Effect of sulphuric acid and copper sulphate concentrations on the morphology of silver deposit in the cementation process

Abstract

The silver ion cementation on copper was investigated in the presence or absence of oxygen in solutions containing 1.85 × 10 −4 M Ag + at 25 °C. The influence of sulphuric acid and copper sulphate concentration (0.005–0.5 M) on the silver cement morphology was studied in details and results were linked with the previously determined kinetics data of the process. The morphology of silver deposit was found to be independent of the presence of oxygen in the system as well as the sulphuric acid concentration. Contrary, the concentration of copper sulphate strongly influenced the morphology of silver deposit. At the beginning of the cementation process silver covers uniformly the copper surface. Afterwards, a growth of dendrites is initiated on preferential parts of the surface. The growing dendrite behaves as cathodic sites, with relatively huge surface area and promotes the creation of anodic sites in a close neighbourhood. Finally, the anodic site encloses the dendrite island and develops its area inward the copper material. Copper ions at low concentration modified slightly silver dendrites but the increase in concentration up to 0.5 M Cu 2+ leads to completely disappearance of dendrites from the surface. The lack of dendrites on the surface is a result of the competitive process that consumes additional silver ions, occurring in the bulk of the solution. The morphology of silver deposit cemented in the deoxygenated solution containing 0.5 M H 2SO 4 + 0.5 M CuSO 4 depends strongly on the mechanism of the process.