Nucleation and growth of calcium carbonate by an electrochemical scaling process

Calcium carbonate scale was electrochemically deposited from carbonically pure hard waters on gold electrodes of an electrochemical quartz crystal microbalance. Various data concerning the rate of the scaling process were deduced from the chronoelectrogravimetric responses. The nucleation rate of CaCO3 crystals and the surface coverage were evaluated from SEM image analysis. The effects of a surface pretreatment, the oxygen concentration and the degree of hardness of the water were investigated. Transmission electron microscopy was used to identify the crystal structure of small nuclei. Calcite, aragonite or vaterite crystal forms were obtained depending on experimental conditions. It was shown that at room temperature calcite was predominantly formed for conditions which were favorable to a fast nucleation rate whereas the vaterite form is systematically obtained for experimental conditions leading to a slow nucleation rate. The temperature increase favored the formation of either aragonite needles or vaterite crystallites with a different morphology. (C) 1999 Published by Elsevier Science B.V. All rights reserved.