JP2010095415A - Sialon holding magnetism and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide sialon further improved of mechanical and structural characteristics of an electromagnetic material holding magnetic characteristics by using sialon, which is excellent in characteristics as structural materials holding high strength and high toughness, also as the electromagnetic material; and a method for producing the same. <P>SOLUTION: There is provided a method for producing sialon holding magnetism which comprises a stage of mixing silicon nitride, aluminum nitride, alumina and a rare-earth element oxide; and a stage of firing the mixture under nitrogen atmosphere so that the sialon exhibits a saturated magnetization value in a range of 0.15-0.24 emu/g. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sialon possessing magnetism and a method for producing the same, and more particularly, comprising mixing silicon nitride, aluminum nitride, alumina and rare earth oxide; and sintering the mixture in a nitrogen atmosphere. , A method for producing sialon having magnetism, which expresses a saturation magnetization value range of 0.15 to 0.24 emu / g, wherein the mixture is further mixed with iron (Fe) and iron silicide The magnetic properties of sialon can be further enhanced by generating.

  Sialon (SiAlON) is a “ceramic alloy” of silicon nitride that exists as two crystal structures of α ′ phase and β ′ phase, in a network of silicon nitride tetrahedra based on α-silicon nitride and β-silicon nitride. This is generated by replacing a part of silicon atoms with aluminum atoms and a part of nitrogen atoms with oxygen atoms.

  Such sialon is traditionally high in hardness, excellent in wear resistance, and excellent in high-temperature strength or oxidation resistance, so it is widely applied in related fields, mainly extrusion dies for ferrous and non-ferrous metals. It is used for high-temperature structural members such as welding nozzles and automobile engine parts.

  Such a sialon has recently been expanded to a fluorescent material for application as a white LED as well as a structural material. This is disclosed in Patent Documents 1 and 2 and the like. In other words, due to the excellent mechanical properties that have already been established as the characteristics of sialon, there was a tendency to concentrate on application and technology development in related fields, but there was an interest in new fields that were not anticipated recently. The reality is that it is increasing.

  Therefore, the present applicant has not only considered the physical properties of sialon as a traditional structural material, but also has the potential as an electromagnetic material, and has developed technology for its practical use. In particular, sialon has a magnetic property (magnetic property). As a result of research on this fact, the present invention has been reached.

At present, no research has been reported on the application to magnetic materials by implementing magnetic properties by doping such functional sialons, especially sialon, with other elements.
Korean Patent Application No. 2007-7000098 Specification Korean Patent Application No. 2007-0026854 Specification

  The present invention was made in order to pioneer a new technical area of sialon as described above, and the present invention is a sialon that has been evaluated as having excellent strength as a structural material with high strength and high toughness. Is also used as an electromagnetic material, and the purpose is to present the possibility of further improving the mechanical structural properties that were inferior or outside of interest in electromagnetic materials possessing magnetic properties. To do.

  In addition, the present invention further improves the magnetic properties by adding not only rare earth elements but also metals such as iron and cobalt or metal oxides thereof to sialon. As a result, the application area of sialon as an electromagnetic material is further increased. Another purpose is to expand.

  In order to achieve the object as described above, the present invention includes mixing silicon nitride, aluminum nitride, alumina and rare earth oxide to obtain a mixture; and sintering the mixture in a nitrogen atmosphere. Provided is a method for producing a magnetized sialon that allows the sialon to exhibit a saturation magnetization range of 0.15 to 0.24 emu / g.

  In the manufacturing method, the sintering is preferably performed by gas pressure sintering at a temperature of 1700 to 1900 ° C.

  In the manufacturing method, it is preferable that iron (Fe) oxide is further mixed with the mixture, and the saturation magnetization value of sialon is increased in proportion to the amount of iron input.

  The mixture containing iron is preferably sintered by gas pressure sintering at a temperature in the range of 1500 to 1700 ° C.

  It is preferable that the mixture in which the iron (Fe) oxide is mixed is sintered to produce an iron silicide, and the iron silicide exhibits magnetic properties.

It is preferable that the iron silicide produced by sintering the mixture in which the iron (Fe) oxide is mixed is FeSi or Fe ₅ Si ₃ .

