JP2015005550A - Rare earth magnet powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide magnet powder including a Sm-Fe-N based material and arrange to be able to have a large coercive force even when the powder has a relatively large grain diameter.SOLUTION: Magnet powder comprises a Sm-Fe-N based material; the main phases of which have an average crystal grain diameter of 1 μm or less. The ratio of the intensity of an Fe (110) peak to that of a SmFe(303) peak measured by X-ray diffraction method is 0.01-0.80.

Description

  The present invention relates to a rare earth magnet powder, particularly a magnet powder composed of an Sm—Fe—N-based material and a method for producing the same.

Rare earth magnets are used for various applications as extremely strong permanent magnets with high magnetic flux density. As a typical rare earth magnet, a neodymium magnet having Nd ₂ Fe ₁₄ B as a main phase is known. In general, dysprosium is added to the neodymium magnet to enhance heat resistance and coercive force. However, dysprosium is a rare rare earth element, and since the production area is limited, the price is not stable, and there is a demand for a rare earth magnet that does not use dysprosium as much as possible.

  Under such circumstances, as a rare earth magnet not using dysprosium, a magnet using Sm as a rare earth attracts attention. As such a magnet containing Sm, an Sm-Fe-N magnet is known (Patent Document 1). As a method for producing such magnet powder, a method of treating raw material Sm—Fe metal alloy powder, Sm oxide and reducing agent by a reduction diffusion method is known (Patent Document 2).

JP 2000-1114018 A JP 2006-269637 A

  In the method described in Patent Document 2, since the raw material powder is made by pulverizing the master alloy, the raw material powder is almost made of a single crystal, and the crystal grain size is about the same as the particle size of the powder. Therefore, there is a problem that a necessary coercive force cannot be obtained when the particle size of the raw material powder is 10 μm or more. On the other hand, when applied to a bonded magnet, it is desirable that the particle size of the powder be large in terms of filling properties. When the particle size of the magnet powder is smaller than 10 μm, the filling property of the magnet powder into the resin is lowered, and the saturation magnetic flux density of the bonded magnet is lowered. Moreover, when the particle size of the powder is smaller than 10 μm, there is a risk of ignition.

  Accordingly, an object of the present invention is to provide a magnet powder composed of an Sm—Fe—N-based material that can have a high coercive force even if the powder particle size is relatively large.

  As a result of diligent investigations to solve the above problems, the present inventors have made the magnetic powder composed of the Sm-Fe-N-based material into a polycrystal or fine structure to reduce the average crystal grain size of the main phase. The inventors have found that a high coercive force can be achieved even when the powder particle size is relatively large by setting the Fe phase present in addition to the main phase to a predetermined ratio.

According to a first aspect of the present invention, there is provided a magnetic powder composed of Sm-Fe-N based material, an average grain size of the main phase does not exceed 1μm or less, Sm ₂ measured by X-ray diffractometry A magnet powder is provided in which the intensity ratio of the Fe (110) peak to the Fe ₁₇ (303) peak is 0.01 to 0.80.

  According to a second aspect of the present invention, there is provided a method for producing the above-mentioned magnet powder, wherein the raw material powder composed of samarium and iron is heated under a hydrogen atmosphere, and subsequently heated under reduced pressure, Then, a manufacturing method including nitriding is provided.

According to the present invention, the average crystal grain size of the main phase is 1 μm or less, and the intensity ratio of the Fe (110) peak to the Sm ₂ Fe ₁₇ (303) peak measured by the X-ray diffraction method is 0.01 to 0.80. Thus, a magnetic powder composed of an Sm—Fe—N-based material that can have a high coercive force even when the powder particle size is relatively large is provided.

FIG. 1 is an image of a cross section of the magnet powder of Example 1 taken with a scanning transmission electron microscope (TEM).

