A method for preparing β-SiC powder

Abstract

The invention provides a preparation method of beta-SiC powder, comprising: firstly, mixing a carbon source solution, a silicon source solution and ammonia water, and then fully stirring to form a uniform sol; secondly, heating the sol in a water bath to form a wet gel; thirdly, placing the wet gel in a surface modification solution for immersion exchange treatment; thirdly, heating and drying the wet gel at normal pressure to obtain a dry gel; and finally, placing the dry gel in a graphite sintering furnace for a carbothermal reduction reaction to prepare the beta-SiC powder. The invention firstly adds a surface modification solution to a solvent replaced by the wet gel, thereby shortening the preparation cycle of the beta-SiC powder; meanwhile, the surface-modified wet gel generates lower capillary tension during the normal pressure drying process, so that the wet gel will not generate a large shrinkage even during the normal pressure drying process, thereby making the particle size dispersion of the beta-SiC powder generated after the carbothermal reduction more uniform.

Description

Technical Field

[0001] The invention relates to the technical field of silicon carbide materials, and in particular to a method for preparing β-SiC powder. Background Art

[0002] Silicon carbide (SiC) is a recognized excellent ceramic material. It has excellent physical properties such as high strength at high temperature, high melting point, high hardness, high thermal conductivity, high thermal stability, high thermal shock resistance, and good wear resistance. Silicon carbide has excellent mechanical properties and is increasingly attracting attention as a structural ceramic material. In recent years, silicon carbide single crystals have become a semiconductor material that is expected to replace silicon semiconductors due to their wide band gap and good thermal stability.

[0003] At present, there are three methods for preparing silicon carbide powder: solid phase method, liquid phase method and gas phase method. Different processes have their own advantages. The solid phase method can prepare high-purity SiC powder. The preparation process is simple, but it is easy to introduce impurities. The synthesized SiC powder has a high content of N elements and cannot meet the use requirements of semi-insulating single crystal substrates. The gas phase method can prepare high-purity SiC powder, but the particle size is usually at the nanometer level, which is not easy to collect, has low efficiency and high cost. The liquid phase method generally uses a sol-gel method combined with a thermal carbon reduction method. The prepared SiC powder can be used for the growth of single crystals, but the preparation cycle is long, so it has not been applied on a large scale. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem of long preparation period of β-SiC powder prepared by the existing liquid phase method.

[0005] In order to solve the above technical problems, the present invention first provides a method for preparing β-SiC powder, comprising:

[0006] S10, mixing a carbon source solution, a silicon source solution and ammonia water to form a mixed solution, wherein the mixed solution is fully stirred to form a uniform sol, wherein the carbon source solution includes a phenolic resin, and the silicon source solution includes any one of tetraethyl orthosilicate and tetramethyl orthosilicate;

[0007] S20, heating the sol in a water bath to form a wet gel;

[0008] S30, placing the wet gel in a surface modification solution for immersion exchange treatment;

[0009] S40, performing a heating and drying process on the wet gel at normal pressure to obtain a dry gel;

[0010] S50, placing the dry gel in a graphite sintering furnace for a carbothermal reduction reaction to prepare β-SiC powder.

[0011] Preferably, in step S10, any one of tetraethyl orthosilicate and tetramethyl orthosilicate is dissolved in oxalic acid or hydrochloric acid and stirred for 10 minutes for pre-hydrolysis to form a silicon source solution.

[0012] Preferably, in step S10, the C / Si molar ratio in the carbon source solution and the silicon source solution is 2.2-3.0.

[0013] Preferably, in step S10, the pH value of the mixed solution is 6.5-7.

[0014] Preferably, step S20 specifically includes:

[0015] S201, seal the sol and place it in a water bath at 60-80°C for more than 3 hours until the sol loses fluidity;

[0016] S202, the sol is further heated and aged for 12 to 24 hours to form a wet gel.

[0017] Preferably, in step S30, the mass fraction of the surface modifier in the surface modification solution accounts for 10-20% of the total mass of the surface modification solution.

[0018] Preferably, in step S30, the surface modifier is any one of trimethylchlorosilane, methyltriethoxysilane, trimethylethoxysilane and hexamethyldisilazane.

[0019] Preferably, step S40 specifically includes: placing the wet gel in an oven at 60° C. and drying it at normal pressure for 3 to 5 hours to form a dry gel.

[0020] Preferably, in step S50, the carbon thermal reduction process for forming the β-SiC powder is as follows: the reduction carbonization temperature is 1600-1800° C., the holding time is 4-6 hours, and the argon gas flow rate is 0.1 L / min.

