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Filtering characteristics of porous silicon carbide candle filters with high surface area were investigated. Cogwheel type silicon carbide ceramic filters consisting of a highly porous support and a filtration layer were fabricated by extrusion forming. Tube typed ceramic candle filters were also fabricated for compari son. The cogwheel type filter showed much less pressure drops than the tube typed one according to an in crease of flow rate or continuous mass loading. While the cogwheel shape did not greatly affect the separa tion efficiency, it clearly affected the cleaning efficiency. Additionally, the cogwheel type filter showed better cleaning characteristics. It is suggested that the cogwheel shape is beneficial to decrease pressure drop and thus improves the operating performance.

Silicon nitride ceramics were prepared by new nitrided pressureless sintering (NPS) process in this study. The microstructures, strengths and thermal properties of the NPS silicon nitride ceramics containing three types of Al2O3 and Y2O3 sintering additives were investigated. Additionally, we have investigated the effect of silicon metal contents changing with 0, 5, 10, 15 and 20 wt% in each composition. The silicon nitride was successfully densified using NPS process, particularly at the starting composition of 5 wt.% Al2O3, 5 wt.% Y2O3, and 5 wt.% Si addition. The maximum flexural strengths and relative densities of these specimens were 500 MPa and 98%, respectively. The flexural strength of sintered specimens after the thermal shock test between 30oC and 1300oC for 20,000 cycles was maintained with the original laboratory strength of 500MPa by low thermal expansion coefficient, 2.9 × 10-6/oC, and high thermal conductivity, 28 W/m⋅oC.