Method for producing Sm-Fe-based alloy powder

Abstract

To stably produce an Sm-Fe-based alloy powder in which troubles such as nozzle blockage are hard to be generated, and an Sm yield is high with respect to the blending of raw material in a gas atomization method.SOLUTION: Regarding a method for producing a Sm-Fe-based alloy powder in which, in a gas atomization device having: a crucible; a molten metal discharge nozzle member for releasing a molten metal to a vapor phase space; and a movable stopper capable of abutting on and separating from the molten metal discharge nozzle member, parts at least in contact with the crucible, the molten metal discharge nozzle member and the stopper are composed of boron nitride (BN) or yttrium oxide (Y2O3), and an inert gas other than nitrogen is used as an atmospheric gas and a cooling gas of the vapor phase space.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a method for producing Sm-Fe alloy powder by gas atomization. [Background technology]

[0002] Sm2Fe 17 Sm-Fe alloys at or near their stoichiometric composition exhibit ferromagnetism. Compositions in which nitrogen (N) is introduced into such Sm-Fe alloys (a typical compositional formula is Sm2Fe) 17 The N3) powder exhibits excellent hard magnetic properties and is useful as a material for bonded magnets. In this specification, a powder composition in which N is introduced into an Sm-Fe alloy and exhibits ferromagnetism is referred to as "Sm-Fe-N magnetic powder." Sm-Fe-N magnetic powder is expected to see expanded use in automotive motors and sensors.

[0003] Sm-Fe alloy powders can be used as intermediates for producing Sm-Fe-N magnetic powders. Specifically, Sm-Fe-N magnetic powders can be obtained by nitriding Sm-Fe alloy powders. Known synthesis methods for Sm-Fe alloy powders include gas atomization and reduction-diffusion methods using Ca or other reducing agents.

[0004] Patent Document 1 describes how Sm2Fe is produced by gas atomization. 17 Spherical alloy particles are synthesized, and the resulting powder is subjected to nitriding treatment in a tubular furnace to produce Sm2Fe. 17 It is stated that an alloy powder with an N3 composition was obtained. The average particle size of the particles obtained by the gas atomization method was 110 μm (paragraph 0012) or 80 μm (paragraph 0014).

[0005] Patent Document 2 describes an example of synthesizing magnetic powders with compositions aimed at increasing coercivity by adding elements such as Si to Sm-Fe or Sm-Fe-C compositions using atomization methods involving gas spraying, gas-water spraying, and water spraying. By nitriding the obtained particles, Sm-Fe-(C)-Si-N powders are obtained. The particle size is approximately 80 to 110 μm (paragraph 0019).

[0006] Patent Document 3 describes the gas atomization method for Sm2Fe with a particle size of 30 μm or less (page 16, line 3). 17 It is stated that spherical particles of the alloy can be obtained, and that these can be nitrided to obtain an SmFeN magnetic alloy (page 15, lines 24-25). Furthermore, it is stated that Sm2Fe can be produced by the gas atomization method. 17 By impacting the molten alloy with a jet stream of N2 gas, Sm2Fe particles with a particle size of 30 μm or less and an outer shape that is nearly spherical (page 16, line 3) are produced. 17 It is described that fine powder of N alloy can be obtained (page 22, lines 2-8). It is stated that by improving the method of blowing N2 gas as described above, ultrafine powder with a particle size of 2 to 10 μm can be obtained (page 22, lines 20-27).