  The rare earth oxide is at least one selected from yttrium (Y), ytterbium (Yb), samarium (Sm), gadolinium (Gd), and erbium (Er) oxide, and is based on the total weight of the mixture. It is preferable to mix in 10 to 20 weight%.

  In order to achieve the above object, the present invention provides a magnetized sialon having a saturation magnetization value range of 0.15 to 0.24 emu / g by adding a rare earth oxide or a rare earth element to sialon. I will provide a.

  Further, in order to achieve the above object, the present invention adds the rare earth oxide or rare earth element and iron (Fe) or iron (Fe) oxide to the sialon, thereby increasing the amount of iron or iron oxide added. Provided is a magnetized sialon having an increased saturation magnetization value.

  According to the present invention, a motivation can be provided so that sialon can be used not only as a traditional structural material but also as an electromagnetic material.

  In addition, the present invention further expands the application area of sialon as an electromagnetic material as a result of improving magnetic characteristics by adding not only rare earth elements but also metals such as iron and cobalt or metal oxides thereof to sialon. There is an effect that can be done.

  Hereinafter, the present invention will be specifically described with reference to the accompanying drawings and examples. In addition, this invention is not limited to a following example, A various change is possible.

  The following examples relate to the magnetic behavior of rare earth doped sialon with various compositions. In particular, the examples are doped with yttrium (Y), ytterbium (Yb), samarium (Sm), gadolinium (Gd), erbium (Er), iron (Fe) and cobalt (Co) and gas pressure sintered. About sialon. Here, gas pressure sintering is merely an example of a sintering method, and it is obvious that a sintering method other than gas pressure sintering may be used.

  In the sialon as the final product thus produced, the composition and ratio of the α-phase (α-sialon) and β-phase (β-sialon) are the same as those of X-ray diffraction (XRD) and scanning electron microscope (SEM). It could be clearly confirmed by various analyzers.

  The magnetic hysteresis loop data of the sialon sample according to the example could be obtained by measuring using a vibrating sample magnetometer at room temperature. As a result, it has been found that the magnetic hysteresis of doped sialon, particularly α-sialon, appears to a more obvious degree than expected. Compared to the general ferrite, the parameters corresponding to the magnetic hysteresis curve of doped sialon were not large, but in addition to this, sialon has excellent structural properties. It can be said that sialon possessing even the characteristics has high possibility of expansion to a new application field as an electromagnetic material.

  Also in the case of doped β-sialon, a magnetic hysteresis behavior similar to α-sialon was expressed. At the same time, iron (Fe) and cobalt (Co) were introduced into the sialon in order to improve the magnetic properties of the sialon according to the present invention. In the case of sialon containing iron, it has been found that the magnetic properties are clearly enhanced.

Sialon is recognized as a good material in engineering fields where excellent mechanical properties at high temperatures, chemical safety and high wear resistance are required. β-sialon (β ′) is a solid solution of β-silicon nitride in which a part of silicon atoms (Si) and a part of nitrogen atoms (N) are respectively replaced by aluminum atoms (Al) and oxygen atoms (O). The chemical formula can be expressed by Si _6-z Al _z O _z N _8-z . Here, z is introduced for a quantitative concept capable of switching aluminum (Al), and its value has a range of 0 <z <4.2. α-silicon nitride forms a solid solution limited by β-silicon nitride, which is called α-sialon (a ′). α-Sialon has a substitutional form similar to β-sialon, but a metal cation (such as M = calcium) is added to α-sialon to further enhance the stability of α-sialon. These cations are partially located in the two gigantic interstitial lattice spaces of the α-silicon nitride unit cell. Such metal cations must be large enough to occupy an interstitial volume and have a radius of about 1 cm or less.

α-sialon is generally expressed by a chemical formula such as M ^{v +} _{m / v} Si _{12- (m + n)} Al _{m + n On} N _16-n . Here, v is the valence of the metal cation M.

  The α-sialon and β-sialon according to the present invention are densified by a transition liquid sintering process and are a basic material for forming an oxynitride liquid, and a metal oxide is used as an additive. Since sialon has excellent properties as a structural material, sialon possessing magnetic properties has great significance in material engineering applications.

