Method for producing a silicon nitride mixture, and method for producing a silicon nitride sintered body

Abstract

Properly manufacture a silicon nitride sintered body. 【Solution means】The method for manufacturing a silicon nitride mixture includes a step of obtaining a silicon nitride mixture by mixing and pulverizing silicon nitride particles 1 and a sintering aid 2. In the step of obtaining the silicon nitride mixture, silicon nitride particles 1 with an oxygen content of 0.5 wt% or more and 5.0 wt% or less are used, and the silicon nitride mixture is manufactured so that Δ shown in the following formula (1) is 0.06 or more and 0.4 or less. Δ={O B , C , C , A , C , B , A , B -(O B +O C )} / (O B +O C )···(1) Here, O A is the oxygen content (wt%) contained in the silicon nitride mixture, O B is the oxygen content (wt%) contained in the silicon nitride particles, and O C is the oxygen content (wt%) contained in the sintering aid.

Description

Technical Field

[0001] The present invention relates to a method for producing a silicon nitride-based mixture and a method for producing a silicon nitride-based sintered body.

Background Art

[0002] A method of producing a silicon nitride-based sintered body by molding a silicon nitride-based mixture containing silicon nitride and firing the molded body is known. For example, Patent Document 1 describes that silicon nitride powder and a sintering aid powder are crushed and mixed by a ball mill to obtain a silicon nitride-based mixture. Further, Patent Document 2 describes that a raw material powder, which is a silicon nitride-based mixture, is prepared using methods such as refinement and sieving by a ball mill or a jet mill.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Thus, when producing a silicon nitride-based sintered body from a silicon nitride-based mixture, it is required to appropriately produce the silicon nitride-based sintered body.

[0005] An object of the present invention is to provide a method for producing a silicon nitride-based mixture and a method for producing a silicon nitride-based sintered body, which can appropriately produce a silicon nitride-based sintered body.

Means for Solving the Problems

[0006] The method for manufacturing a silicon nitride-based mixture according to the present disclosure includes a step of obtaining a silicon nitride-based mixture by mixing and pulverizing silicon nitride-based particles and a sintering aid. In the step of obtaining the silicon nitride-based mixture, the silicon nitride-based particles having an oxygen content of 0.5 wt% or more and 5.0 wt% or less are used, and the silicon nitride-based mixture is manufactured so that Δ shown in the following formula (1) is 0.6 or more and 0.4 or less.

[0007] Δ={O -(O B +O C )} / (O B +O C ) ···(1) Here, O A is the oxygen content (wt%) contained in the silicon nitride-based mixture, O B is the oxygen content (wt%) contained in the silicon nitride-based particles, O C is the oxygen content (wt%) contained in the sintering aid.

[0008] The method for manufacturing a silicon nitride-based sintered body according to the present disclosure manufactures a silicon nitride-based sintered body by firing the silicon nitride-based mixture obtained by the method for manufacturing a silicon nitride-based mixture.

Advantages of the Invention

[0009] According to the present invention, a silicon nitride-based sintered body can be appropriately manufactured.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a flowchart for explaining the method for manufacturing a silicon nitride-based sintered body according to the present embodiment. [Figure 2] FIG. 2 is a schematic diagram for explaining the pulverization and mixing step. [Figure 3] FIG. 3 is a schematic diagram for explaining an example of the spray drying method. [Figure 4] FIG. 4 is a schematic diagram of a STEM image of a cross section of a silicon nitride-based sintered body. [Modes for carrying out the invention]

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Note that the present invention is not limited to these embodiments, and if there are multiple embodiments, they may be constructed by combining these embodiments. Numerical values ​​are rounded to the nearest whole number.

[0012] (Method for manufacturing silicon nitride sintered bodies) Figure 1 is a flowchart illustrating the method for manufacturing a silicon nitride sintered body according to this embodiment. The silicon nitride sintered body manufactured in this embodiment is a sintered body of silicon nitride, and is manufactured by sintering a silicon nitride mixture containing silicon nitride particles and a sintering aid.

[0013] (Crushing and mixing process) Figure 2 is a schematic diagram illustrating the crushing and mixing process. As shown in Figure 1, in this manufacturing method, a silicon nitride mixture 10A is obtained by performing a crushing and mixing process (step S10). As shown in Figure 2, in the crushing and mixing process, silicon nitride particles 1, sintering aid 2, solvent 4, and media M are mixed and crushed in a container 20. Dispersants and the like are added to the solvent 4 as needed. In this embodiment, the silicon nitride mixture 10A refers to the mixture of crushed silicon nitride particles 1 and sintering aid 2. The silicon nitride mixture 10C refers to the mixture of silicon nitride particles 1 and sintering aid 2 before crushing. In addition, mixing of solvent 4 and media M is not essential in the crushing and mixing process; at least the silicon nitride particles 1 and sintering aid 2 should be mixed and crushed.

