China's Refractories

Abstract: A reaction bonding technique and a method of layer coating were developed to fabricate porous SiC. The green body was prepared using 250.0 μm SiC particles as the raw material, fine α-Al2O3 and SiC powders with mass ratio of 2.5:1 as sintering additives, 65.2 μm graphite as the pore-forming agent and polyvinyl alcohol (PVA) as the binder. The micro powders were coated on the surface of coarse SiC particles. After sintering, fine SiC particles were oxidized to silica (SiO2) then transforming into cristobalite, which finally reacted with α-Al2O3 to produce mullite (3Al2O3·2SiO2). The results show that SiC particles are bonded by the mullite and oxidation-derived SiO2. The apparent porosity of the specimens decreases from 31.3% to 20.5% with the amount of micro powders increasing from 5 mass% to 20 mass%. The bending strength increases at the first stage and then decreases with the increase of fine powders, and the specimen with 10 mass% of fine powders shows relatively high bending strength of 23.5 MPa.

Key words: porous silicon carbide, powders, reaction bonding, porosity, bending strength