Oxidation behavior of silicon nitride fibers obtained from polycarbosilane fibers via electron beam irradiation curing

Abstract

Near-stoichiometric silicon nitride (Si₃N₄) fibers, which were successfully prepared from polycarbosilane fibers via electron beam irradiation curing, were heat-treated at elevated temperature for 2 h in the air atmosphere. The compositions and microstructures of silicon nitride fibers before and after heat treatment were investigated by XRD, XPS, NMR, SEM and TEM analyses. Tensile properties of the untreated and heat-treated fibers were also studied. The results show that the untreated fibers were mainly composed of amorphous silicon nitride and a few Si₂N₂O phases. During the heat treatment process, the oxidation of the fibers from silicon nitride to silicon dioxide initiated at 1100 °C. As the treatment temperature increased to 1400 °C, an oxidation layer with a thickness of ∼2 μm was formed on the fiber surface. Besides, when the treatment temperature was up to 1200 °C, the strength retention of the fibers still was 50.29%, which indicates that the fiber might possess a high serving life at a temperature lower than 1200 °C.