Method for manufacturing metal nitrides

Abstract

In a direct nitriding method utilizing the self-combustion of raw metal powder, the present invention provides a method for producing metal nitrides with high yield and high efficiency by suppressing the generation of unreacted material due to cracks occurring in the raw metal powder packing layer filled in a flattened crucible, and by facilitating the removal of reaction products from the crucible. [Solution] In producing metal nitrides by a direct nitriding method utilizing the self-combustion of raw metal powder, raw metal powder is packed into a flat crucible, then grooves are formed in the raw metal powder packed layer to divide it into multiple blocks, and then at least one block is ignited under a nitrogen atmosphere to obtain metal nitrides.

Description

Technical Field

[0001] The present invention relates to a novel method for producing metal nitrides.

Background Art

[0002] Metal nitrides such as silicon nitride, aluminum nitride, and boron nitride have attracted attention as ceramic raw materials for various industrial materials because their sintered bodies generally have excellent properties such as high thermal conductivity, high insulation, and high strength.

[0003] For example, silicon nitride is added with various sintering aids and sintered at high temperature. Among various ceramic sintered bodies, the silicon nitride sintered body is light, has high mechanical strength, high chemical resistance, high electrical insulation, etc. It is used as wear-resistant members such as ball bearings and members for high-temperature structures. In addition, by devising the type of aid and sintering conditions, the thermal conductivity can also be increased, so it has come to be used as a thin and high-strength heat dissipation substrate material.

[0004] As a method for producing the above silicon nitride, a method for synthesizing silicon nitride by a direct nitridation method using self-combustion (hereinafter also referred to as combustion synthesis method) is known (see Patent Document 1). In this method, silicon powder is used as a raw material, and a part of the raw material powder filled in a crucible is ignited in a nitrogen atmosphere, and the heat generated by the self-heating in the nitridation reaction of the raw material silicon powder is propagated to the entire filled raw material silicon powder to carry out a synthesis reaction.

[0005] Also, in the above combustion synthesis method, in order to prevent the nitridation reaction from explosively chain-reacting and the generated silicon nitride particles from fusing, a method of mixing silicon nitride powder as a diluent with the raw material silicon powder and performing combustion synthesis has also been proposed (see Patent Document 2).

[0006] The crucible used in the industrial implementation of the above combustion synthesis method has a flat shape like a lid, and this crucible is filled with a raw material metal powder such as silicon powder, optionally mixed with a diluent.

[0007] The aforementioned flattened crucible, on an industrial scale, is 0.3 m 2 Often, materials with the above-mentioned surface area are used, and the metal nitride obtained after filling these with raw metal powder and carrying out a combustion synthesis method is in the form of relatively strong, plate-shaped aggregates with the aforementioned surface area. To avoid contamination during grinding, the above-mentioned plate-shaped aggregates are divided into blocks of appropriate size by hand, and these blocks are then crushed by bringing the aggregates into contact with each other in a coarse grinding device that does not use media such as balls, a method known as "co-crushing" to obtain coarse metal nitride powder, and this coarse powder is then finely ground as needed.

[0008] However, in the coarse crushing of the aggregates, manually dividing the plate-shaped aggregates is extremely time-consuming, and the resulting blocks are irregularly shaped with varying sizes. When attempting to crush these blocks by co-crushing in a coarse crushing device, clogging occurs if relatively large blocks are present when feeding them into the device, and there is room for improvement in the crushing efficiency by co-crushing. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2000-264608 [Patent Document 2] WO2018 / 110565 publication [Overview of the project] [Problems that the invention aims to solve]

[0010] Accordingly, the object of the present invention is to improve the work efficiency in dividing the metal nitride, which is in the form of a plate-like, relatively firm aggregate obtained after the reaction of a raw material metal powder packed layer in a flat crucible, in a method for producing metal nitride by combustion synthesis, and to improve the grinding efficiency in coarse grinding. [Means for solving the problem]

[0011] The inventors conducted research to achieve the aforementioned objective in a method for producing metal nitrides by combustion synthesis. As a result, they discovered that by forming grooves in a layer of raw metal powder packed in a flat crucible to divide it into multiple blocks, the firmly aggregated plate-like metal nitride obtained after the reaction can be efficiently recovered by dividing it into blocks. Furthermore, the blocks can be made of uniform size, making them easy to feed into a coarse grinding device. In addition, the presence of artificially formed edges on each block effectively improves the grinding efficiency in coarse grinding. Based on these findings, the inventors completed the present invention.