[0014] (Silicon nitride particles) The silicon nitride-based particles 1 used in the crushing and mixing process are silicon nitride-based particles (powder). Examples of the silicon nitride-based material include at least one selected from silicon nitride (Si3N4) and sialon. Sialon is a ceramic containing a β-sialon phase or an α-sialon phase, and may contain both the β-sialon phase and the α-sialon phase. β-sialon is represented by Si 6-z Al z O z N 8-z (0 < z ≤ 4.2). Further, α-sialon is a ceramic containing a phase of M x (Si,Al) 12 (O,N) 16 (where M is any one of Li, Mg, Ca, Y, lanthanoid metals other than La and Ce, 0 < x ≤ 2).

[0015] The silicon nitride-based particles 1 contain an oxygen component. The amount of oxygen O B contained in the silicon nitride-based particles 1 is 0.5 wt% or more and 5.0 wt% or less, more preferably 0.6 wt% or more and 3.0 wt% or less, and even more preferably 0.8 wt% or more and 2.0 wt% or less, based on the whole of the silicon nitride-based mixture 10C. When the amount of oxygen O B is 0.5 wt% or more, at the time of sintering, the oxygen component and the sintering aid 2 are appropriately arranged at the interface of the silicon nitride-based particles 1, improving the sinterability and enabling the appropriate production of the silicon nitride-based sintered body. Also, when the amount of oxygen O B is 5.0 wt% or less, excessive weight loss due to the oxygen component volatilized during firing is suppressed, enabling the appropriate production of the silicon nitride-based sintered body. Here, the amount of oxygen O B refers to the amount of O element contained in the silicon nitride-based particles 1, and may refer to both elemental O2 and O (O as an ion) contained in a compound. For example, the O element contained in the silicon oxide (e.g., SiO2) coated on the surface of the silicon nitride-based particles 1 may be the O element contained in the silicon nitride-based particles 1. The amount of oxygen O BThis can be measured using an oxygen analyzer by inert gas fusion-infrared absorption method (JIS R1603:2007) and calculated from the blending amount.

[0016] D of silicon nitride particles 1 used in the crushing and mixing process 50 The particle size is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.2 μm or more and 1.8 μm or less, even more preferably 0.3 μm or more and 1.5 μm or less, and even more preferably 0.4 μm or more and 1.2 μm or less. 50 This range allows for dense sintering, enabling the proper manufacture of silicon nitride sintered bodies. 50 This refers to the 50% particle size based on volume in the cumulative particle size distribution. 50 This can be measured using a particle size analyzer by the laser diffraction / scattering method (JIS Z 8825:2022).

[0017] (Sintering aid) The sintering aid 2 used in the crushing and mixing process may consist of any components, but it is preferable that it contains two or more elements selected from, for example, Y, Al, Mg, Si, Ti, W, Mo, Hf, La, Nd, Gd, Er, Yb, Lu, and C. In this case, the sintering aid 2 may be one raw material (compound) containing the above two or more elements, or it may contain multiple raw materials (compounds) containing at least one of the above two or more elements. Furthermore, the sintering aid 2 may be at least one of oxides, nitrides, and carbides, and is preferably an oxide. For example, if sintering aid 2 contains element Y, it is preferable that sintering aid 2 contains yttrium oxide (Y2O3), and if sintering aid 2 contains element Al, it is preferable that sintering aid 2 contains at least one of aluminum oxide (Al2O3), aluminum nitride (AlN), and MgO·Al2O3 spinel. Also, for example, if sintering aid 2 contains element Mg, it is preferable that sintering aid 2 contains at least one of magnesium oxide (MgO) and MgO·Al2O3 spinel, and if sintering aid 2 contains element Si, it is preferable that sintering aid 2 contains at least one of silicon oxide (SiO2) and silicon carbide (SiC). Also, for example, if sintering aid 2 contains element Ti, it is preferable that sintering aid 2 contains at least one of titanium oxide (TiO2) and titanium nitride (TiN), and if sintering aid 2 contains element Hf, it is preferable that sintering aid 2 contains hafnium oxide (HfO2). Furthermore, for example, if the sintering aid 2 contains the element La, it is preferable that it contains lanthanum oxide (La2O3); if it contains the element Nd, it is preferable that it contains neodymium oxide (Nd2O3); if it contains the element Gd, it is preferable that it contains gadolinium oxide (Gd2O3); if it contains the element Er, it is preferable that it contains erbium oxide (Er2O3); if it contains the element Yb, it is preferable that it contains ytterbium oxide (Yb2O3); and if it contains the element Lu, it is preferable that it contains lutetium oxide (Lu2O3). Furthermore, for example, if the sintering aid 2 contains the element Mo, it is preferable that the sintering aid 2 contains at least one of molybdenum oxide (MoO2) or molybdenum carbide (Mo2C); and if the sintering aid 2 contains the element C, it is preferable that the sintering aid 2 contains at least one of silicon carbide (SiC), titanium carbide (TiC), or titanium carbonitride (TiCN).