[0007] On the other hand, using a reduction-diffusion method with Ca as a reducing agent, it is possible to obtain fine Sm-Fe alloy powders with a particle size of approximately 10 μm or less. However, the remaining reducing agent components such as Ca in the obtained powder are unavoidable. For example, Patent Document 4 discloses a technique for obtaining magnetic powders such as Sm-Fe-N alloys using a reduction-diffusion method and nitriding treatment, in which the reduction reaction is carried out in two stages, thereby obtaining powders with an average particle size of 5 μm or less without using any grinding steps. It states that for the powder after the second reduction step, "after washing with water, calcium is thoroughly separated using a weak acid such as acetic acid" (paragraph 0028). Even so, 0.01 wt% of Ca remains in the powder obtained in the example (paragraphs 0034, 0037, 0047, 0050, 0060). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-11307 [Patent Document 2] Japanese Patent Publication No. 2001-68315 [Patent Document 3] International Publication No. WO02 / 00379 [Patent Document 4] Japanese Patent Application Publication No. 11-310807 [Overview of the project] [Problems that the invention aims to solve]

[0009] When we attempted to synthesize Sm-Fe alloy powder by rapidly cooling and solidifying particles of molten metal mainly composed of Sm and Fe using a gas atomization apparatus comprising a crucible for producing molten metal, a molten metal discharge nozzle member attached to the bottom of the crucible for discharging the molten metal into a gas phase space, a movable stopper that can contact and separate from the molten metal discharge nozzle member, and a gas injection nozzle for blowing cooling gas onto the molten metal discharged into the gas phase space, we found that there was a problem of nozzle clogging being easily caused, and even when discharge was possible, there was a problem of the Sm content in the obtained powder being significantly reduced.

[0010] After various investigations into these issues, it was found that while alumina (Al2O3) is commonly used for equipment that comes into contact with molten metal in gas atomizing devices, particularly when alumina is used for the molten metal discharge nozzle or stopper, a high-viscosity Sm-Al-Fe-O compound is generated, which easily causes nozzle blockage. Furthermore, even if discharge is possible, the Sm content in the resulting powder may be significantly reduced.

[0011] Sm2Fe 17The critical particle size at which a single magnetic domain is formed is thought to be around 1 μm, and synthesizing particles as close to this size as possible is advantageous from the viewpoint of improving coercivity. According to the gas atomization apparatus disclosed in Patent Document 3, Sm-Fe alloy powder with a particle size of 30 μm or less can be obtained, and by using N2 as the cooling gas and devising a gas blowing method, Sm-Fe-N magnetic powder with a particle size of 2 to 10 μm can be obtained directly. However, particles obtained using N2 gas in the atomization process tend to have an uneven nitriding state, and it is difficult to directly synthesize Sm-Fe-N magnetic powder with a homogeneous nitriding state of individual particles using the gas atomization method. Uneven characteristics of individual particles are a negative factor in improving magnetic properties. Furthermore, Patent Document 3 does not provide any teachings regarding the materials of the crucible or molten metal discharge nozzle, taking into account the reactivity with Sm. The examples shown are of Nd-Fe-B powder synthesis, and no specific examples of powder containing Sm synthesis are shown. If an attempt were made to synthesize Sm-Fe alloy powder or Sm-Fe-N magnetic powder using the gas atomization method described in Patent Document 3, even if it were possible to synthesize particles with a particle size of approximately 30 μm or less, it would be extremely difficult to industrially produce particles with a good Sm yield and low impurity content while maintaining good equipment durability.

[0012] On the other hand, using reduction-diffusion methods and nitriding treatments with Ca and other reducing agents makes it possible to obtain Sm-Fe-N magnetic powders composed of fine particles. However, the residue of reducing agent components such as Ca and other alkaline earth metals and alkali metals is unavoidable. The alkaline earth metals and alkali metals remaining in the magnetic powder tend to gel the resin when the powder is used as a material to manufacture bonded magnets, which reduces the manufacturability of bonded magnets.

