A covalent micro/nano-composite resistant to high-temperature oxidation

Abstract

ADVANCED ceramic materials that can withstand high temperatures (over 1,500 °C) without degradation or oxidation are needed for applications such as structural parts for motor engines, gas turbines, catalytic heat exchangers and combustion systems^1,2. Hard, oxidation-resistant ceramic composites and coatings are also in demand for use on aircraft and spacecraft. Silicon nitride (Si₃N₄) and silicon nitride/carbide (Si₃N₄ /SiC) composites are good candidates for such high-temperature applications^2,3. Commercial Si₃N₄ parts can be used in oxidizing environments up to 1,200–1,300 °C (ref. 4), but are oxidized at still higher temperatures. Here we describe the synthesis of a covalent ceramic composite which is resistant to oxidation at temperatures up to 1,600 °C. The composite is formed from an amorphous silicon carbonitride, which crystallizes at high temperature into a composite of α-Si₃N₄ microcrystals and α-SiC nanocrystals. The oxidation resistance stems from the formation of a passivating surface layer of SiO₂ a few micrometres thick.