Gas/solid reaction during sintering of Si3N4 ceramics in an air furnace

Solid/gas reaction during sintering of Si3N4 ceramics in an air atmosphere was investigated. The Si3N4 specimens were prepared from β-powder with MgO and Al2O3 5 wt% each as sintering aids. The oxygen content of the mixtures after milling increased with increasing milling time. The SiO2 content was found to cause more significant mass loss of the sintered specimens than the sintering temperature. There was also a gradient of the oxygen partial pressure ( P O 2 ) in the crucible during sintering resulting in the formation of silicon oxynitride (Si2N2O) on the surfaces of Si3N4 specimens in different quantities. The mass loss reaction, amount of mass loss as a function of soaking time and sintering temperature, mass loss difference between the top and the bottom of specimens and the formation of Si2N2O are discussed.