[0013] The object of the present invention is to provide a gas atomization method for synthesizing Sm-Fe alloy powders, which are useful as intermediates for producing Sm-Fe-N magnetic powders, that is less prone to problems such as nozzle clogging, which have been a problem in the past, and that can stably synthesize powders with an Sm content ratio close to that of the raw materials. [Means for solving the problem]

[0014] This specification discloses the following inventions. [1] When synthesizing Sm-Fe alloy powder by rapidly cooling and solidifying particles of molten metal mainly composed of Sm and Fe using a gas atomizing device comprising a crucible for producing molten metal, a molten metal discharge nozzle member attached to the bottom of the crucible for discharging the molten metal into a gas phase space, a movable stopper that can contact and separate from the molten metal discharge nozzle member, A method for producing Sm-Fe alloy powder, wherein at least the parts of the crucible, the molten metal discharge nozzle member, and the stopper that come into contact with the molten metal are made of boron nitride (BN) or yttrium oxide (Y2O3), and an inert gas other than nitrogen is used as the atmospheric gas in the gas phase space and the cooling gas. [2] A method for producing an Sm-Fe alloy powder according to [1] above, wherein the cumulative 50% particle size D50 in the volume-based particle size distribution by laser diffraction and scattering method is 25.0 μm or less. [3] A method for producing an Sm-Fe alloy powder according to [1] or [2] above, wherein the Sm-Fe alloy powder has a composition in which the molar ratio of Sm to Fe, Sm / Fe, is 0.09 or more and 0.25 or less. Here, "separation" in [1] above means that the two objects move away from each other with a distance between them. [Effects of the Invention]

[0015] According to the present invention, a gas atomization method can be used to stably synthesize Sm-Fe alloy powder with a high yield of Sm relative to the raw material composition and low impurity content. The gas atomization apparatus used in the present invention is highly reliable in preventing problems such as nozzle clogging and leakage, despite handling molten metal containing Sm, and also improves the durability of the components that come into contact with the molten metal. The present invention contributes to improving the productivity and quality of Sm-Fe-N magnetic powder, which is useful as a material for bonded magnets.

Brief Description of Drawings

[0016] [Figure 1] A diagram schematically illustrating the structure of a gas atomization device. [Figure 2] A diagram schematically showing an example of the cross-sectional structure near the bottom of the crucible of a gas atomization device.

Modes for Carrying Out the Invention

[0017] [Gas Atomization Device] Figure 1 schematically illustrates the configuration of a gas atomizing device that can be used in the present invention. Here, a device having two independent upper and lower spaces within a chamber is used as an example, but the device used in the present invention is not limited to this type. The two upper and lower spaces can be evacuated by a vacuum exhaust device 10, and by introducing gas from atmospheric gas supply sources 11a and 11b, each can be made into a gas phase space with a predetermined gas atmosphere. The upper space contains a crucible 1, in which the raw material is melted to form molten metal 5. As a method of heating the raw material, induction heating using a high-frequency coil 4 can be used, for example. A molten metal discharge nozzle member 2 for discharging the molten metal 5 into the lower gas phase space is attached to the bottom of the crucible 1. The molten metal flow path is blocked by pressing the stopper 3 against the molten metal discharge nozzle member 2 until the molten metal 5 is discharged. After the molten metal 5 is sufficiently homogenized and a predetermined temperature is obtained, the gas supply device 13 for molten metal discharge supplies gas at a predetermined pressure to the surface of the molten metal in the crucible 1, and the stopper 3 is raised to discharge the molten metal 5 from the tip of the molten metal discharge nozzle member 2 into the lower gas phase space. The lower gas phase space is equipped with a cooling gas injection nozzle 6 for blowing cooling gas onto the discharged molten metal 5. Before discharge begins, the supply of cooling gas from the cooling gas supply device 12 to the cooling gas injection nozzle 6 is started, and the cooling gas is injected from the cooling gas injection nozzle 6 at a high pressure. By applying this strong jet of cooling gas to the molten metal 5, fine particles of the molten metal 5 are formed, and these fine particles are rapidly cooled and solidified. The solidified metal particles 7 accumulate at the bottom of the lower gas phase space.

