Preparation method of submicron silicon nitride powder

Abstract

The invention belongs to the technical field of inorganic non-metallic materials, and particularly discloses a preparation method of submicron silicon nitride powder, which comprises the following steps: 1) adding a surface modifier, an alpha-phase silicon nitride seed crystal and a solvent into amorphous silicon nitride powder, and grinding to obtain a mixture; the surface modifying agent comprises an organic surface active agent, an inorganic surface modifying agent and a high-molecular surface modifying agent; 2) drying and crushing the obtained mixture; and 3) performing crystallization roasting on the dried mixture powder in inert and reducing atmospheres to obtain alpha-phase silicon nitride crystal powder. According to the invention, amorphous silicon nitride and alpha-phase silicon nitride seed crystals are ground more sufficiently, and the mixing effect is better. The crystallization roasting temperature of the amorphous silicon nitride powder subjected to surface modification is reduced, and the obtained silicon nitride powder has the characteristics of high dispersity and submicron level.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic non-metallic materials, and particularly relates to a method for preparing submicron-sized silicon nitride powder. Background Art

[0002] Semiconductor devices are developing in the direction of high power, high frequency, and integration, which puts forward higher requirements for the flexural strength, stability, and heat dissipation ability of the heat-conducting substrate for packaging chips. Silicon nitride (Si3N4) substrates have higher flexural strength (600 - 800 MPa) and better cyclic stability (≥5000 times) than traditional Al2O3 and AlN ceramic substrates. For the preparation of Si3N4 ceramic substrates with high thermal conductivity and high flexural strength, the raw material powder not only needs to have high purity, but also needs to meet the indexes of low oxygen, ultra-fine, and high α-phase, etc. High-quality powder is the primary prerequisite for preparing high-performance Si3N4 ceramic substrate materials.

[0003] The high α-phase silicon nitride powder produced by the liquid-phase ammonolysis method has high purity, small particle size, and good sintering activity, and is a high-quality raw material for producing silicon nitride ceramics. However, in the preparation process, the primary particle size of the intermediate amorphous silicon nitride powder is small, and there are surface groups such as Si-NH2, Si2-NH, Si-OH, Si-H, Si-H2, and Si2-O on the surface of the powder particles, which are prone to agglomeration between particles, resulting in problems such as uneven particle size distribution and too large agglomerate size. Moreover, the powder is fluffy, difficult to form, and cannot be sintered densely. At the same time, the high-temperature phase transformation of amorphous silicon nitride powder into α-phase silicon nitride requires a relatively high temperature, which has high requirements for crystallization equipment and high energy consumption. To improve the efficiency of the transformation of silicon nitride from amorphous to α-phase, crystal seeds are usually introduced. However, since both amorphous silicon nitride and crystal seeds are solid powders, uneven mixing will occur during the mixing process, resulting in uneven particle size distribution in the α-phase silicon nitride. Summary of the Invention

[0004] In order to overcome the above deficiencies in the prior art, where the intermediate amorphous silicon nitride particles are prone to agglomeration and uneven mixing occurs during the mixing process with crystal seeds, resulting in uneven particle size distribution in the α-phase silicon nitride, the present invention provides a method for preparing submicron-sized silicon nitride powder. Under the combined action of a surface modifier and crystal seeds, the particle size of the ground amorphous silicon nitride is reduced, and the α-phase silicon nitride crystal seeds therein are more uniformly dispersed and smaller in size, so that the crystallization temperature is reduced, and the α-phase content in the silicon nitride powder after high-temperature crystallization is increased, and the size of the silicon nitride particles can be reduced, obtaining advantages such as a near-equiaxed morphology, etc.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for preparing submicron-sized silicon nitride powder, comprising the following steps: 1) Add a surface modifier, α-phase silicon nitride seeds and a solvent to amorphous silicon nitride powder, and grind to obtain a mixture; the surface modifier includes one or more of an organic surfactant, an inorganic surface modifier and a polymer surface modifier; 2) Dry and crush the obtained mixture; 3) Crystallize and roast the dried mixture powder in an inert and reducing atmosphere to obtain α-phase silicon nitride crystalline powder.

