Abstract

The spontaneous deposition of molybdenum over zinc in ammonia solutions with a rotatory electrode system has been studied. The effect of variables such as temperature and pH of the bath, disk rotational speed and concentration of molybdenum was analyzed. The results indicate a process with two stages, where stage 1 presents a higher rate than stage 2; the lower reaction rate in stage 2 was attributed to the nature of the film formed by a mixture of oxides and/or hydroxides of zinc and molybdenum. The analysis of the data indicates a mixed control, controlled by diffusion through the liquid film and chemical reaction; nevertheless, the results are not consistent with the diffusion of MoO4-2 because the rate of the process increases with the decrease in the concentration of molybdate, probably due to a phenomenon of proton diffusion towards the surface