Effect of Pore-forming Agent on Porous Reaction-bonded Silicon Nitride Ceramics

Porous reaction-bonded silicon nitride(RBSN) ceramics were fabricated by using potassium chloride(KCl) and urea(CO(NH2)(2)) as pore-forming agent, respectively. Green bodies with 30% in mass KCl were subjected to presinter in Ar atmosphere at 1200 degrees C and then reaction-sintered. The properties of porous silicon nitride ceramics adding different pore-forming agent were explored. And the influence of presintering on apparent porosity, bulk density and bending strength of porous ceramics were investigated. The results indicated that the porosity of Si3N4 ceramics showed a nearly linear increase as the content of KCl increasing, but urea was not. And after presintering, the porosity had small decrease, but bending strength increased obviously. Low bulk density with about 58.6% porosity Si3N4 ceramic was prepared by adding 50wt% KCl, and the main phase composition of porous ceramic was alpha-Si3N4. Lots of needle-liked alpha-Si3N4, especially in the pores, could be observed.