[0007] Preferably, the organic surfactant includes one or more of a silane coupling agent, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, or the inorganic surface modifier includes one or more of potassium hydroxide, sodium hydroxide, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, or the polymer surface modifier includes one or more of polystyrene, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone.

[0008] Preferably, the particle size of the amorphous silicon nitride powder is 0.005 - 40 μm, and the specific surface area is 5 - 1500 m 2 / g.

[0009] Preferably, the particle size of the amorphous silicon nitride powder is 0.01 - 2 μm.

[0010] Preferably, the addition amount of the α-phase silicon nitride seeds is 1 - 40 wt% of the amorphous silicon nitride powder, the purity > 99%, and the particle size is 50 - 1000 nm.

[0011] Preferably, the particle size of the α-phase silicon nitride powder is 50 - 200 nm, and the oxygen content < 0.8 wt%.

[0012] Preferably, the crystallization roasting process is: heating to 1200 - 1500 °C at a heating rate of 5 - 30 °C / min and holding for 2 - 8 h.

[0013] Preferably, the crystallization roasting process is: heating to 1450 - 1500 °C at a heating rate of 15 - 20 °C / min and holding for 2 - 3 h.

[0014] Preferably, the solvent includes but is not limited to ethanol, acetone, ethyl acetate, isopropanol, methanol.

[0015] Preferably, the grinding is wet ball milling, the ball milling medium is silicon nitride balls, and the added mass of the grinding solvent is 0.5 - 20 times that of the amorphous silicon nitride powder.

[0016] Preferably, the grinding speed is 20 - 1500 rpm and the grinding time is 1 - 8 h.

[0017] Preferably, the drying methods in step 2) include vacuum drying, atmospheric drying, and microwave drying. The vacuum degree of vacuum drying is 10 -3 -10 Pa, and the drying time is 1 - 8 h;

[0018] Preferably, the solvent content of the dried powder is < 2 wt%.

[0019] Preferably, in the mixture of inert gas and reducing gas, the inert gas includes one or more of nitrogen and argon, and the reducing gas includes one or more of hydrogen and carbon monoxide.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The present invention discloses a method for surface modifier-assisted doping and grinding of amorphous silicon nitride, which makes the grinding of amorphous silicon nitride and α-phase silicon nitride seeds more sufficient and the mixing effect better. The crystallization roasting temperature of the surface-modified amorphous silicon nitride powder is reduced, and the obtained silicon nitride powder has the characteristics of high dispersibility and sub-micron size.

[0022] (2) The present invention solves the problems of uneven particle size distribution, uneven crystal seed doping, and too high crystallization temperature of the intermediate amorphous silicon nitride powder in the preparation of high-α-phase silicon nitride by the existing ammonolysis method. During the grinding process of amorphous silicon nitride powder, a surface modifier and crystal seeds are added simultaneously. The surface modifier adsorbs on the surface of amorphous silicon nitride particles to form a charge layer or steric hindrance, preventing particle agglomeration; under the action of the surface modifier, the added α-phase silicon nitride crystal seeds can be more evenly distributed in amorphous silicon nitride. Under the combined action of the surface modifier and crystal seeds, the particle size of the ground amorphous silicon nitride decreases, and the α-phase silicon nitride crystal seeds therein are more evenly dispersed and smaller in size, resulting in a lower crystallization temperature, and the α-phase content in the silicon nitride powder after high-temperature crystallization increases, and the size of the silicon nitride particles can be reduced, obtaining a near-equiaxed morphology.

[0023] (3) The properties of amorphous silicon nitride are more active than those of common crystalline silicon nitride powders. In air and water, its surface is easily oxidized to silicon dioxide. To avoid oxidation, amorphous silicon nitride and crystal seeds are dry-mixed and ground under the protection of an inert gas, but it is found that the mixing is uneven and the grinding and crushing effect is also very poor. When wet-mixed grinding is used, the solvent used cannot contain a large amount of water, and only some volatile organic solvents can be selected. During the solvent evaporation process, the powder will contact with air and oxidize, so the methods of rotary evaporation and vacuum drying are selected. During the material transfer process, it is inevitable to contact with air. Therefore, through a reducing atmosphere, the surface silicon dioxide is reduced and reacts with nitrogen in the atmosphere to form silicon nitride, thereby reducing the oxygen content.

