Very High Pressure Hot Pressing of Oxidized Silicon Nitride Powders without Additives

Silicon nitride powders operated by oxidation in air at 1200°C for 70 to 210min, in which the oxygen content was from 2.8 to 8.9 wt%, were sintered without additives under the pressure of 3.0GPa. The influence of oxygen on the characteristics of the sintered bodies was studied. Various amounts of α phase remained in sintered bodies depending on the oxygen content in the operated powders. Vickers microhardness of the sintered body prepared from the powder containing 2.8 wt% oxygen was higher than that of the sintered body from the starting powder at elevated temperature up to 1300°C.