[0021] Preferably, in step S50, the crystal particle size distribution of the formed β-SiC powder is 1-10 um, and the purity is greater than 99%.

[0022] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a method for preparing β-SiC powder, the preparation method comprising: firstly, mixing a carbon source solution, a silicon source solution and ammonia water to form a mixed solution, the mixed solution is fully stirred to form a uniform sol, the carbon source solution comprises a phenolic resin, the silicon source solution comprises any one of tetraethyl orthosilicate and tetramethyl orthosilicate, secondly, heating the sol in a water bath to form a wet gel, thirdly, placing the wet gel in a surface modification solution for immersion exchange treatment, thirdly, heating and drying the wet gel at normal pressure to obtain a dry gel, and finally, The gel is placed in a graphite sintering furnace for a carbon thermal reduction reaction to prepare a β-SiC powder. The present invention firstly adds a surface modification solution to the solvent replaced by the wet gel to reduce the surface tension of the wet gel, so that the liquid inside the wet gel is more easily exchanged, thereby quickly removing impurities and moisture, reducing the replacement time, and further shortening the preparation cycle of the β-SiC powder. At the same time, the wet gel after the surface modification generates a lower capillary tension during the normal pressure drying process, so that the wet gel will not shrink significantly even during the normal pressure drying process, thereby making the particle size dispersion of the β-SiC powder generated after the carbon thermal reduction more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of a method for preparing β-SiC powder provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention provides a method for preparing β-SiC powder, comprising:

[0026] S10, mixing a carbon source solution, a silicon source solution and ammonia water to form a mixed solution, and the mixed solution is fully stirred to form a uniform sol, the carbon source solution includes phenolic resin, and the silicon source solution includes any one of tetraethyl orthosilicate and tetramethyl orthosilicate.

[0027] Specifically, S10 also includes:

[0028] First, phenolic resin is dissolved in ethanol to prepare a carbon source solution;

[0029] Secondly, any one of tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) is dissolved in oxalic acid or hydrochloric acid and stirred for pre-hydrolysis to form a silicon source solution;

[0030] Finally, the carbon source solution and the silicon source solution are mixed, and the C / Si molar ratio is controlled to be between 2.2 and 3.0. Ammonia water is added and stirred for 0.5 to 1 hour for sufficient reaction to form a uniform sol.

[0031] Furthermore, the phenolic resin is a solid phenolic resin or a liquid phenolic resin.

[0032] Furthermore, the C / Si molar ratio is controlled between 2.2 and 3.0 because in the subsequent carbon thermal reduction reaction, a portion of carbon will react with oxygen to generate CO. Therefore, appropriately increasing the carbon source ratio is beneficial to improving the synthesis purity of β-SiC powder.

[0033] Furthermore, ammonia water is used as a catalyst to adjust the pH value of the mixed solution to 6.5-7, so as to promote the gelation reaction of the carbon source solution and the silicon source solution, thereby generating a sol containing silicon dioxide.

[0034] Furthermore, the above sol is formed by particles dispersed in a fluid, and is characterized by uniform dispersion, controllable size, and the presence of a distinct phase interface. Under certain conditions, the colloidal particles or polymers of the sol will connect with each other to form a spatial network structure, in which the structural gaps are filled with a liquid as a dispersion medium.

[0035] S20, heating the sol in a water bath to form a wet gel.

[0036] Specifically, step S20 also includes:

[0037] S201, seal the sol and place it in a water bath at 60-80°C for more than 3 hours until the sol loses fluidity;

[0038] S202, the sol is further heated and aged for 12 to 24 hours to form a wet gel.

[0039] Furthermore, the wet gel is formed by a solid three-dimensional network structure, has no fluidity, and contains a large amount of solvent and a small amount of raw materials that do not participate in the reaction.

[0040] S30, placing the wet gel into a surface modification solution for immersion treatment.

[0041] Specifically, step S30 also includes:

[0042] First, the wet gel is immersed in a surface modification solution for 0.5 to 1 hour, wherein the surface modification solution is prepared by adding 10-20% mass fraction of a surface modifier to ethanol or n-hexane, and the surface modifier is one of trimethylchlorosilane (TMCS), methyltriethoxysilane (MTES), trimethylethoxysilane (TMES) and hexamethyldisilazane (HMDS).

[0043] Secondly, after the wet gel is soaked, it is washed several times with ethanol or n-hexane to wash away the excess surface modification solution and the water in the gel.

