Electrodeposition of nanocrystalline Co-W coatings from citrate electrolytes under conditions of controlled hydrodynamic: II. The electrodeposition rate and composition of the coatings

The influence of the ionic mass-transfer effects on the deposition rate, the current efficiency, and the composition and morphology of the coatings has been studied using a rotating cylindrical electrode in a citrate electrolyte containing CoSO 4 (0,2 mol/l) and Na 2 WO 4 (0.2 mol/l) (pH = 6.8) at the electrodeposition temperature of 60°C. It has been found that the decrease of the electrodeposition potential and the tungsten concentration in the coating with the current efficiency increase upon the Re number growth (Re ≥ 200) occur only under galvanostatic conditions. At the potentiostatic mode, similar of influence fails to be observed. It is shown that the estimated effects take place due to the electrodeposition through the nonstoichiometric surface coating layer with electronic conductivity, the composition components of which are in electrochemical equilibrium with the components of the solution at the film-solution boundary.