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Title: Aluminum and Other Coatings for the Passivation of Tritium Storage Vessels

Using a highly sensitive residual gas analyzer, the off gassing of hydrogen, water, and hydrocarbons from surface treated storage vessels containing deuterium was measured. The experimental storage vessels were compared to a low off-gassing, electro-polished 304L canister. Alternative vessels were made out of aluminum, or were coatings on 304L steel. Coatings included powder pack aluminide, electro-plated aluminum, powder pack chromide, dense electro-plated chromium, copper plated, and copper plated with 25 and 50 percent nano-diamond. Vessels were loaded with low pressure deuterium to observe exchange with protium or hydrogen as observed with formation of HD and HDO. Off gas of D2O or possible CD4 was observed at mass 20. The main off gas in all of the studies was H2. The studies indicated that coatings required significant post coating treatment to reduce off gas and enhance the permeation barrier from gases likely added during the coating process. Dense packed aluminum coatings needed heating to drive off water. Electro-plated aluminum, chromium and copper coatings appeared to trap hydrogen from the plating process. Nano-diamond appeared to enhance the exchange rate with hydrogen off gas and its coating process trapped significant amounts of hydrogen. Aluminum caused more protium exchange than chromium treated surfaces. Aluminummore » coatings released more water but pure aluminum vessels released small amounts of hydrogen, little water, and generally performed well. Chromium coating had residual hydrogen that was difficult to totally outgas but otherwise gave low residuals for water and hydrocarbons. Our studies indicated that simple coating of as received 304L metal will not adequately block hydrogen. The base vessel needs to be carefully out gassed before applying a coating and the coating process will likely add additional hydrogen that must be removed. Initial simple bake out and leak checks up to 350° C for a few hours was found to be inadequate. All of the studies indicated that vessels needed several days of vacuum baking at 350-450° C to fully outgas the residual gases, which were mostly hydrogen. The current standard practice of out gassing from ultra-clean, electro-polished 304L vessels with both vacuum bake out and followed by an oxidative bake out to enhance the chromium surface performed the best in these studies.« less
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  1. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
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Resource Type:
Technical Report
Research Org:
Savannah River Site (SRS), Aiken, SC (United States)
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Country of Publication:
United States