Synthesis under NH3 and thermal behaviour of SiCNAlO polymer-derived nanopowders

The influence of a reactive atmosphere (Ar/NH3) on the composition of SiCNAlO powders was studied at 1400 °C, with a total gas flow rate of 3 L min−1 and an ammonia content of 0-25 vol.%. Powders with a large range of carbon amount (3-23 wt.%) were synthesized at 1400 °C in a Ar/NH3 atmosphere. Elemental analyses showed that in reducing conditions, the presence of reacting species in the heating zone implied the nitridation of the system, with amounts of nitrogen included in the range 35-47 wt.%. The thermal stability of the different batches was then tested by TGA experiments, up to 1550 °C in a N2/He mixture. For C/N ≥ 0.8, the powder thermal stability is limited and the main crystalline phase is β-SiC. On the contrary, for C/N < 0.8, the powder mass loss is negligible and both α- and β-Si3N4 are detected after the heat-treatment. The sinterability of such powders was evaluated by preliminary tests, a higher shrinkage of the pellets, containing aluminum and oxygen elements, was evidenced.