Mitigation of Silver Ion Loss from Solution by Polymer Coating of Metal Surfaces, Part V, and Related Developments



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2023 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, including tubing with fittings subject to several assembly/disassembly cycles. 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. Testbed systems were developed to investigate the performance of parylene-C barrier coatings, under more challenging and realistic conditions, in order to evaluate potential suitability for use. In Part V of this series, we report on the current operational configuration of the Bellows Testbed and experimental Ag+ loss mitigation performance with Parylene-C coating on a 316L edge-welded bellows under long-duration cyclic operation. Significant improvement in Ag+ retention over bare metal was observed during extended operation (26 weeks, nearly 2000 bellows cycles). In addition, we report limited continuation work with parylene-C coated coupons (with total immersion duration of 3 years) and tubing with fittings for Ag+ loss mitigation, and Ag+ compatibility with rigid PEI and PVDF engineering polymers. Finally, we report on Ag+ loss mitigation experiments with thermal CVD hard coatings (Dursox™ and Dursan™) on 316L and on compatibility experiments with PEU elastomer.


John Vance, KBR / NASA Ames Research Center, USA
Lance Delzeit, NASA Ames Research Center, USA
ICES303: Physio-Chemical Life Support- Water Recovery & Management Systems- Technology and Process Development
The 52nd International Conference on Environmental Systems was held in Calgary, Canada, on 16 July 2023 through 20 July 2023.


silver, silver ion, biocide, mitigation, polymer coating, polymer, parylene, potable water, bellows, testbed, CVD, hard coating, engineering polymers, Dursox, polyetherurethane, bladder tank