CN107128925A - A kind of method that non-hydrolytic sol-gel combination carbothermic method prepares SiC powder - Google Patents

Abstract

The invention relates to a method for preparing SiC powder by a non-hydrolytic sol-gel combined with a carbothermal reduction method, which belongs to the technical field of material science. The preparation method of the powder includes: firstly, using FeCl ₃ , Si(OC ₂ H ₅ ) ₄ and SiCl ₄ as raw materials to prepare a reaction solution, and through gelation treatment to trigger a non-hydrolytic sol-gel reaction to synthesize SiO ₂ gel, SiO ₂ xerogels were obtained after ultrasonication, washing and drying in CH ₂ Cl ₂ . Then, mix it with carbon black (graphite or activated carbon) to obtain a mixed powder, add an appropriate amount of absolute ethanol, ball mill, dry, and then add a PVA aqueous solution with a concentration of 2wt% to obtain a homogenized mixture. Finally, the homogenized mixture is molded by a press, and the SiC powder is prepared by a reduction carbonization reaction in a tube-type atmosphere furnace under an argon atmosphere by adopting a buried carbon method. The SiC powder prepared by the invention has low synthesis temperature, good powder dispersibility, high purity and small particle size, and can provide a new type of functional material for military, civilian and other fields.

Description

A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method

technical field

The invention belongs to the technical field of material science, and in particular relates to a method for preparing SiC powder by a non-hydrolytic sol-gel combined with a carbothermal reduction method.

Background technique

Silicon carbide (SiC) has attracted great attention due to its excellent mechanical strength, chemical stability, corrosion resistance and high thermal conductivity, and is widely used in abrasives, refractory materials, metallurgy, and high-temperature structural ceramics. and many other industrial fields. At the same time, as a wide-bandgap semiconductor, silicon carbide not only has adjustable resistivity and wide absorption frequency band, but also has the characteristics of high temperature resistance, high strength, and low density. At the same time, its oxidation resistance is better than that of carbon-based wave-absorbing materials. It is the first choice material to realize light weight, thin layer, broadband high temperature resistance and microwave absorption.

At present, the preparation methods of SiC materials mainly include vapor phase deposition (CVD), traditional carbothermal reduction method, etc. Among them, the CVD method is expensive in equipment and high in process requirements, which is not conducive to large-scale production; while the traditional carbothermal reduction method consumes a lot of energy. , and the prepared SiC has poor sintering activity. Therefore, the sol-gel method is usually used to prepare the precursor first, and then the SiC powder with a relatively uniform particle size is prepared at a lower temperature by the carbothermal reduction method.

For example, Song Yongcai et al. used industrial silica sol and water-soluble phenolic resin as raw materials to prepare organic-inorganic hybrid precursors by sol-gel method, and obtained β-SiC micropowder with high purity through carbothermal reduction reaction, but the micropowder is A mixture of particles and whiskers, and there is agglomeration. (Preparation of SiC nano-powders from organic-inorganic hybrid precursors [J]. Journal of Materials Science and Engineering, 2004, 22(3):341-343) Wu Xiangyang et al. used sol-gel method, using Fe as catalyst, through carbon Irregular β-SiC particles with different particle sizes were prepared by thermal reduction. With the increase of Fe content, the particle size and average grain size of β-SiC powder increase, while the stacking defect density and specific surface area decrease. (Effect of the amount of Fe catalyst in sol-gel on the stacking defects and morphology of β-SiC[J]. New Carbon Materials, 2005, 20(4):324-328)

When using the sol-gel method to prepare SiC materials, factors such as hydrolysis time, solution pH, and heat treatment temperature have a great influence on the preparation of SiC materials. The prepared SiC materials are compatible with target materials with good crystallization, high purity, and controllable shape and particle size. There is still a certain gap in comparison. In view of the shortcomings of the above-mentioned hydrolytic sol-gel method in the preparation of SiC powder, the non-hydrolytic sol-gel technology proposed by RobertJ.P. Gel is formed by polycondensation reactions such as dehalogenated alkanes or deether polycondensation. This method has a simple process, and the prepared oxide powder has fine particles, large specific surface area, high activity, and has high reactivity, small particle size, and high specific surface area. Precursor, which can promote the carbothermal reduction reaction.

For example, L. Bourget et al. used silicon tetrachloride (SiCl ₄ ) as raw material to prepare silica powder with a surface area of up to 869m ² /g by non-hydrolytic sol-gel method, and it also has more mesopores. structure, which is conducive to the progress of carbothermal reduction reactions dominated by diffusion reactions. (Non-hydrolytic sol-gel routes to silica [J]. Journal of Non-Crystalline Solids, 1998, 242: _81-91 ) Therefore, if it is easy to control, the process is simple, and it can obtain SiO 2nm with higher activity The combination of the non-hydrolytic sol-gel method of the precursor and the carbothermal reduction nitriding method is of great significance for reducing the synthesis temperature of SiC powder and shortening the reaction time.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings in the above existing SiC powder preparation technology, and provide a method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method.