[0044] Furthermore, the surface modifier in the surface modification solution can react with the wet gel to form hydrophobic groups on the surface of the wet gel, thereby making it easier to exchange the water inside the wet gel, thereby making it less likely for the surface structure of the wet gel to collapse during the subsequent drying process.

[0045] S40, subjecting the wet gel to a heating and drying process at normal pressure to obtain a dry gel.

[0046] Specifically, step S40 also includes:

[0047] Under normal pressure, the replaced gel is placed in an oven at 60° C. for drying for 3-5 hours to obtain a dry gel; at this time, the dry gel is a mixed gel composed of silica and phenolic resin.

[0048] S50, placing the dry gel in a graphite sintering furnace for a carbothermal reduction reaction to prepare β-SiC powder.

[0049] Specifically, step S50 also includes: loading the dry gel into a graphite crucible and placing it in a graphite sintering furnace, performing a carbon thermal reduction reaction at 1600-1800°C in an Ar atmosphere with a flow rate of 0.1 L / min, and keeping the temperature for 4-6 hours; high-purity β-SiC powder can be obtained through the above process steps.

[0050] Furthermore, in an Ar atmosphere at a temperature of 1600-1800°C, the phenolic resin in the dry gel decomposes into free carbon, which undergoes a carbothermal reduction reaction with the silica in the dry gel to generate high-purity β-SiC powder and CO.

[0051] Preferably, in step S50, the crystal particle size distribution of the formed β-SiC powder is 1-10 um, and the purity is greater than 99%.

[0052] The technical solution of the present invention is now further described in conjunction with specific embodiments.

[0053] Embodiment 1:

[0054] In this Example 1, tetraethyl orthosilicate (TEOS) is used as a silicon source and phenolic resin is used as a carbon source to prepare silica gel. After gelation, surface modification, solvent replacement, and normal pressure drying, a dry gel is prepared. The β-SiC powder is prepared by a pyrolysis precursor carbon thermal reduction method.

[0055] Specific implementation steps:

[0056] Step 1: dissolve phenolic resin in ethanol, dissolve tetraethyl orthosilicate (TEOS) in 0.2 mol / L oxalic acid solution and stir for 10 min for pre-hydrolysis, add the above solution for mixing, the C / Si molar ratio is 2.6, add 1 mol / L ammonia water to adjust the pH value to 6.5, stir for 0.5 h for sufficient reaction to form a uniform sol.

[0057] Step 2: The above sol is sealed and placed in a 60° C. water bath. After about 3 hours, the sol loses fluidity. After further heating and aging at 80° C. for 20 hours, the wet gel is prepared.

[0058] Step three, add 20% of the surface modifier trimethylchlorosilane (TMCS) to ethanol, soak the gel in the solution for 30 minutes, and then soak and wash it with ethanol for 3 times.

[0059] Step 4: Place the replaced gel in an oven at 60° C. for drying for 4 hours to obtain a dried gel.

[0060] Step 5: Load the dry gel into a graphite crucible and place it in a graphite sintering furnace. Carbothermal reduction reaction is carried out at 1800° C. in a high-purity Ar atmosphere with a flow rate of 0.1 L / min for 6 hours.

[0061] In this embodiment 1, high-purity β-phase silicon carbide powder can be obtained through the above process steps. According to XRD test, the sample only contains β-SiC powder, the crystal particle size distribution is 1~10um, and the purity is 99.91%.

[0062] Embodiment 2:

[0063] In this Example 2, tetramethyl orthosilicate (TMOS) is used as a silicon source and phenolic resin is used as a carbon source to prepare silica gel. After gelation, surface modification, solvent replacement, and normal pressure drying, a dry gel is prepared. The β-SiC powder is prepared by a pyrolysis precursor carbon thermal reduction method.

[0064] Specific implementation steps:

[0065] Step 1: dissolve phenolic resin in ethanol, dissolve tetramethyl orthosilicate (TMOS) in 0.2 mol / L hydrochloric acid solution and stir for 10 min for pre-hydrolysis, add the above solution to mix, control the C / Si molar ratio to 2.8, add 1 mol / L ammonia water to adjust the pH to 7, stir for 0.5 h for sufficient hydrolysis to form a uniform sol.

[0066] Step 2: The above sol is sealed and placed in a 60° C. water bath. After about 3 hours, the sol loses fluidity. After further heating and aging at 80° C. for 24 hours, the wet gel is prepared.