[0012] In other words, the present invention provides a method for producing metal nitrides by a combustion synthesis method of raw material metal powder, characterized by filling a flat crucible with raw material metal powder, then forming grooves in the raw material metal powder-filled layer to divide it into multiple blocks, and finally igniting at least one of the blocks under a nitrogen atmosphere.

[0013] The groove is formed by pressing a tapered blade, which widens upward at least at the lower part, from the top of the raw metal powder packed layer to create an upwardly widening tapered shape. This increases the density of the raw metal powder in the portion forming the side wall of the groove and ensures that the shape of the groove forming the edge is reliably maintained.

[0014] Furthermore, it is preferable that the opening width of the groove be 1 mm or more in order to prevent aggregation between partitioned blocks and to facilitate the division of the resulting metal nitride into blocks.

[0015] Furthermore, it is preferable that the grooves be formed so that their depth is 2 / 3 or more of the thickness of the raw material metal powder packing layer, as this allows the metal nitride obtained with less load to be divided into blocks.

[0016] Furthermore, it is preferable to set the maximum width of the groove to 5 mm or less, as this ensures reliable heat transfer between blocks due to self-heating.

[0017] In carrying out the present invention, it is preferable to form the groove by pushing a jig having blades arranged in a lattice pattern from above the raw material metal powder filling layer, as this can efficiently form the groove.

[0018] For the above reasons, it is preferable that the shape of the blade of the jig is a tapered shape that widens upward at least at the lower part.

[0019] Further, in the method of the present invention, after forming a groove in the raw material metal powder layer, it is preferable to fill the groove with metal nitride powder to more efficiently conduct heat in the groove.

[0020] The method of the present invention is effective when using a large crucible with a bottom area of the flat crucible of 0.3 m 2 or more.

Effect of the Invention

[0021] According to the present invention, by partitioning the raw material metal powder filling layer in the flat crucible into a plurality of blocks, the aggregates of the metal nitride, which are reaction products, can be easily divided into small blocks and taken out of the crucible, and high efficiency of such work can be achieved.

[0022] Further, since the divided blocks have a substantially rectangular parallelepiped or substantially cubic shape, they have edges on each side. According to the confirmation by the present inventors, compared with the amorphous blocks obtained by manual division, the blocks having the above edges exhibit the effect of improving the pulverization efficiency because the edge portions effectively act on other blocks when performing rough pulverization by co-grinding in a pulverization device that does not use a medium.

Brief Description of the Drawings

[0023] [Figure 1] It is a schematic diagram showing one aspect of forming a groove in the raw material metal powder layer filled in the crucible. [Figure 2]This is a schematic diagram showing one embodiment of a jig for forming grooves in a raw metal powder layer. [Figure 3] This is a process diagram showing one embodiment of the method for producing metal nitrides according to the present invention. [Modes for carrying out the invention]

[0024] This invention relates to a method for producing metal nitrides by a direct nitriding method, also known as a combustion synthesis method, that utilizes the self-combustion of raw metal powders. (raw metal powder) In the present invention, examples of raw material metal powders include silicon powder, aluminum powder, and boron powder, with silicon powder being particularly preferred.

[0025] Although silicon and boron are nonmetallic elements, elemental silicon is sometimes called metallic silicon and elemental boron is sometimes called metallic boron. Therefore, in this specification, silicon powder and boron powder are also included in the category of metallic powder.

[0026] The above raw material metal powder preferably has an average particle size D50 in the range of 1 to 10 μm and is of high purity. For example, if the metal powder is silicon powder, the Al and Fe content is preferably 200 ppm or less, each. If the metal powder is aluminum powder, the Si and Fe content is preferably 200 ppm or less, each. Furthermore, if the metal powder is boron powder, the Fe content is preferably 200 ppm or less. The presence of such metal elements may reduce the sinterability of the resulting metal nitride and may also reduce the strength and other properties of the resulting sintered body. For similar reasons, the content of high-melting-point metals such as W and Mo is also preferably 200 ppm or less.

[0027] In the present invention, the metal powder used as a raw material powder may be obtained by any means, but it is preferable that its purity and particle size are adjusted to the predetermined range described above. For example, if the metal powder is silicon powder, it is generally economical to recover and use the fine powder generated in the process of crushing semiconductor polycrystalline silicon rods to produce nuggets. Alternatively, commercially available industrial raw materials can be crushed and used.

