JP4304668B2 - Metal fine particles and method for producing metal fine particles - Google Patents

Description

  The present invention relates to a magnetic metal particle used as a raw material for a magnetic recording medium such as a magnetic tape and a magnetic recording disk, and an electronic device (soft magnetic shape body such as a yoke) such as a radio wave absorber, an inductor, and a printed board, 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 size of the magnetic particles applied to the magnetic tape and increase the magnetization.

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 substance 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. However, since metal particles easily oxidize, problems such as deterioration of magnetism and violent oxidation and burning of particles occur, making it difficult to handle them as dry particles. Therefore, oxide particles such as ferrite and magnetite have been widely used (Patent Document 1).

  When handling metal particles with a particle size of 1 μm or less as dry particles, in order not to impair the metal function, a coating is applied to the particle surface to prevent the particles from directly contacting the atmosphere (oxygen). Is essential. Therefore, a technique for coating metal particles with graphite has been reported (Patent Document 2). In addition, coating of metal particles with boron nitride (BN) can be given.

  By the above coating, for example, Fe nanoparticles can be stably synthesized. In general, Fe has a stable body-centered cubic α-phase at room temperature and normal pressure. However, as described in Non-Patent Document 1, when the particle size is made finer than 75 nm, the face-centered cubic structure γ-phase becomes room temperature / normal. It is known to exist stably under pressure. Since the γ phase exhibits paramagnetism at room temperature, the appearance of the γ phase causes a decrease in Fe magnetic properties. The minute γ-Fe particles are not transformed into the α phase by simple cooling, and the transformation is induced by an external force such as stress.

JP 2000-30920 A (pages 9-11, FIG. 2) JP-A-9-143502 (pages 3-4, FIG. 5) Acta Metallurgica 15 1967 (1967), p. 1133

  Metal particles having a size of 1 μm or less can be synthesized by a surface-coated fine particle synthesis method. However, when the metal Fe particles are made finer, a paramagnetic γ phase having a face-centered cubic structure is precipitated, so that there is a problem that the magnetic properties are deteriorated. The present invention suppresses the precipitation of the γ phase.

  As a result of intensive studies on a method for suppressing γ-phase precipitation in fine particles composed of metallic Fe, the present invention has been achieved.

(1) The metal fine particles of the present invention are metal fine particles obtained by reducing an oxide of Fe, and have metal particles mainly composed of α-Fe,
The surface of the metal particles is coated with a compound containing at least one selected from boron, nitrogen, and carbon as a main element,
The average particle size is 1 μm or less.

  Hereinafter, “a compound containing at least one selected from boron, nitrogen, and carbon as a main element” is referred to as a B / C / N compound. This compound includes, for example, BN and BNC. More preferably, the fine metal particles have an average particle diameter of 0.1 μm or less.

  Here, the average particle diameter is measured, for example, by taking an electron micrograph using a fine powder as a sample. The average value is obtained by measuring the diameters of fine particles within an arbitrary area in the photograph. That is, for N fine particles (N ≧ 50 particles), the diameter is measured and expressed as average diameter = (total of measured diameters) / N. Instead of a photograph, an image may be acquired and the diameter may be measured using a personal computer and image processing software. The reason why N is increased is to average and smooth the case where the cross section of the fine particles passes through the center of gravity. Furthermore, the particle diameter of each fine particle corresponds to, for example, the outer diameter of a single fine particle when the observed cross section is viewed. When the cross section is not circular, the average value of the maximum length and the minimum length is regarded as the particle size of the fine particles.

  (2) In the metal fine particles described in (1) above, except that Fe is a main element, element X (X is at least one selected from the following elements: Al, As, Be, Cr, Ga, Ge) , Mo, P, Sb, Si, Sn, Ti, V, W, Zn) is characterized by containing 1 mass% or more and less than 50 mass%. Here, “mass%” represents the amount of the element X1 contained in 100 as a percentage when the unit mass of the metal fine particles of the present invention is 100.

  (3) In the fine metal particles described in (2) above, (111) diffraction peak of γ-Fe having a face-centered cubic structure and (110) diffraction peak of α-Fe having a body-centered cubic structure in the X-ray diffraction pattern The intensity ratio I (111) / I (110) is 0.3 or less.

(4) The metal fine particles according to (2) above, wherein the saturation magnetization is 100 Am ² / kg or more. Here, the equation of saturation magnetization ≧ 100 Am ² / kg corresponds to the equation of saturation magnetization ≧ 100 emu / g.