[0018] Figure 2 schematically shows an example of the cross-sectional structure near the bottom of the crucible of a gas atomizing device. The molten metal discharge nozzle member 2 attached to the bottom of the crucible 1 has a discharge port 21, which is the opening at the tip of the nozzle, and a stopper contact surface 22. The stopper 3 is movable in the vertical direction and has the function of blocking the flow path of the nozzle by contacting the stopper contact surface 22 of the molten metal discharge nozzle member 2, and opening the flow path of the nozzle by moving away from the stopper contact surface 22 when molten metal is discharged.

[0019] Attempts have been made to synthesize Sm-Fe-based powders using the gas atomization method (e.g., Patent Documents 1-3). However, Sm readily reacts with the ceramics used in the gas atomization method, making it difficult to industrially synthesize fine powders of a predetermined target composition while maintaining a high yield of Sm using conventionally known gas atomization methods. Besides Sm, Nd is another representative rare earth element used in magnetic materials. According to the Ellingham diagram, Sm is as easily oxidized as Nd. However, when molten metals containing Sm or Nd are actually prepared and their reactivity with ceramics is compared, Sm-containing alloys are more reactive, making industrial production of these alloys more difficult. This is likely because Sm has a higher vapor pressure than Nd at the same temperature.

[0020] The inventors have experimentally investigated the reactivity of molten Sm-Fe alloys with various ceramics and have repeatedly considered suitable apparatus configurations for directly synthesizing Sm-Fe alloy powder of a target composition using the gas atomization method. As a result, the inventors have found that it is extremely effective to construct at least the parts of the crucible (reference numeral 1 in Figure 2), the molten metal discharge nozzle member (reference numeral 2 in Figure 2), and the stopper (reference numeral 3 in Figure 2) that come into contact with the molten metal with boron nitride (BN) or yttrium oxide (Y2O3).

[0021] Experiments showed that yttrium oxide (Y2O3) had lower reactivity with molten Sm-Fe alloys compared to other ceramics. Of the crucible, molten metal discharge nozzle, and stopper, it is particularly preferable to construct the molten metal contact area of ​​the stopper from yttrium oxide (Y2O3).

[0022] Methods for constructing the parts of equipment that come into contact with molten metal using specific ceramics such as yttrium oxide (Y2O3) or boron nitride (BN) include forming the entire equipment from the specific ceramic, or forming the interior from a different material and then coating the surface with the specific ceramic. Thermal spraying is one example of a coating method.

[0023] [Atmospheric gas and cooling gas in the gas phase space] Both the atmospheric gas in the gas phase space where the molten Sm-Fe alloy is discharged and the cooling gas sprayed onto the discharged molten metal shall be inert gases excluding nitrogen. Examples of inert gases excluding nitrogen include Ar, He, etc. Using nitrogen (N2) as the atmospheric gas or cooling gas in the gas phase space may cause over-nitriding or insufficient nitriding, and there is a risk of synthesizing Sm-Fe-N-based magnetic powder that is non-uniformly nitrided. Such Sm-Fe-N-based magnetic powder with poor homogeneity cannot exhibit its original excellent magnetic properties. Therefore, in the present invention, Sm-Fe-based alloy powder, which corresponds to an "intermediate" for obtaining Sm-Fe-N-based magnetic powder by nitriding treatment in a subsequent process, is synthesized by the gas atomization method.

[0024] [Particle size] When the particle size increases, the number of magnetic domains constituting a multi-domain structure within one crystal grain increases, and the coercive force decreases. Therefore, in the gas atomization method, it is desirable to synthesize particles with as small a particle size as possible. Specifically, it is preferable to synthesize Sm-Fe-based alloy powder with a cumulative 50% particle size D50 of 25.0 μm or less in the volume-based particle size distribution by the laser diffraction / scattering method. If Sm-Fe-based alloy powder with D50 of 25.0 μm or less can be synthesized by the gas atomization method, fine Sm-Fe-based alloy particles with D50 in the range of, for example, 2.0 to 11.0 μm can be selected by classification performed in a subsequent process. It is more preferable to synthesize Sm-Fe-based alloy powder with D50 of 20.0 μm or less. The particle size can be controlled by conditions such as nozzle diameter, molten metal pressure (differential pressure), spraying pressure, and cooling rate.

