| SiC has the characteristics of high hardness, high strength, high thermal conductivity, excellent mechanical behavior under high temperature, acid resistance, alkali resistance and so on, which take more attention in preparing high performance ceramics.More and more researchers try to obtain greater high performance ceramics by surface modification and gradation.Compared with a-SiC, β-SiC has more excellent sintering activity, which make it sintered and densificated at lower temperature and easier process facility. However, recently many researches focus on a-SiC, which make the report about β-SiC less. So β-SiC is as the object of the study, by physical modification and gradation, trying to solve the problem ra ised by ultrafine powder. Powder with good flow, uniformity and good fo rmability was made which satisfied the requirement of dry pressing and slurry with high solid content and low viscosity satisfying the requirements of slip casting was fabricated.The study showed that the best surface modifier of the ultrafine β-SiC powder was PAA in the dry molding, of which the optimal dosage was 2wt%. The comprehensive liquidity index increased from 47 to 58.5 and the dispersion and liquidity was improved. The middle particle size D50 of the powder reduced from the original 0.92μm to 0.79μm, making the dispersibility improved. Combining modification with spray granulation, the optimum dosage of binder was 2wt%. Spray granulation made powder form a good sphericity and the fluidity index of the original powder increased from 47 to 93, which is better than Saint-Gobain granulation powder. After being molded, PAA modified β-SiC powder biscuit density was 1.78g/cm3. The spray granulation powder biscuit density was 1.88g/cm3. The spray granulated powder green density was 1.92g/cm3 whose binder is bakelite. Compared to the French Saint-Gobain SiC granulation powder whose compact density was 1.97 g/cm3, the flowability of spray granulation powsder prepared in this paper is obviously close to the international level.In slip casting, polycarboxylic acid was an optimum modifier for slurry. When it’s addition amount is 0.5 wt%, it can make the maximum solids content of the slurry increase to 58 wt% from 39wt% of the original powder. The middle particle size D50 was reduced to 0.71μm from 0.94μm. The powder modified by polycarboxylate achieve a maximum potential absolute value in p H=8. The value are increased from the original 37.9mv(-37.9mv, pH=8)to 49.9mv(-49.9mv, pH=8). The modification improved the suspension stability of the β-SiC ultrafine powders in suspension. After a settlement of 36 h, The sedimentation height of the original powder was 56 ml, and the sedimentation height of the modified powder was 96 ml increasing by 71%. Under the optimum condition in pH = 10, we use β-SiC ultrafine powder and alpha silicon carbide meal to make a gradation, we optimized the best gradation which is 50wt% +50wt%. Finally, we prepared a solid content of 60 vol.%, the viscosity of 960 mPa.s, high solid content low viscosity slurry which can meet the the requirements of slip casting. Compared with the slurry made by Saint-Gobain whose solid content was 53 vol.% and Henan Yi city whose solid content was 50 vol.%, the solid content of slurry made by us was higher. |
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