JP2006319349A - Magnetic material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain, a metastable compound, α"-Fe<SB>16</SB>N<SB>2</SB>depositing accompanied by a phase transformation of crystallizing from martensite phase of α'-Fe(N) not as a compound in a matrix but as a bulk substance isolated as a single phase. <P>SOLUTION: The magnetic material comprises a particle aggregation substantially comprising the α"-Fe<SB>16</SB>N<SB>2</SB>crystal of body-centered cubic (bct). The magnetic material is synthesized directly by making microparticles of α-Fe react with a nitrogen-containing gas at a temperature of ≤200°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention is a high saturation magnetic flux density obtained by chemically synthesizing metastable phase α "-Fe ₁₆ N ₂ as an isolated crystal, which originally crystallizes when annealing martensite in which nitrogen is dissolved. The present invention relates to a magnetic material with

Of Fe-N compounds, α "-Fe ₁₆ N ₂ is known as a metastable compound that crystallizes when martensite that dissolves nitrogen is annealed for a long time. This α" -Fe ₁₆ The crystal of N ₂ has a bct structure (body-centered tetragonal crystal) and is expected as a giant magnetic substance having a large saturation magnetization, but there is no example of chemically synthesizing this compound in an isolated state.

So far, various methods such as vapor deposition, MBE (molecular epitaxial method), ion implantation, sputtering, ammonia nitriding, etc. have been tried to produce α ″ -Fe ₁₆ N ₂ . "-Fe ₁₆ N ₂ quasi and be stable phase, which more stable γ'-Fe ₄ N or ε-Fe _2-3 α etc. can easily produce such N" -Fe ₁₆ N ₂ single compounds with difficulty be prepared isolated _and even as α "-Fe ₁₆ N ₂ crystals were obtained thin film, there is a limitation in application to magnetic material with a thin film.

For this reason, various attempts have been made to produce α ″ -Fe ₁₆ N ₂ powder. In JP-A-8-165502, Fe (N) powder is quenched from the γ phase (austenite phase). Further, it is made a powder of Fe (N) with a lot of α ′ (martensite phase) by a process of pulverizing to produce processing-induced martensite, and this martensite phase powder is annealed to obtain α ″ -Fe _16. A method for crystallizing N ₂ has been proposed. However, it cannot be denied that α-Fe remains even by this method. In fact, in the examples described in the publication, the content of α ″ -Fe ₁₆ N ₂ is less than 80% by weight, and α ″ -Fe ₁₆ N ₂ single-phase powder cannot be obtained.

In JP-A-7-118702, pure iron powder is reacted and held at a high temperature with a mixed gas of ammonia and hydrogen to form an austenite single-phase powder, which is rapidly cooled from the high-temperature austenite single-phase powder. By subjecting this to an aging treatment, a powder in which a small amount of α "-Fe ₁₆ N ₂ phase is precipitated in nitrogen solid solution martensite is obtained, and further pulverized in a nitrogen atmosphere to precipitate α" -Fe ₁₆ N ₂ . A method for promoting the above has been proposed. However, even by this method, the content of the α ″ -Fe ₁₆ N ₂ phase is about 70% by volume.

In the method of crystallizing α "-Fe ₁₆ N ₂ from the martensite phase [α'-Fe (N)], α" -Fe ₁₆ N ₂ exists as a precipitated phase in the metal structure. the ₁₆ N ₂ crystal compound that is difficult to separate a single phase. Therefore, such phase transformation involving alpha "of -Fe ₁₆ N ₂ at crystallization method alpha" of -Fe ₁₆ N ₂ single phase It is not possible to obtain a magnetic material, even if the material is in a powder form, and the same applies to the method of crystallizing α "-Fe ₁₆ N ₂ in the powder as seen in the above publication. I can say that.

Moreover, even if a thin film of α ″ -Fe ₁₆ N ₂ is obtained by the thin film forming method, there are problems in productivity and economical efficiency for making a general-purpose magnetic material.

Therefore, the object of the present invention is to obtain an α "-Fe ₁₆ N ₂ crystalline compound in a form separated from the parent phase, unlike the crystallization by the heat treatment accompanied by the phase transformation as described above. An object of the present invention is to provide a magnetic material substantially consisting of an α ″ -Fe ₁₆ N ₂ crystalline compound.