  In order to observe the magnetic behavior of sialon, sialon samples doped with various rare earth elements were reacted with permanent magnets. As a result, a certain degree of magnetic properties could be observed. Therefore, in this embodiment, various dopants, that is, yttrium (Y), ytterbium (Yb), samarium (Sm), gadolinium (Gd), erbium (Er), iron (Fe), and cobalt (Co) are used. Consider the manufacturability of a series of doped sialons and the magnetic behavior of doped sialons for this purpose. Thus, by conducting research on the magnetic behavior of sialon, useful information related to the role of the dopant in the base material can be obtained, and the characteristics of the magnetic interaction can be grasped.

<Experimental example>
Starting materials for producing sialon according to the present invention are α-silicon nitride (UBE grade SN E10), aluminum nitride (AlN, Starck HC, Grade B), alumina (Sumitomo, AKP-30), rare earth oxide (99. 9% purity, Sigma-Aldrich Korea) and iron (III), cobalt (II, III) oxide (99.9% purity, Sigma-Aldrich Korea). Here, the rare earth oxide and the oxides of iron and cobalt can be used in a single state that is not an oxide.

  An appropriate amount of a starting material prepared in various compositions (m = 1.5, n = 1.5 & m = 2, n = 2 in the above-described chemical formula of α-sialon), ethyl alcohol as a medium, Mixing was performed with a rotating jar using silicon nitride balls. The composition as described above corresponds to a weight ratio of 10 to 20% by weight of the dopant based on the total weight of the starting mixed powder and the atomic weight of the rare earth oxide. In sialon, in order to introduce a large amount of rare earth cations, an appropriate m value and an n value corresponding thereto were selected.

  The starting material weighed 30 g and mixed for about 60 hours to obtain a wet powder. After mixing, the wet powder was sieved through a 38 μm size sieve and dried to obtain a dry powder.

  Next, the dry powder is hydrostatically molded at 200 MPa to produce a disk-type pellet having a diameter of 16 mm and a thickness of 3.5 mm, and a cylinder-type pellet having a diameter of 6 mm and a height of 5 mm. did. Disk-type pellets are manufactured for analysis, and cylinder-type pellets are manufactured for grasping magnetic characteristics.

  Thereafter, these pellets containing rare earth cations were pressure sintered at 1800 ° C. for 3 hours at a nitrogen gas pressure of 0.9 MPa to obtain disk samples. Here, the sintering temperature can be adjusted within a range of 1700 to 1900 ° C. Further, iron (III) and cobalt (II & III) oxides were sintered at 1600 ° C. under the same conditions as described above. The reason for setting the sintering temperature low is that the melting points of various oxides / silicides of iron and cobalt are about 1600 ° C. Here, the sintering temperature can be adjusted within a range of 1500 ° C to 1700 ° C. The heating rate was 10 ° C./min in all cases.

  Each disk sample thus sintered was analyzed by X-ray (Rigaku D / Max 2200, Japan) using Cu-Kα as a target.

  Meanwhile, in order to observe the microstructure of the sintered disk sample using a scanning electron microscope (SEM), the sample was polished with diamond paste. Thereafter, the polished sample was coated with gold (Au), and the microstructure was observed using a scanning electron microscope equipped with an EDS (Energy Dispersive X-ray) analyzer.

  The density of the sample was determined using the Archimedes principle.

  In addition, magnetic hysteresis curve data of the doped sialon sample was collected at room temperature with a vibrating sample magnetometer (7400 series, Lake Shore). In the present invention, magnetic properties can be measured as a function of magnetic field, temperature and sample frequency. The change in magnetic flux generated by placing the sample in the detection coil and applying mechanical vibrations induces a voltage in the detection coil, which is proportional to the magnetic moment of the sample.

Sintered sialon samples exhibited very high density. The density value represented a value of about 3200 kg / m ³ depending on the type of dopant. The analysis result by X-ray diffraction of sialon doped with rare earth elements is shown in FIG. Here, it was confirmed that the main crystal phase was α ′, and the analysis result as described above could be confirmed also in the fine structure observation with a scanning electron microscope.

