CHARACTERIZING MATERIALS FOR WALLS OF FUSION-REACTORS

Experiments in which a permeation flux through a membrane specimen is modulated have been shown to provide valuable insight into permeation processes. In particular, surface and bulk effects can be separately i dentified from the experimental data. This approach requires an analyt ical model of the process in terms of absorption steps and bulk transp ort. A basic model has been developed to account for permeation throug h a binary membrane comprising a coating and a substrate. The interfac e reaction kinetics including trapping are taken into account in terms of rate constants. It is shown that given adequate knowledge of the s ubstrate then the permeation parameters of the coating can be deduced. This greatly extends the range of materials which can be examined, pa rticularly those materials which cannot be obtained as foils such as c eramics. Some strategies for first wall reactor materials combine a lo w diffusivity ceramic coating on a mechanical substrate; such binary ( and even more complex) structures can now be assessed through the modu lated permeation method, taking full account of the interface. As an e xample, recent measurements on a titanium carbide-molybdenum alloy sys tem (TiC-TZM) are discussed.