Investigation of electrochemical calcareous scaling - Nuclei counting and morphology

The nucleation/growth process of electrochemically deposited calcium carbon ate was investigated by means of image analysis from SEM observations. Firs t, a model based on a diffusion-controlled process, where the area of the n uclei increases proportionally with time, is proposed. An estimation of the geometric quantities, which can be evaluated by statistical counting and i mage analysis, is given. Namely, the number of nuclei and the area covered by the nuclei are evaluated. Limiting values for instantaneous and progress ive nucleation is given. The comparison of these quantities with experiment al data allows the number of active sites, the nucleation rate and the rate constant of the nucleus size to be estimated. Various experimental conditi ons, which control the nucleation/growth rate were investigated: surface pr etreatment of the electrode surface, concentration of the dissolved oxygen, concentration in calcium carbonate, and electrolyte flow rate. For each se t of experimental conditions, the morphology of the deposited scale was obs erved. A neat correlation between the crystal habit and the nucleation rate is demonstrated. (C) 2001 Elsevier Science B.V. Ah rights reserved.