Synthesis and oxidation behaviour of polymer-derived Si-Al-C-N and SiCN amorphous ceramics

In this paper we present the results on the synthesis of polymer derived SiCN and SiAlCN and their oxidation behavior. The oxidation kinetics are obtained by measuring the thickness of the oxide scale as a function of annealing time. The results revealed that the oxidation of SiCN exhibit parabolic behavior, and both, the rate constant and activation energy of SiCN are close to those for silicon, indicating that the oxidation mechanism of SiCN is by oxygen diffusion through silicon dioxide layer. While the oxidation of SiAlCN follows parabolic behavior at earlier stage, the increase in the thickness of the oxide layer stops after a certain time. The X-ray elemental mapping indicated that the oxide layer of SiAlCN had a uniform distribution of Si, Al and O. The mechanism of the high oxidation resistance exhibited by SiAlCN is not fully clear yet, the possible explanation being the low diffusion rate of oxygen through the Si-Al-O network. The high oxidation resistance of SiAlCN material suggests that it is a promising material for many high temperature applications, e.g. environmental barrier coatings and matrixes for composites.