a diffraction angle range of 2θ = 20 ° to 80 °, it was confirmed that a diffraction peak corresponding to Ti oxide appeared in addition to α-Fe. The diffraction intensity, the peak half-value width, and the peak intensity ratio to the Fe (110) peak intensity are shown in the table for the peak having the maximum intensity among the peaks. The peak half-value width is as small as 0.3 or less, and the peak intensity is 0.001 or more.

(Comparative Example 1)
Mixing and heat treatment were performed in the same procedure as in Example 1 except that carbon black powder having an average particle size of 0.02 μm was used instead of TiC which is the starting material of Example 3. As a result of TEM observation of the obtained produced powder, Fe particles coated with a C film having a thickness of about 10 nm were confirmed. Further, magnetic particles were purified from the produced powder by the same procedure as in Example 1. The saturation magnetization, average particle diameter d50, and elution amount of the obtained magnetic particles are summarized in a table. Each measurement and evaluation method is the same as in Example 1.

Example 4
Mixing and heat treatment were performed in the same procedure as in Example 2, except that Al powder having an average particle diameter of 3 μm was used instead of TiC which is the starting material of Example 3. The obtained produced powder was observed by TEM. FIG. 10 shows an example of the observation, and FIG. 11 shows a schematic diagram thereof. Tissue can be confirmed _{that the Al} 2 _{O 3} film of 5nm thickness covers the Fe particles. Further, only magnetic particles were purified from the produced powder in the same manner as in Example 1. Table 1 shows the saturation magnetization, average particle diameter d50, and elution amount of the obtained magnetic particles. Further, as a result of performing X-ray diffraction measurement on the obtained magnetic particles in the same manner as in Example 3, a diffraction peak corresponding to Al oxide appeared. The peak with the highest diffraction intensity shows the diffraction angle, peak half-width, and peak intensity ratio with respect to the α-Fe (110) peak intensity in the table. The peak half-value width was as small as 0.3 or less, and the peak intensity ratio was 0.001 or more.

  The present invention relates to magnetic recording media such as magnetic tapes and magnetic recording disks, electronic devices such as radio wave absorbers, inductors and printed boards (soft magnetic shapes such as yokes), magnetic beads for nucleic acid extraction, and medical microspheres. The present invention can be used for magnetic metal particles used as sphere raw materials and a method for producing the same.

2 is a graph showing an X-ray diffraction pattern of a sample powder of Example 1. It is a microscope picture of the section structure of the particle concerning Example 1 observed with the electron microscope. It is the schematic for demonstrating the structure of FIG. 2 typically. 4 is a graph showing an X-ray diffraction pattern of a sample powder of Example 2. It is a microscope picture of the cross-sectional structure of the particle | grains concerning Example 2 observed with the electron microscope. It is the schematic for demonstrating the structure of FIG. 5 typically. It is the microscope picture of the particle | grains which concern on Example 3 observed with the electron microscope. It is the schematic for demonstrating the structure of FIG. 7 typically. FIG. 8 is an energy dispersive spectroscopy (EDX) spectrum of an Fe particle part and a coating part of the particle of FIG. 7. FIG. It is the microscope picture of the particle | grains which concern on Example 4 observed with the electron microscope. It is the schematic for demonstrating the structure of FIG. 10 typically.

Explanation of symbols

1, 2, 3, 4, 9, 11: Fe particles,
5: Ti ₃ O ₅ ,
6: Cavity,
7: Fe particles,
8: SiO ₂
10: TiO
12: Al ₂ O ₃

Claims (8)

An oxide powder of the metal M1 and a powder containing an element M2 in which the standard free energy of formation of oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O are mixed, and the mixed powder is heat-treated in a non-oxidizing atmosphere. Then, the surface of the metal fine particles of the metal M1 reduced by the element M2 is covered with at least one of M2, M2 oxide, and M2 nitride.   The method for producing fine metal particles according to claim 1, wherein the metal M1 is Fe, and the element M2 contains at least one of Al, Mn, Nb, Ti, and V. The surface of the metal fine particle of the metal M1 is covered with at least one of the elements M2, M2 oxide, and M2 nitride in which the standard free energy of formation of the oxide satisfies the relationship of ΔG _M1-O > ΔG _M2-O Metal fine particles characterized by being made. In the base particles composed of at least one of the elements M2, M2 oxide, and M2 nitride satisfying the relationship of ΔG _M1-O > ΔG _M2-O with respect to the metal M1, the standard free energy of formation of the oxide is A metal fine particle comprising two or more particles of metal M1.   Among the diffraction peaks of any of the elements M2, M2 oxides, and M2 nitrides in the X-ray diffraction pattern of the metal fine particles, the peak with the highest intensity has a half-value width of 0.3 ° or less, and the metal 5. The metal fine particle according to claim 3, wherein an intensity ratio with respect to a peak having the highest intensity among diffraction peaks of M <b> 1 is 0.001 or more.   The metal fine particle according to any one of claims 3 to 5, wherein the metal M1 is Fe, and the element M2 is at least one of Al, Mn, Nb, Ti, and V. The value of saturation magnetization is 100-180A * m < ² > / kg, The metal microparticle of Claim 6 characterized by the above-mentioned. The amount of Fe elution into the pure water when 1 part by mass of the metal fine particles is added to 100 parts by mass of pure water and held for 1 hour is 0.10 ppm or less. Or metal fine particles according to 7.