Mathematical Modeling of the Formation of Calcareous Deposits on Cathodically Protected Steel in Seawater

A first principle mathematical model of the formation of calcareous deposits on a cathodically protected steel rotating disk electrode in seawater is presented. The model includes equations which transport phenomena, electrochemical reactions, precipitation reactions, and a homogeneous reaction involved in the formation of calcareous deposits on an electrode surface. Predicted concentration profiles show that a high concentration of OH− ions on the electrode surface leads to the formation of calcareous deposits. The calcareous deposits contain mostly , but the initial deposits are predicted to contain more than . The predicted calcareous deposits on the electrode surface reduce the active surface area available for the electrochemical reactions, which results in a decrease in the cathodic current density. The predicted current density as a function of time during the formation of deposits agrees qualitatively with experimental data.