[0024] (4) In the present invention, the surface of pure silicon nitride particles presents a tertiary amine (Si3N) structure, and groups such as Si-NH2, Si-NH2, Si-OH, Si-H, and Si2O exist on the surface of the silicon nitride particles. In addition, especially the amorphous silicon nitride surface contains more unsaturated covalent bonds, such as silicon dangling bonds, nitrogen dangling bonds, etc. Due to the existence of these dangling bonds and surface groups, there is a strong agglomeration tendency between the silicon nitride particles. Therefore, it is necessary to modify the surface of silicon nitride to solve the agglomeration problem. The surface modifier combines with the dangling bonds and surface groups on the surface of silicon nitride, making the surface of silicon nitride carry the same charge and present the same properties, so as to repel each other and avoid agglomeration. On the other hand, the macromolecular surface modifier adsorbs on the particles to form an adsorption layer, generating steric hindrance repulsion and weakening the agglomeration between the particles.

[0025] (5) In the present invention, a surface modifier is added during the grinding process of amorphous silicon nitride to change the surface activity of the additive α-phase silicon nitride crystal seeds, reduce agglomeration, make them disperse more uniformly as crystal seeds in the amorphous silicon nitride, and make the size of the particles after crystallization smaller. The uniformity of the particles after crystallization is improved.

[0026] (6) After drying in the present invention, due to electrostatic force and van der Waals force, the powder will form loose agglomerates. The amorphous silicon nitride powder doped with crystal seeds can be easily pulverized and classified after simple pulverization. The powder particle size before crystallization is uniform and the agglomeration is less, and it is easier to control the shape and size of the particles after crystallization.

[0027] (7) In the present invention, the surface modifier is used to assist in grinding and mixing amorphous silicon nitride and α-phase crystal seeds, which can reduce the particle size before crystallization, increase the surface energy, make surface-driven nucleation dominant, refine the grains, lower the crystallization temperature, and reduce the equipment requirements and energy consumption.

[0028] (8) In the present invention, a mixed atmosphere of inert gas / reducing gas is used in the high-temperature roasting stage. On the one hand, the oxides on the particle surface are removed to improve the powder purity. On the other hand, the surface state of the powder particles is changed to improve the sintering activity.

[0029] (9) The additive of the present invention has low cost and simple synthesis process. It does not require high-energy pulverization and pickling of the prepared α-phase silicon nitride powder, and the process is easy to control, with broad industrialization prospects; the prepared silicon nitride powder has the characteristics of high α-phase content, small particle size, uniform particle size distribution, and high sintering activity. Detailed Embodiments

[0030] The present invention will be further described below in conjunction with specific embodiments.

[0031] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains.

[0032] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. All raw materials of the present invention are purchased from the market.

[0033] In addition, it should also be understood that when the terms "comprising" or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and their combinations.

[0034] The silicon nitride ceramic powder is detected in accordance with the national standard GB / T37258-2018. According to the highest grade of Class A, the particle size D50 of the silicon nitride powder is 0.3 - 0.5μm, the α-phase content > 85%, Fe / Al / Ca < 0.03wt%, O < 1.5wt%, C < 0.1wt%; in actual applications, it is difficult for the average particle size of directly prepared silicon nitride particles to be lower than 0.5μm, mostly in the range of 1 - 2μm, and smaller sizes need to be obtained after high-energy crushing.

[0035] In the present invention, the high-temperature roasting is carried out in a vacuum; or the high-temperature roasting is carried out in a mixed gas of an inert and reducing atmosphere, the inert gas is an inert rare gas such as nitrogen or argon, the reducing atmosphere is hydrogen, carbon monoxide, etc., and the gas pressure is 0 - 4MPa.