[0018] Amount of oxygen contained in sintering aid 2: C The amount of oxygen is 0.5 wt% to 19.5 wt%, more preferably 1.0 wt% to 14.5 wt%, and even more preferably 1.1 wt% to 11.5 wt%, relative to the total amount of silicon nitride mixture 10C. C Being within this range allows for the proper manufacture of silicon nitride sintered bodies. Note that the amount of oxygen here is O C This refers to the amount of elemental oxygen (O) contained in sintering aid 2, and may refer to both the surface oxide film and the O (oxygen as ions) contained in the compound. Oxygen content of sintering aid 2: C This can be calculated from the amount and composition of sintering aid 2.

[0019] D of sintering aid 2 used in the crushing and mixing process 50 The particle size is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.2 μm or more and 1.8 μm or less, even more preferably 0.3 μm or more and 1.5 μm or less, and even more preferably 0.4 μm or more and 1.2 μm or less. 50 This range allows for dense sintering, enabling the proper manufacture of silicon nitride sintered bodies. Sintering aid 2 D 50 This can be measured using a particle size analyzer by laser diffraction and scattering.

[0020] (solvent) The solvent 4 used in the crushing and mixing process is a component that is liquid at room temperature, such as 20°C. Solvent 4 can be any component, but a liquid with a Hildebrand solubility parameter of 9.7 to 23.4 is preferred. Examples include water and ethanol. However, as mentioned above, solvent 4 is not an essential component in the crushing and mixing process and does not need to be added during that process. As a dispersant to be added as needed, pH adjusters, surfactants, polymer dispersants, etc., can be appropriately selected and added to dissociate the silicon nitride particles 1 and sintering aid 2 and to mix them better. Basic pH adjusters can be basic organic substances, such as ammonia, alkanolamines like monoethanolamine, diethanolamine, and triethanolamine, choline, guanidines, and quaternary ammonium salts like tetramethylammonium hydroxide. Acidic pH adjusters can include inorganic acids, organic acids, and their salts, such as phosphoric acid, nitric acid, citric acid, malic acid, acetic acid, lactic acid, oxalic acid, tartaric acid, and their salts, as well as amphoteric salts of amino acids. Examples of surfactants include alkylamine salts, aliphatic or aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts such as pyridinium and imidazolium, phosphonium or sulfonium salts containing aliphatic or heterocyclic compounds, and acetylene glycol. Examples of polymer dispersants include polymers having primary to tertiary amines, quaternary ammonium bases, or quaternary phosphonium bases in the polymer main chain or side chains, homopolymers of acrylic acid or its salts, water-soluble aminocarboxylic acid polymers, or (co)polymers of acrylic acid esters.

[0021] (media) The media M used in the crushing and mixing process is a media for crushing silicon nitride particles 1 and sintering aid 2. The media M may be made entirely of the same material as the silicon nitride particles 1, or it may be a base material of any material with a layer of the same material as the silicon nitride particles 1 coated on its surface. By using the same material as the silicon nitride particles 1 as the media M, the inclusion of foreign matter during crushing and mixing is suppressed, and a silicon nitride sintered body can be manufactured appropriately. However, as mentioned above, media M is not an essential component in the crushing and mixing process and does not need to be added during the crushing and mixing process.

[0022] The shape of the media M used in the crushing and mixing process can be arbitrary, but it may be spherical, for example. Here, "spherical" is not limited to a perfect sphere. Furthermore, the diameter of the media M is preferably 0.1 mm to 50 mm, more preferably 0.3 mm to 10 mm, and even more preferably 0.5 mm to 5 mm. By using media M of such size, the silicon nitride particles 1 and sintering aids can be properly crushed. Note that the diameter of media M may refer to the maximum distance between any two points on the outer surface of media M.

[0023] (container) Container 20 is a container into which silicon nitride particles 1, sintering aid 2, solvent 4, and media M are placed. The shape, size, and composition of container 20 may be arbitrary, but it is preferable that it contains at least one of polyethylene resin, polypropylene resin, and nylon resin.

[0024] (Conditions for crushing and mixing) Next, we will describe the conditions for adding silicon nitride particles 1, sintering aid 2, solvent 4, and media M into container 20, and then mixing and crushing them.

[0025] (addition ratio) In the crushing and mixing process, the amount of sintering aid 2 added relative to the total amount of silicon nitride particles 1 and sintering aid 2 is preferably 1 wt% to 20 wt%, more preferably 1.5 wt% to 15 wt%, and even more preferably 2 wt% to 10 wt%. By setting the amount of sintering aid 2 added within this range, a silicon nitride sintered body can be appropriately manufactured. In the crushing and mixing process, the amount of media M added is preferably 15 vol% to 40 vol% of the volume of container 20. By setting the amount of media M within this range, the silicon nitride particles 1 and sintering aid can be properly crushed. Furthermore, the total amount of silicon nitride particles 1, sintering aid 2, and solvent 4 filled is preferably 15 vol% to 40 vol% of the volume of container 20. In the crushing and mixing process, the amount of solvent 4 added relative to the total amount of silicon nitride particles 1, sintering aid 2, and solvent 4 is preferably 30 wt% to 80 wt%, more preferably 35 wt% to 70 wt%, and even more preferably 40 wt% to 60 wt%. By setting the amount of solvent 4 added within this range, a silicon nitride sintered body can be appropriately manufactured.