  Vibration of sialon samples doped with various rare earth elements (at least one element selected from yttrium (Y), ytterbium (Yb), samarium (Sm), gadolinium (Gd), erbium (Er), etc.) As a result of an experiment using a type sample magnetometer (VSM), it was found that a magnetic hysteresis curve appeared. On the other hand, as a result of observing the magnetic hysteresis behavior of the doped sialon powder sample, no significant change was observed. FIG. 2 shows a typical magnetic hysteresis curve of sialon doped with rare earth elements. Such a typical tendency of the magnetic hysteresis curve has been observed for other types of ceramics containing rare earth cations having different compositions. The behavior of the material with respect to the hysteresis curve is dependent on the reaction of orbital electrons when the material is exposed to an applied magnetic field. Rare earth atoms or ions in the material can possess pure magnetic moments due to unpaired atoms that partially fill the atomic orbitals.

As can be seen from FIG. 2, the gradient change of the magnetic moment curve with respect to the magnetic field of the sialon containing various rare earth elements can be seen. As shown, sialons containing various rare earth elements have different magnetic susceptibilities. The magnitude of the magnetic susceptibility calculated from the slope of the curve can be compared with the magnitude of the magnetic susceptibility of the rare earth element. However, it is very important to recognize the fact that rare earth atoms are bonded to neighboring atoms in the sialon structure. Yttrium α-sialon is composed of yttrium trivalent cations (Y ³⁺ ) surrounded by seven (N, O) atoms while maintaining different separation distances, from which the structure of yttrium α-sialon can be defined.

  FIG. 2A shows a hysteresis curve, and FIG. 2B shows a central portion of the hysteresis curve. As shown, the saturation magnetization value changes from 0.16 emu / g to 0.24 emu / g, the coercive field magnitude changes from 400 G to 900 G, and the remanence magnetization value is 0. It was within the range of 01 to 0.02 emu / g. Β-sialon containing rare earth elements also exhibits magnetic hysteresis behavior similar to that of α-sialon.

  The hysteresis behavior of the doped sialon sample can also be compared with the powdered rare earth element pure oxide sample, and the hysteresis behavior of such a pure oxide sample is shown in FIG. As shown in FIG. 3, the sialon sample and the corresponding powdery rare earth element pure oxide sample show a similar reaction to an external magnetic field and show a small area hysteresis curve. (Soft magnetic material). However, the sialon doped with a specific rare earth element and the corresponding pure oxide sample have different curve slopes because the values of magnetic susceptibility are different from each other (see FIGS. 2 and 3). This is because, as described above, the rare earth atoms are bonded to oxygen in the oxide, and are bonded to atoms in the sialon structure in the sialon structure.

  The value related to the magnetic hysteresis of sialon doped with rare earth elements is lower than the value of normal ferrite. In order to confirm this, sialon doped with rare earth elements is shown in FIG. 4 in comparison with ferrite containing strontium (Sr). Although the hysteresis behavior of sialon doped with rare earth elements represents a significant phenomenon in terms of material science, in order to be practically applied, it must show a more obvious phenomenon, and therefore a larger A value is required.

Therefore, in this example, in order to improve the magnetic properties of the sialon doped with the rare earth element, iron or cobalt was further added to the sialon structure as individual cations together with the rare earth element. When iron or cobalt is further added to a sialon containing a rare earth element (for example, α-sialon), α-sialon to which a double doping system is applied can be obtained. Here, the radii of ions of iron trivalent cation (Fe ³⁺ ) and cobalt trivalent cation (Co ³⁺ ) can be compared with ionic radii of rare earth ions that act as stabilizers for α-sialon. . However, a metal cation such as iron or cobalt does not act as an effective stabilizer for the α-sialon structure, so a large amount cannot be added. Therefore, in this example, sialon was synthesized by adding various amounts of iron (III) oxide or cobalt (II & III) oxide within a range of 10% by weight to a single rare earth element. At this time, the composition of sialon was fixed to values of m = 2 and n = 2. It was found that doped sialon samples containing iron react strongly to magnetic fields.

