Fabrication of continuously porous SiC–Si3N4 composite using SiC powder by extrusion process

Large amounts of waste SiC sludge containing small amounts of Si and organic lubricant were produced during the wire cutting process of single crystal silicon ingots. Waste SiC sludge was purified by washing it with organic solvent and purified SiC powder was used to fabricate the continuously porous SiC–Si₃N₄ composites, using an extrusion process, in which carbon, 6 wt% Y₂O₃ + 2 wt% Al₂O₃ and ethylene vinyl acetate were added as a pore-forming agent, sintering additives and binder, respectively. In the burning-out process, the binder and carbon were fully removed and continuously porous SiC–Si₃N₄ composites were successfully fabricated. The green bodies containing waste SiC, Si powder and sintering additives were nitrided at 1400 °C in a flowing N₂ + 10% H₂ gas mixture. The continuously porous composites contained SiC, α-Si₃N₄, β-Si₃N₄ and few Fe phases. The pore size of the second passed and third passed SiC–Si₃N₄ composites was 260 μm and 35 μm in diameter, respectively. The values of bending strength and hardness in the second passed and third passed samples were 62.97 MPa, 388 Hv and 77.82 MPa, 423 Hv, respectively.