阅读说明：本技术 一种电子封装用碳化硅粉体的制备方法 (Preparation method of silicon carbide powder for electronic packaging ) 是由 黄威 徐天兵 刘峰 黄叶任 韩平 左立杰 于 2021-10-29 设计创作，主要内容包括：本发明属于碳化硅技术领域,具体涉及一种电子封装用碳化硅粉体的制备方法,以活性氧化铝为基底,通过吸附沉积与气相沉积,得到碳化硅基氧化铝,经去基底处理,得到碳化硅粉体。本发明解决了现有工艺的问题,采用的原料简单易得,有利于降低成本,同时步骤简单,可操作性强,且制备的碳化硅粒径小,且粒径分布均匀,杂质量少。(The invention belongs to the technical field of silicon carbide, and particularly relates to a preparation method of silicon carbide powder for electronic packaging. The method solves the problems of the prior art, adopts simple and easily-obtained raw materials, is favorable for reducing the cost, and has the advantages of simple steps, strong operability, small particle size of the prepared silicon carbide, uniform particle size distribution and less impurity amount.)

1. A preparation method of silicon carbide powder for electronic packaging is characterized by comprising the following steps: the method comprises the following steps:

step 1, putting an active alumina block into a reaction kettle, introducing silicon chloride gas in an inert gas atmosphere, standing for 20-30min, and then blowing at constant temperature to obtain plating solution film active alumina;

step 2, standing the plating solution film active alumina in an inert gas atmosphere containing water vapor, then adding alumina-based particles, and standing for 5-8h at constant temperature to obtain plating film active alumina;

step 3, putting the coated alumina into a deposition furnace and introducing methane for deposition reaction to obtain silicon carbide coated alumina;

and 4, introducing the silicon carbide coated alumina into the reaction kettle, continuously introducing mixed gas until the precipitate is not reduced any more, cooling and filtering to obtain precipitate, and then sintering the precipitate in a gradient manner to obtain silicon carbide powder.

2. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the inert gas in the step 1 is helium or argon, the introducing speed of the silicon chloride is 20-30mL/min, the volume ratio of the silicon chloride to the inert gas is 1:9-20, and the standing temperature is 60-70 ℃.

3. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the temperature of the constant-temperature purging in the step 1 is 50-55 ℃, the gas of the constant-temperature purging is inert gas, and the purging speed is 5-10 mL/min.

4. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: and (3) recovering silicon chloride and inert gas from the gas after purging in the step (1) at the temperature of 10-20 ℃.

5. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the volume of the water vapor in the inert gas atmosphere in the step 2 accounts for 5-9%, and the standing temperature is 20-40 ℃; the alumina-based particles adopt an active alumina-based composite water absorbent; the temperature of the constant temperature standing is 80-100 ℃.

6. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the atmosphere of the deposition reaction in the step 3 is a methane-argon composite system, and the volume ratio of methane to argon is 2-3:7.

7. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the deposition temperature in the step 3 is 800-1200 ℃, and the pressure is 0.1-20 kPa.

8. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the mixed gas in the step 4 is mixed gas of ethanol, ether and hydrogen chloride, and the volume ratio of the ethanol to the ether to the hydrogen chloride is 2:2: 5.

9. The method for producing a silicon carbide powder for electronic packaging according to claim 1, wherein: the reaction temperature in the step 4 is 100-

10. The method for producing a silicon carbide powder for electronic packaging according to claim 9, wherein: and inert gas purging is adopted between the first gradient sintering and the second gradient sintering.

Technical Field

The invention belongs to the technical field of silicon carbide, and particularly relates to a preparation method of silicon carbide powder for electronic packaging.

Background

With the rapid development of the information industry and the progress of the microelectronic technology, new electronic components are developing towards high voltage resistance, large capacity, high frequency, high reliability and high integration, and silicon nitride has the characteristics of wide forbidden band, high thermal conductivity, high breakdown electric field, high radiation resistance and the like, and becomes a representative of third-generation wide-band-gap semiconductor materials.