[0028] The raw material metal powder may be mixed with a diluent. The reaction between metal powder and nitrogen is an exothermic reaction, and the surface reaction is the rate-limiting reaction. Therefore, as the amount of metal powder increases, it becomes more difficult to control the temperature of the raw material powder. However, by mixing a diluent with the raw material metal powder, the amount of raw material metal powder in the raw material powder is reduced, making it easier to control the temperature during the reaction.

[0029] As the diluent, metal nitride powder is preferred, and in particular, in order to avoid the need to remove the diluent contained in the raw material powder from the metal nitride after the metal powder has reacted to form the metal nitride, it is preferable that the metal nitride powder used as the diluent be a nitride powder of the same metal element as the raw material metal powder. For example, if the metal powder is silicon powder, the metal nitride powder used as the diluent is preferably silicon nitride; if the metal powder is aluminum powder, the metal nitride powder used as the diluent is preferably aluminum nitride; and if the metal powder is boron powder, the metal nitride powder used as the diluent is preferably boron nitride. As these diluents, for example, metal nitrides produced by the metal nitride production method of the present invention can be used.

[0030] The optimal amount of the diluent to be used varies depending on the reaction heat of the raw metal powder and cannot be limited in general, so the optimal amount to be used should be determined as appropriate. For example, when the raw metal powder is silicon powder, it is preferable to use it in a ratio of 0 to 80 parts by mass per 100 parts by mass of the raw metal powder. The content of the diluent is more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the raw metal powder. Furthermore, from the viewpoint of controlling the temperature of the raw powder, the content of the metal nitride is more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the metal powder.

[0031] In the present invention, the raw material metal powder is packed into a flattened crucible. The size of the crucible is not particularly limited, but in the case of effective industrial-scale implementation of the present invention, the bottom surface area is 0.3 m². 2 Crucibles of the above size are preferred. While square and rectangular bases are common, circular and other shapes can also be used. The height of the crucible should be determined appropriately according to the thickness of the packed layer. Considering the reaction in the aforementioned area, the thickness of the raw metal powder packed layer is generally 1 to 10 cm, particularly 2 to 7 cm. Carbon is commonly used as the material for the crucible.

[0032] The most distinctive feature of the manufacturing method of the present invention is that grooves are formed in the raw material metal powder packed layer, which is formed by filling the flattened crucible with raw material metal powder, thereby dividing it into multiple blocks. By forming grooves in the raw material metal powder layer and dividing it into multiple blocks, the metal nitride obtained after the reaction, which has strongly aggregated, can be divided into blocks and recovered efficiently. Furthermore, the blocks obtained in this way can be crushed with high crushing efficiency when co-crushing is performed.

[0033] Furthermore, by forming grooves in the raw material metal powder packing layer and dividing it into multiple blocks, when the crucible is moved to the reaction vessel after the raw material metal powder has been packed, the effects of degassing and gas supply during gas replacement to create a nitrogen atmosphere in the reaction vessel can cause stress on the raw material metal powder packing layer inside the crucible, which can lead to large cracks in certain areas. However, according to the present invention, the stress can be distributed among the partitioned blocks, and the propagation of heat due to self-heating can be partially blocked by the occurrence of the large cracks, which can prevent an increase in the proportion of unreacted material in the resulting metal nitride.

[0034] The details will be explained below with reference to Figure 1. Figure 1 is a schematic diagram showing one embodiment of forming grooves in the raw material metal powder layer packed in a crucible in the present invention. In Figure 1, (a) is a schematic diagram showing the state in which grooves 3 are formed in the raw material metal powder packed layer of crucible 1 and divided into a plurality of blocks 2, and (b) is a cross-sectional view AA' thereof. A partially enlarged section of the cross-sectional view AA' is shown below.

[0035] As shown in Figure 1, the raw material metal powder filling layer formed by filling a flat crucible 1 with raw material metal powder is divided into multiple blocks 2 by forming grooves 3. 4 indicates an igniter. Furthermore, to prevent deterioration of the crucible, it is preferable to form a protective layer made of metal nitride powder on the inner surface of the crucible, specifically the bottom and outer circumference.

