阅读说明：本技术 一种高密度低游离硅含量反应烧结碳化硅陶瓷材料的制备方法 (Preparation method of high-density low-free silicon content reaction sintered silicon carbide ceramic material ) 是由 齐小君 于 2020-05-26 设计创作，主要内容包括：本发明提供一种高密度低游离硅含量反应烧结碳化硅陶瓷材料的制备方法,该制备方法包括混料、真空除气、注浆成型、脱模干燥和烧结处理步骤,其中选取合理的原料粒度级配,并采用压力注浆成型,增强了产品素坯的密度；在烧结过程中采用优化的烧结曲线,有机物排除同预烧合二为一,在不影响产品质量的情况下降低烧结成本,减少碳化硅陶瓷素坯在高温排除有机物过程中发生的坯体的变形或开裂问题；使高密度坯体能够在较低温度下充分反应烧结,生成高密度、低游离硅陶瓷制品,保证了碳化硅陶瓷素坯显微结构均匀,大大提高了陶瓷材料的强度及结构稳定性。(The invention provides a preparation method of a high-density low-free silicon content reaction sintering silicon carbide ceramic material, which comprises the steps of mixing, vacuum degassing, slip casting, demoulding, drying and sintering, wherein reasonable raw material grain size distribution is selected, and pressure slip casting is adopted, so that the density of a product biscuit is enhanced; an optimized sintering curve is adopted in the sintering process, organic matter removal and pre-sintering are combined into a whole, the sintering cost is reduced under the condition that the product quality is not influenced, and the problem of deformation or cracking of a blank body of the silicon carbide ceramic biscuit in the process of removing the organic matter at high temperature is solved; the high-density green body can be fully reacted and sintered at a lower temperature to generate the high-density low-free silicon ceramic product, so that the uniform microstructure of the silicon carbide ceramic biscuit is ensured, and the strength and the structural stability of the ceramic material are greatly improved.)

1. A preparation method of a high-density low-free-silicon-content reaction-sintered silicon carbide ceramic material is characterized by comprising the steps of mixing materials, vacuum degassing, slip casting, demolding, drying and sintering.

2. The preparation method of claim 1, wherein the mixing material and raw material slurry composition comprises the following components in parts by weight:

5-10% of carbon black, 60-70% of silicon carbide micro powder, 1-2% of dispersing agent, 0.2-0.6% of binder, 0.2-0.6% of deflocculant and 18-25% of purified water;

the particle size of the carbon black is 20-100 nm;

the particle size of the silicon carbide micro powder is 3-90um, wherein the particle size of 3-5um accounts for 20% of the total weight, the particle size of 40-46um accounts for 40% of the total weight, and the particle size of 85-90um accounts for 40% of the total weight.

3. The preparation method according to claim 1, wherein a calcine is added in the sintering treatment, and the calcine comprises, by weight, 18-24 parts of metal silicon powder, 0.2-0.5 part of boron nitride powder, 0.2-0.5 part of carbon black, and 1-3 parts of glue;

the granularity of the metal silicon powder is 1-5 mm;

the glue comprises PVK90 and has a concentration of 20-25%.

4. The method according to claim 1, wherein the sintering process includes a heating and temperature-raising process, and the heating and temperature-raising process includes: heating from normal temperature to 300 ℃ for 1.5-2 hours, and keeping the temperature for 20-30 minutes; heating at the temperature of between 301 and 600 ℃ for 2.5 to 3 hours, and keeping the temperature for 30 to 35 minutes; 601-800 ℃ heating time is 2-2.5 hours, and constant temperature is 1-1.5 hours.

5. The preparation method according to claim 1, wherein the sintering treatment further comprises vacuum sintering, the vacuum degree is maintained below 3pa, and the temperature control time is as follows: heating at the temperature of 801-; 1101-1400 ℃ heating time is 3.5-4 hours, and constant temperature is 30-40 minutes; 1401 and 1700 ℃ for 4 hours, and keeping the temperature for 3-3.5 hours.

6. The preparation method according to claim 1, wherein the sintering treatment further comprises dewaxing while heating, and the nitrogen flow rate is 80-85L/min.

7. The method according to claim 1, wherein the pressure in the slurry tank reaches 0.3-0.35MPa in the slip casting.

8. The method according to claim 1, wherein the step of drying by demolding comprises drying at a low temperature and then drying at a high temperature; drying at low temperature of 20-50 ℃; and drying at high temperature of 50-90 ℃.

9. The production method according to claim 1, wherein the vacuum degassing is performed in a degree of vacuum of 100Pa or less.

10. The method according to claim 1, wherein in the sintering treatment, the addition amount of the calcine is 30-50% of the weight of the biscuit.

