Tungstate-Borate Ionic Liquids: Structure, Electrochemical Behavior and Electrodeposition of Tungsten Coatings

Abstract

To study the ionic composition of Na2WO4-B2O3 melts, EMF measurements of electrochemical circuits containing platinum-oxygen indicator and tungsten electrodes relative electrodes versus platinum-oxygen reference electrodes were performed. Experimental dependences of the potential of platinum-oxygen and tungsten electrodes on the B2O3 concentration are explained by the formation of ditungstate ions W2O7 2- in the melt. Studies of the electroreduction of ditungstate ions indicate that the electrode process is controlled by the electroactive particles diffusion to the electrode. At the same time, the formation rate of these electroactive particles does not limit the electrode process. Charge transfer occurs reversibly, which is confirmed by the electrochemical measurements results in stationary and non-stationary polarization modes. Thus, in Na2WO4-B2O3 melts, realization of multi-electron equilibrium and electroreduction of tungsten from its dimeric anionic form is possible. The obtained results served as the basis for the development of tungsten coatings electrodeposition processes. Corrosion potentials of electrodes made of substrate materials (copper, nickel, steel) were measured. The influence of B2O3 concentration, temperature, cathodic current density and duration of electrolysis on the composition and structure of cathodic deposits was studied, and the optimal parameters of the reverse deposition mode were found.