(5) The method for producing metal fine particles of the present invention comprises an Fe oxide powder and an element X (X is at least one selected from the following elements: Al, As, Be, Cr, Ga, Ge, Mo, Compound powder containing P, Sb, Si, Sn, Ti, V, W, Zn) or a compound powder containing element X alone and at least one of boron or carbon as main elements (however, the compound powder includes At least one selected from boron, nitrogen, and carbon by heat-treating a powder mixed with boron or a simple carbon powder in an atmosphere containing nitrogen to reduce the oxide of Fe. In addition to the formation of fine metal particles coated with a compound containing
In the metal fine particles, the elements X and Fe are alloyed, and the (111) diffraction peak of γ-Fe having a face-centered cubic structure and the (110) diffraction of α-Fe having a body-centered cubic structure in the X-ray diffraction pattern. The peak intensity ratio I (111) / I (110) is 0.3 or less . Here, a compound containing at least one selected from boron, nitrogen, and carbon as a main element is referred to as a B / C / N compound. The mixing ratio of the compound powder containing at least one of boron and carbon as the main element is more preferably the compound powder containing at least one of boron and carbon as the main element is more than the stoichiometric ratio. Is preferred.

  (6) In the method for producing metal fine particles according to (5), the mixing is performed while mechanically pulverizing.

  (7) In the method for producing metal fine particles according to (5), the heat treatment is performed at a temperature of 800 ° C. or higher.

  The metal fine particles of the present invention are metal fine particles produced by the production method of (5) above, and the surface of the metal particles is a compound containing at least one of boron, nitrogen, and carbon as a main element (hereinafter, B / C / N compound), and an ultrafine metal particle having an average particle diameter of 1 μm or less.

  Furthermore, the metal fine particles of the present invention are metal fine particles produced by the production method of (5) above, and the (111) diffraction peak of γ-Fe having a face-centered cubic structure in the X-ray diffraction pattern and the body-centered cubic. Γ-Fe, which is an ultrafine metal particle characterized in that the intensity ratio I (111) / I (110) of the (110) diffraction peak of α-Fe having a structure is 0.3 or less It is a metal fine particle which suppressed phase precipitation.

  According to the present invention, it is possible to obtain metal fine particles that suppress the precipitation of the γ phase, have excellent oxidation resistance, and have good magnetic properties.

The present invention (1) corresponds to a method for synthesizing metal fine particles and a method for coating metal fine particles. The particle size of the Fe oxide powder used in the above production method can be freely selected according to the target particle size of the metal fine particles. Practically, the range of 1 to 1000 nm is preferable. Examples of the Fe oxide powder include Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO.
Element X (X is at least one selected from the following elements: Al, As, Be, Cr, Ga, Ge, Mo, P, Sb, Si, Sn, Ti, V, W, Zn used in the above manufacturing method ) Can be freely selected according to the target particle size of the metal fine particles. Practically, the range of 1 to 10,000 nm is preferable. In the present specification, the range of 1 to 10000 nm corresponds to the range of 1 nm or more and 10,000 nm.

  The element X is preferably selected from elements that can stabilize the α phase even at a high temperature of 1000 ° C. or higher when alloyed with Fe. Al, As, Be, Cr, Ga, Ge, Mo, P, Sb, Si , Sn, Ti, V, W, and Zn. When the compound powder containing the element X is finally made into metal fine particles, the element X is preferably contained in the range of 1 to 50 mass% in order to suppress the γ phase. By adding the element X, α-Fe phase fine particles are formed, and the (111) diffraction peak of γ-Fe having a face-centered cubic structure and (110) of α-Fe having a body-centered cubic structure in the X-ray diffraction pattern. ) The diffraction peak intensity ratio I (111) / I (110) is 0.3 or less.

  The compound containing element X may be element X alone, but is carbide (X-C), boride (X-B), nitride (X-N), or oxide (X-O). It doesn't matter. In particular, in the case of X-O, it is preferable that it can be reduced by a compound powder containing carbon and boron described later during the heat treatment.

  The particle size of the compound powder containing at least one of boron and carbon as a main element is preferably in the range of 1 nm to 1 mm, and more preferably in the range of 1 nm to 0.1 mm for more efficient reduction reaction.

  Powder of Fe oxide and element X (X is at least one selected from the following elements: Al, As, Be, Cr, Ga, Ge, Mo, P, Sb, Si, Sn, Ti, V, W , Zn) and a compound powder containing at least one of boron and carbon as a main element are mixed with a mortar, a stirrer, a V-shaped mixer, a ball mill, a vibration mill, and other general stirrers. You can choose from. In order to avoid aggregation of the powder and to mix more uniformly, wet mixing using an organic solvent or water is preferable.

  The mixing ratio of the compound powder containing at least one of boron and carbon as a main element is preferably near the stoichiometric ratio for reducing the oxide of Fe, more preferably at least one of boron and carbon as the main element. It is preferable that the compound powder to be included is in excess of the stoichiometric ratio. If the compound powder containing at least one of boron and carbon as a main element is insufficient, not only the Fe oxide powder is not sufficiently reduced during the heat treatment, but also the Fe oxide powder is sintered. It is not suitable because it becomes bulky.

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.

  Metal particles obtained by reducing an oxide of Fe by the above-described production method, wherein the surface of the metal particles includes at least one of boron, nitrogen, and carbon as a main element (hereinafter referred to as B / It is possible to obtain metal fine particles characterized by being coated with a (C / N compound) and having an average particle size of 1 μm or less.