[0025] [Composition] In the Sm-Fe-based alloy, it is considered that the closer the molar ratio of Sm to Fe (Sm / Fe molar ratio) is to the stoichiometric composition of the intermetallic compound Sm2Fe 17 the more advantageous it is in terms of magnetic properties, but it also exhibits ferromagnetism in the surrounding composition range. Sm2Fe 17The Sm / Fe molar ratio in the stoichiometric composition is approximately 0.12. Considering the need to ensure effective coercivity as a material for bonded magnets, it is preferable to have a composition with an Sm / Fe molar ratio in the range of 0.09 to 0.25. The composition of the molten metal melted in the crucible can be roughly the same as the composition of the target Sm-Fe alloy powder.

[0026] Alkaline earth metals and alkali metals have the effect of gelling the resin used in bonded magnets. Magnetic field orientation is usually performed during the manufacturing process of bonded magnets. Using Sm-Fe-N magnetic powder with the lowest possible content of alkaline earth metals and alkali metals is advantageous for improving the manufacturability and performance of bonded magnets. It is preferable to have a Ca content of 0.002 mass% or less (20 ppm or less) in the Sm-Fe alloy powder, and more preferably 0.001 mass% or less (10 ppm or less), as this range has very low reactivity with the resin constituting the bonded magnet. Furthermore, it is desirable that the total amount of alkaline earth metals, including Ca, in the Sm-Fe alloy powder be 0.003 mass% or less. It is also desirable that the total amount of Na and other alkali metals in the Sm-Fe alloy powder be 0.003 mass% or less.

[0027] From the viewpoint of ensuring high magnetization (saturation magnetization, remanent magnetization) in Sm-Fe-N magnetic powders, it is preferable that the total content of Sm and Fe in the intermediate Sm-Fe alloy powder is 95% by mass or more.

[0028] [Molten metal temperature during dispensing] The molten metal temperature at the time of discharge is preferably in the range of 1400 to 1900°C. [Examples]

[0029] [Example 1] (Production of Sm-Fe alloy powder by gas atomization method) We attempted to produce Sm-Fe alloy powder using a gas atomization apparatus with the configuration shown in Figures 1 and 2. In this example, the entire crucible was constructed from boron nitride (BN), the entire molten metal discharge nozzle component was also constructed from boron nitride (BN), and at least the portion of the stopper that is immersed in the molten metal was constructed from yttrium oxide (Y2O3). The inner diameter of the nozzle of the molten metal discharge nozzle component was set to 3.0 mm.

[0030] As raw material, fragments of a pre-melted Sm-Fe alloy were used. Analysis revealed that the Sm / Fe molar ratio of this raw material alloy was 0.16, and the Ca content in the raw material alloy was 0.002 mass%. 996.7 g of this raw material was placed in a crucible and melted by high-frequency induction heating in an Ar atmosphere. After the raw material alloy was completely molten, at 27 minutes from the start of heating, the molten metal at 1637°C was discharged from a nozzle into the lower gas phase space. Hereafter, the discharge of the molten metal from the crucible through the nozzle will be referred to as "discharging." In this example, the entire amount of molten metal in the crucible was successfully discharged. The maximum supply pressure of the gas for discharging the molten metal during discharging was 65 kPa in differential pressure with the atmosphere gas pressure. Ar was used as the cooling gas. The lower gas phase space was also an Ar atmosphere. All of the obtained powder was recovered.

[0031] The powder obtained by gas atomization was heated, dissolved, and diluted with hydrochloric acid, and analyzed using an ICP emission spectrometer (Agilent 720, Agilent Technologies). The Sm / Fe molar ratio was 0.16, which was equivalent to that of the raw alloy. The content of each element in the powder is shown in Table 1. The Ca content was less than 0.001% (below the detection limit). This powder was confirmed to be an Sm-Fe alloy.

