Preparation Of High-performance Silicon Carbide Ceramic Materials Technology Research

In recent years, silicon carbide ceramic shows its unique advantages and gradually begins to attract the people attention as components suitable for high temperature structural materials in the harsh environment, such as high temperature-resistance, heat impact-resistance, corrupt- resistance.By pressureless sintering, not only complex-shape and large-dimension parts of silicon carbide can be prepared, but also industrialized production for silicon carbide products can be completed. Because of low-cost advantage, pressureless sintering becomes one key technology in course of practical production. Pressureless sintering includes solid phase sintering and liquid phase sintering, which were both studied in the thesis, but the solid phase sintering was researched in detail.High-quality silicon carbide powder was gotten through ultra-fine treatment, pickling, purification technology and spraying granulating. At the same time, high performance product has been received by optimizing composition and sintering techniques. The research contents and results are introduced as the following:The super-fine treatment of SiC powder was carried out by fluidized bed opposed jet mill, and the results showed that the effects of super-fine treatment increased with the increase of sorter frequency and crushing pressure. A better grinding effect was achieved by using a higher sorter frequency (40Hz), a higher crushing pressure (0.7MP.a) and few milling times (1).In these conditions, the compacts had relatively high density and micro structural homogeneity. The experimental results show that sintering temperature of the compact decreased and the surface microstructure, densification and mechanical properties of the sintered body can be ameliorated obviously by super-fine treatment.The purification treatment of SiC powder was completed by the method mixed acid.The purification method was perfect under the conditions with proportion 1:1 of picking solution (HF:HNO₃),0.1mol/L of concentration and 2h of pickling time. In the condition, we got high-fine silicon carbide powder.The spraying granulating of SiC powder was finished by pressure spraying drying equipment, which can improve the fluxion of SiC powder. Compared with no spraying, the loose density of the SiC granular powder increased by 30%-50% after spraying, and the angle of repose reduced by 10°—15°.The density of green body of silicon carbide was the highest, and the grain was more uniform. The experimentation data showed that the reasonable spraying granulating techniques is that solid phase content, binder content, outlet temperature and inlet temperature of gas were 70wt%, 0.5wt% , 320℃and 90℃respectively.The densification of SiC composite powders was accomplished by vacuum pressureless sintering. Under the ingredient of 2%C+1.0%B+97.0%SiC and the sintering temperature of 2150 for 2 hours, we prepared superior silicon carbide ceramic. By physical and chemical analysis, silicon carbide ceramic showed that the bending strength is 470Mpa, fracture toughness is 5.06 MPa.m^1/2 and the density is 3.12g/cm³.