At present, the growth of silicon carbide single crystal uses physical vapor deposition (PVT) as the main growth mode, and has been proved to be the most mature method for growing SiC crystal. High-purity SiC powder with proper bulk density is taken as a source, the SiC powder is heated to 2300 ℃, and is sublimated and crystallized to form blocky crystals in an inert gas atmosphere such as argon gas.

However, in the conventional silicon carbide process, since impurities in the raw material are large and it is difficult to control the impurities, it is impossible to produce a high-purity silicon carbide powder.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a preparation method of silicon carbide powder for electronic packaging, which solves the problems of the prior art, adopts simple and easily-obtained raw materials, is beneficial to reducing the cost, and has the advantages of simple steps, strong operability, small particle size of the prepared silicon carbide, uniform particle size distribution and less impurity amount.

In order to achieve the technical purpose, the technical scheme of the invention is as follows:

a preparation method of silicon carbide powder for electronic packaging comprises the following steps:

step 1, putting an active alumina block into a reaction kettle, introducing silicon chloride gas under the atmosphere of inert gas, standing for 20-30min, and then purging at constant temperature to obtain plating solution film active alumina, wherein the inert gas is helium or argon, the introduction speed of the silicon chloride is 20-30mL/min, the volume ratio of the silicon chloride to the inert gas is 1:9-20, the standing temperature is 60-70 ℃, the temperature of purging at constant temperature is 50-55 ℃, the gas of purging at constant temperature is inert gas, and the purging speed is 5-10 mL/min; and recovering silicon chloride and inert gas from the purged gas at 10-20 ℃.

Step 2, standing the plating liquid film active alumina in an inert gas atmosphere containing water vapor, then adding alumina-based particles, standing for 5-8h at a constant temperature to obtain plating film active alumina, wherein the volume of the water vapor in the inert gas atmosphere accounts for 5-9%, and the standing temperature is 20-40 ℃; the alumina-based particles adopt an active alumina-based composite water absorbent; the temperature of the constant-temperature standing is 80-100 ℃;

step 3, putting the coated alumina into a deposition furnace, and introducing methane for deposition reaction to obtain silicon carbide coated alumina, wherein the atmosphere of the deposition reaction is a methane-argon composite system, the volume ratio of the methane to the argon is 2-3:7, the deposition temperature is 800-1200 ℃, and the pressure is 0.1-20 kPa;

and 4, introducing the silicon carbide coated alumina into the reaction kettle, continuously introducing mixed gas until the precipitate is not reduced any more, cooling and filtering to obtain the precipitate, and then performing gradient sintering on the precipitate to obtain silicon carbide powder, wherein the mixed gas is the mixed gas of ethanol, ether and hydrogen chloride, the volume ratio of the ethanol, ether and hydrogen chloride is 2:2:5, the reaction temperature is 100-120 ℃, the gradient sintering is performed by adopting two-gradient sintering, the temperature of the first gradient is 200-300 ℃, the time is 0.5-2h, the temperature of the second gradient is 800-1000 ℃, and the time is 2-5h, and further, inert gas is adopted for purging between the first gradient sintering and the second gradient sintering.

The filtrate generated after filtration in the step 4 is mainly aluminum chloride, hydrogen chloride, diethyl ether, ethanol and water, and in order to ensure the recycling of aluminum salt, the filtrate is recovered according to the following steps: a1, adding ammonium carbonate into the filtrate, stirring uniformly, and then completely settling the bottom to obtain a deposition filtrate; the adding amount of the ammonium carbonate is 100-200g/L, and the stirring speed is 500-1000 r/min; a2, refluxing and heating the deposition filtrate for reaction for 1-2h, cooling and filtering to obtain a precipitate; the temperature of reflux heating is 80-90 ℃, the cooling temperature in reflux is 10-20 ℃, and the temperature of cooling and filtering is 10-20 ℃; a3, performing two-gradient sintering treatment on the precipitate to obtain activated alumina, wherein the activated alumina is used in the step 1, the temperature of the first gradient in the two-gradient sintering is 110-120 ℃, the time is 30-60min, the temperature of the second gradient is 200-250 ℃, and the time is 2-6 h.

