Oxidation Behavior of Amorphous Nano-Si3N4 Powders

The traditional method preparing Si3N4/Si2N2O composite ceramic is to sinter alpha-Si3N4 powder with additives at relatively high temperatures. But the intergranular phase transformed from the sintering additives can degrade the high-temperature mechanical behavior. Amorphous nano-Si3N4 is used to fabricate Si3N4/Si2N2O composite ceramic by its oxidation and nitridation without sintering additives at low temperatures. Thus, it is essential to study the oxidation behavior and mechanism of amorphous nano-Si3N4. Amorphous nano-Si3N4 powders were oxidized in different atmospheres, at varying temperatures and for various different length of time. The oxidation process and products was analyzed by means of XRD, TGA and FTIR. The results showed that amorphous nano-Si3N4 could be oxidized into SiO2 from 600 degrees C to 1300 degrees C. Below 1300 degrees C, the oxidation became serious as the temperature increased. Besides, the longer the oxidation time and the lager the ratio of O-2/N-2 partial pressure was, the deeper the oxidation level was. When the temperature was above 1300 degrees C, amorphous nano-Si3N4 was completely oxidized into SiO2.