The magnet powder of the present invention is composed of an Sm—Fe—N-based material, has a fine structure including a main phase (crystal grains) and a grain boundary layer, and an average crystal grain size of the main phase is 1 μm or less, The intensity ratio of Fe (110) peak to Sm ₂ Fe ₁₇ (303) peak measured by X-ray diffraction method is preferably 0.01 to 1.00, preferably 0.01 to 0.80. It is characterized by being. The magnet powder of the present invention has a very high coercive force by having an average crystal grain size in the above range and an intensity ratio of the Fe (110) peak to the Sm ₂ Fe ₁₇ (303) peak.

Here, the main phase means a phase having the highest abundance ratio among phases constituting the magnet powder. In the magnet powder of the present invention, the Sm ₂ Fe ₁₇ N _x (x is 2 to 4) phase. It is. Moreover, a grain boundary layer means the layer which exists between main phases, and may contain Fe phase.

  The average crystal grain size is obtained by, for example, obtaining a cross-sectional image (hereinafter also referred to as a TEM image) of a magnet powder with a scanning transmission electron microscope (TEM), and using an intercept method, specifically, a plurality of vertical and horizontal TEM images. This is obtained by arbitrarily drawing 10 lines, for example, 10 lines, counting the number of crystal grains on each line, dividing the length of the line by the number of crystal grains, and calculating the average value of 20 lines. Can do.

The intensity ratio of the Fe (110) peak with respect to the Sm ₂ Fe ₁₇ (303) peak is obtained by sampling a plurality of, for example, three times from the population using an X-ray diffractometer and measuring each peak to obtain the intensity ratio. It can be obtained by calculating an average value of three times.

  In one aspect, the magnet powder of the present invention may have an average particle size of 10 to 300 μm, preferably 10 to 50 μm, more preferably 20 to 40 μm, as measured by dry laser diffraction. By setting it as such an average particle diameter, a high coercive force is obtained and the filling property to resin when applying to a bond magnet improves.

  In this specification, the average particle size means an average particle size D50 (particle size equivalent to a volume-based cumulative percentage of 50%). The average particle diameter D50 can be measured by, for example, a laser diffraction particle size distribution measuring device (LA-950, manufactured by Horiba, Ltd.).

  In one embodiment, the magnet powder of the present invention has an intensity ratio of the Sm peak of the grain boundary layer to the Sm peak of the main phase measured by energy dispersive X-ray (EDX) spot analysis of a transmission electron microscope (TEM), It may be 0.7 to 1.0.

  The spot diameter of the above EDX spot analysis is equal to the thickness of the grain boundary layer, specifically 1 to 30 nm, for example, 10 nm. The boundary between the main phase and the grain boundary layer can be determined by TEM electron diffraction analysis.

  The magnet powder of the present invention preferably has a Sm: Fe: N ratio (at%) of 9 to 11:76 to 81:11 to 14. By setting the Sm: Fe: N atomic ratio within such a range, a high coercive force can be obtained. The above ratio can be obtained by fluorescent X-ray analysis.

  The magnet powder of the present invention can have a coercive force of 400 kA / m or more.

  The magnet powder of the present invention can be produced as follows.

(1) Preparation of raw material magnetic powder First, raw material metals samarium and iron are blended. Although the blending ratio of samarium and iron is not particularly limited, for example, samarium is 10 to 20 atomic%, preferably 13 to 15 atomic%, and the remainder is iron.

  A mixture of samarium and iron blended in the above proportion is, for example, melt-cast to obtain a base material, which is pulverized to obtain an Sm—Fe-based raw magnet powder.

  The melt casting is not particularly limited, but is preferably performed by ultrasonic melting in an inert gas atmosphere, for example, an argon atmosphere. In order to homogenize the structure of the obtained base material, it is preferable to further heat-treat the base material. Such heat treatment is preferably performed in an inert gas atmosphere, for example, in an argon atmosphere, at 1000 to 1200 ° C., for example, 1100 ° C., for 24 to 96 hours, for example, 50 hours.

  The base material can be pulverized by a method known per se. For example, it can be pulverized by a crusher, a stamp mill, a ball mill or the like.

