TitleAging and Performance Evaluation of Marine Antifouling Coatings
Publication TypeThesis
Year of Publication2015
AuthorsBunn, MD
UniversityOregon State University
CityCorvallis, Or.
Thesis TypeDissertation

Marine biofouling is a major problem in many industries. Shipping has been afflicted with reduced vessel speed and hindered maneuverability due to organisms attaching since the dawn of sailing. To date, the primary method developed to prevent fouling is the application of biocide laden coatings with various release mechanisms. Mass loss and coating degradation are the fundamental operational principles by which these coatings operate, which in turn limit their operational lifetime, requiring hull dry-docking to recoat for continued fouling prevention. With the advent of marine hydrokinetic technology as a possible contributor to the renewable energy landscape, there is a real need for longer life antifouling systems, since frequent dry-docking of these hulls is undesirable. Electrochemical antifouling systems with very long operational lifetimes may fulfill this need. These systems utilize electricity and the chloride found abundantly in seawater to sterilize surfaces, which replaces coating degradation as the operating principle of these systems. In support of system development and future design engineering, contributing to the body of knowledge in this new technology, test methods have been developed to determine threshold conditions under which fouling is effectively prevented in local conditions, accelerated aging tests of the electrochemical performance of the coatings were measured, and the surface concentration of electrochemically generated oxidizer species are determined. Using simple potentiostatic control circuits designed specifically for these experiments, it was determined that a threshold applied potential of 1.12 V vs. Ag/AgCl(seawater) reference electrodes is required for effective biofouling prevention. The electrochemical reaction kinetics have been modeled and verified in purpose built electrochemical reactors, yielding parameters measured as a function of galvanostatic aging. The vast majority of the experiments showed no statistically significant change in the operational parameters for the electrochemically active coatings, indicating that this biofouling prevention technology has the potential for very long operational lifetimes. Determining the effectiveness of oxidizer production in chloride bearing systems (3.5% w/v NaCl and synthetic seawater) shows that the trace bromide present in seawater does slightly enhance the system performance, and that the electrochemical work carried out in 3.5% NaCl therefore yields a lower bound estimate of the energy consumption of the process. Further, from the combined use of the flow cell and modelling we were able to determine that at the 1.12V threshold voltage determined, the concentration of oxidizer species in the transition layer at the surface of the chloride oxidation reactor is 1.5ppm, which is comparable with the ca. 0.5 - 1.5 ppm range of concentrations required to effectively sterilize swimming pool water.