[0026] (Disintegration time) In the crushing and mixing process, the time taken to mix and crush the silicon nitride particles 1 and the sintering aid 2 after adding them to the container 20 is defined as the crushing time. In this case, the crushing time is preferably 8 hours or more and 126 hours or less, more preferably 12 hours or more and 108 hours or less, and even more preferably 18 hours or more and 96 hours or less. By setting the crushing time within this range, the silicon nitride particles 1 and the sintering aid 2 can be properly mixed and crushed.

[0027] (Rotation speed) The method for crushing and mixing the silicon nitride particles 1 and the sintering aid 2 may be arbitrary, but in this embodiment, the silicon nitride particles 1 and the sintering aid 2 are mixed and crushed by the media M by rotating the container 20 into which the silicon nitride particles 1 and the sintering aid 2 are placed. The critical rotational speed Nc (rpm), which is the minimum speed at which the media M placed in the container 20 rotates while remaining pressed against the inner wall of the container, can be expressed by the following formula, where D (m) is the inner diameter of the container 20 and d (m) is the diameter of the media M. Nc = 42.3 / (Dd) 1 / 2 In this case, the rotational speed N (rpm) of the container 20 is preferably 40% to 80% of the critical rotational speed Nc, and more preferably 60% to 80%. By setting the rotational speed N of the container 20 within this range, mixing and crushing can be performed appropriately.

[0028] (atmosphere) The atmosphere in which the silicon nitride particles 1 and the sintering aid 2 are crushed and mixed (the atmosphere in which the crushing and mixing process is carried out) may be arbitrary, but for example, it may be an atmospheric atmosphere.

[0029] (drying process) As shown in Figure 1, in this manufacturing method, after performing the crushing and mixing step, a drying step is performed (step S12). In the drying step, the silicon nitride slurry 10, which is a mixture of silicon nitride particles 1, sintering aid 2, and solvent 4 after crushing and mixing, is dried to remove the solvent 4 and obtain a silicon nitride mixture 10A. In this embodiment, the crushing and mixing step yields a mixture of silicon nitride particles 1, sintering aid 2, solvent 4, and media M. Subsequently, components other than media M (silicon nitride slurry 10) are extracted from the mixture of silicon nitride particles 1, sintering aid 2, solvent 4, and media M. Then, the solvent 4 is removed from the extracted silicon nitride slurry 10 to obtain a silicon nitride mixture 10A. That is, the silicon nitride mixture 10A contains silicon nitride particles 1A, which are the silicon nitride particles 1 after crushing and mixing, and sintering aid 2A, which are the sintering aid 2 after crushing and mixing, but does not contain solvent 4 and media M. However, if solvent 4 is not used in the crushing and mixing step, the drying step may be omitted. In this case, components other than media M are extracted from the mixture of silicon nitride particles 1A, sintering aid 2A, and media M after crushing and mixing to obtain silicon nitride mixture 10A.

[0030] The drying process may be carried out by any method, but in this embodiment, the solvent 4 is removed from the silicon nitride slurry 10 by spray drying to obtain a silicon nitride mixture 10A. An example of the spray drying method will be described below, but even if spray drying is not used, a silicon nitride sintered body can be appropriately manufactured by performing the crushing and mixing process described above.

[0031] The following describes a specific example of the spray drying method. Figure 3 is a schematic diagram illustrating an example of the spray drying method. As shown in Figure 3, in this example, spray drying is performed using a spray drying apparatus 100. The spray drying apparatus 100 has a tank 30 and a dryer 40. The tank 30 is a tank in which the silicon nitride slurry 10 is stored. The dryer 40 is a device that removes the solvent 4 (liquid component) contained in the sprayed silicon nitride slurry 10 by drying, and extracts the silicon nitride mixture 10A, which is the solid component. Specifically, the dryer 40 has a main body 42, a disc 44, and a gas supply unit 46. The main body 42 is a hollow container. The disc 44 is a rotatable hollow rotating body with an opening formed on its outer circumference. The disc 44 is attached to the opening formed at the vertically upper end of the main body 42. The disc 44 is also connected to the tank 30 via piping to which a pump P is provided. The gas supply unit 46 is a lid-shaped member provided at the vertically upper end of the main body 42 so as to cover the disc 44. The gas supply unit 46 is connected to a piping that contains a blower B for taking in outside air and a heater H for heating the taken-in outside air.