Further, the alumina-based particles in the step 2 adopt an alumina-based water absorbent with active alumina as a shell and polyacrylic acid and vermiculite as a composite core, and the preparation method of the active alumina-based particles comprises the following steps: b1, adding ethyl cellulose and polyacrylic acid into ethanol, and stirring to form viscous liquid, wherein the mass ratio of the ethyl cellulose to the polyacrylic acid is 5:2-4, and the concentration of ethyl cellulose in ethanol is 70-90 g/L; b2, adding vermiculite into the viscous liquid, stirring uniformly to form suspension, and then granulating and drying to obtain prefabricated particles, wherein the adding amount of the vermiculite is 60-80% of the mass of the ethyl cellulose, and the granulating and drying temperature is 80-90 ℃; b3, adding aluminum isopropoxide into isopropanol to form a dissolving solution, spraying the dissolving solution on the surface of the prefabricated particles, standing and drying to obtain coated particles, wherein the concentration of the aluminum isopropoxide in the isopropanol is 100-200g/L, and the spraying amount is 5-10mL/cm²Standing and drying at 80-90 deg.C; b4, standing the coated particles for 1-2h, and carrying out ultraviolet irradiation treatment for 1-3h to obtain the alumina-based water absorbent, wherein the content of water vapor in the standing environment is 3-6%, the temperature of the ultraviolet irradiation treatment is 250-300 ℃, and the irradiation intensity is 10-20W/cm². The ethyl cellulose in the inner layer can form a porous structure, and the requirement of expansion of vermiculite and polyacrylic acid after a small amount of water absorption is met.

The pretreatment method of the activated alumina block comprises the following steps: c1, adding the activated alumina block into a reaction kettle, introducing ether gas, and then cooling to form a liquid film alumina block, wherein the introduction speed of the ether gas is 10-20mL/min, the temperature is 50-60 ℃, and the temperature for cooling is 5-10 ℃; c2, slowly putting the liquid film alumina block into ethanol, uniformly stirring, heating for 2-5h to obtain an active alumina block with a clean surface, wherein the temperature of the heating is 50-60 ℃, and the temperature of the c3 is constant temperature drying, the active alumina block after the c2 treatment is dried at constant temperature, and the temperature of the constant temperature drying is 70-100 ℃.

From the above description, it can be seen that the present invention has the following advantages:

1. the invention solves the problems of the prior art, adopts simple and easily obtained raw materials, is beneficial to reducing the cost, and has simple steps and strong operability.

2. The silicon carbide prepared by the method has small particle size, uniform particle size distribution and small impurity amount.

3. The invention adopts physical deposition, and combines the adsorption effect of activated alumina to sequentially form the sedimentation coverage of a silicon source and a carbon source, thereby reducing the entering of impurities, and simultaneously the adsorbability of the activated alumina disappears based on the temperature rise to form alpha-alumina.

4. The invention utilizes a recoverable way to recover the used gas and the aluminum liquid, thereby greatly reducing the cost of raw materials.

Detailed Description

The present invention is described in detail with reference to examples, but the present invention is not limited to the claims.

Example 1

A preparation method of silicon carbide powder for electronic packaging comprises the following steps:

step 1, the pretreatment method of the activated alumina block comprises the following steps: c1, adding the activated alumina block into a reaction kettle, introducing ether gas, and then cooling to form a liquid film alumina block, wherein the introduction speed of the ether gas is 10mL/min, the temperature is 50 ℃, and the temperature for cooling is 5 ℃; c2, slowly putting the liquid film alumina block into ethanol, uniformly stirring, heating for 2 hours to obtain an active alumina block with a clean surface, wherein the temperature of the heating is 50 ℃, c3, and drying the active alumina block treated by c2 at a constant temperature to obtain an active alumina block, wherein the temperature of the drying at the constant temperature is 70 ℃; putting an activated alumina block into a reaction kettle, introducing silicon chloride gas under the inert gas atmosphere, standing for 20min, and then purging at constant temperature to obtain plating solution film activated alumina, wherein the inert gas is helium, the introduction speed of the silicon chloride is 20mL/min, the volume ratio of the silicon chloride to the inert gas is 1:9, the standing temperature is 60 ℃, the temperature of the constant temperature purging is 50 ℃, the gas purged at constant temperature is inert gas, and the purging speed is 5 mL/min; and recovering silicon chloride and inert gas from the purged gas at 10 ℃.

