| 摘要 |
PURPOSE:To obtain the title high-density silicon nitride sintered body wherein the pinholes deteriorating the high-temp. characteristic are not left even when the sintered body is secondarily calcined at a high gas pressure by preforming silicon nitride and a sintering assistant, and secondarily calcining the primarily calcined presintered body at specified temp. and pressure. CONSTITUTION:The silicon nitride powder and sintering assistant are preformed into a specified shape. The preform is primarily calcined in a gaseous nitrogen atmosphere, and then secondarily calcined in a compressed inert gas atmosphere to produce a densified silicon nitride sintered body. The secondary calcination is carried out by the following schedule. (1) The preform is heated to the temp. at which a liq. phase is formed in the sintered body at <=300atm, and (2) heated at a temp. higher than the temp. at which the liq. phase is formed while gradually increasing the pressure from 300atm to a specified pressure. In this production process, the condition that an open cell is not formed in the primarily sintered body must be fulfilled. When the open cell is formed, pinholes are left remaining even by the above-mentioned schedule. |
