This project proposes a solution to the stability of biocidal silver in water treatment and storage systems of the International Space Station. Silver is known to react with some of the metallic (e.g. 316 stainless steel, Inconel 718, and titanium 6A1-4V) components of the water storage system, which result in a gradual loss of biocidal silver ions over time in the water. Various studies have been conducted to investigate these surface interactions over conventional spacecraft materials, e.g., stainless steel, Inconel, Teflon and titanium, as well as, different surface treatments, e.g., acid passivation, silver plating, electropolishing and heat treatment. In general, more favorable outcomes have been obtained at lower surface to volume (S/V) ratios, with thermal oxidation, electropolishing and silver pre-treatment whereas higher S/V shows ineffective results. The traditional materials on ISS are stainless steel 316L (¼ inch ID pipes), titanium (½ inch ID pipes), Inconel 718 (bellows tanks). The choice of materials for the water system will be an important factor to ensure the success of silver as a biocide for spacecraft water systems. Silver loss on surface is thought to be done through a galvanic deposition process, with a concomitant oxidation of the substrate and reduction of silver ions to metallic silver/silver oxides on the surface. The goal of this proposal is to address the challenges with surface with S/V of 2 cm-1 and higher using an innovative surface coating of redox insulator that is effective and has not experimented previously. This will be done by coating a two dimensional (2D) materials (below 100 nm) on the surface of the stainless steel. This of thin and homogeneous layer of insulating materials can reduce silver reduction and biocidal loss in the water.
A potable water treatment process is needed to prevent microbial growth in the water storage and distribution system for long duration missions. there remain significant challenges on its fast dissolution rate for an effective solution at preventing biofilm formation. It demands a surface coating what inhibits red-ox reaction on the surface at tanks and pipes at ISS station. This project will be directly applicable to high S/V ratio structures relevant to exploration-class missions.
2D ceramic coating possess good thermal and insulation properties. They are resistant to oxidation and erosion in high temperature environment. This property is a very important factor in the applications such as pipelines, castings and automotive industry. These materials can be implemented in many industrial fields i.e. surface passivation, gas diffusion barriers, anti-reflection layers