Step 2, standing the plating liquid film active alumina in an inert gas atmosphere containing water vapor, then adding alumina-based particles, and standing for 5 hours at a constant temperature to obtain plating film active alumina, wherein the volume of the water vapor in the inert gas atmosphere accounts for 5%, and the standing temperature is 20 ℃; the alumina-based particles adopt an active alumina-based composite water absorbent; the temperature of the constant-temperature standing is 80 ℃; adopts activated alumina as a shell and adopts polyacrylic acid and vermiculite as a composite coreA water absorbing agent, and a method for producing the active alumina-based particles, comprising the steps of: b1, adding ethyl cellulose and polyacrylic acid into ethanol, and stirring to form viscous liquid, wherein the mass ratio of the ethyl cellulose to the polyacrylic acid is 5:2, and the concentration of the ethyl cellulose in the ethanol is 70 g/L; b2, adding vermiculite into the viscous liquid, stirring uniformly to form suspension, and then granulating and drying to obtain prefabricated particles, wherein the adding amount of the vermiculite is 60% of the mass of the ethyl cellulose, and the granulating and drying temperature is 80 ℃; b3, adding aluminum isopropoxide into isopropanol to form a dissolving solution, spraying the dissolving solution on the surface of the prefabricated particles, standing and drying to obtain coated particles, wherein the concentration of the aluminum isopropoxide in the isopropanol is 100g/L, and the spraying amount is 5mL/cm²Standing and drying at the temperature of 80 ℃; b4, standing the coated particles for 1h, and carrying out ultraviolet irradiation treatment for 1h to obtain the aluminum oxide-based water absorbent, wherein the content of water vapor in the standing environment is 3%, the temperature of the ultraviolet irradiation treatment is 250 ℃, and the irradiation intensity is 10W/cm²；

Step 3, putting the coated alumina into a deposition furnace, and introducing methane for deposition reaction to obtain silicon carbide coated alumina, wherein the atmosphere of the deposition reaction is a methane-argon composite system, the volume ratio of methane to argon is 2:7, the deposition temperature is 800 ℃, and the pressure is 0.1 kPa;

and 4, introducing silicon carbide coated alumina into the reaction kettle, continuously introducing mixed gas until the precipitate is not reduced any more, cooling and filtering to obtain precipitate, then performing gradient sintering on the precipitate to obtain silicon carbide powder, wherein the mixed gas is the mixed gas of ethanol, ether and hydrogen chloride, the volume ratio of the ethanol, ether and hydrogen chloride is 2:2:5, the reaction temperature is 100 ℃, the gradient sintering is performed by adopting two-gradient sintering, the temperature of the first gradient is 200 ℃, the time is 0.5h, the temperature of the second gradient is 800 ℃, the time is 2-5h, and further, inert gas purging is adopted between the first gradient sintering and the second gradient sintering.

The filtrate generated after filtration in the step 4 is mainly aluminum chloride, hydrogen chloride, diethyl ether, ethanol and water, and in order to ensure the recycling of aluminum salt, the filtrate is recovered according to the following steps: a1, adding ammonium carbonate into the filtrate, stirring uniformly, and then completely settling the bottom to obtain a deposition filtrate; the adding amount of the ammonium carbonate is 100g/L, and the stirring speed is 500 r/min; a2, refluxing and heating the deposition filtrate for 1 hour, cooling and filtering to obtain a precipitate; the temperature of reflux heating is 80 ℃, the cooling temperature in reflux is 10 ℃, and the temperature of cooling and filtering is 10 ℃; a3, performing two-gradient sintering treatment on the precipitate to obtain activated alumina, wherein the activated alumina is used in the step 1, the temperature of the first gradient in the two-gradient sintering is 110 ℃, the time is 30min, and the temperature of the second gradient is 200 ℃, and the time is 2 h.