  FIG. 5 is a photograph of a sialon sample doped with iron reacted with a permanent magnet. As shown, the sample reacted strongly to the permanent magnet. However, this behavior did not appear in the cobalt doped sample.

  The hysteresis behavior of sialon doped with rare earth cations and 10 wt% iron relative to the total weight of sialon is shown in FIG. To compare the iron cobalt doping effect, the hysteresis behavior of a sialon sample doped with 10 wt% cobalt relative to the total sialon weight was also shown. However, as shown in the figure, it has been found that the cobalt doping effect for enhancing the magnetic properties of sialon is insignificant. This is probably because cobalt silicide (CoSi) is a diamagnetic semimetal. It was also found that the saturation magnetization value (Ms) increases as the amount of iron oxide added increases. This saturation magnetization value can be increased in proportion to the amount of iron oxide introduced.

  FIG. 7 shows the change in hysteresis behavior of doubly doped sialon due to the change in iron content. The increase in the saturation magnetization value in the sialon sample is due to a quantitative increase in the magnetic component. That is, the saturation magnetization and the Ms value reached the maximum values when the maximum addition amount (10% by weight) of iron oxide was added. The saturation magnetization value of sialon doped with 10 wt% iron appeared as approximately 10 emu / g. The coercive field corresponding to this was about 8000G.

  FIG. 8 shows the microstructure photograph and X-ray diffraction result of sialon doped with iron, observed by SEM using EDS analysis. Here, it turns out that the iron element which exists as a form of a silicide is a spherical particle which has an average particle diameter of several micrometers.

  FIG. 9 shows the microstructure of an ion-doped sialon observed by SEM using a back scattered electron mode (BSE). As shown in the figure, β-sialon has needle-like grains, and it is observed that the rare earth has a relatively black color without being dissolved, and α-sialon stabilized by the rare earth solid solution. The base showed a relatively bright color compared to β-sialon, and the iron silicide showed a color close to white, so the distinct phases were distinct. This is because the BSE image reflects the contrast due to the difference in atomic numbers.

As a result of EDS analysis of the particles, it was confirmed that the iron silicide particles were FeSi. Some silicide particles sometimes contained an Fe ₅ Si ₃ component. Iron (Fe) was not observed in the α ′ particles, and it was found accurately that rare earth elements were contained. The X-ray analysis results of the sialon thus produced are shown in FIG. Here, not only FeSi and Fe ₅ Si ₃ but also α ′ and β ′ phases were clearly observed. The iron silicide particles in sialon contribute to the improvement of the saturation magnetization value. From this point of view, the contribution of rare earth cations can be said to be relatively low. Iron - present iron silicide phase five in silicon system, which FeSi _{2, FeSi,} Fe ₅ Si 3, is known as _Fe 2 Si and _{Fe 3} Si, _Fe 5 Si 3 and FeSi is a magnetic Known to be tinged. Factors and impurities such as the iron / silicon (Fe / Si) atomic number ratio affect the magnetic behavior of iron silicides.

  As can be seen from FIG. 6, in the case of the sample doped with iron, the saturation magnetization value is high, but it can be said that not only the coercive force and the remanence magnetization value but also the hysteresis curve region appears relatively narrow. This is because the physical properties corresponding to the soft magnetic material are expressed, and it can be said that the amount of hysteresis loss is relatively small.

  It can be said that the sialon having such characteristics can be applied to a high speed radio wave transformer core, an electromagnetic core, and the like. Samples containing iron silicide are also characterized by high density and high strength, which can be confirmed from reports that sialon-iron silicide composites have high mechanical strength. As a result, sialon doped with iron is evaluated as an excellent material having both magnetic properties and excellent durability. Further, even if a positive electric field is applied and then released, the amount of magnetization that remains is very small. This is because the magnetic moment is very close by the applied magnetic field. Therefore, if the applied magnetic field changes according to the sine curve, an output pattern similar to the input pattern is generated without distortion. This is a characteristic that makes it very useful when converting signals.