Example 1
73 g of α-Fe ₂ O ₃ powder having an average particle diameter of 0.03 μm, 2.7 g of Ge powder having an average particle diameter of 20 μm, and 24.3 g of carbon black powder having an average particle diameter of 0.02 μm were weighed and mixed in a ball mill mixer. Mixed for 16 hours. In the above formulation, the mass ratio is Fe: Ge = 95: 5. An appropriate amount of the obtained mixed powder was filled in an alumina boat, and heat treatment was performed at 1000 ° 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 analysis software “Jade, ver. 5” manufactured by Rigaku, the diffraction patterns in FIG. 1 were identified as γ-Fe (111) having a face-centered cubic structure and α-Fe (110) having a body-centered cubic structure. The horizontal axis of the graph in FIG. 1 corresponds to 2θ (°) of diffraction, and the vertical axis corresponds to intensity, that is, the intensity of diffraction I (where unit (au) is a relative value). Table 1 shows the ratio of the diffraction peak intensities (I (111) / I (110)). Moreover, the average particle diameter of α-Fe obtained from the half width was 92 nm.

  Table 1 shows the results of measuring the magnetic properties of the powder sample with a VSM (vibrating magnetometer). Compared to a comparative example described later, the peak intensity is small, and high saturation magnetization is obtained.

(Example 2)
A sample powder was prepared in the same manner as in Example 1 except that Al was used instead of Ge. The X-ray diffraction pattern of the sample powder is shown in FIG. When analyzed by analysis software “Jade, ver. 5” manufactured by Rigaku, the diffraction patterns in FIG. 1 were identified as γ-Fe (111) having a face-centered cubic structure and α-Fe (110) having a body-centered cubic structure. Table 1 shows the average particle diameter of α-Fe obtained from the ratio of each diffraction peak intensity and the half-value width.

  Table 1 shows the magnetic characteristics of the sample powder measured by VSM. Compared to a comparative example described later, the peak intensity is small, and high saturation magnetization is obtained.

(Example 3)
73 g of α-Fe ₂ O ₃ powder having an average particle size of 0.03 μm, 3.8 g of vanadium carbide (VC) powder having an average particle size of 20 μm, and 23.2 g of carbon black powder having an average particle size of 0.02 μm were weighed respectively. It mixed for 16 hours with the mixer. In the above formulation, the mass ratio is Fe: V = 95: 5. An appropriate amount of the obtained mixed powder was filled in an alumina boat, and heat treatment was performed at 1000 ° 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. Table 1 shows the ratio of the diffraction peak intensities and the average particle diameter of α-Fe. Table 1 shows the magnetic characteristics of the sample powder measured by VSM. Compared to a comparative example described later, the peak intensity is small, and high saturation magnetization is obtained.

(Comparative Example 1)
Without adding the compound containing the element X, 75 g of α-Fe ₂ O ₃ powder having an average particle size of 0.03 μm and 25 g of carbon black powder having an average particle size of 0.02 μm were weighed, and 16 hours in a ball mill mixer. Mixed. An appropriate amount of the obtained mixed powder was filled in an alumina boat, and heat treatment was performed at 1000 ° 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. Table 1 shows the intensity ratio (I (111) / I (110)), average particle diameter, and magnetic properties obtained in the same manner as in the examples. It can be seen that the I (111) peak intensity is large and the saturation magnetization is low compared to Examples 1-3.

  The present invention relates to magnetic metal particles used as raw materials for magnetic recording media such as magnetic tapes and magnetic recording disks, and electronic devices (soft magnetic shapes such as yokes) such as radio wave absorbers, inductors and printed circuit boards, and methods for producing the same. It can be used.

It is a graph which shows the X-ray-diffraction pattern of sample powder.

Claims (2)

Fe oxide powder and element X (X is at least one selected from the following elements: Al, As, Be, Cr, Ga, Ge, Mo, P, Sb, Si, Sn, Ti, V, W, Zn ) and single compound powder or elements X including, boron Motowaka Shikuwa compound powder containing at least one as a main element of carbon (where, the said compound powder, boric Motowaka Shikuwa containing carbon single powder) and were mixed By heat-treating the powder in an atmosphere containing nitrogen, the Fe oxide is reduced to form fine metal particles coated with a compound containing at least one selected from boron, nitrogen, and carbon as a main element. And
In the metal fine particles, the elements X and Fe are alloyed, and the (111) diffraction peak of γ-Fe having a face-centered cubic structure and the (110) diffraction of α-Fe having a body-centered cubic structure in the X-ray diffraction pattern. A method for producing metal fine particles, wherein the peak intensity ratio I (111) / I (110) is 0.3 or less . 2. The metal according to claim 1, wherein a mixing ratio of the compound powder containing at least one of boron and carbon as a main element is more than a stoichiometric ratio for reducing the Fe oxide. A method for producing fine particles.

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