Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces, Part III

�Spacecraft potable water systems require a biocidal agent that effectively provides both immediate and residual disinfection over long periods of time. Ionic silver (Ag+) is a leading candidate for this application, but suffers from rapid concentration loss due to interactions with the metal storage containers and tubing. In order to maintain biocidal efficacy in systems with long periods of dormancy and to reduce the required rate of Ag+ injection, it is necessary to develop alternative materials and coatings for certified metal alloys that significantly reduce the Ag+ loss.� We have previously reported that parylene-C coatings on 316L stainless steel allow for near-total reduction in Ag+ loss rates at biocidal concentrations, and offer apparent long-term adhesion, free of visible blisters, in static soak tests after one year of cumulative immersion. In Part III of this series, we continue our work, broadening the range of substrates coated, with 25 ?m parylene-C films on Inconel 718 and Ti-6Al-4V, and on 316L stainless steel with TIG welds and various surface treatments, in order to investigate the range of coating applicability. In addition, we began investigations of: the effect of coating thickness on Ag+ loss mitigation performance, the adhesion performance of parylene-C at 90 �C, the film resilience upon dis/reassembly with several different types of tube fittings, the performance of surface structuring on 316L for mechanical anchoring of parylene-AF4, the contribution of small area defects to Ag+ loss, and the leaching of organics from parylene films.