The present inventors have found that "the result of extensive research various tests for -Fe ₁₆ N ₂ of chemical synthesis, alpha" the problem to solve the alpha as a bulk material -Fe ₁₆ N ₂ crystal single phase We have succeeded in synthesizing α "-Fe ₁₆ N _2. That is, the crystal of α" -Fe ₁₆ N ₂ , which is a metastable compound, can be chemically obtained without crystallization through the conventional phase transformation process. Was synthesized. Therefore, according to the present invention, there is provided a magnetic material comprising a collection of particles substantially consisting of α ″ -Fe ₁₆ N ₂ crystals having body-centered tetragonal crystals (bct). It is a single phase of -Fe ₁₆ N ₂ crystal, and this particle powder has a high saturation magnetic flux density (saturation magnetization).

Such α ″ -Fe ₁₆ N ₂ crystal single-phase particle powder is obtained by converting α-Fe fine particles into a nitrogen-containing gas such as ammonia at a temperature of 200 ° C. or lower, preferably 150 ° C. or lower, more preferably 120 ° C. or lower. It can be synthesized directly by reacting with a gas.

As mentioned above, α ″ -Fe ₁₆ N ₂ is expected to be a giant magnetized material with large saturation magnetization, but examples of successful α ”-Fe ₁₆ N ₂ as single-phase bulk materials are Therefore, there is no example in which α ″ -Fe ₁₆ N ₂ is used as a general-purpose magnetic material. The inventors of the present invention have found that α ”-when fine α-iron particle powder is nitrided under certain conditions. I found out that Fe ₁₆ N ₂ single phase crystals can be synthesized. The obtained α ″ -Fe ₁₆ N ₂ crystal particle powder was confirmed to have a large saturation magnetization, and was found to be an excellent magnetic material.

Regarding Fe-N-based compounds, there are many iron nitrides having a composition such as n = 8, 4, 3, 2, and 1 in terms of Fe _n N. In nitriding, the compounds of each phase coexist and form. The present inventors previously conducted an ammonia nitriding experiment with Fe foil, and found that a crystalline phase with a low nitrogen content was formed as the nitriding temperature was lowered. Then, it was confirmed that α ″ -Fe ₁₆ N ₂ was formed at a low temperature of 210 ° C. or lower. However, at such a low temperature, diffusion of nitrogen atoms was slow, so that the α ″ -Fe ₁₆ N ₂ single phase was formed. It was difficult to do.

However, a fine powder of αFe as a raw material, which upon prolonged nitriding treatment at a low temperature of 100 to 200 ° C. in a nitrogen-containing gas, α "-Fe ₁₆ N ₂ .α was found to produce" -Fe ₁₆ In order to obtain a particle powder composed of N ₂ single phase crystals, the particle size, composition and purity of the raw iron powder, the type and concentration of nitriding gas, nitriding temperature (reaction temperature), retention time (reaction time), etc. Various factors are involved, but the smaller the particle size of the iron powder, the better.

  As the nitriding gas, nitrogen gas, nitrogen + hydrogen mixed gas, ammonia gas, or the like can be used, but ammonia gas is convenient for use. Prior to the nitriding treatment, it is preferable to reduce the oxide film present on the surface of the raw iron powder with hydrogen gas.

Nitriding temperature and holding time are important requirements for producing an α "-Fe ₁₆ N ₂ single phase, and when nitriding with ammonia gas using Fe fine particles having a particle size of 20 nm as a raw material as shown in the examples described later. In this case, the temperature is 120 ° C. or lower for 1 day or longer, preferably 100 to 120 ° C. for 1 to 12 days, and most preferably α ″ -Fe ₁₆ N ₂ by treatment at 110 ° C. for 10 days. It was found that single phase particle powder was obtained. The optimum range of the reaction time and holding time of the nitriding treatment varies depending on the form (particle size and composition) of the iron powder used and the type and concentration of the nitriding gas used, but when using iron powder of 50 nm or less as a raw material, It is considered that it may be in the range of 0.5 to 12 hours in a temperature range of about 100 to 200 ° C.

The α ″ -Fe ₁₆ N ₂ of the present invention will be specifically described below with reference to examples.

    An iron powder having a particle size of 20 nm (measured from the X-ray half width) having the composition (% by weight) shown in Table 1 was prepared.