[0036] The size of each block partitioned by the groove 3 is not particularly limited, but considering ease of handling when supplying to the subsequent crushing process, 20 to 500 cm is appropriate. 2 It is preferable to divide the area into blocks of a certain size. Furthermore, it is preferable that the size of each block be uniform, but they may vary slightly.

[0037] Furthermore, it is preferable that the groove 3 is formed by pressing a tapered blade, which widens upward at least at its lower end, into the top of the raw metal powder packing layer to create an upwardly widening tapered shape. By pressing such a tapered blade into the raw metal powder packing layer to form a groove, the density of the raw metal powder in the portion where the tapered surface forms the side wall of the groove can be increased, and the shape of the groove can be reliably maintained. The angle (total angle) of the taper is preferably 1 to 30°, and more preferably 1 to 20°.

[0038] Furthermore, it is preferable that the opening width (w) of the groove shown in the partially enlarged view be 1 mm or more, in order to prevent the groove from disappearing due to agglomeration of the wall surfaces of the partitioned blocks during the reaction, and to facilitate the division of the resulting metal nitride into each block.

[0039] Furthermore, it is preferable that the groove 3 is formed such that its depth (h) is 2 / 3 or more of the thickness of the raw metal powder packing layer, because this allows the resulting metal nitride to be divided into blocks with less load.

[0040] Furthermore, it is preferable to set the maximum width of the groove, including the opening width of the groove, to 5 mm or less, so that even if the groove reaches the bottom end of the raw metal powder packed layer, heat can be reliably transmitted due to self-heating in the portion isolated by the groove.

[0041] In carrying out the method of the present invention, it is preferable to efficiently form the grooves by pressing a jig 5, in which blades are arranged in a grid pattern so as to be the dimensions of the block 2, from above the raw metal powder packed layer, as shown in Figure 2. The jig 5 can be made the same size as the bottom area of ​​the crucible so that grooves dividing the raw metal powder packed layer into blocks can be formed in one step, but it may also be made the same size as two or more divisions of the bottom area of ​​the crucible so that grooves dividing the block into blocks can be formed in multiple steps.

[0042] In the jig 5 described above, as shown in Figure 2(b), the shape of the blade is preferably a tapered shape that widens upward at least at the lower part.

[0043] In the method of the present invention, it is preferable to fill the grooves 3 with metal nitride powder after forming grooves 3 in the raw material metal powder layer, as this allows for more efficient heat transfer in the portion isolated by the grooves.

[0044] In the present invention's method for producing metal nitrides, at least one block of the raw material metal powder layer packed in a crucible is ignited under a nitrogen atmosphere, and the heat generated by the self-combustion due to the nitriding reaction of the metal powder is propagated throughout the raw material metal powder to obtain a metal nitride.

[0045] The method for producing metal nitrides according to the present invention, which includes forming grooves in the raw material metal powder layer packed in the crucible, will be described in detail below with reference to Figure 3. Figure 3 is a process diagram showing one embodiment of the method for producing metal nitrides according to the present invention.

[0046] In the manufacturing method of the present invention, first, as shown in Figure 3(a), raw material metal powder is packed into a flat crucible 1 to form a raw material metal powder packed layer 2'. In the figure, an igniter 4 is shown to be set in advance, but the igniter may be set after forming grooves in the raw material metal powder packed layer to divide it into multiple blocks. Furthermore, the position where the igniter is placed may be at the edge of the packed layer or in the center, and one or more igniters may be placed. In addition, the igniter 4 can also be replaced with known methods such as ignition by arc discharge, ignition by energizing a carbon or metal heater, or ignition by laser irradiation, in which case the above-mentioned igniter does not need to be set.

[0047] Next, as shown in Figure 3(b), a jig 5 with blades arranged in a grid pattern is pressed from above the raw metal powder packed layer 2' to form grooves 3, thereby dividing the raw metal powder packed layer into multiple blocks 2.

[0048] After forming the groove 3 described above, it is preferable to fill the groove with the same metal nitride powder as the reaction product, as described above. Furthermore, as shown in Figure 3(d), it is preferable to form an insulating layer 6 so as to cover the entire raw material metal powder filling layer partitioned into blocks, in order to prevent the radiation of combustion heat. The insulating layer 6 may be formed from metal nitride powder, or an insulating material with a structure that does not affect the reaction, such as graphite fibers or porous ceramic plates, may be placed therein. The thickness of such an insulating layer is not particularly limited, but about 1 to 50 mm is appropriate.