Technical Field

The invention belongs to the technical field of ceramic material preparation, and particularly relates to a preparation method of a high-density low-free silicon content reaction sintered silicon carbide ceramic material.

Background

The silicon carbide ceramic is an industrial material with the characteristics of high mechanical strength, high hardness, high temperature resistance, chemical corrosion resistance, oxidation resistance, excellent thermal shock resistance, good thermal conductivity, low expansion coefficient and the like, particularly the oxidation resistance is the best of all non-metallic ceramics, wherein the silicon carbide prepared by the reaction sintering method has the advantages of low temperature and net size, is a method widely adopted in industry, and is often used for producing complex special-shaped parts in the electronic packaging, aerospace, military, automobile industry and the like.

The existence of residual silicon in the reaction sintering silicon carbide is inevitable, and the use temperature and the use environment of the reaction sintering silicon carbide are limited. However, the decrease of the silicon content in one way cannot improve the overall performance of the silicon carbide ceramic, and for example, the adjustment of the content of the raw material may cause the decrease of the product density and may cause incomplete sintering reaction of the product. The content of silicon is reduced to obtain purer silicon carbide ceramic, the elastic modulus, the mechanical property and the corrosion resistance of the reaction sintering silicon carbide can be improved, and the method has important theoretical significance and application prospect. The invention prepares the complex silicon carbide ceramic material with low residual silicon content and high density by a low-temperature direct reaction method with different grain compositions, so that the silicon carbide ceramic obtains the improvement of the structure and the performance on the basis of the traditional reaction sintering.

At present, the preparation process of the reaction sintering silicon carbide ceramic mainly comprises dry pressing, extrusion forming, injection forming and slip casting. Wherein, the dry pressing forming process is a forming method for pressing the dry powder blank for preparing the silicon carbide ceramic into a compact body in a model by using pressure; the extrusion molding is a molding method for forming a blank body with a simple shape by stirring raw materials into slurry containing less water and extruding the slurry under pressure; the injection molding process mainly comprises the following steps: preparing materials, mixing (binder and feed are needed), injection molding, degreasing and sintering; the slip casting is a method for forming a desired shape by mixing and stirring all materials into a flowable slurry with high solid content and injecting the flowable slurry into a gypsum mold. However, although the silicon carbide ceramic prepared by the dry pressing process has high density, the structure uniformity is poor, and the silicon carbide ceramic cannot be prepared into products with complex shapes, mainly in the form of sheet plates; although the density of the product manufactured by extrusion molding is higher than that of the product manufactured by slip casting, the product with a complex shape cannot be manufactured, and mainly takes a rod-shaped beam shape as a main part; the injection molding process needs a large amount of organic binders, ceramic biscuit shrinkage is large, and the silicon carbide ceramic material with high volume fraction cannot be prepared, so that the silicon carbide ceramic material with high performance requirement cannot be realized; the existing grouting forming method can produce special-shaped products with complex shapes, but the product density is low and can only reach 3.06-3.08g/cm3 at most, the requirement of high mechanical property can not be met, and the method can not be applied to the field with higher technical requirements.

Disclosure of Invention

In order to solve the problems in the prior art and further optimize the prior art, the invention provides a preparation method of a high-density low-free-silicon-content reaction sintering silicon carbide ceramic material, which aims to reduce the free silicon content in the ceramic material, improve the density of the ceramic material, realize uniform structure and improve the mechanical property of the silicon carbide ceramic material.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a high-density low-free-silicon-content reaction sintered silicon carbide ceramic material is characterized by comprising the steps of mixing materials, vacuum degassing, slip casting, demoulding, drying and sintering;

the mixed material is composed of raw material slurry and comprises the following components in parts by weight:

5-10% of carbon black, 60-70% of silicon carbide micro powder, 1-2% of dispersing agent, 0.2-0.6% of binder, 0.2-0.6% of deflocculant and 18-25% of purified water;

the particle size of the carbon black is 20-100 nm; preferably, the particle size is 36-40 nm;

the silicon carbide micro powder has the grain diameter of 3-90um, wherein the grain diameter of 3-5um accounts for 20 percent of the total weight, the grain diameter of 40-46um accounts for 40 percent of the total weight, and the grain diameter of 85-90um accounts for 40 percent of the total weight;

the binder is CMC cellulose sodium;

the dispersant is a carboxylic acid preparation;

preferably, the dispersant is a polycarboxylic acid sodium salt dispersant, OROTAN 731A;

the deflocculant is sodium polycarboxylates;

preferably, the deflocculant is DOLAPIX PC 67;

vacuum degassing is carried out, and the vacuum degree is below 100 Pa; the treatment time is 2-20 min;

the pressure in the slurry tank reaches 0.3-0.35MPa after the slurry is injected and molded; naturally dehydrating and curing the slurry in a mould for 24 hours after grouting;

the demolding and drying comprise low-temperature drying and high-temperature drying; drying at low temperature of 20-50 ℃ for 24-30 h; drying at high temperature of 50-90 ℃ for 12-24 h;

the sintering treatment needs to add a roasting material, and the composition of the roasting material comprises, by weight, 18-24 parts of metal silicon powder, 0.2-0.5 part of boron nitride powder, 0.2-0.5 part of carbon black and 1-3 parts of glue