This fine iron powder was subjected to ammonia nitriding using the apparatus shown in FIG. In FIG. 1, reference numeral 1 denotes an electric furnace. A reaction tube (quartz tube) 2 having an inner diameter of 30 mm is installed in the electric furnace 1, and a tray 4 containing an iron powder sample 3 is set in the reaction tube. An N ₂ gas source 5, a hydrogen gas source 6, and an ammonia gas source 7 are connected to the reaction tube 2 through respective flowmeters, and are used as a desiccant in the middle of these gas introduction channels to the reaction tube 2. The zeolite layer 8 is interposed, thereby preventing the iron powder from being oxidized by water vapor contained in a trace amount in the gas. An oil trap 9 is provided on the gas outlet side in order to prevent oxygen and water vapor from entering the air.

[Example 1]
Put 5g of the above iron powder into the tray 4, introduce hydrogen gas into the reaction tube at a flow rate of 100ml / min, keep the temperature in the reaction tube at 500 ° C and reduce the oxide film on the iron powder surface, then cool to room temperature did. Subsequently, it switched to ammonia gas, this ammonia gas was continuously introduce | transduced into the reaction tube at the flow volume of 100 ml / min in the reaction tube 2, and ammonia nitriding treatment was performed for 10 days, maintaining the tube temperature at 120 degreeC. The obtained product was immersed in silicon oil in N ₂ gas to prevent oxidation by oxygen in the air, a sample was taken, and the crystal phase was identified by a powder X-ray diffractometer. The X-ray diffraction patterns are shown in FIGS. FIG. 2B is an enlarged view of the 2θ: 38-50 ° portion of FIG.

[Example 2]
Example 1 was repeated (retention time 10 days) except that the reaction temperature (in-tube temperature) was changed to 110 ° C. The X-ray diffraction pattern is also shown in FIG.

[Example 3]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 100 ° C. and the holding time at that temperature was 10 days. The X-ray diffraction pattern is also shown in FIG.

[Example 4]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 150 ° C. and the holding time at that temperature was 3 days. 3A and B show the X-ray diffraction patterns. FIG. 3B is an enlarged view of the 2θ: 38-50 ° portion of FIG.

[Example 5]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 120 ° C. and the holding time at that temperature was 4 days. The X-ray diffraction pattern is also shown in FIG.

[Example 6]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 100 ° C. and the holding time at that temperature was 3 days. The X-ray diffraction pattern is also shown in FIG.

[Example 7]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 300 ° C. and the holding time at that temperature was half a day. FIG. 4 shows the X-ray diffraction pattern.

[Example 8]
Example 1 was repeated except that the reaction temperature (in-tube temperature) was 200 ° C. and the holding time at that temperature was 3 days. FIG. 4 also shows the X-ray diffraction pattern.

  For each product obtained in Examples 1 to 8, crystals identified from the X-ray diffraction are shown in Table 2.

From the results of Table 2, it can be seen that α "-Fe ₁₆ N ₂ crystals are formed in all of Examples 1 to 6. More specifically, even when the reaction temperature is high (Example 3), the retention time is high. Even if it is short (Example 6), other phases coexist, but at an appropriate reaction temperature and holding time (for example (Examples 1, 2, 5), it is almost α "-Fe ₁₆ N ₂ , which is In the case of 2, it can be seen that a crystal of only α ″ -Fe ₁₆ N ₂ without any other phase was obtained. When the reaction temperature was high and the retention time was short as in Examples 7-9. In this case, α ″ -Fe ₁₆ N ₂ does not appear at all and Fe ₂ N becomes the main phase.

From the X-ray diffraction results, the Rietveld analysis was performed on the particle powder consisting of only the α "-Fe ₁₆ N ₂ crystal obtained in Example 2, and the lattice constant and atomic coordinates were obtained. The results are shown in FIG. , Α ″ -Fe ₁₆ N ₂ is a body-centered tetragonal crystal (bct) having a space group of I4 / mmm and lattice constants of a = 0.571 nm and c = 0.628 nm.

Mossbauer measurement was performed on the particle powder consisting only of α ″ -Fe ₁₆ N ₂ crystals obtained in Example 2. The Mossbauer spectrum was shown in FIG. 6. As a result, the third adjacent Fe atom adjacent to N was measured. The internal magnetic field was found to have a value of 40.3 T. Also, the values of the internal magnetic fields of the N first adjacent Fe atom, the second adjacent Fe atom, and the third adjacent Fe atom (29.8, 31 respectively). 7) and 40.3 T), the magnetic moment of each Fe atom was calculated, and the saturation magnetization of the α "-Fe ₁₆ N ₂ single crystal was calculated from the calculated value. As a result, it was 245.2 emu / g.