  The pulverization is preferably performed in an inert gas atmosphere having a low oxygen concentration, for example, an oxygen concentration of 100 ppm or less, preferably 10 ppm or less, for example, an argon atmosphere.

  Next, the obtained raw magnet powder is gradually oxidized. The gradual oxidation can be performed, for example, by placing the raw magnet powder in an inert gas atmosphere and gradually replacing the inert gas with oxygen.

  The raw material magnetic powder treated as described above is an Sm—Fe binary alloy, and has an average particle diameter D50 (corresponding to a volume-based cumulative percentage of 50%) of 10 to 300 μm, preferably 10 to 50 μm. . This average particle diameter D50 can be measured, for example, with a laser diffraction particle size distribution measuring apparatus (LA-950, manufactured by Horiba, Ltd.).

(2) Hydrogenation / decomposition reaction-dehydrogenation / recombination reaction (HDDR) treatment The raw material magnet powder obtained above is heat-treated in a hydrogen atmosphere to produce a hydrogenation / disproportionation reaction. (HD: Hydrogenation Disproportionation) is generated, and the Sm—Fe binary alloy is decomposed into an SmH ₂ phase and an Fe phase (hereinafter, the heat treatment is also referred to as “HD treatment”).

  In the HD treatment described above, the hydrogen partial pressure is 50 to 500 kPa, preferably 100 to 200 kPa.

  In the above HD treatment, the heating temperature is 700 to 900 ° C., preferably 800 ° C.

  In the above HD treatment, the heating time is 10 minutes to 300 minutes, preferably 30 minutes to 120 minutes.

  Subsequent to the HD treatment described above, the raw magnet powder is heat-treated under reduced pressure to discharge hydrogen to cause dehydrogenation and recombination (DR) in the raw magnet powder. The binary alloy is reformed (hereinafter, the heat treatment is also referred to as “DR treatment”).

  In the above-described DR treatment, “under reduced pressure” means a pressure of 50 Pa or less, preferably 10 Pa or less.

  In the DR treatment, the heating temperature is 700 to 900 ° C, preferably 760 to 840 ° C. The rate of dehydrogenation / recombination reaction can be adjusted by the heating temperature.

  In the DR treatment, the heating time is 10 minutes to 300 minutes, preferably 30 to 120 minutes.

  A series of treatment methods of the above hydrogenation / decomposition reaction and dehydrogenation / recombination reaction is called HDDR method. By processing the raw magnet powder by the HDDR method, fine crystals can be obtained and high coercive force can be achieved.

(3) Nitriding treatment The raw material magnetic powder treated as described above is heat-treated in a nitrogen atmosphere, so that nitrogen is taken into the crystal (nitriding) and is composed of the Sm—Fe—N-based material of the present invention. Magnet powder is obtained.

  In the above nitriding treatment, the partial pressure of nitrogen is 50 to 500 kPa, preferably 100 to 200 kPa.

  In said nitriding process, heating temperature is 300-600 degreeC, Preferably it is 400-500 degreeC.

  In the above nitriding treatment, the heating time is 1 to 72 hours, preferably 12 to 48 hours. By adjusting the heating time, the amount of nitrogen taken into the magnet powder can be adjusted.

  The magnet powder of the present invention obtained by the method including the treatments (1) to (3) has a very high coercive force even if the particle size of the magnet powder is not less than 10 μm. Such a magnet powder is suitable for bonded magnets because of its high filling ability into the resin.

  That is, the present invention provides a method for producing a magnet powder composed of an Sm—Fe—N-based material, which includes heating a raw material powder composed of samarium and iron in a hydrogen atmosphere and then heating in a vacuum. Also provide.

(Example)
-Examples 1-7 and Comparative Examples 1-7
Raw metal samarium and iron were weighed so as to have the composition shown in Table 1, and melted and cast in an argon atmosphere in a high frequency melting furnace to produce 30 g of a master alloy. This was heat-treated in argon gas at 1100 ° C. for 50 hours to homogenize the structure of the master alloy. The homogenized master alloy was pulverized in the order of a crusher, a stamp mill, and a ball mill in an argon atmosphere with an oxygen concentration of 10 ppm or less, and passed through a sieve having an opening of 40 μm to obtain a raw material powder.

