Luo, Jiunn-Shyong

The influence of impressed current density and
potential upon the nature of calcareous deposits formed . on
a cathodic steel surface has been investigated. The
experiments included potentiostatic, galvanostatic and
mixed mode combined galvanostatic and potentiostatic
techniques for affecting polarization. Specific attention
was focused upon the thickness, morphology and composition
of the deposits. A Mg 2+ depletion model has been developed
as a possible explanation for the nucleation and growth
behavior of calcareous deposits formed under combined mode
operation.

A procedure has been devised to characterize the adhesion of calcareous deposits formed upon steel in association with cathodic polarization in seawater. This involved bending the substrate in-situ and characterization of deposit debonding in terms of visual appearance, changes in the cathodic current density and the net charge transferred in association with film disruption. Specific attention has been focused upon the influence of exposure time, applied potential, flow rate, temperature, substrate surface finish and electrolyte type upon deposit adhesion. Presence of a Mg-rich, inner film as well as the impingement of CaCO3 particles enhanced the adhesion of calcareous deposits. Electrostatic forces, Van der Waals attraction, and chemical alteration of precipitates could be important factors contributing to deposit adhesion.