Thermal stability of a silicon nitride based fibre

摘要

The thermal stability of amorphous silicon nitride based fibers prepared according to a vapor-solid process was studied in argon, nitrogen and oxygen atmospheres (100kPa). The fibers are stable in nitrogen up to 1450°C (10h) in terms ofcomposition, structure and mechanical behavior owing to their high processing temperature (1450°C) and the nitrogen pressure preventing decomposition. A superficial crystallisation of Si{sub}3N{sub}4 is only observed at 1500°C inducing a moderate decrease of strength. In argon, decomposition starts at 1400°C yielding gaseous species (SiO and N{sub}2), crystalline Si{sub}3N{sub}4 and free silicon beyond 1400°C and induces in a catastrophic drop of strength. Annealing in oxygen results in a growth of aprotective SiO{sub}2 scale, amorphous or partially crystalline at 1400°C.