[0032] In the spray drying apparatus 100, silicon nitride slurry 10 is stored in the tank 30. The silicon nitride slurry 10 in the tank 30 is prepared to have the viscosity μ described above. The spray drying apparatus 100 takes in outside air with a blower B, heats the taken-in outside air with a heater H, and then supplies the heated outside air (heated outside air) into the gas supply unit 46. The heated outside air supplied into the gas supply unit 46 is supplied into the main body 42 through an opening at the top of the main body 42, heating the inside of the main body 42. The spray drying apparatus 100 also drives a pump P to supply the silicon nitride slurry 10 from the tank 30 into the disc 44, and rotates the disc 44 to which the silicon nitride slurry 10 has been supplied. As a result, the silicon nitride slurry 10 in the disc 44 is sprayed into the main body 42 while diffusing radially outward, and descends while swirling inside the main body 42. As the silicon nitride slurry 10 descends while swirling inside the main body 42, it is heated by the heated outside air inside the main body 42, the solvent 4 is removed, and the remaining solid component, the silicon nitride mixture 10A, is extracted from the vertically downward opening of the main body 42.

[0033] Furthermore, the main body 42 may be connected to the recovery unit 50. The recovery unit 50 is a hollow container and a device that forms a swirling flow inside. The vertically upper end of the recovery unit 50 is connected to a pipe equipped with a blower B that discharges the gas inside the recovery unit 50. The recovery unit 50 is connected to the main body 42 via a pipe 52. One end of the pipe 52 is connected to the outer circumferential surface of the main body 42, and the other end is connected to the outer circumferential surface of the recovery unit 50. In the spray drying apparatus 100, the gas inside the recovery unit 50 is discharged by the blower B connected to the recovery unit 50. As a result, gas containing solid components that were not extracted from the vertically lower opening of the main body 42 is introduced from the main body 42 into the recovery unit 50 via the pipe 52. In the recovery unit 50, a downward flow that swirls downward and an upward flow that swirls upward radially inside the downward flow are generated. The solid components contained in the gas introduced into the recovery unit 50 are joined to the downward flow by centrifugal force and extracted as a silicon nitride mixture 10A from an opening located vertically below the recovery unit 50.

[0034] In the spray drying apparatus 100 of this example, the silicon nitride mixture 10A from which the solvent 4 has been removed is extracted from the dryer 40 and the recovery unit 50 in this manner. However, the apparatus configuration of the spray drying apparatus 100 in Figure 3 is just one example, and any configuration is acceptable.

[0035] (Silicon nitride mixture) The silicon nitride mixture 10A obtained as described above is used as a raw material for a silicon nitride sintered body. The silicon nitride mixture 10A is a mixture of silicon nitride particles 1 and sintering aid 2 after the crushing and mixing process has been carried out. In this embodiment, media M and solvent 4 are also added during the crushing and mixing process, so the silicon nitride mixture 10A is obtained by removing solvent 4 and media M from the mixture of silicon nitride particles 1, sintering aid 2, solvent 4 and media M after crushing and mixing. In this embodiment, as described above, the silicon nitride mixture 10A is obtained by the drying process.

[0036] (Oxygen level) Here, the oxygen ratio Δ is given by the following equation (1).

[0037] Δ={O A -(O B +O C )} / (O B +O C ) ···(1)

[0038] O in equation (1) A This is the amount of oxygen (wt%) contained in silicon nitride mixture 10A, O B This is the amount of oxygen (wt%) contained in silicon nitride particles 1 before crushing and mixing, O C This represents the amount of oxygen (wt%) contained in the sintering aid 2 before crushing and mixing. In other words, the oxygen ratio Δ is an indicator of the amount of oxygen increased by the crushing and mixing process. Furthermore, when the sintering aid 2 is an oxide, it is assumed that the amount of oxygen does not change due to crushing and mixing, so the oxygen ratio Δ can also be said to be an indicator of the amount of oxygen newly bonded to the silicon nitride particles 1 by the crushing and mixing process. Oxygen content of silicon nitride particle 1 O Band the amount of oxygen in silicon nitride mixture 10A O A The oxygen content of sintering aid 2 can be measured using an oxygen analyzer by inert gas fusion-infrared absorption spectroscopy. C If sintering aid 2 contains nitrides and carbides, the oxygen content can be measured using an oxygen analyzer by inert gas fusion-infrared absorption spectroscopy; if sintering aid 2 contains only oxides, the oxygen content can be calculated from the composition.

[0039] In this embodiment, the oxygen content ratio Δ is preferably 0.06 or more and 0.42 or less, preferably 0.10 or more and 0.38 or less, and more preferably 0.15 or more and 0.35 or less. By having an oxygen content ratio Δ of 0.06 or more, it is possible to suppress the oxygen near the crushed surface of the silicon nitride particles 1 (silicon nitride particles 1 after crushing and mixing) contained in the silicon nitride mixture 10A, so that the oxygen component and the sintering aid 2 are appropriately arranged at the interface of the silicon nitride particles 1 during sintering, improving sinterability and enabling the proper production of a silicon nitride sintered body. Furthermore, by having an oxygen content ratio Δ of 0.42 or less, it is possible to suppress the oxygen contained in the silicon nitride particles 1 contained in the silicon nitride mixture 10A, so that the weight loss due to volatile oxygen components during firing is suppressed and the silicon nitride sintered body can be properly produced.

