Development of CaO coatings by thermal and chemical vapor deposition

We conducted several experiments to test electrically insulating CaO coatings on a V–4Cr–4Ti alloy for application in the Li environment of liquid metal blankets in fusion reactors. Two processes that involve double Ca deposition/oxidation steps were developed to successfully coat V–4Cr–4Ti alloy samples with stable CaO. During the study, we examined several geometrical arrangements, using tabs and/or rod specimens. After Ca deposition from the vapor phase, the specimens were oxidized in an Ar–10 vppm O2 environment at ≈600 °C to convert the deposited metal into oxide, whereupon they exhibited insulating characteristics. Several coated specimens were then exposed to Li–2.8 at.%Ca at 500–700 °C to determine chemical compatibility and mechanical integrity. Depth profile analysis of the coatings was conducted to evaluate the compositional changes in the coatings and to assess the transport, if any, of substrate and coating constituents. Microstructural characteristics of the coatings were evaluated by scanning electron microscopy. The preliminary results indicate that CaO is a viable coating for V–Li advanced blankets.