Some problems of the corrosion and protection of materials in liquid metal MHD generators

Because of its high electroconductivity, copper is the most promising material for the electrodes in a projected molten lead MHD generator. However, copper has a low stability in molten lead which necessitates that it be protected by a material which has both high stability and acceptable electroconductivity. Tungsten seems to satisfy these requirements but information on its solubility in molten lead is sparse. Experiments are described which test the influence of molten lead on a tungsten coating deposited by chemical vapour deposition on a copper substrate. It is established that, provided local corrosion is low, the tungsten coating is quite stable in liquid lead turbulent flow. More prolonged tests are necessary to estimate the non-susceptibility of the coatings to local corrosion damage under these conditions. An analysis of the equilibrium states in the Pb-H2O and W-H2O systems is also reported since water vapour is used as a working fluid in the generator and interactions between it and liquid lead and tungsten are a necessary part of the investigation. (UK)