[0040] The oxygen ratio Δ can be set within the above range by appropriately adjusting the process conditions in the crushing and mixing process. For example, the oxygen ratio Δ can be adjusted by at least one of the following: the crushing time, the type and presence or absence of solvent 4, and the atmosphere in which the crushing and mixing process is carried out. For example, the oxygen ratio Δ increases as the crushing time increases. The oxygen ratio Δ also changes depending on the type and presence or absence of solvent 4 and the atmosphere; for example, if the Hildebrand solubility parameter of solvent 4 is low, the oxygen ratio Δ will be low.

[0041] Oxygen content of silicon nitride mixture 10A A The amount of oxygen is 1 wt% to 20 wt%, more preferably 1.5 wt% to 15 wt%, and even more preferably 1.8 wt% to 12 wt%, relative to the total amount of silicon nitride mixture 10A. ABeing within this range allows for the proper manufacture of silicon nitride sintered bodies.

[0042] (particle size) D of silicon nitride mixture 10A 90 The particle size is preferably 0.6 μm or more and 3.5 μm or less, and more preferably 0.9 μm or more and 3.0 μm or less. D of silicon nitride mixture 10A 90 By setting the range to this extent, the risk of large particles being unevenly distributed is reduced, and the thickening of the silicon nitride slurry by fine powder is suppressed, enabling the proper manufacture of silicon nitride sintered bodies. Note D 90 This refers to the 90% particle size on a volume basis in the cumulative particle size distribution, and is D in silicon nitride mixture 10A. 90 This can be measured using a particle size analyzer by laser diffraction / scattering (JIS Z 8825:2022). 90 , D 50 , D 10 The measurement method may be similar.

[0043] Furthermore, the content ratio of silicon nitride particles 1A and sintering aid 2A in the silicon nitride mixture 10A after crushing and mixing may be the same as the addition ratio of silicon nitride particles 1 and sintering aid 2 in the crushing and mixing process.

[0044] (molding process) As shown in Figure 1, after the drying process is performed, the molding process is performed (step S14). In the molding process, the silicon nitride mixture 10A is molded into a desired shape to obtain a silicon nitride molded body, which is a molded body of the silicon nitride mixture 10A. In the molding process, the silicon nitride mixture 10A may be molded by any method, for example, a die press or a cold isostatic press (CIP) may be used. Alternatively, for example, a binder may be added to the silicon nitride mixture 10A, and the silicon nitride mixture 10A with the binder added may be molded to obtain a silicon nitride molded body. If a binder is added, a degreasing process may be performed to remove the binder before the subsequent firing process. The degreasing process may be performed under any conditions, for example, by heating at a temperature of 300°C to 600°C.

[0045] (Firing process) As shown in Figure 1, after the molding process is performed, the firing process is performed (step S16). In the firing process, the silicon nitride molded body obtained in the molding process is heated in a non-oxidizing atmosphere to sinter the silicon nitride molded body and obtain a silicon nitride sintered body 10B. The firing process may be carried out under any conditions, but for example, the silicon nitride molded body may be heated at a heating temperature of 1600°C to 1900°C. Examples of non-oxidizing atmospheres include a nitrogen atmosphere and an argon atmosphere. Depending on the application, the silicon nitride sintered body 10B may also be subjected to hot isostatic pressing (HIP) treatment. In the HIP treatment, heating may be performed at a pressure of 10 MPa or more and at a heating temperature of 1500°C to 1900°C.

[0046] (Silicon nitride sintered body) The silicon nitride sintered body 10B obtained by the firing process is a sintered body of silicon nitride. The silicon nitride sintered body 10B can be used for any application, but for example it may be used in bearing balls, heat dissipation substrates, rolling mill rolls, friction stir welding tools, hot working tools, heaters, etc.

[0047] Figure 4 is a schematic diagram of a STEM image of a cross-section of a silicon nitride sintered body. As shown in Figure 4, it is preferable that the silicon nitride sintered body 10B includes silicon nitride particles 1B and a grain boundary phase 2B located around the silicon nitride particles 1B. The silicon nitride particles 1B are a phase containing silicon nitride, and the grain boundary phase 2B is a phase containing elements contained in the sintering aid 2A. Here, "around" does not refer to the entire outer circumference of the silicon nitride particles 1B, but may refer to a portion of the entire outer circumference of the silicon nitride particles 1B. In other words, the grain boundary phase 2B is not precipitated inside the silicon nitride particles 1B, but rather is located outside the silicon nitride particles 1B (adjacent to the silicon nitride particles 1B). Figure 4 schematically shows an example of an image (STEM image) obtained when a cross-section of the silicon nitride sintered body 10B is photographed with a STEM (scanning transmission electron microscope). The presence of silicon nitride particles 1B and grain boundary phase 2B in the silicon nitride sintered body 10B can be determined from the compositional distribution obtained by STEM-EDX (energy-dispersive X-ray spectroscopy) mapping. For example, if an arbitrary cross-section of the silicon nitride sintered body 10B is processed into a thin section of 100 nm or less using FIB (focused ion beam: Helios1200, FEI), and a compositional mapping image is obtained using STEM-EDX (TEM: JEM-2010F, EDX: JED-2300, analyzer: JEOL analysis station), areas with high nitrogen concentration can be identified as silicon nitride particles 1B, and areas with high oxygen concentration can be identified as grain boundary phase 2B. Areas with high concentration can be visually identified when a mapping image is created with low concentration areas in black and high concentration areas in any color other than black.