[0036] Example 1: A method for preparing submicron-sized silicon nitride powder is disclosed in the present invention, which includes the following steps: 1) Add a surface modifier, α-phase silicon nitride seeds, and a solvent to the amorphous silicon nitride powder, and perform wet ball milling. The ball milling speed is 300rpm, and the ball milling time is 2h to obtain a mixture; the surface modifier includes an inorganic surface modifier, and the inorganic surface modifier is a 10wt% NaOH solution. Among them, the particle size of the amorphous silicon nitride powder is 0.005μm, and the specific surface area is 120m 2 / g. The addition amount of the α-phase silicon nitride seeds is 5wt% of the total amount of the amorphous silicon nitride and the seed powder, the purity > 99%, the particle size is 50nm, and the oxygen content < 0.8wt%. The solvent is ethanol. The weight ratio of the amorphous silicon nitride powder, 10wt% NaOH solution, α-phase silicon nitride seeds, and ethanol is 95:50:5:850. 2) Dry, crush, and classify the obtained mixture; the drying method is vacuum drying, the vacuum degree of the vacuum drying is 10 -3 Pa, and the drying time is 1h; the solvent content of the dried powder < 2wt%. 3) The dried mixture powder is subjected to crystallization roasting in an atmosphere of an inert and reducing gas mixture to obtain α-phase silicon nitride crystalline powder; wherein, the crystallization roasting process is: heating to 1200 °C at a heating rate of 5 °C / min and holding for 8 h. In this example, the inert gas is nitrogen with a nitrogen pressure of 0.3 MPa. The powder of this example is placed in a graphite crucible and placed in a high-temperature furnace. The α-phase content of the high-purity silicon nitride powder prepared in Example 1 is 95.2%, the average particle size is 0.6 μm, the oxygen content is 0.8 wt%, the carbon content is 0.05 wt%, the Fe / Al / Ca metal impurity content is 43 ppm, and the chlorine content is 45 ppm.

[0037] Example 2: A method for preparing submicron silicon nitride powder disclosed in the present invention includes the following steps: 1) Add a surface modifier, α-phase silicon nitride crystal seeds and a solvent to the amorphous silicon nitride powder, and perform wet ball milling at a ball milling speed of 300 rpm for 2 h to obtain a mixture; the surface modifier uses a polymer surface modifier, and the polymer surface modifier uses polyvinyl alcohol; wherein, the particle size of the amorphous silicon nitride powder is 20 μm and the specific surface area is 0.3 m 2 / g. The addition amount of the α-phase silicon nitride crystal seeds is 5 wt% of the total amount of the amorphous silicon nitride and the crystal seed powder, and the purity > 99%, the particle size is 1000 nm, and the oxygen content < 0.8 wt%. The solvent is ethanol. The weight ratio of the amorphous silicon nitride powder, polyvinyl alcohol, α-phase silicon nitride crystal seeds, and ethanol is 95:5:5:895. 2) Dry, crush and classify the obtained mixture; the drying method is vacuum drying, the vacuum degree of the vacuum drying is 10 Pa, and the drying time is 8 h; the solvent content of the dried powder < 2 wt%. The powder crushing method is mechanical crushing. 3) The dried mixture powder is subjected to crystallization roasting in an atmosphere of an inert and reducing gas mixture to obtain α-phase silicon nitride crystalline powder; wherein, the crystallization roasting process is: heating to 1450 °C at a heating rate of 20 °C / min and holding for 3 h. In this example, the inert gas is nitrogen with a nitrogen pressure of 4 MPa. The α-phase content of the high-purity silicon nitride powder prepared in Example 2 is 98.4%, the average particle size is 0.4 μm, the oxygen content is 0.79 wt%, the carbon content is 0.13 wt%, the Fe / Al / Ca metal impurity content is 39 ppm, and the chlorine content is 88 ppm.