  Next, argon and oxygen were gradually replaced to gradually oxidize the raw material powder. The composition quantitatively analyzed with a fluorescent X-ray analyzer (XRF) (manufactured by Horiba: MESA50; radiation source: RhKα) is also shown in Table 1 (in terms of Sm-Fe binary alloy).

  The gradually oxidized raw material powder was placed in an alumina crucible and heat-treated at 800 ° C. for 60 minutes in a 101 kPa hydrogen atmosphere (hydrogenation / decomposition (HD) treatment). Subsequently, hydrogen was discharged with a vacuum pump, and heat treatment was performed at a temperature shown in Table 1 under reduced pressure (5 Pa) for 30 minutes (dehydrogenation / recombination (DR) treatment). The heat-treated raw material powder was heat treated and nitrided at 470 ° C. for 24 hours under a nitrogen atmosphere of 101 kPa to obtain a magnet powder composed of an Sm—Fe—N-based material.

Comparative Example 8
Raw metal samarium and iron were weighed so as to have the composition shown in Table 1, and melted and cast in an argon atmosphere in a high frequency melting furnace to produce 30 g of a master alloy. This was heat-treated in argon gas at 1100 ° C. for 50 hours to homogenize the structure of the master alloy. The homogenized master alloy was pulverized in the order of a crusher, a stamp mill, and a ball mill in an argon atmosphere with an oxygen concentration of 10 ppm or less, and passed through a sieve having an opening of 40 μm to obtain a raw material powder.

  Next, argon and oxygen were gradually replaced to gradually oxidize the raw material powder. The composition quantitatively analyzed with a fluorescent X-ray analyzer (XRF) (manufactured by Horiba: MESA50; radiation source: CuKα) was 11.8 atomic% of samarium and iron was the balance in terms of Sm-Fe binary alloy.

  The gradually oxidized raw material powder was put in an alumina crucible and subjected to nitriding by heat treatment at 470 ° C. for 24 hours under a 101 kPa nitrogen atmosphere to obtain a magnet powder of Comparative Example 8.

(Evaluation)
-Average particle diameter About each of the magnetic powder of Examples 1-7 obtained above and Comparative Examples 1-8, average particle diameter D50 was measured with the laser diffraction type particle size distribution measuring apparatus (the Horiba make, LA-950). It was measured. The results are also shown in Table 1.

Scanning Transmission Electron Microscope (TEM) Analysis The magnet powder of Example 1 obtained above was thinly processed by ion milling the powder, and the scanning transmission electron microscope (TEM) (Hitachi High Technologies) A cross-sectional image was taken with HD-2300A). The obtained image is shown in FIG.

As is apparent from FIG. 1, the obtained powder is composed of a main phase of fine crystal grains, and there are finer crystals (average crystal grain size is about 3 nm) at the crystal grain boundaries. Was confirmed. An electron diffraction pattern was photographed using TEM for the crystal grains of the main phase and the crystallites present at the crystal grain boundaries. From the position of the obtained diffraction pattern, the main phase was Sm ₂ Fe ₁₇ N _x (x is It was confirmed that the microcrystalline body was an α-Fe phase.

  For each of the magnetic powders of Examples 1 to 7 and Comparative Examples 1 to 8, the Sm and Fe contents were measured by quantitative analysis using a fluorescent X-ray analyzer (XRF) (Horiba Seisakusho: MESA50; radiation source: CuKα). The N content was measured with an oxygen / nitrogen analyzer (Horiba, Ltd .: EMGA-920). From the obtained value, the ratio (atomic%) of each atom to the total of 100 atomic% of the three components of Sm—Fe—N was determined. The results are also shown in Table 1.