[0049] In the present invention, the ignition of the raw material metal powder is generally carried out by placing a crucible filled with the raw material metal powder in a pressure-resistant, sealed reaction vessel 7 having an ignition device and a gas supply and discharge mechanism, reducing the pressure inside the vessel to remove air, and then supplying nitrogen gas to replace it with nitrogen to create a nitrogen atmosphere, as shown in Figure 3(e).

[0050] The above reaction may be carried out under atmospheric pressure or under pressure, but it is preferable to carry it out under pressure. In particular, when carrying out the reaction to obtain silicon nitride as a metal nitride, it is preferable to carry it out under pressure from the viewpoint of facilitating the nitriding reaction. Specifically, it is preferable to carry it out at a pressure of atmospheric pressure to 1 MPa, and this pressure is achieved by the nitrogen pressure supplied to the closed reactor.

[0051] Upon ignition, the nitriding reaction by autocombustion of the raw metal powder begins. When the raw metal powder is metallic silicon powder, the reaction temperature is approximately 1500-2000°C. The heat of combustion propagates between the raw metal powder particles and even between blocks within the crucible, causing the entire raw metal powder in the crucible to be nitrided, and a metal nitride is obtained.

[0052] The metal nitride obtained by the above reaction is obtained in a relatively strongly aggregated state. However, in the present invention, since the raw material metal powder packed layer is divided into blocks, the aggregated metal nitride obtained can be easily divided into block pieces 8 corresponding to the size of the block, as shown in Figure 3(f), and recovered.

[0053] The metal nitride obtained by the method of the present invention is obtained as appropriately sized block pieces 8 formed by the aggregation of metal nitride powder, making it easy to handle. As shown in Figure 3(g), the feeding operation into the grinding device 9 can be performed stably, and as shown in Figure 3(h), metal nitride powder 10 can be obtained.

[0054] The grinding device 9 described above preferably uses a grinding device that performs coarse grinding by co-crushing. A typical example of such a grinding device is a vibratory mill that does not use media. In the coarse grinding described above, the block pieces 8 obtained by the method of the present invention can be efficiently co-crushed by the effective action of their edges, thereby obtaining metal nitride powder 10. The average particle size of the metal nitride powder obtained by coarse grinding is not particularly limited, but is preferably about 5 to 20 μm. The grinding described above may be performed in batches, but it is preferable to perform it in a continuous manner because by maintaining an environment in which block pieces 8 with edges are always present, the effect of improving grinding efficiency by these edges can be continuously maintained.

[0055] Furthermore, the metal nitride powder 10 obtained by the above coarse grinding may be further finely ground using a grinding device such as a vibratory mill, jet mill, mascolloider, or bead mill.

[0056] The metal nitride powder obtained as described above can be suitably used in the production of metal nitride sintered bodies.

[0057] For example, if the metal nitride powder is silicon nitride powder, a sintered body can be obtained by mixing the silicon nitride powder with sintering aids such as yttria, magnesia, zirconia, and alumina, and then firing it. The resulting metal nitride sintered body can be suitably used as a substrate material for heat dissipation and the like. [Examples]

[0058] The present invention will be described in more detail below by showing examples, but the present invention is an embodiment of these examples. It is not limited to that.

[0059] In the following examples and comparative examples, the following raw material powders were used. • Silicone powder High-purity polycrystalline silicon suitable for solar cell applications was used as raw material powder A, obtained by grinding it to an average particle size of approximately 5 μm using a silicon nitride-lined air-jet mill. The oxygen content of the silicon powder obtained was approximately 0.3% by mass. The impurity content was 10 ppm for Fe and 5 ppm for Al. • Silicon nitride powder (diluent) Silicon nitride powder with an average particle size of 1 μm was used.

[0060] <Example 1> 7.2 kg of silicon powder was used as the raw material metal powder, and 1.8 kg of silicon nitride powder was mixed with it as a diluent. As shown in Figure 3(a), this mixture was packed into a flat crucible 1 to form a raw material metal (silicon) powder packed layer 2'. The flat crucible 1 used was a carbon crucible measuring 1.04 m (width) × 0.40 m (length) × 0.06 m (depth). A mixture of aluminum powder and silicon nitride powder was placed in the center of the packed layer as an ignition agent. In addition, a protective layer of silicon nitride powder was formed on the inner surface of the crucible when filling it with the raw material powder.

