Corrosion Protection of Steel by Calcareous Electrodeposition in Seawater (Part 1)

摘要

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 cathodic 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 zeta-potentials of colloidal particles of CaCO_3 and Mg(OH)_2suspended in seawater were measured as a function of pH. With increasing pH, the amount of formed solids increased, hut its zeta-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.