[0038] Example 3: A method for preparing submicron silicon nitride powder disclosed in the present invention includes the following steps: 1) Add a surface modifier, α-phase silicon nitride seeds, and a solvent to amorphous silicon nitride powder, and perform wet ball milling at a ball milling speed of 300 rpm for 2 h to obtain a mixture; the surface modifier includes an organic surfactant, and the organic surfactant is a silane coupling agent KH550; among them, the particle size of the amorphous silicon nitride powder is 0.2 μm, and the specific surface area is 30 m 2 / g. The addition amount of the α-phase silicon nitride seeds is 40 wt% of the total amount of amorphous silicon nitride and seed powder, and the purity > 99%, the particle size is 50 nm, and the oxygen content < 0.8 wt%. The solvent is ethanol. The weight ratio of amorphous silicon nitride powder, coupling agent KH550, α-phase silicon nitride seeds, and ethanol is 60:5:40:895. 2) Dry, crush, and classify the obtained mixture; the drying method is microwave drying, and the solvent content of the dried powder < 2 wt%. The powder crushing method is jet milling. 3) Crystallize and roast the dried mixture powder under an atmosphere of an inert and reducing gas mixture to obtain α-phase silicon nitride crystalline powder; among them, the crystallization roasting process is: raise the temperature to 1450 °C at a heating rate of 15 °C / min and hold for 3 h. In this example, the inert gas is a mixture of 4 vol.% hydrogen and 96 vol.% nitrogen, and its nitrogen pressure is 0.3 MPa. The α-phase content of the high-purity silicon nitride powder prepared in Example 3 is 98.7%, the average particle size is 0.2 μm, the oxygen content is 0.62 wt%, the carbon content is 0.04 wt%, the Fe / Al / Ca metal impurity content is 42 ppm, and the chlorine content is 30 ppm.

[0039] Example 4: A method for preparing submicron silicon nitride powder disclosed in the present invention includes the following steps: 1) Add a surface modifier, α-phase silicon nitride seeds, and a solvent to amorphous silicon nitride powder, and perform wet ball milling at a ball milling speed of 300 rpm for 2 h to obtain a mixture; the surface modifier includes an inorganic surface modifier, and the inorganic surface modifier is a 13 wt% NaOH solution; among them, the particle size of the amorphous silicon nitride powder is 40 μm, and the specific surface area is 0.15 m 2 / g. The addition amount of the α-phase silicon nitride seeds is 1 wt% of the total amount of amorphous silicon nitride and seed powder; and the purity > 99%, the particle size is 200 nm, and the oxygen content < 0.8 wt%. The solvent is ethyl acetate. The weight ratio of amorphous silicon nitride powder, 13 wt% NaOH solution, α-phase silicon nitride seeds, and ethyl acetate is 99:50:1:850. 2) Dry, crush, and classify the obtained mixture; the drying method is atmospheric drying, and the solvent content of the dried powder < 2 wt. The powder crushing method is mortar grinding. 3) The dried mixture powder is subjected to crystallization roasting in an atmosphere of an inert and reducing gas mixture to obtain α-phase silicon nitride crystalline powder; wherein, the crystallization roasting process is as follows: heating to 1500 °C at a heating rate of 30 °C / min and holding for 2 h. In this example, the inert gas is a mixture of 4 vol.% hydrogen and 96 vol.% nitrogen. The α-phase content of the high-purity silicon nitride powder prepared in Example 4 is 96.3%, the average particle size is 1.1 μm, the oxygen content is 0.54 wt%, the carbon content is 0.04 wt%, the Fe / Al / Ca metal impurity content is 45 ppm, and the chlorine content is 22 ppm.

[0040] Comparative Example 1: Amorphous silicon nitride powder and ethanol are mixed in a ratio of 150:850, and then ball-milled at a ball-milling speed of 300 rpm for 2 h. The slurry after ball-milling is dried by rotary evaporation at 60 °C. The dried powder is dry-milled by ball-milling and then passed through a 200-mesh sieve; then the powder is placed in a graphite crucible and placed in a high-temperature furnace, nitrogen gas at 0.3 MPa is introduced, heated to 1450 °C at a heating rate of 20 °C / min, and held for 3 h. The α-phase content of the high-purity silicon nitride powder prepared in this Comparative Example 1 is 88.5%, the average particle size is 2.0 μm, the oxygen content is 0.74 wt%, the carbon content is 0.09 wt%, the Fe / Al / Ca metal impurity content is 56 ppm, and the chlorine content is 35 ppm.

