Abstract
Isothermal oxidation experiments were carried out with TiSi 2 and MoSi 2 in air between 1000 and 1400°C. The oxidation rate of TiSi 2 can be approximated at 1100°C by a linear rate law and at 1200 and 1300°C by a parabolic one. The scale formed at 1100°C consists of an outer layer of TiO 2 and an inner layer of a mixture of SiO 2 and TiO 2. Increasing temperature increases the SiO 2 content in the outer layer and at T>1200° C a SiO 2 scale with precipitates of Ti-Si oxides is found. TiSi 2 possesses optimum oxidation resistance between 1200 and 1300°C. The oxidation of MoSi 2 leads to the formation of the volatile oxide MoO 3 which evaporates at T>1200° C. This process favours the formation of a rather pure and very protective SiO 2 layer on the surface. Obviously the evaporation occurs after solid-state diffusion through the SiO 2 at the SiO 2/gas interface.
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