ELECTROSURFACE TRANSFER IN THE CAWO4-WO3 SYSTEM

A novel solid-phase phenomenon is studied, namely, transfer of WO3 ont o inner surface of the CaWO4 ceramics induced by an electric field. Th e phenomenon is shown to be intrinsic to any CaWO4 ceramics notwithsta nding the technique of its production. The mass of WO3 transferred and the front penetration depth are found to be proportional to the charg e passed. The process rate depends linearly on the porosity of the cer amics, which determines the magnitude of cross-section for the surface charge and mass transfer. The transfer is shown to be an activation p rocess with an activation energy of 110 +/- 4 W mol(-1). In order to c haracterize the activity of the substrates and the current efficiency of the process, a carry-away coefficient is introduced, which is defin ed as the number of equivalents of WO3 transported by a faraday of ele ctricity. The surface compositions of the initial ceramics and the CaW O4-WO3 composite produced are shown to be close to [W]/[Ca] = 2.