-Average crystal grain size For each of the magnet powders of Examples 1 to 7 and Comparative Examples 1 to 8, a TEM image with a magnification of 50000 times was taken in the same manner as described above, and the crystal grain size was obtained from this TEM image by the intercept method. It was. That is, arbitrarily draw 10 straight lines in the vertical and horizontal directions on the TEM image, count the number of crystal grains on each straight line, divide the length of the straight line by the number of crystal grains, and obtain the average of 20 lines. Was the average crystal grain size. The results are also shown in Table 1.

X-ray diffraction (XRD) peak intensity ratio For each of the magnetic powders of Examples 1 to 7 and Comparative Examples 1 to 8, an X-ray diffraction device (manufactured by Rigaku Corporation; Miniflex II Cu tube specification) and an X-ray detection device ( Using D / teX Ultra), the diffraction intensity of the magnet powder was measured with a step width of 0.05 ° and a step time of 3 seconds, and α relative to the peak height of the (303) plane of the Sm ₂ Fe ₁₇ phase. The ratio of the peak height of the (110) plane of -Fe was determined, and measurement was performed at three locations to determine the average value thereof, which was taken as the XRD peak intensity ratio. The results are also shown in Table 1.

Energy dispersive X-ray (EDX) peak intensity ratio For each of the magnetic powders of Examples 1 to 7 and Comparative Examples 1 to 8, using the above TEM, Sm ₂ Fe ₁₇ N _x main phase and grain boundary layer part The sample was irradiated with an electron beam having a beam diameter equivalent to the thickness of the grain boundary layer (for example, 3 nm), and energy dispersive X-ray spot analysis was performed. For the Sm peak having a fluorescent X-ray energy of 5.6 keV, the intensity ratio of the grain boundary layer peak to the peak of the Sm ₂ Fe ₁₇ N _x main phase was calculated, and this was used as the EDX peak intensity ratio. The results are also shown in Table 1.

-Coercive force For each of the magnet powders of Examples 1 to 7 and Comparative Examples 1 to 8, magnetic powder was filled in a container having an internal volume of 0.07 cm ³ , and maximum was obtained with a BH tracer (manufactured by Nippon Electron Sokki) A coercive force was measured by applying a magnetic field of 55 kOe. The results are also shown in Table 1.

As is clear from Table 1, Examples 1 to 7 in which the intensity ratio of the Fe (110) peak to the Sm ₂ Fe ₁₇ (303) peak measured by X-ray diffraction method is 1.00 or less are average crystal grain sizes. However, it was confirmed that it has a high coercive force as compared with Comparative Examples 1 to 7 in which the intensity ratio is larger than 1.00. In addition, Examples 1 to 7 in which the average crystal grain size of the main phase is 1 μm or less are higher than those in Comparative Example 8 in which the above-mentioned strength ratio is 1.00 or less but the average crystal grain size is 26 μm. It was confirmed to have a magnetic force (HcJ: intrinsic coercive force).

  The magnet powder of the present invention can be used in a wide variety of applications such as bonded magnets and motor magnets.

Claims (5)

A magnet powder composed of an Sm—Fe—N-based material, the average crystal grain size of the main phase is 1 μm or less, and Fe (110) with respect to the Sm ₂ Fe ₁₇ (303) peak measured by the X-ray diffraction method A magnet powder having a peak intensity ratio of 0.01 to 1.00.   The magnet powder according to claim 1, wherein the average particle size of the powder measured by a dry laser diffraction method is 10 to 300 μm.   The Sm peak intensity ratio of the grain boundary layer with respect to the main phase measured by energy dispersive X-ray spot analysis of a transmission electron microscope is 0.7 to 1.0. Magnet powder.   It is a manufacturing method of the magnet powder in any one of Claims 1-3, Comprising: The raw material powder comprised from samarium and iron is heated in hydrogen atmosphere, and then it heats under reduced pressure, and then nitrides. Manufacturing method.   The manufacturing method according to claim 4, wherein heating under reduced pressure is performed at 760C to 840C.