Reclamation of Abrasive Slurry to Obtain SiC Ceramic Material

In the period of silicon and silicon carbide wafer slicing process, the abrasive oil, silicon carbide (SiC), silicon and trace elements e.g., iron, zinc, copper, and nickel is generated as an oily mixture of insoluble matter. The SiC is the main component (>70%) in the abrasive slurry and the extraction of SiC from the slurry can eliminate the risk of illegal waste disposal and reduce the cost for the enterprises. In this study, a chemical separation process is applied to remove silicon particles and SiC can be extracted from the slurry mixtures. The X-ray diffraction analysis revealed that recycled material is moissanite with two crystalline polymorphs. The 3C and 6H X-ray powder pattern is observed and the cubic and hexagonal crystalline structure is revealed. The particle size distribution analysis showed that median value of purified SiC powder material is 9.8 μm.

Crack Evolution and Oxidation Failure Mechanism of a SiC-Ceramic Coating Reactively Sintered on Carbon/Carbon Composites

A SiC ceramic coating was prepared on carbon/carbon composites by pack cementation. The phase composition and microstructure of the coated specimens were characterized using X-ray diffraction instrument and scanning electron microscope. The results showed that the mass-loss percentage of the coated specimen was 9.5% after being oxidized for 20 h. The oxidation failure of the SiC ceramic coating at 1773 K was analysed by non-destructive X-ray computed tomography. The effective self-healing of cracks with widths below 12.7 μm introduced during the coating preparation process and generated while the specimens cooled down from the high oxidation temperature prevented the oxidation of carbon/carbon composites. X-ray computed tomography was used to obtain three-dimensional images revealing internal damage caused by spallation and open holes on the coating. Stress induced by heating and cooling caused the formation, growth and coalescence of cracks, which in turn led to exfoliation of the coating and subsequent failure of oxidation protection.