SOLID-STATE SYNTHESIS AND CHARACTERIZATION OF THE TERNARY PHASE TI3SIC2

Ti3SiC2 is the only true ternary compound in the Ti-Si-C system. It seems to exhibit promising thermal and mechanical behaviour. With the exception of its layered crystal structure, most of its properties are unknown, owing to the great difficulty of synthesis. A new procedure of solid-state synthesis with several steps is proposed, which results in Ti3SiC2 with less than 5 at% of TiC. Ti3SiC2 is Stable at least up to 1300-degrees-C. Beyond this temperature, it can decompose with formation of non-stoichiometric titanium carbide and gaseous silicon, with kinetics highly dependent on the nature of the surroundings. As an example, graphite can initiate this process by reacting with silicon, while alumina does not favour the decomposition which remains very slow. The oxidation of Ti3SiC2 under flowing oxygen starts at 400-degrees-C with formation of anatase-type TiO2 film, as studied by TGA, XRD, SEM and AES. Between 650 and 850-degrees-C both rutile and anatase are formed, rapidly becoming protecting films and giving rise to slow formation of SiO2 and more TiO2. The oxidation kinetics is slower than for TiC, owing to a protecting effect of silica. By increasing the temperature, both oxidation processes (i.e. direct reaction and diffusion through oxide layers) are activated and an almost total oxidation is achieved between 1050 and 1250-degrees-C resulting in titania (rutile) and silica (cristobalite).