Thermo-oxidation of hard carbon films with tungsten surface impurity

The removal of codeposited tritiated carbon films from the next generation of fusion reactors may involve baking in an O2 environment. Experimental results have indicated that thermo-oxidation can be effective in the removal of such films, however, wide variations have been observed in the oxidation rates of various types of carbon films. In the current experiments, we have investigated the role of metallic impurities by sputter-depositing tungsten onto hard a-C:D films, and exposing them to O2 gas at 623 K. It was found that rather than catalysing the oxidation of the hydrogenated carbon film, the W deposit tended to inhibit the film removal at this temperature. This suggests that film structure is the predominant factor determining the oxidation rate of tokamak codeposits.