[0032] The particle size distribution of Sm-Fe alloy powder obtained by gas atomization was measured using a laser diffraction particle size distribution analyzer (Microtrac HRA, manufactured by Nikkiso Co., Ltd.). As a result, the cumulative 50% particle size D50 in the volume-based particle size distribution obtained by laser diffraction and scattering was 18.89 μm. The cumulative particle size values ​​D10 to D90 in 10% increments, and the cumulative 95% particle size D95 are shown in Table 2. The value of (D90-D10) / D50, which is the left side of equation (1) above, was 2.77.

[0033] Table 3 shows the conditions and results of the gas atomization method (the same applies to each example below). In this example, the reaction between Sm and ceramics was suppressed, and an Sm-Fe alloy powder with an Sm / Fe molar ratio nearly equal to that of the raw material was obtained.

[0034] (classification) The Sm-Fe alloy powder obtained by the gas atomization method described above was classified using an ultrasonic sieving machine equipped with a sieve with a mesh size of 16 μm to remove larger particles. The analytical composition of the classified Sm-Fe alloy powder, determined by the same method as described above, is shown in Table 1.

[0035] To improve the performance of bonded magnets, it is advantageous to have a small average particle size and minimal variation in particle size of the magnetic particles used. It is desirable to adjust the particle size distribution through classification so that D50 is between 2.0 and 11.0 μm and satisfies equation (1) below. (D90-D10) / D50≦1.10 …(1) In particular, it is more preferable to adjust the particle size distribution to satisfy equation (1) above, and to have "D10 of 2.0 μm or more and D90 of 17.0 μm or less".

[0036] The volume-based particle size distribution was determined by laser diffraction and scattering using the same method as described above. The cumulative particle size values ​​D10 to D90 in 10% increments, and the cumulative 95% particle size value D95 are shown in Table 2. As a result of the classification, the cumulative 50% particle size value D50 was 10.82 μm. The value of (D90-D10) / D50, which is the left side of equation (1) above, was 0.97. Through classification, it was possible to prepare an Sm-Fe alloy powder with little variation in particle size that satisfies equation (1) above.

[0037] (nitriding) The Sm-Fe alloy powders selected by the above classification were charged into a tubular furnace and subjected to nitriding treatment by exposing them to a reducing mixed gas with a composition of 35% by volume of ammonia (NH3) and 65% by volume of hydrogen (H2) for 60 minutes while the temperature was raised to 420°C.

[0038] Table 1 shows the analytical composition of the powder after nitriding treatment, determined using the same method as described above. The Sm / Fe molar ratio was 0.17, which was approximately the same as that of the raw material alloy. The N / Fe molar ratio was 0.19. The Ca content was less than 0.001% (below the detection limit). This powder was confirmed to be an Sm-Fe-N alloy.

[0039] The volume-based particle size distribution of the Sm-Fe-N powder after nitriding treatment was determined by laser diffraction and scattering using the same method as described above. The cumulative particle diameters D10 to D90 in 10% increments, and the cumulative 95% particle diameter D95 are shown in Table 2. The cumulative 50% particle diameter D50 was 10.39 μm. The value of (D90-D10) / D50, which is the left side of equation (1) above, was 0.98. This Sm-Fe-N powder satisfies equation (1) above, confirming that it is a powder with little variation in particle size.

[0040] (Measurement of magnetic properties) The magnetic properties of the Sm-Fe-N powder obtained by the above nitriding treatment were measured using a VSM (Quantum Design, DynaCool). The measurement conditions were a maximum applied magnetic field of 2T, a sweep rate of 0.01T / s, a time constant of 1s, an amplitude of 2mm, and a frequency of 40kHz. The measurement results showed that the saturation magnetization at a temperature of 300K was 87A·m 2 / kg, remanent magnetization 40 A·m 2 The coercivity was 117.7 kA / m (1476 Oe) in kg. This Sm-Fe-N powder was confirmed to be a magnetic powder.