[0041] Comparative Example 2: Amorphous silicon nitride powder, polyvinyl alcohol, α-phase silicon nitride seeds, and ethanol are mixed in a ratio of 95:400:5:500, and then ball-milled at a ball-milling speed of 300 rpm for 2 h. The addition amount of the α-phase silicon nitride seeds is 5 wt% of the amorphous silicon nitride powder. The slurry after ball-milling is dried by rotary evaporation at 60 °C. The dried powder is dry-milled by ball-milling and then passed through a 200-mesh sieve; then the sieved powder is placed in a graphite crucible and placed in a high-temperature furnace, nitrogen gas at 0.3 MPa is introduced, heated to 1500 °C at a heating rate of 20 °C / min, and held for 2 h. The α-phase content of the high-purity silicon nitride powder prepared in this Comparative Example 2 is 98.2%, the average particle size is 0.5 μm, the oxygen content is 2.08 wt%, the carbon content is 3.2 wt%, the Fe / Al / Ca metal impurity content is 37 ppm, and the chlorine content is 27 ppm.

[0042] Comparative Example 3: Amorphous silicon nitride powder, α-phase silicon nitride seeds, and ethanol were mixed in a ratio of 60:40:900, and then ball-milled at a rotation speed of 300 rpm for 2 h. The slurry after ball-milling was dried by rotary evaporation at 60 °C. The addition amount of the α-phase silicon nitride seeds was 40 wt% of the amorphous silicon nitride powder. After the dried powder was dry-milled by ball-milling, it was pulverized using a jet mill; then the pulverized powder was placed in a graphite crucible and placed in a high-temperature furnace, and a mixed gas of 4 vol.% hydrogen and 96 vol.% nitrogen was introduced and heated to 1450 °C at a heating rate of 20 °C / min, and held for 3 h. The high-purity silicon nitride powder prepared in this Comparative Example 3 had an α-phase content of 94.0%, an average particle size of 0.9 μm, an oxygen content of 0.67 wt%, a carbon content of 0.07 wt%, a Fe / Al / Ca metal impurity content of 33 ppm, and a chlorine content of 29 ppm.

[0043] Comparative Example 4: Amorphous silicon nitride powder, coupling agent KH550, and ethanol were mixed in a ratio of 95:50:855, and then ball-milled at a rotation speed of 300 rpm for 2 h. The slurry after ball-milling was dried by rotary evaporation at 60 °C. After the dried powder was dry-milled by ball-milling, it was pulverized using a jet mill; then the pulverized powder was placed in a graphite crucible and placed in a high-temperature furnace, and nitrogen gas was introduced and heated to 1500 °C at a heating rate of 20 °C / min, and held for 2 h. The high-purity silicon nitride powder prepared in this Comparative Example 4 had an α-phase content of 91.0%, an average particle size of 0.8 μm, an oxygen content of 1.27 wt%, a carbon content of 0.06 wt%, a Fe / Al / Ca metal impurity content of 50 ppm, and a chlorine content of 28 ppm.

[0044] Comparative Example 5: Amorphous silicon nitride powder, coupling agent KH550, and ethanol were mixed in a ratio of 95:50:855, and then ball-milled at a rotation speed of 300 rpm for 2 h. The slurry after ball-milling was dried by rotary evaporation at 60 °C. After the dried powder was dry-milled by ball-milling, it was pulverized using a jet mill; then the pulverized powder was placed in a graphite crucible and placed in a high-temperature furnace, and a mixed gas of 10 vol.% CO and 90 vol.% nitrogen was introduced and heated to 1500 °C at a heating rate of 20 °C / min, and held for 2 h. The high-purity silicon nitride powder had an α-phase content of 94.1%, an average particle size of 0.8 μm, an oxygen content of 0.65 wt.%, a carbon content of 0.05 wt.%, a Fe / Al / Ca metal impurity content of 45 ppm, and a chlorine content of 22 ppm.

