Metallic Vessel Surface Oxidation for Silver Ion Stability
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Solution Overview
Problem
Metallic water storage vessels for spacecraft face challenges in maintaining effective silver ion concentrations for microbial control due to rapid depletion of silver ions when in contact with metallic surfaces, which is exacerbated by the high surface-to-volume ratio, leading to inadequate antimicrobial protection over time.
Innovation Solution
Heating the metallic surface to temperatures between 480°C and 870°C and exposing it to oxygen to oxidize potential reduction sites, combined with treating the surface with an oxidizing agent or silver plating, to reduce the reduction potential of the metallic surface and maintain silver ion concentrations in stored potable water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metallic vessels are used for water storage, then structural strength and robustness are improved, but silver ion depletion occurs rapidly due to reduction sites on the metallic surface
Solution Approach 1:
The metallic surface is oxidized before water storage to create a protective layer that prevents subsequent silver ion reduction. This preliminary oxidation action eliminates the reduction sites that would otherwise cause rapid silver ion depletion, allowing the metallic vessel to maintain both strength and silver ion stability.
Solution Approach 2:
An oxidizing agent is introduced as an intermediary substance that converts the metallic surface into an oxidized state. This intermediary oxidation layer acts as a barrier between the metallic surface and silver ions, preventing direct contact and reduction while maintaining the structural integrity of the metallic vessel.
2Loss of substance
If plastic vessels are used for water storage, then silver ion stability is improved, but structural robustness is insufficient for spacecraft launch and landing conditions
Solution Approach 1:
The solution creates a composite structure by forming an oxidized layer on the metallic surface, combining the strength of metal with the silver ion stability provided by the oxidized surface. This composite approach allows the vessel to have both the robustness of metallic construction and the silver ion stability typically associated with plastic vessels.
3Measurement precision
If the surface area to volume ratio is increased, then water quality monitoring is improved, but silver ion depletion time is shortened
Solution Approach 1:
By performing preliminary oxidation of the metallic surface, the invention creates a protective barrier that prevents silver ion reduction regardless of the surface area to volume ratio. This allows high surface area to volume ratios (which improve monitoring) without the penalty of rapid silver ion depletion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively maintains antimicrobial silver ion concentrations in potable water for extended periods, preventing microbial growth and ensuring the water remains safe for consumption during long-duration space missions.
Implementation Method 1
heating the metallic surface to a temperature between about 480° C. (900° F.) and about 870° C. (1600° F.), exposing the metallic surface to oxygen during heating to oxidize potential reduction sites on the metallic surface
Implementation Method 2
studies have shown that silver ions are rapidly depleted in vessels having metallic surfaces. Initial concentrations of silver ions present in potable water up to 0.4 ppm can be reduced below detection limits
Data Source
AI summary
A method for controlling microbial growth in potable water stored in a vessel having a metallic surface includes heating the metallic surface to a temperature between about 480° C. (900° F.) and about 870° C. (1600° F.), exposing the metallic surface to oxygen during heating to oxidize potential reduction sites on the metallic surface and charging potable water containing silver ions to the vessel. A vessel having a metallic surface is prepared for long-term storage of potable water containing silver ions by heating the metallic surface to a temperature between about 480° C. (900° F.) and about 870° C. (1600° F.) and exposing the metallic surface to oxygen during heating to oxidize electropositive metals on the metallic surface or by treating the metallic surface with an aqueous solution containing on oxidizing agent to oxidize potential reduction sites on the metallic surface.