The silicon carbide powder prepared in this example had a particle size of 1 μm, a purity of 99.8%, a uniform particle size distribution, a hardness of 2810kg/mm, and a heat of fracture of 3.1MPa/m²。

Example 2

A preparation method of silicon carbide powder for electronic packaging comprises the following steps:

step 1, the pretreatment method of the activated alumina block comprises the following steps: c1, adding the activated alumina block into a reaction kettle, introducing ether gas, and then cooling to form a liquid film alumina block, wherein the introduction speed of the ether gas is 20mL/min, the temperature is 60 ℃, and the temperature for cooling is 10 ℃; c2, slowly putting the liquid film alumina block into ethanol, uniformly stirring, heating for 5 hours to obtain an active alumina block with a clean surface, wherein the temperature of the heating is 60 ℃, and the temperature of c3 is 100 ℃, and drying the active alumina block treated by c2 at constant temperature to obtain an active alumina block; putting an activated alumina block into a reaction kettle, introducing silicon chloride gas under the inert gas atmosphere, standing for 30min, and then purging at constant temperature to obtain plating solution film activated alumina, wherein the inert gas is argon, the introduction speed of the silicon chloride is 30mL/min, the volume ratio of the silicon chloride to the inert gas is 1:20, the standing temperature is 70 ℃, the constant-temperature purging temperature is 55 ℃, the constant-temperature purging gas is inert gas, and the purging speed is 10 mL/min; and recovering silicon chloride and inert gas from the purged gas at 20 ℃.

Step 2, standing the plating solution film active aluminaIn an inert gas atmosphere containing water vapor, then, adding alumina-based particles, and standing for 8 hours at a constant temperature to obtain coated active alumina, wherein the volume of the water vapor in the inert gas atmosphere accounts for 9%, and the standing temperature is 40 ℃; the alumina-based particles adopt an active alumina-based composite water absorbent; the temperature of the constant-temperature standing is 100 ℃; the preparation method of the active alumina-based particles adopts the alumina-based water absorbent with active alumina as a shell and polyacrylic acid and vermiculite as a composite core, and comprises the following steps: b1, adding ethyl cellulose and polyacrylic acid into ethanol, and stirring to form viscous liquid, wherein the mass ratio of the ethyl cellulose to the polyacrylic acid is 5:4, and the concentration of the ethyl cellulose in the ethanol is 90 g/L; b2, adding vermiculite into the viscous liquid, stirring uniformly to form suspension, and then granulating and drying to obtain prefabricated particles, wherein the adding amount of the vermiculite is 80% of the mass of the ethyl cellulose, and the granulating and drying temperature is 90 ℃; b3, adding aluminum isopropoxide into isopropanol to form a dissolving solution, spraying the dissolving solution on the surface of the prefabricated particles, standing and drying to obtain coated particles, wherein the concentration of the aluminum isopropoxide in the isopropanol is 200g/L, and the spraying amount is 10mL/cm²Standing and drying at the temperature of 90 ℃; b4, standing the coated particles for 2h, and performing ultraviolet irradiation treatment for 3h to obtain the aluminum oxide-based water absorbent, wherein the water vapor content in the standing environment is 6%, the temperature of the ultraviolet irradiation treatment is 300 ℃, and the irradiation intensity is 20W/cm²；