In order to realize the purpose of the above invention, the present invention provides the following technical solutions: (1) Prepare a reaction liquid with anhydrous ferric chloride, tetraethyl orthosilicate and silicon tetrachloride in a certain molar ratio, and then heat the reaction liquid to solidify Gelling treatment, triggering non-hydrolytic sol-gel reaction to synthesize SiO ₂ gel, and SiO ₂ gel was ultrasonically washed and dried in dichloromethane to obtain SiO ₂ xerogel; (2) SiO ₂ xerogel Glue and carbon black (graphite or activated carbon) are mixed in a certain proportion to obtain a mixed powder. Add an appropriate amount of absolute ethanol to the mixed powder. After ball milling and drying at 60°C, add a PVA aqueous solution with a concentration of 2wt% and mix evenly. The homogenized mixture is obtained after the material is trapped at room temperature; (3) The homogenized mixture is formed by a press, and the SiC powder is prepared by a reduction carbonization reaction in a tubular atmosphere furnace in an argon atmosphere by using the buried carbon method.

The composition of the reaction solution is: the mass percentage of anhydrous ferric chloride is 0.05%~0.5%, the mass percentage of tetraethyl orthosilicate is 45%~65%, and the mass percentage of silicon tetrachloride is 34.5%~54.95% .

The temperature control of the heating and gelation treatment of the reaction solution is as follows: the heating temperature is 90-130° C., and the gelation time is 5-20 hours.

The composition of the mixed powder is: the mass ratio of _SiO2 xerogel to carbon black (graphite or activated carbon) is 0.5-2.

The composition of the homogenized mixture is as follows: the mass percentage of the PVA aqueous solution with an added concentration of 2wt% is 1-10%, and the material trapping time is 12-24h.

The molding process parameters of the homogenized mixture are: the molding pressure is 1-20MP, and the holding time is 10-60s.

The carbothermal reduction process of the SiC powder is as follows: the reduction carbonization temperature is 1200-1600°C, the heating rate is 1-10°C/min, the holding time is 0.5-5h, and the flow rate of argon gas is 1.5 L/min.

The characteristics of the SiC powder prepared by the non-hydrolytic sol-gel combined with carbothermal reduction method in the present invention are: good crystallinity, high purity and uniform particle size distribution. Compared with the prior art, the invention can simplify the preparation process of the SiC powder, reduce the synthesis temperature, reduce the preparation cost, and improve the wave-absorbing performance of the powder. The SiC powder prepared by the invention can be used as a high-temperature resistant wave-absorbing material.

Beneficial effect

Compared with the hydrolysis sol-gel technology, the _SiO2 precursor prepared by the non-hydrolysis method has a higher specific surface area and higher activity, which can not only solve the shortcomings of the _SiO2 precursor prepared by the hydrolysis sol-gel method , and combined with carbothermal reduction technology can reduce the SiC powder synthesis temperature, shorten the reaction time, and reduce production costs. The invention can provide a new type of functional material in the fields of high-temperature structural ceramics, aerospace, military industry and the like in my country, and has broad application prospects and technical progress significance.

Specific implementation cases

Example 1

Use 0.0195g of anhydrous ferric chloride, 13.5ml of tetraethyl orthosilicate and 6.9ml of silicon tetrachloride as raw materials to prepare a reaction solution, seal and stir until the anhydrous ferric chloride is completely dissolved, then quickly transfer the reaction solution to a container In the bomb, react at 110°C for 12h to obtain SiO ₂ gel. The SiO ₂ gel was ultrasonically washed with dichloromethane, and dried at 110° C. for 3 h to prepare the SiO ₂ xerogel. Take SiO ₂ xerogel as the silicon source, carbon black as the carbon source, mix the two according to the mass ratio of SiO ₂ : carbon black as 3:2, add an appropriate amount of absolute ethanol to the mixed powder, and put it into a ball mill In the process, dry at 60°C after grinding for 2 hours, add PVA aqueous solution with a concentration of 2wt% according to its mass percentage of 5%, mix evenly, and obtain a homogenized mixture after 12 hours at room temperature. , SiC powder can be obtained after reducing and carbonizing at 1500℃ in a tubular atmosphere furnace for 2.5h at a heating rate of 3℃/min and an argon flow rate of 1.5 L/min by buried carbon method. The particle size is about 80nm, and the dispersion Good sex, high purity.