[0048] The relative density of silicon nitride sintered body 10B is the bulk density ρb (g / cm³). 3 ) and true density ρs(g / cm³) 3 It can be calculated from the following formula. Relative density (%) = bulk density ρb / true density ρs × 100 The bulk density can be measured according to the method for measuring the apparent density, bulk density, and open porosity of sintered fine ceramics (JIS R1634:1998). The true density is calculated from the addition ratio of silicon nitride particles 1 and sintering aid 2. The relative density is preferably 95% or higher, and more preferably 97% or higher. If the relative density is within this range, the sintered body will be suitable for further densification by HIP treatment.

[0049] The weight loss of the silicon nitride sintered body 10B is preferably 4.50 wt% or less, and more preferably 4.30 wt% or less. A weight loss within this range reduces the amount of oxygen volatilized from the surface during firing, thereby densifying the structure near the surface. The weight loss refers to the ratio of the difference between the weight of the silicon nitride mixture 10A (or silicon nitride molded body) before sintering and the weight of the silicon nitride sintered body 10B, i.e., "(weight of mixture - weight of sintered body) / weight of mixture".

[0050] (effect) A method for producing a silicon nitride mixture 10A according to a first aspect of this disclosure includes the step of obtaining a silicon nitride mixture 10A by mixing and crushing silicon nitride particles 1 and a sintering aid 2. In the step of obtaining the silicon nitride mixture 10A, silicon nitride particles 1 having an oxygen content of 0.5 wt% or more and 5.0 wt% or less are used, and the silicon nitride mixture 10A is produced such that the oxygen content ratio Δ is 0.06 or more and 0.4 or less. According to this disclosure, by using silicon nitride particles 1 with an oxygen content within the above range and producing the silicon nitride mixture 10A such that the oxygen content ratio Δ is within the above range, a silicon nitride sintered body 10B can be appropriately produced using the silicon nitride mixture 10A.

[0051] A method for producing silicon nitride mixture 10A according to a second aspect of this disclosure is a production method according to the first aspect, wherein the mixing and crushing time (crushing time) is preferably 8 hours or more and 126 hours or less. By setting the crushing time within this range, the silicon nitride particles 1 and the sintering aid 2 can be appropriately mixed and crushed.

[0052] A method for producing a silicon nitride mixture 10A according to a third aspect of this disclosure is a production method according to the first or second aspect, wherein when mixing and crushing silicon nitride particles 1 and a sintering aid 2, it is preferable to also mix in media M having a silicon nitride surface and a diameter of 0.1 mm or more and 50 mm or less. By using such media M, foreign matter contamination is suppressed during crushing and mixing, and crushing can be performed appropriately, so that a silicon nitride sintered body can be produced appropriately.

[0053] A method for producing a silicon nitride mixture 10A according to a fourth aspect of this disclosure is a production method according to any of the first to third aspects, wherein the silicon nitride particles 1 are preferably silicon nitride or sialon. According to this disclosure, sintered bodies of silicon nitride or sialon can be appropriately produced.

[0054] A method for producing a silicon nitride mixture 10A according to the fifth aspect of this disclosure is a production method according to any of the first to fourth aspects, wherein the sintering aid 2 preferably contains two or more elements selected from Y, Al, Mg, Si, Ti, W, Mo, Hf, La, Nd, Gd, Er, Yb, Lu, and C. According to this disclosure, a silicon nitride sintered body can be appropriately produced by using such a sintering aid 2.

[0055] A method for producing a silicon nitride sintered body 10B according to the sixth aspect of this disclosure involves firing a silicon nitride mixture 10A obtained by the method for producing a silicon nitride mixture 10A according to the first to fifth aspects to produce a silicon nitride sintered body 10B. According to this disclosure, a silicon nitride sintered body 10B can be produced appropriately.

[0056] (Examples) Next, we will describe the examples. Table 1 shows the manufacturing conditions and test results for each example.