  Magnetic properties are greatly affected by the microstructure of the material. Therefore, it can be said that the coercive force and the residual magnetic value are also affected by the fine structure. Microstructurally possible parameters that can influence domain wall motion are the morphology and distribution of iron silicide particles, the presence of grain boundaries, iron particles There is a residual stress generated due to a difference in thermal expansion coefficient between the sialon crystal and the sialon crystal. If the parameter interrupts the domain wall motion, a high coercive force is generated. This can be said to be a phenomenon showing that the application field of magnetic sialon can be expanded.

  The present invention uses sialon having high strength and high toughness as an electromagnetic material to further improve mechanical structural characteristics, and in addition to rare earth elements, sialon includes a metal such as iron or cobalt or a metal oxide thereof. As a result of improving the magnetic characteristics by addition, the application area of sialon as an electromagnetic material can be further expanded and applied to the field of electromagnetic materials such as a high-speed radio wave transformer core and an electromagnetic core.

It is a graph which shows the X-ray-analysis result of ytterbium (Yb) / alpha-sialon by one Example of this invention. (A) is a magnetic hysteresis curve graph of a sialon doped with a rare earth element according to an embodiment of the present invention, and (b) is a graph showing a central portion of the hysteresis curve of (a). It is a magnetic hysteresis curve graph with respect to the pure oxide powder of a rare earth sample. FIG. 6 is a diagram comparing the magnetic hysteresis behavior of sialon doped with rare earth elements with the magnetic hysteresis behavior of ferrite (Sr11) containing strontium (Sr), according to one embodiment of the present invention. 4 is a photograph of reacting a sialon sample containing iron (Fe) to a permanent magnet according to an embodiment of the present invention. 6 is a graph showing hysteresis behavior when 10 wt% iron (Fe) is added to sialon containing various rare earth elements according to an embodiment of the present invention. 6 is a graph showing a change in the critical value of the magnetism of sialon when the double doping is performed by changing the iron (Fe) content according to an embodiment of the present invention. (A) is a photograph showing the fine structure of iron silicide particles in a sialon produced according to an embodiment of the present invention, and (b) and (c) are X-ray diffraction results. 6 is a photograph showing a microstructure of sialon doped with ytterbium (Yb) according to an embodiment of the present invention when 10 wt% iron (Fe) is added. It is a graph which shows the analysis result by X-ray diffraction when 10 weight% iron (Fe) is added to the sialon doped with ytterbium (Yb) by one Example of this invention.

Claims (9)

Mixing silicon nitride, aluminum nitride, alumina and rare earth oxide; and sintering the mixture in a nitrogen atmosphere;
The sialon represents a saturation magnetization value in the range of 0.15 to 0.24 emu / g,
A manufacturing method of sialon possessing magnetism. The sintering is performed by gas pressure sintering at a temperature of 1700 to 1900 ° C.,
The method for producing sialon having magnetism according to claim 1. Adding iron (Fe) oxide to the mixture;
The saturation magnetization value of sialon increases in proportion to the input amount of iron,
The method for producing sialon having magnetism according to claim 1. The sintering of the mixture containing iron is performed by gas pressure sintering at a temperature in the range of 1500 to 1700 ° C.
The manufacturing method of the sialon which possesses the magnetism of Claim 3. Sintering the mixture in which the iron (Fe) oxide is mixed to produce iron silicide, wherein the iron silicide exhibits magnetic properties,
The manufacturing method of the sialon which possesses the magnetism of Claim 3. The iron silicide produced by sintering the mixture in which the iron (Fe) oxide is mixed is FeSi or Fe ₅ Si ₃ ,
A method for producing sialon having magnetism according to claim 5. The rare earth oxide is at least one selected from the group consisting of yttrium (Y) oxide, ytterbium (Yb) oxide, samarium (Sm) oxide, gadolinium (Gd) oxide, and erbium (Er) oxide. Seeds,
The rare earth oxide is mixed at 10 to 20% by weight with respect to the total weight of the mixture,
A method for producing sialon having magnetism according to claim 1 or 3. Rare earth oxides or rare earth elements are added,
The saturation magnetization value is in the range of 0.15 to 0.24 emu / g,
Sialon possessing magnetism. Rare earth oxide or rare earth element and iron (Fe) or iron (Fe) oxide are added,
The saturation magnetization value increases as the addition amount of iron or iron oxide increases,
Sialon possessing magnetism.