[0041] In this example, it was confirmed that by modifying the material of the ceramic component of the gas atomization apparatus as described above, the reaction between Sm and ceramics was suppressed, and a fine Sm-Fe-N magnetic powder having an Sm / Fe molar ratio nearly equal to that of the raw material composition could be obtained. 17We synthesized an Sm-Fe alloy powder having an excess Sm content relative to the stoichiometric composition. The Sm-Fe-N magnetic powder obtained by nitriding treatment exhibits coercivity useful as a material for bonded magnets.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Comparative Example 1] In this example, we attempted to produce Sm-Fe-N magnetic powder under the same conditions as in Example 1, except that the gas atomizing apparatus with the configuration shown in Figures 1 and 2 was constructed with aluminum oxide (Al2O3) for the entire crucible, boron nitride (BN) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper that is immersed in the molten metal; Sm-Fe alloy fragments were used as the raw material, with an Sm / Fe molar ratio of 0.13; the total mass of the raw material was 622.0 g; the discharge temperature during gas atomization was 1660°C; the molten metal was discharged after 25 minutes from the start of heating; and the exposure time to the reducing mixed gas in the nitriding process was 180 minutes.

[0045] In this case as well, the entire volume of molten metal in the crucible could be dispensed. However, compositional analysis of the powder obtained by gas atomization revealed that the Sm / Fe molar ratio was 0.07, indicating that a powder of Sm-Fe alloy with a significantly lower Sm yield relative to the raw alloy was obtained. The reason for the decrease in Sm yield is thought to be that the Sm in the molten metal reacted with the ceramics of the crucible or stopper. The cumulative 50% particle size of the Sm-Fe-N magnetic powder obtained after classification and nitriding was fine at 12.7 μm, but because the composition fell outside the specified range of the present invention, the coercivity was significantly lower than in Example 1 at 24.5 kA / m. 2 (307Oe)

[0046] [Comparative Example 2] In this example, the gas atomization apparatus, as shown in Figures 1 and 2, was constructed using boron nitride (BN) for the entire crucible, boron nitride (BN) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper that is immersed in the molten metal. The raw material used was Sm-Fe alloy fragments with a Sm / Fe molar ratio of 0.13. The total mass of the raw material was 957.8 g. The gas atomization temperature was 1660°C, and the molten metal was dispensed 31 minutes after the start of heating. The experiment was conducted under the same conditions as in Example 1.

[0047] In this case as well, it was possible to extract the entire volume of molten metal from the crucible. However, compositional analysis of the powder obtained by gas atomization revealed that the Sm / Fe molar ratio was 0.11, indicating that a powder of Sm-Fe alloy with a significantly lower Sm yield relative to the raw alloy was obtained. The reason for the decrease in Sm yield is thought to be that the Sm in the molten metal reacted mainly with the ceramic stopper.

[0048] [Comparative Example 3] In this example, the experiment was conducted under the same conditions as in Example 1, except that the gas atomizing apparatus with the configuration shown in Figures 1 and 2 was constructed entirely of aluminum oxide (Al2O3), the entire molten metal discharge nozzle component was made entirely of aluminum oxide (Al2O3), and at least the portion of the stopper immersed in the molten metal was made entirely of aluminum oxide (Al2O3); fragments of Sm-Fe alloy were used as the raw material, with an Sm / Fe molar ratio of 0.13; the total mass of the raw material was 3396.3 g; and at 48 minutes after the start of heating, the maximum supply pressure of the molten metal discharge gas was set to a differential pressure of 40 kPa from the ambient gas pressure, and molten metal was attempted to be dispensed at a temperature of 1700°C. In this case, nozzle blockage occurred, and molten metal could not be dispensed.