[0067] Step three, add 20% of the surface modifier trimethylchlorosilane (TMCS) into n-hexane, soak the wet gel in the solution for 30 minutes, and soak and wash it with n-hexane for 3 times.

[0068] Step 4: Place the replaced gel in an oven at 60° C. for drying for 3.5 h to obtain a dry gel.

[0069] Step 5: Load the dry gel into a graphite crucible and place it in a graphite sintering furnace. Carbothermal reduction reaction is carried out at 1750° C. in a high-purity Ar atmosphere with a flow rate of 0.1 L / min for 6 hours.

[0070] In this embodiment 2, high-purity β-phase silicon carbide powder can be obtained through the above process steps. According to XRD test, the sample only contains β-SiC powder, the crystal particle size distribution is 1~10um, and the purity is 99.89%.

[0071] Compared with the prior art, the present invention has the following advantages:

[0072] First, the conventional gel solvent replacement process usually takes a long time and is replaced 4-5 times. The present invention reduces the surface tension by adding a surface modifier to the solvent replaced by the wet gel, making it easier to exchange the liquid inside the wet gel, thereby quickly removing impurities and moisture and reducing the replacement time.

[0073] Second, in order to reduce the shrinkage caused by capillary force during the drying process of gel, the supercritical drying process usually produces better results, but the equipment used in this method is complicated to operate and takes a long time; this method uses a normal pressure drying process with simple conditions. The modified and solvent-replaced gel produces lower capillary tension during the normal pressure drying process, so that the gel will not shrink significantly even during the normal pressure drying process, thereby making the SiC grain size dispersion produced after carbothermal reduction more uniform.

[0074] In summary, the present invention firstly adds a surface modification solution to the solvent replaced by the wet gel to reduce the surface tension of the wet gel, so that the liquid inside the wet gel is more easily exchanged, thereby quickly removing impurities and moisture, reducing the replacement time, and further shortening the preparation cycle of the β-SiC powder. At the same time, the wet gel after surface modification generates lower capillary tension during the normal pressure drying process, so that the wet gel will not shrink significantly even during the normal pressure drying process, thereby making the particle size dispersion of the β-SiC powder produced after carbothermal reduction more uniform.

[0075] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0076] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing β-SiC powder, characterized in that: include: S10, mixing a carbon source solution, a silicon source solution and ammonia water to form a mixed solution, wherein the mixed solution is fully stirred to form a uniform sol, wherein the carbon source solution includes a phenolic resin, and the silicon source solution includes any one of tetraethyl orthosilicate and tetramethyl orthosilicate; S20, heating the sol in a water bath to form a wet gel; S30, placing the wet gel in a surface modification solution for immersion exchange treatment; the mass fraction of the surface modifier in the surface modification solution accounts for 10-20% of the total mass of the surface modification solution; the surface modifier is any one of trimethylchlorosilane, methyltriethoxysilane, trimethylethoxysilane and hexamethyldisilazane; S40, placing the wet gel in an oven at 60° C. and drying at normal pressure for 3 to 5 hours to obtain a dry gel; S50, placing the dry gel in a graphite sintering furnace for a carbothermal reduction reaction to prepare β-SiC powder.

2. The method for preparing β-SiC powder according to claim 1, characterized in that: In the step S10, any one of tetraethyl orthosilicate and tetramethyl orthosilicate is dissolved in oxalic acid or hydrochloric acid, and stirred for 10 minutes for pre-hydrolysis to form the silicon source solution.

3. The method for preparing β-SiC powder according to claim 1, characterized in that: In the step S10, the C / Si molar ratio of the carbon source solution to the silicon source solution is 2.2-3.

0.

4. The method for preparing β-SiC powder according to claim 1, characterized in that: In the step S10, the pH value of the mixed solution is 6.5-7.

5. The method for preparing β-SiC powder according to claim 1, characterized in that: The step S20 specifically includes: S201, sealing the sol and placing it in a water bath at 60-80° C. for more than 3 hours until the sol loses fluidity; S202, further heating and aging the sol for 12 to 24 hours to form the wet gel.

6. The method for preparing β-SiC powder according to claim 1, characterized in that: In the step S50, the carbon thermal reduction process for forming the β-SiC powder is as follows: the reduction carbonization temperature is 1600-1800° C., the insulation time is 4-6 hours, and the argon gas flow rate is 0.1 L / min.

7. The method for preparing β-SiC powder according to claim 1, characterized in that: In the step S50, the β-SiC powder is formed with a crystal particle size distribution of 1-10 um and a purity greater than 99%.

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