Oxidation behavior of Si3N4 fibers derived from polycarbosilane

Si3N4 fibers prepared from polycarbosliane are exposed in dry and wet air respectively from 800 to 1300 degrees C for up to 1 h. After dry air oxidation, an uniform SiO2 coating doped with nitrogen is formed on fiber surface. However, the coating obtained in wet air is much thicker with more complex microstructure containing sub layers of N-doped SiO2, near stoichiometric Si3N4 and graphite-like nanoribbons. Activation energy for oxidation in wet and dry air is determined as 108 and 152 kJ mol(-1), respectively. Both of the values are lower than the known Si3N4 materials with E-a of 259-485 kJ mol(-1).