Electrochemical formation of ternary oxide films - an EQCM approach to galvanostatic deposition of alkali earth metal tungstates and molybdates

Galvanostatic deposition of barium and strontium tuagstates and molybdates on tungsten and molybdenum electrodes in alkaline media (pH congruent to 12 ) was studied by means of Electrochemical Quartz Crystal Microbalance (EQCM ). Formation of surface ternary oxide layers proceeds via dissolution and p recipitation mechanism when the initial electrochemical formation of tungst en/molybdenum oxides is followed by the oxide dissolution and tungstate/mol ybdate precipitation. Mass change signals were used to comprehend different regimes of the tungstate/molybdate deposition with respect to deposition e fficiency, While the formation of molybdates is restricted by dissolution p rocess, the tungstates formation is limited by transport of film forming ca tions to the electrode. (C) 1999 Elsevier Science Ltd. All rights reserved.