[0049] [Comparative Example 4] In this example, the gas atomizing apparatus, as shown in Figures 1 and 2, was constructed using boron nitride (BN) for the entire crucible, boron nitride (BN) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper immersed in the molten metal. The raw material used was Sm-Fe alloy fragments with a Sm / Fe molar ratio of 0.13. The total mass of the raw material was 1080.3 g. The experiment was conducted under the same conditions as in Example 1, except that the molten metal was attempted to be dispensed at a temperature of 1502°C after 41 minutes from the start of heating. In this case, nozzle blockage occurred, and molten metal could not be dispensed.

[0050] [Comparative Example 5] In this example, the experiment was conducted under the same conditions as in Example 1, except that the gas atomizing apparatus with the configuration shown in Figures 1 and 2 was constructed with boron nitride (BN) for the entire crucible, boron nitride (BN) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper that is immersed in the molten metal; Sm-Fe alloy fragments were used as the raw material, with an Sm / Fe molar ratio of 0.13; the total mass of the raw material was 1050.4 g; and the attempt was made to dispense molten metal at a temperature of 1563°C after 41 minutes from the start of heating. In this case, nozzle blockage occurred, and molten metal could not be dispensed.

[0051] [Comparative Example 6] In this example, the gas atomizing apparatus with the configuration shown in Figures 1 and 2 was constructed using yttrium oxide (Y2O3) for the entire crucible, yttrium oxide (Y2O3) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper that is immersed in the molten metal. The raw material used was fragments of Sm-Fe alloy with a Sm / Fe molar ratio of 0.16. The total mass of the raw material was 991.5 g. At the time elapsed from the start of heating, the experiment was conducted under the same conditions as in Example 1, except that the nozzle became clogged and the molten metal could not be discharged.

[0052] [Comparative Example 7] In this example, the experiment was conducted under the same conditions as in Example 1, except that the gas atomizing apparatus with the configuration shown in Figures 1 and 2 was constructed with boron nitride (BN) for the entire crucible, boron nitride (BN) for the entire molten metal discharge nozzle component, and aluminum oxide (Al2O3) for at least the portion of the stopper that is immersed in the molten metal; Sm-Fe alloy fragments were used as the raw material, with an Sm / Fe molar ratio of 0.16; the total mass of the raw material was 1008.0 g; and the attempt was made to dispense molten metal at a temperature of 1648°C after 26 minutes of elapsed time from the start of heating. In this case, nozzle blockage occurred, and molten metal could not be dispensed.

[0053] [Table 3] [Explanation of Symbols]

[0054] 1 crucible 2. Molten metal discharge nozzle component 3 Stopper 4. High-frequency coil 5. Molten metal 6. Cooling gas injection nozzle 7. Solidified metal particles 10 Vacuum exhaust system 11a, 11b Atmosphere gas supply source 12 Cooling gas supply device 13. Gas supply device for molten metal discharge 21 Discharge port 22 Stopper contact surface

Claims

1. A gas atomizing apparatus including a crucible for preparing a molten metal, a molten metal discharge nozzle member attached to the bottom of the crucible for discharging the molten metal into a gas phase space, a movable stopper that can be brought into contact with and separated from the molten metal discharge nozzle member, and a gas injection nozzle for spraying a cooling gas onto the molten metal discharged into the gas phase space, rapidly solidifying particles of a molten metal mainly composed of Sm and Fe to synthesize an Sm-Fe alloy powder, At least the portions of the crucible, the molten metal discharge nozzle member, and the stopper that come into contact with the molten metal are made of boron nitride (BN) or yttrium oxide (Y ２ O ３ ) and an inert gas other than nitrogen is used as the atmospheric gas in the gas phase space and the cooling gas.

2. 2. The method for producing Sm—Fe based alloy powder according to claim 1, wherein the Sm—Fe based alloy powder has a cumulative 50% particle diameter D50 of 25.0 μm or less in a volume-based particle size distribution determined by a laser diffraction / scattering method.

3. 3. The method for producing Sm-Fe based alloy powder according to claim 1, wherein the Sm-Fe based alloy powder has a composition in which the molar ratio of Sm to Fe, Sm / Fe, is 0.09 or more and 0.25 or less.