[0061] Next, as shown in Figure 3(b), a jig 5, which has tapered blades arranged in a grid pattern, is pressed from above the raw silicon powder packed layer 2' to divide the packed layer 2' into 4cm (width) x 8cm (length) sections, thereby forming grooves 3 with an opening width (w) of 5mm and a taper angle (total angle) of 4.6° down to the bottom end of the packed layer, and dividing the raw metal powder packed layer into multiple blocks 2.

[0062] After forming the grooves 3 described above, silicon nitride powder was filled into the grooves, and a 1 cm thick layer was also filled into the surface of the block to form an insulating layer 6.

[0063] A crucible filled with raw silicon powder was placed in a pressure-resistant, sealed reactor 7 equipped with an ignition device and a gas supply and discharge mechanism. After reducing the pressure inside the container to remove air, nitrogen gas was supplied to replace the atmosphere with nitrogen.

[0064] After degassing the sealed reactor 7 by reducing the pressure, nitrogen gas was supplied to replace the atmosphere with nitrogen. Then, nitrogen gas was gradually supplied until the pressure rose to 0.7 MPa, at which point the igniter was ignited, and silicon nitride was obtained by carrying out a combustion synthesis reaction.

[0065] After the combustion synthesis reaction described above, the silicon nitride in the flat crucible 1 removed from the sealed reactor 7 was observed after removing the insulating layer. No large cracks had formed except for the gaps between the blocks, and each block could be easily separated and recovered as block pieces 8. These could then be stably fed from the hopper into a grinding device to obtain silicon nitride powder 10. The grinding was performed by co-grinding using a vibrating mill, and after 20 minutes of grinding, 95% of the total material was ground to 500 μm or less. The average particle size of the obtained crude silicon nitride powder was 8.5 μm.

[0066] The above crude silicon nitride powder was further finely ground using a vibratory mill to obtain silicon nitride powder with an average particle size of 0.9 μm and substantially 100% β-type silicon nitride. Furthermore, no unreacted silicon was detected in the obtained silicon nitride powder.

[0067] <Comparative Example 1> In Example 1, silicon nitride powder was produced under similar conditions, except that grooves were not formed in the raw material metal (silicon) powder packed layer 2'.

[0068] After the combustion synthesis reaction, the silicon nitride aggregates in the flattened crucible 1, removed from the closed reactor 7, were manually divided. The resulting blocks were irregular in shape and size, causing clogging in the input hopper of the grinding device. Therefore, the blocks were removed, divided, and then input. Grinding for 20 minutes using a vibrating mill allowed 77% of the total to be ground to 500 μm or less. The average particle size of the resulting crude silicon nitride powder was 9.2 μm. [Explanation of symbols]

[0069] 1. Flat crucible 2 blocks 3 grooves 4. Fire starter 5. Jig 6. Insulation layer 7. Sealed reactor 8 block pieces 9. Crushing device 10 Metal nitride powder

Claims

1. A method for producing metal nitrides by a direct nitriding method utilizing the self-combustion of raw metal powder, characterized by filling a flat crucible with raw metal powder, then forming grooves in the raw metal powder-filled layer to divide it into multiple blocks, and finally igniting at least one of the blocks under a nitrogen atmosphere.

2. The method for producing a metal nitride according to claim 1, wherein the groove has an upwardly tapered shape, formed by pressing a tapered blade that widens upward at least in its lower part from the upper part of the raw material metal powder packing layer.

3. The method for producing a metal nitride according to claim 1, wherein the opening width of the groove is 1 mm or more.

4. The method for producing a metal nitride according to claim 3, wherein the depth of the groove is formed to be 2 / 3 or more of the thickness of the raw material metal powder packed layer.

5. The method for producing a metal nitride according to claim 3, wherein the maximum width of the groove is 5 mm or less.

6. The method for producing a metal nitride according to claim 1, wherein the grooves are formed by pressing a jig having blades arranged in a grid pattern from above the raw material metal powder packed layer.

7. The method for producing a metal nitride according to claim 6, wherein the shape of the blade is a tapered shape that widens upward at least at the lower part.

8. The method for producing a metal nitride according to claim 1, wherein the groove is filled with metal nitride powder.

9. The base area of ​​the flattened crucible is 0.3 m². ２ The method for producing a metal nitride according to claim 1, as described above.

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