Highly porous LAS-SiC ceramic with near-zero thermal expansion prepared via aqueous gel-casting combined with adding pore-forming agents

Abstract

The main problem during preparing high porosity ceramics via aqueous gel-casting is the large drying shrinkage of green bodies. In this work, carbon fibers with high aspect ratio were introduced into aqueous gel-casting processes, which significantly inhibited the drying shrinkage of green bodies by overlapping fibers. At the same time, exhaustible carbon fibers sintered in air also act as sacrificial templates to further improve the porosity. Through the above method, porous LAS/SiC ceramics with high porosity and near-zero expansion were prepared. Drying shrinkage of the green bodies was reduced from 25.2% to 5.7% with the increase of fibers. The porosity of the obtained LAS/SiC ceramic is as high as 76.2%. When the fibers content is 20 vol% and LAS to SiC volume ratio is 6: 4, the composite has maximum value of compression and bending strength (18.2 and 14.0 MPa) and near-zero CTE (0.9 × 10−6 /K).