Preferably, the material comprises 20 parts of metal silicon powder, 0.3 part of boron nitride powder, 0.5 part of carbon black and 2 parts of glue;

the granularity of the metal silicon powder is 1-5 mm;

the glue comprises PVK90 and has a concentration of 20-25%;

in the sintering treatment, the addition amount of the roasting material is 30-50% of the weight of the biscuit;

the sintering treatment comprises a heating temperature rise process, wherein the heating temperature rise process comprises the steps of heating from normal temperature to 300 ℃ for 1.5-2 hours and keeping the temperature for 20-30 minutes; heating at the temperature of between 301 and 600 ℃ for 2.5 to 3 hours, and keeping the temperature for 30 to 35 minutes; 601-800 ℃ heating time is 2-2.5 hours, and constant temperature is 1-1.5 hours;

preferably, the heating to raise the temperature includes: heating from normal temperature to 300 ℃ for 1.5 hours, and keeping the temperature for 20 minutes; heating at the temperature of 301-600 ℃ for 2.5 hours, and keeping the temperature for 30 minutes; 601-800 ℃ heating time is 2 hours, and the temperature is kept for 1 hour;

the sintering treatment also comprises dewaxing in the heating and temperature rising process, and the nitrogen flow rate is 80-85L/min;

the sintering treatment further comprises vacuum sintering, the vacuum degree is maintained below 3pa, and the temperature control time is as follows: heating at the temperature of 801-; 1101-1400 ℃ heating time is 3.5-4 hours, and constant temperature is 30-40 minutes; 1401 and 1700 ℃ for 4 hours, and keeping the temperature for 3-3.5 hours;

preferably, the vacuum sintering is carried out for the following time period: heating at the temperature of 801-; 1101-1400 ℃ heating time is 3.5 hours, and the temperature is kept for 30 minutes; 1401-;

the sintering treatment comprises stopping heating, and naturally cooling the electric furnace to room temperature;

by adopting the preparation method of the invention, reasonable raw material grain size distribution is selected, so that silicon carbide particles and carbon black particles can be uniformly dispersed in water, and the density of the biscuit of the product is enhanced by combining pressure grouting forming; meanwhile, an optimized sintering curve is adopted in the sintering process, organic matter removal and pre-sintering are combined into a whole, the sintering cost is reduced under the condition that the product quality is not influenced, and the problem of deformation or cracking of a blank body of the silicon carbide ceramic biscuit in the process of removing the organic matter at high temperature is solved; the high-density green body can be fully reacted and sintered at a lower temperature to generate the high-density low-free silicon ceramic product, so that the uniform microstructure of the silicon carbide ceramic biscuit is ensured, and the strength and the structural stability of the ceramic material are greatly improved.

By adopting the technical scheme, the invention has the beneficial effects that:

1. the density of the reaction sintering silicon carbide ceramic material prepared by the preparation method of the silicon carbide ceramic material reaches 3.13-3.14g/cm3, reaches the international highest level at present, exceeds the density of ceramic produced by dry pressing and extrusion molding, and obtains a product with higher mechanical property;

2. compared with the reaction sintering silicon carbide ceramic material prepared by adopting the preparation method of the silicon carbide ceramic material, the free silicon content of the prepared reaction sintering silicon carbide ceramic material is only 4-5%, and the free silicon content of the reaction sintering silicon carbide product in the prior art is 8-10% or even more than 15%, the free silicon content is greatly reduced, and the application of the product is wider;

3. by adopting the preparation method of the silicon carbide ceramic material and adopting the slip casting process, a product with a complex special-shaped structure can be prepared, and the product has a uniform structure; the silicon carbide ceramic material with high strength, uniform structure, higher temperature of the use environment and better performance, which can meet the use requirement of the product without processing, can be obtained.

4. The reaction sintering silicon carbide ceramic material prepared by the preparation method of the silicon carbide ceramic material has higher use environment temperature which is increased from 1380 ℃ to 1760-1788 ℃.

5. The preparation method of the silicon carbide ceramic material has low production cost and is suitable for batch industrial production.

The specific implementation mode is as follows:

the invention is further illustrated below with reference to specific examples.