[0057] [Table 1]

[0058] (Example 1) In Example 1, 272.00 g of silicon nitride particles (Denka silicon nitride: SN-9FWS), 7.07 g of MgO·Al2O3 spinel (Iwatani SP-12-M) as a sintering aid, 256.52 g of water as a solvent, 5.98 g of a 35 wt% aqueous solution of quaternary ammonium salt (Seichem) as a dispersant, and 700 g of silicon nitride media were placed in a polypropylene container. The container had a volume of 1 L and an inner diameter of 92 mm. The average particle size and oxygen content of the silicon nitride particles were measured. B , average particle size and oxygen content of sintering aid O C The average particle size of media M was as shown in Table 1. The particle size and oxygen content were measured using the methods described in this embodiment. The mixture of silicon nitride particles, sintering aid, solvent, and media placed in the container was then mixed and crushed by rotating it on a turntable at 100 rpm for the crushing time shown in Table 1. Subsequently, a silicon nitride slurry containing silicon nitride particles, a sintering aid, and a solvent was extracted from the container, and the solvent was removed from the silicon nitride slurry to obtain a silicon nitride mixture containing silicon nitride particles and a sintering aid. The oxygen content of the silicon nitride particles contained in the silicon nitride mixture was O A , D 90 The results are shown in Table 1, D 90 and oxygen amount O A The oxygen content ratio Δ was measured using the method described in this embodiment. The oxygen content ratio Δ was as shown in Table 1. Subsequently, the obtained silicon nitride mixture was granulated using a rotary granulator with a composition of 100g silicon nitride mixture, 30g ethanol, and 5g polyvinyl butyral (PVB). 40g of this granule was then press-molded to obtain a silicon nitride molded body. Subsequently, the silicon nitride molded body was fired under a nitrogen atmosphere at 1700°C for 15 hours to obtain a silicon nitride sintered body.

[0059] (Examples 2-6) In Examples 2 to 6, silicon nitride sintered bodies were obtained using the same method as in Example 1, except for the conditions shown in Table 1. In Example 4, 272.00 g of silicon nitride particles (Denka silicon nitride: SN-9FWS), 7.07 g of MgO·Al2O3 spinel (Iwatani SP-12-M) as a sintering aid, 187.89 g of ethanol as a solvent, 5.98 g of a 40 wt% ethanol solution of maleic anhydride-based polymer dispersant (Nippon Oil & Fats Co., Ltd.) as a dispersant, and 700 g of silicon nitride media were placed in a polypropylene container.

[0060] (evaluation) In the evaluation, the bulk density and weight loss of the silicon nitride sintered body were measured. The bulk density and weight loss were measured using the method described in the above embodiment, and the relative density was calculated using the method described in the above embodiment. In the evaluation, a product was deemed to pass if it met both conditions: a relative density of 95% or higher and a weight loss of less than 4.50. A product was deemed to fail if it did not meet at least one of these conditions.

[0061] As shown in Table 1, in Examples 1 to 3, which are examples, the evaluation was satisfactory, indicating that silicon nitride sintered bodies can be manufactured appropriately. On the other hand, in Comparative Examples 4 to 5, the oxygen content ratio Δ was excessive, resulting in a high weight loss, indicating that silicon nitride sintered bodies could not be manufactured appropriately. Furthermore, in Comparative Example 6, the oxygen content ratio Δ was insufficient, resulting in a low relative density, indicating that silicon nitride sintered bodies could not be manufactured appropriately.

[0062] Although embodiments of the present invention have been described above, the embodiments are not limited to those described herein. Furthermore, the aforementioned components include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Moreover, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above. [Explanation of Symbols]

[0063] 1, 1A silicon nitride particles 2. 2A Sintering aid 4 Solvents 10 Silicon nitride slurry 10A Silicon Nitride Mixture 10B Silicon nitride sintered body 20 containers M Media

Claims

1. The process includes the step of obtaining a silicon nitride mixture by mixing silicon nitride particles with a sintering aid and crushing them, In the step of obtaining the silicon nitride mixture, Using silicon nitride particles having an oxygen content of 0.5 wt% or more and 5.0 wt% or less, The silicon nitride mixture is manufactured such that Δ shown in the following equation (1) is 0.06 or more and 0.4 or less. A method for producing a silicon nitride mixture. Δ={O Ａ - (O Ｂ +O Ｃ )} / (O Ｂ +O Ｃ ) ・・・(1) Here, O Ａ This is the amount of oxygen (wt%) contained in the silicon nitride mixture, O Ｂ This is the amount of oxygen (wt%) contained in the silicon nitride particles, O Ｃ This is the amount of oxygen (wt%) contained in the sintering aid.

2. The mixing and crushing time shall be between 8 hours and 126 hours. A method for producing a silicon nitride mixture according to claim 1.

3. When mixing and crushing the silicon nitride particles and the sintering aid, media with a silicon nitride surface and a diameter of 0.1 mm to 50 mm are also mixed in. A method for producing a silicon nitride mixture according to claim 1 or claim 2.

4. The silicon nitride particles are silicon nitride or sialon. A method for producing a silicon nitride mixture according to claim 1 or claim 2.

5. The method for producing a silicon nitride mixture according to claim 1 or claim 2, wherein the sintering aid comprises two or more elements selected from Y, Al, Mg, Si, Ti, W, Mo, Hf, La, Nd, Gd, Er, Yb, Lu, and C.

6. A silicon nitride sintered body is produced by firing the silicon nitride mixture obtained by the method for producing a silicon nitride mixture according to claim 1 or claim 2. A method for manufacturing a silicon nitride sintered body.

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