HYDROGEN INTERACTION WITH CVD TITANIUM CARBIDE COATINGS ON METALS - ASTUDY BY A VOLUME MODULATION TECHNIQUE

The volume-modulated absorption and desorption of hydrogen by a thin T iC coating has been studied experimentally. The temperature range was 883 K - 1083 K, and the pressure interval was 4 Pa - 74 Pa. The coatin g, deposited on the high temperature molybdenum alloy TZM, had a thick ness of 8 mum and was obtained by Chemical Vapor Deposition (CVD). The pressure response lagged behind the cyclic volume modulation and vari ed with the oscillation frequency. This frequency dependence was analy tically modelled taking into account atomic diffusion in the coating a nd surface reactions. Dynamic equilibrium was assumed to be satisfied at the substrate/coating interface and in the substrate. Data fitting gave a high Sieverts' constant, a low diffusivity and low surface rate constants for hydrogen in the coating, when compared to the substrate values.