Step 3, putting the coated alumina into a deposition furnace, and introducing methane for deposition reaction to obtain silicon carbide coated alumina, wherein the atmosphere of the deposition reaction is a methane-argon composite system, the volume ratio of methane to argon is 3:7, the deposition temperature is 1200 ℃, and the pressure is 20 kPa;

and 4, introducing silicon carbide coated alumina into the reaction kettle, continuously introducing mixed gas until the precipitate is not reduced any more, cooling and filtering to obtain precipitate, then performing gradient sintering on the precipitate to obtain silicon carbide powder, wherein the mixed gas is the mixed gas of ethanol, ether and hydrogen chloride, the volume ratio of the ethanol, ether and hydrogen chloride is 2:2:5, the reaction temperature is 120 ℃, the gradient sintering is performed by adopting two-gradient sintering, the temperature of the first gradient is 300 ℃, the time is 2 hours, the temperature of the second gradient is 1000 ℃, the time is 5 hours, and further, inert gas is adopted for purging between the first gradient sintering and the second gradient sintering.

The filtrate generated after filtration in the step 4 is mainly aluminum chloride, hydrogen chloride, diethyl ether, ethanol and water, and in order to ensure the recycling of aluminum salt, the filtrate is recovered according to the following steps: a1, adding ammonium carbonate into the filtrate, stirring uniformly, and then completely settling the bottom to obtain a deposition filtrate; the adding amount of the ammonium carbonate is 200g/L, and the stirring speed is 1000 r/min; a2, refluxing and heating the deposition filtrate for 2 hours, cooling and filtering to obtain a precipitate; the temperature of reflux heating is 90 ℃, the cooling temperature in reflux is 20 ℃, and the temperature of cooling and filtering is 10-20 ℃; a3, performing two-gradient sintering treatment on the precipitate to obtain activated alumina, wherein the activated alumina is used in the step 1, the temperature of the first gradient in the two-gradient sintering is 120 ℃, the time is 30-60min, and the temperature of the second gradient is 250 ℃, and the time is 6 h.

The silicon carbide powder prepared in this example had a particle size of 1.4 μm, a purity of 99.8%, a uniform particle size distribution, a hardness of 2840kg/mm, and a heat of fracture of 3.4MPa/m²。

Example 3

A preparation method of silicon carbide powder for electronic packaging comprises the following steps:

step 1, the pretreatment method of the activated alumina block comprises the following steps: c1, adding the activated alumina block into a reaction kettle, introducing ether gas, and then cooling to form a liquid film alumina block, wherein the introduction speed of the ether gas is 15mL/min, the temperature is 55 ℃, and the cooling temperature is 8 ℃; c2, slowly putting the liquid film alumina block into ethanol, uniformly stirring, heating for 4 hours to obtain an active alumina block with a clean surface, wherein the temperature of the heating is 55 ℃, c3, and drying the active alumina block treated by c2 at a constant temperature to obtain an active alumina block, wherein the temperature of the constant-temperature drying is 90 ℃; putting an activated alumina block into a reaction kettle, introducing silicon chloride gas under the inert gas atmosphere, standing for 25min, and then purging at constant temperature to obtain plating solution film activated alumina, wherein the inert gas is helium or argon, the introduction speed of the silicon chloride is 25mL/min, the volume ratio of the silicon chloride to the inert gas is 1:15, the standing temperature is 65 ℃, the temperature of constant-temperature purging is 50-55 ℃, the gas of constant-temperature purging is inert gas, and the purging speed is 5-10 mL/min; and recovering silicon chloride and inert gas from the purged gas at 15 ℃.

Step 2, standing the plating liquid film active alumina in an inert gas atmosphere containing water vapor, then adding alumina-based particles, and standing for 7 hours at a constant temperature to obtain plating film active alumina, wherein the volume of the water vapor in the inert gas atmosphere accounts for 8%, and the standing temperature is 30 ℃; the alumina-based particles adopt an active alumina-based composite water absorbent; the temperature of the constant-temperature standing is 90 ℃; the preparation method of the active alumina-based particles comprises the following steps: b1, adding ethyl cellulose and polyacrylic acid into ethanol, and stirring to form viscous liquid, wherein the mass ratio of the ethyl cellulose to the polyacrylic acid is 5:3, and the concentration of the ethyl cellulose in the ethanol is 80 g/L; b2, adding vermiculite into the viscous liquid, stirring uniformly to form suspension, and then granulating and drying to obtain prefabricated particles, wherein the adding amount of the vermiculite is 70% of the mass of the ethyl cellulose, and the granulating and drying temperature is 85 ℃; b3, adding aluminum isopropoxide into isopropanol to form a dissolving solution, spraying the dissolving solution on the surface of the prefabricated particles, standing and drying to obtain coated particles, wherein the concentration of the aluminum isopropoxide in the isopropanol is 150g/L, and the spraying amount is 8mL/cm²Standing and drying at 85 ℃; b4, standing the coated particles for 2h, and carrying out ultraviolet irradiation treatment for 2h to obtain the aluminum oxide-based water absorbent, wherein the content of water vapor in the standing environment is 5%, the temperature of the ultraviolet irradiation treatment is 280 ℃, and the irradiation intensity is 15W/cm²；

