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



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51st International Conference on Environmental Systems


Ionic silver (Ag+) biocide is a leading candidate to provide residual microbial control in spacecraft potable water systems, but suffers from rapid concentration loss due to interactions with the metallic containers and tubing. One approach to mitigate this is the coating of metal surfaces with an inert barrier film. In previous reports, we have described our investigations addressing Ag+ loss mitigation and adhesion performance of parylene barrier coatings on coupons of several metal alloys and 316L tubing under static immersion. In such conditions, parylene-C and -AF4 coatings have shown excellent Ag+ loss mitigation and mixed long-term adhesion performance, depending on parylene species and substrate surface chemistry/structure. In Part IV of this series, we report on our work to investigate the performance of parylene-C barrier coatings, under more challenging and realistic conditions, in order to evaluate potential suitability for use. The resilience and associated Ag+ loss with Parylene-C coating on 316L tubing and fittings under medium-term immersion and repeated fitting dis/reassembly were investigated. Potential mechanical challenges to barrier coatings in spacecraft potable water systems were investigated, with two main focuses being identified: liquid flow/pressure cycling in tubing and cyclic operation of bellows in positive-expulsion storage tanks. Two corresponding testbeds for experimental characterization of coating performance were developed. In the Flow/Pressure Testbed System, Ag+ solution will be pumped through coated 316L tubing, with optional pressure cycling. In the Bellows Tank Testbed System, an internally coated edge-welded 316L bellows containing Ag+ solution will be cyclically extended and compressed, analogous to the operation of bellows tanks used for potable water storage and delivery on the International Space Station. The design and operation of these testbeds are described. Finally, the Ag+ adsorption and saturation behaviors of Kalrez and Viton, for potential use as seal materials in fittings and other connections, were characterized in limited experiments.


Lance Delzeit, NASA, US
ICES303: Physio-Chemical Life Support- Water Recovery & Management Systems- Technology and Process Development
The 51st International Conference on Environmental Systems was held in Saint Paul, Minnesota, US, on 10 July 2022 through 14 July 2022.


silver, silver ion, biocide, mitigation, polymer coating, polymer, parylene, potable water, bellows, flow, pressure, testbed, seal, elastomer, fitting, tube, connection