Example 2

Use 0.0195g of anhydrous ferric chloride, 13.5ml of tetraethyl orthosilicate and 6.9ml of silicon tetrachloride as raw materials to prepare a reaction solution, seal and stir until the anhydrous ferric chloride is completely dissolved, then quickly transfer the reaction solution to a container In the bomb, react at 100°C for 15h to obtain SiO ₂ gel. The SiO ₂ gel was ultrasonically washed with dichloromethane, and dried at 110° C. for 3 h to prepare the SiO ₂ xerogel. Using SiO ₂ xerogel as the silicon source and graphite as the carbon source, mix the two according to the mass ratio of SiO ₂ : graphite at 1:1, add an appropriate amount of absolute ethanol to the mixed powder, and put it into a ball mill, Grinding for 2 hours, drying at 60°C, adding 3% by mass of PVA aqueous solution with a concentration of 2wt%, and mixing evenly, after 15 hours at room temperature, a homogenized mixture was obtained, which was molded by a press at a pressure of 5MP. SiC powder can be prepared by carbon buried method at a heating rate of 2°C/min and an argon flow rate of 1.5 L/min in a tubular atmosphere furnace at 1450°C for 3 hours. The particle size is about 100nm and the dispersion is good. , high purity.

Example 3

Use 0.0195g of anhydrous ferric chloride, 13.5ml of tetraethyl orthosilicate and 6.9ml of silicon tetrachloride as raw materials to prepare a reaction solution, seal and stir until the anhydrous ferric chloride is completely dissolved, then quickly transfer the reaction solution to a container In the bomb, react at 120°C for 10h to obtain SiO ₂ gel. The SiO ₂ gel was ultrasonically washed with dichloromethane, and dried at 110° C. for 3 h to prepare the SiO ₂ xerogel. Using _SiO2 xerogel as the silicon source and activated carbon as the carbon source, mix the two according to the mass ratio of _SiO2 :activated carbon as 2:1, add an appropriate amount of absolute ethanol to the mixed powder, and put it into a ball mill, Grinding for 2 hours, drying at 80°C, adding a PVA aqueous solution with a concentration of 2wt% according to its mass percentage of 7% and mixing evenly, and obtaining a homogenized mixture after 10 hours at room temperature, and molding it with a press at a pressure of 8MP. SiC powder can be prepared by carbon buried method at a heating rate of 3°C/min and argon flow rate of 1.5 L/min in a tubular atmosphere furnace at 1550°C for 2 hours. The particle size is about 90nm and the dispersion is good. , high purity.

Claims (7)

1. A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method, characterized in that the method for preparing SiC powder comprises the following steps: (1) anhydrous ferric chloride, ethyl orthosilicate Esters and silicon tetrachloride prepare the reaction solution according to a certain molar ratio, and then heat the reaction solution to gel, trigger the non-hydrolytic sol-gel reaction to synthesize SiO ₂ gel, and the SiO ₂ gel is dissolved in dichloromethane After ultrasonication, washing and drying, SiO ₂ xerogels are obtained; (2) SiO ₂ xerogels and carbon black (graphite or activated carbon) are mixed in a certain proportion to obtain a mixed powder, and an appropriate amount of absolute ethanol is added to the mixed powder , after ball milling and drying at 60°C, add a PVA aqueous solution with a concentration of 2wt% and mix evenly, and obtain a homogenized mixture after being trapped at room temperature; SiC powder was prepared by reduction carbonization reaction in a tube atmosphere furnace under argon atmosphere. 2. the method for preparing SiC powder by a kind of non-hydrolytic sol-gel combination carbothermal reduction method as claimed in claim 1, it is characterized in that the composition of reaction solution is: the mass percentage of anhydrous ferric chloride is 0.05%～ 0.5%, the mass percentage of ethyl orthosilicate is 45-65%, and the mass percentage of silicon tetrachloride is 34.5%-54.95%. 3. A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method according to claim 1, characterized in that the temperature control of the reaction solution heating and gelling treatment is as follows: the heating temperature is 90 ~ 130 ℃, the gelation time is 5~20h. 4. the method for preparing SiC powder by a kind of non-hydrolytic sol-gel combined with carbothermal reduction method as claimed in claim 1, it is characterized in that the composition of mixed powder is: SiO _Xerogel and carbon black (graphite or activated carbon) with a mass ratio of 0.5~2. 5. A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method as claimed in claim 1, characterized in that the composition of the homogenized mixture is: the added concentration is the mass percentage of 2wt% PVA aqueous solution It is 1~10%, and the stuffing time is 12~24h. 6. A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method as claimed in claim 1, characterized in that the molding process parameters of the homogenized mixture are: the molding pressure is 1~20MP, and the The pressure time is 10~60s. 7. A method for preparing SiC powder by non-hydrolytic sol-gel combined with carbothermal reduction method as claimed in claim 1, characterized in that the carbothermal reduction process of SiC powder is as follows: reduction carbonization temperature is 1200~1600°C , the heating rate is 1~10°C/min, the holding time is 0.5~5h, and the argon gas flow rate is 1.5 L/min.