Magnetization measurement was performed on the particle powder made of only the α "-Fe ₁₆ N ₂ crystal obtained in Example 2. The measurement was performed by changing the external magnetization by 0.1 T in a range of -5 T to 5 T, and 290 K (absolute temperature). 7) and 4K, and the results are shown in Fig. 7 (290K) and Fig. 8 (4K) .For comparison, the measurement results on the fine iron powder of α-Fe used as a raw material are also shown in these figures. Also shown in the figure.

  As seen in FIG. 7, the saturation magnetization at room temperature (290 K) in Example 2 was 162 emu / g, which was larger than 148 emu / g of α-Fe. Similarly, as seen in FIG. 8, even at 4K, it was 172 emu / g, showing a value larger than 152 emu / g of α-Fe. FIG. 9 shows the temperature dependence of magnetization measured by applying an external magnetic field of 0.1 T with respect to the particle powder of Example 2 in the range of 290 K to 4 K and comparing with that of α-Fe. .

The saturation magnetization of α-Fe fine particles at room temperature should originally show 220 emu / g, but it was thought that this was 148 emu / g because the surface was covered with an oxide film. Similarly, the sample of Example 2 may be considered to be covered with an oxide film before the magnetic measurement. Therefore, the amount of oxide film of the fine particle of α-Fe is calculated from the saturation magnetization 148 emu / g of the fine particle at room temperature, and an oxide film equivalent to this oxide film is formed on the surface of the fine particle of Example 2. Assuming that the saturation magnetization of α "-Fe ₁₆ N ₂ has a very large value of 240 emu / g. This value is the saturation magnetization value 245.2 emu obtained from the magnetic moment of each Fe atom. Almost corresponds to / g.

As described above, in the present invention, α ″ -Fe ₁₆ N ₂ , which is a metastable compound that precipitates with a phase transformation of crystallization from the martensite phase of α′-Fe (N), is contained in the matrix. Since it was obtained not as a compound but as a single-phase isolated bulk material, it can provide a novel magnetic material not found in conventional materials, and its synthesis is a simple process at a relatively low temperature. Therefore, a magnetic material having a high saturation magnetic flux density can be obtained economically.

Is a schematic diagram of an apparatus used for the synthesis tests α "-Fe ₁₆ N ₂ according to the present invention. It is an X-ray-diffraction pattern of the product produced | generated when reaction temperature and holding time were changed in the ammonia nitriding process of alpha-Fe fine particles. It is an X-ray-diffraction pattern of the product produced | generated when reaction temperature and holding time were changed in the ammonia nitriding process of alpha-Fe fine particles. It is an X-ray-diffraction pattern of the product produced | generated when reaction temperature and holding time were changed in the ammonia nitriding process of alpha-Fe fine particles. and X-ray diffraction pattern of the "go-obtained alpha the Rietveld analysis from X-ray diffraction results for -Fe ₁₆ N ₂ particles" -Fe ₁₆ N ₂ crystal alpha, is a diagram showing a lattice constant. It is a Mossbauer spectrum about α ”-Fe ₁₆ N ₂ particle powder. The magnetization measurements at 290K for α "-Fe ₁₆ N ₂ particles is a diagram showing, in comparison with that of alpha-Fe fine particles. The magnetization measurements at 4K for α "-Fe ₁₆ N ₂ particles is a diagram showing, in comparison with that of alpha-Fe fine particles. It is the figure which showed the temperature dependence of the magnetization in the temperature range of 290K to 4K about the α "-Fe ₁₆ N ₂ particle powder in comparison with that of the α-Fe fine particles.

Explanation of symbols

1 Electric furnace 2 Reaction tube (quartz tube)
3 Iron powder sample 8 Zeolite layer 9 Oil trap

Claims (2)

A magnetic material comprising a collection of particles substantially consisting of α ″ -Fe ₁₆ N ₂ crystals having body-centered tetragonal crystals (bct). The magnetic material according to claim 1, wherein the particles are a single phase of α ″ -Fe ₁₆ N ₂ crystal.

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