| 摘要 |
Method of manufacturing an object of silicon nitride by isostatic pressing of a preformed body of silicon nitride powder with a pressure medium at a temperature required for sintering the silicon nitride, the preformed body then being subjected to a degassing before the isostatic pressing, characterized in that on the preformed powder body there are applied an inner porous layer of a first material and outside this an outer porous layer of a second material, the inner porous layer, possibly in cooperation with the second material, being transformable into a layer, impermeable for the pressure medium, at a temperature below the sintering temperature for the silicon nitride and the outer porous layer being transformable into a layer, impermeable for the pressure medium, at a temperature which is lower than that for the inner porous layer, whereafter the preformed body is first subjected to a degassing and to a heating to a temperature which is required for the formation of a layer, impermeable for the pressure medium of the outer porous layer but which maintains the inner porous layer porous, and then to a heating to a temperature which is required for the formation of a layer, impermeable for the pressure medium, of the inner porous layer while maintaining a pressure outside said layers which is greater than the gas pressure inside these layers, the isostatic pressing of the preformed product then being carried out. |
