Nucleation-growth process of scale electrodeposition—Influence of the mass transport

An impinging jet cell was used to investigate the influence of the convection on the kinetics of scale deposition in a carbonically pure water. CaCO3 crystallized due to the increase of the local pH obtained by the reduction of dissolved oxygen. The working electrode was the transparent electrode of an electrochemical quartz crystal microbalance which records versus time the mass of the deposit and the microscope image of the electrode/solution interface. The chronoelectrogravimetric curves showed that the rate of the CaCO3 deposition increased with the convection until a limiting value of the Reynolds number Re while the current of oxygen reduction continues to increase following a Re1/2 law. This result was confirmed by the measurement of the growth rate of the two CaCO3 crystal forms obtained by using the optical method. On the contrary, the nucleation rate was not influenced by the flow rate. It was shown that the kinetics of scale deposition was directly linked to the interfacial pH; a theoretical approach gives the interfacial pH with respect to the Re number.