Low-temperature preparation of porous SiC ceramics using phosphoric acid as a pore-forming agent and a binder

Porous SiC ceramics combine the properties of both SiC ceramics and porous materials. Herein, we design a facile method via pressureless sintering at relatively low temperatures for the synthesis of porous SiC ceramics. In the synthesis process, phosphoric acid was used as the sintering additive that reacted with SiO2 on the surface of SiC to form phosphates. The formed phosphates acted as a binder to connect the SiC particles. At a fixed temperature, the phosphates were partially decomposed and released a large amount of gas. This changed the pore structure of the ceramics and greatly improved their porosity. Finally, we obtained the porous SiC ceramics with high porosity and high strength. We investigate the effects of H3PO4 content on the phase composition, microstructure, porosity, mechanical properties and thermal expansion coefficient of the prepared porous SiC ceramics. It was shown that at the sintering temperature of 1200 degrees C, the highest porosity of the samples can reach 70.42% when the H3PO4 content is 25 wt%, and their bending strength reaches 36.11 MPa at room temperature when the H3PO4 content is 15 wt%. In addition, the porous SiC ceramics show good high-temperature stability with a bending strength of 42.05 MPa at 1000 degrees C and the thermal expansion coefficient of 3.966 x 10(-6)/degrees C.