[0045] Comparing Example 1 and Comparative Example 1, it can be seen that the addition of both the surface modifier and the seed crystal in Example 1 reduces the particle size and lowers the crystallization temperature. Comparing Example 2 and Comparative Example 2, it can be seen that adding an excessive amount of surface modifier in Example 2 may cause problems during the washing process and result in a relatively high carbon content. Comparing Example 3 and Comparative Example 3, it can be seen that adding only the seed crystal does not achieve better results, while adding both the surface modifier and the seed crystal has a better effect. Comparing Comparative Example 5 and Comparative Example 4, it can be seen that adding only the surfactant results in a low α-phase content, and a reducing crystallization atmosphere can reduce the oxygen content.

[0046] The above-described embodiments merely represent the preferred embodiments of the present invention, and the description thereof is relatively specific and detailed. However, it should not be construed as a limitation on the scope of the present invention. It should be noted that for those of ordinary skill in the art, various corresponding changes and deformations can be made based on the technical solutions and concepts described above, and all such changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing submicron silicon nitride powder, characterized in that, It includes the following steps: 1) Add a surface modifier, α-phase silicon nitride seeds and a solvent to amorphous silicon nitride powder, and carry out grinding to obtain a mixture; the surface modifier includes one or more of an organic surfactant, an inorganic surface modifier and a polymer surface modifier; 2) Dry and crush the obtained mixture; 3) Crystallize and roast the dried mixture powder under an inert and reducing atmosphere to obtain α-phase silicon nitride crystalline powder.

2. The preparation method of a submicron-sized silicon nitride powder according to claim 1, characterized in that, Wherein the organic surfactant includes one or more of a silane coupling agent, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, or the inorganic surface modifier includes one or more of potassium hydroxide, sodium hydroxide, sodium hexametaphosphate, sodium tripolyphosphate, sodium pyrophosphate, or the polymer surface modifier includes one or more of polystyrene, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone.

3. The preparation method of a submicron silicon nitride powder according to claim 1, characterized in that, The particle size of the amorphous silicon nitride powder is 0.005 - 40 μm, and the specific surface area is 0.15 - 1500 m 2 / g.

4. The preparation method of a sub-micron silicon nitride powder according to claim 3, characterized in that, The particle size of the amorphous silicon nitride powder is 0.01μm - 2μm.

5. A method for preparing submicron silicon nitride powder according to claim 1 or 2 or 3 or 4, characterized in that, The addition amount of the α-phase silicon nitride seeds is 1 - 5wt% of the amorphous silicon nitride powder, the purity > 99%, and the particle size is 50 - 1000nm.

6. The preparation method of a sub-micron silicon nitride powder according to claim 5, characterized in that, The particle size of the α-phase silicon nitride powder is 50 - 200nm, and the oxygen content < 0.8wt%.

7. A method for preparing submicron silicon nitride powder according to claim 1 or 2 or 3 or 4, characterized in that, The crystallization roasting process is: raise the temperature to 1200 - 1500°C at a heating rate of 5 - 30°C / min and hold for 2 - 8h.

8. The preparation method of a sub-micron silicon nitride powder according to claim 7, characterized in that, The crystallization roasting process is: raise the temperature to 1450 - 1500°C at a heating rate of 15 - 20°C / min and hold for 2 - 3h.

9. A method for preparing submicron silicon nitride powder according to claim 1 or 2 or 3 or 4, characterized in that, The grinding is wet ball milling, the ball milling medium is silicon nitride balls, and the added mass of the grinding solvent is 0.5 - 20 times that of the amorphous silicon nitride powder.

10. A method for preparing submicron silicon nitride powder according to claim 1 or 2 or 3 or 4, characterized in that, The grinding speed is 20 - 1500rpm, and the grinding time is 1 - 8h.