Step 3, putting the coated alumina into a deposition furnace, and introducing methane for deposition reaction to obtain silicon carbide coated alumina, wherein the atmosphere of the deposition reaction is a methane-argon composite system, the volume ratio of methane to argon is 3:7, the deposition temperature is 1000 ℃, and the pressure is 10 kPa;

and 4, introducing silicon carbide coated alumina into the reaction kettle, continuously introducing mixed gas until the precipitate is not reduced any more, cooling and filtering to obtain precipitate, then performing gradient sintering on the precipitate to obtain silicon carbide powder, wherein the mixed gas is the mixed gas of ethanol, ether and hydrogen chloride, the volume ratio of the ethanol, ether and hydrogen chloride is 2:2:5, the reaction temperature is 110 ℃, the gradient sintering is performed by adopting two-gradient sintering, the temperature of the first gradient is 250 ℃, the time is 1h, the temperature of the second gradient is 900 ℃, the time is 2-5h, and further, inert gas purging is adopted between the first gradient sintering and the second gradient sintering.

The filtrate generated after filtration in the step 4 is mainly aluminum chloride, hydrogen chloride, diethyl ether, ethanol and water, and in order to ensure the recycling of aluminum salt, the filtrate is recovered according to the following steps: a1, adding ammonium carbonate into the filtrate, stirring uniformly, and then completely settling the bottom to obtain a deposition filtrate; the adding amount of the ammonium carbonate is 150g/L, and the stirring speed is 800 r/min; a2, refluxing and heating the deposition filtrate for 2 hours, cooling and filtering to obtain a precipitate; the temperature of reflux heating is 85 ℃, the cooling temperature in reflux is 10 ℃, and the temperature of cooling and filtering is 15 ℃; a3, performing two-gradient sintering treatment on the precipitate to obtain activated alumina, wherein the activated alumina is used in the step 1, the temperature of the first gradient in the two-gradient sintering is 115 ℃, the time is 50min, the temperature of the second gradient is 230 ℃, and the time is 4 h.

The silicon carbide powder prepared in this example had a particle size of 1.1 μm, a purity of 99.8%, a uniform particle size distribution, a hardness of 2820kg/mm, and a heat of fracture of 3.3MPa/m²。

In summary, the invention has the following advantages:

1. the invention solves the problems of the prior art, adopts simple and easily obtained raw materials, is beneficial to reducing the cost, and has simple steps and strong operability.

2. The silicon carbide prepared by the method has small particle size, uniform particle size distribution and small impurity amount.

3. The invention adopts physical deposition, and combines the adsorption effect of activated alumina to sequentially form the sedimentation coverage of a silicon source and a carbon source, thereby reducing the entering of impurities, and simultaneously the adsorbability of the activated alumina disappears based on the temperature rise to form alpha-alumina.

4. The invention utilizes a recoverable way to recover the used gas and the aluminum liquid, thereby greatly reducing the cost of raw materials.

It should be understood that the detailed description of the invention is merely illustrative of the invention and is not intended to limit the invention to the specific embodiments described. It will be appreciated by those skilled in the art that the present invention may be modified or substituted equally as well to achieve the same technical result; as long as the use requirements are met, the method is within the protection scope of the invention.