Method for producing high density sintered silicon nitride (Si3N4)

摘要

The specification describes a method for producing high density sintered silicon nitride(Si3N4) having a relative density of at least 98%. In a first step, silicon nitride powder is compacted into a desired shape. It is then presintered in a second step, generally, under normal pressure to obtain a presintered body having a relative density of at least 92%. In a third step, the presintered body is subjected to a hot isostatic pressing(HIP) in an inert gas atmosphere of 1500-2100 DEG C. and of nitrogen gas partial pressure of at least 500 atm. Since the presintering does not require any capsule, it is possible to produce high density sintered Si3N4 of complex configurations. As a sintering aid, Y2O3-Al2O3-MgO system sintering aid is particularly effective. To improve the strength of sintered Si3N4, it is effective to add a heat treatment step after the HIP and maintain the temperature of the sintered Si3N4, above 500 DEG C. for a while. Between the second and third steps, the temperature of the presintered body is preferably maintained above 500 DEG C. These temperature controls are effective not only to improve the strength of sintered Si3N4 but also to save the thermal energy and to shorten the production cycle.