ENHANCING THE PERFORMANCE OF PULSED CURRENT APPLIED COATINGS FOR CORROSION PROTECTION

Abstract

Khoi Tu, Doctor of Philosophy.Thesis "Enhancing the Performance of Pulsed Current Applied Coatings for Corrosion Protection", The University of Manchester, 2010.Accelerated Low Water Corrosion (ALWC) is a particularly severe form of microbiologically induced, aggressive and localised form of corrosion. It is most commonly found just above the Lowest Astronomical Tide. The average corrosion rates are typically very high, about 1.0 mm/wetted side/year, so it should be prevented to ensure the lifetime of steel structures in seawater. In this project, in order to deal with ALWC, a pulsed current applied coating, calcareous film, is studied to form after a sequence of electrochemical treatments to clean the corrosion products and kill bacteria. In sea water, calcareous films (deposits of CaCO3 and Mg(OH)2) are produced on steel structures that are cathodically protected. They have two functions: reducing the current demand from the CP system and acting as a protective coating. When deposition conditions are well controlled, they could provide long-term corrosion protection for steel in sea water. The project aims to understand the fundamentals and mechanism of calcareous deposition under a pulsed current with high current density in a short period. The objectives of the project are to understand calcareous scale growth in a short term under pulsed current and to study the effect of deposition conditions on the properties of the calcareous film. The relationship between deposition time and properties of the deposits has been investigated with different conditions of pulsed current to understand the mechanism of deposition and to identify optimal conditions for deposition. Limiting current densities, potentials and deposition times to prevent loss of deposit and blister formation have also been addressed. In order to show the advantages of pulsed current to control the properties of the deposits, a comparison with properties of the deposits forming under DC is presented. Endurance tests have been performed, using EIS to estimate the long-term performance of the deposits and the mechanism of loss of protection.

Date of Award	31 Dec 2010
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Cottis (Supervisor)