Preparation of phosphate bonded silicon nitride porous ceramics in air

Abstract

Silicon nitride porous ceramics were prepared using a new method by combining in-situ forming and low-temperature pressureless sintering in air, in which the Al(H2PO4)3 was used as the binder. The effects of the binder and curing agent content, as well as the temperature to the quality of the green body and setting time were investigated to establish the proper parameters of setting. The green body was sintered at low temperature (1000 − 1300 ˚C) in air. Then we discussed the phase transition during the sintering process and the effects of different sintering temperatures on the microstructure. The results showed that at 50 ˚C, a green body with nearly zero shrinkage and high strength was obtained after 30 minutes of the slurry casted. At 1300 ˚C there was sufficient C-AlPO4 binder phase transformed from Al (H2PO4)3 to bond with the Si3N4 grains, leading to a good adhesion between them. Porous Si3N4 ceramics with a porosity of 46 − 48%, compressive strength of 30 − 50 MPa were ultimately obtained.