Abstract
From a colloid-chemical viewpoint, an attempt was made to elucidate the mechanism of calcareous deposition on steel plates cathodically protected in seawater. When the catholic current density was increased with keeping the total electric quantity passed constant, it was found that the amounts of both calcium carbonate and magnesium hydroxide deposited on the plate took maximum values at respective current densities, and thereafter gradually approached to 0. To account for this phenomenon, the ζ-potentials of colloidal particles of CaCO3 and Mg(OH)2 suspended in seawater were measured as a function of pH. With increasing pH, the amount of formed solids increased, but its ζ-potential decreased. The conclusion was drawn that these two mutually conflicting factors are closely related to the occurrence of the maxima in the above calcareous deposit amount vs. current density curve.
