Aluminum and Other Coatings for the Passivation of Tritium Storage Vessels

Abstract

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. Aluminum 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.

Electroless Plated Nanodiamond Coating for Stainless Steel Passivation

“…Compared to the as-received Cu and ND-Cu coated CFVAs (Table 3-3 and Figure 3-11), the off-gas rates of H 2 , HD and H 2 O were reduced generally by one to two orders of magnitude after vacuum heating (Table 3- [4][5][6][7][8][9][10][11][12][13]. At similar sampling times, the off-gas rates of H 2 , HD and H 2 O for the Cu and ND-Cu coated SS CFVAs (7 days) were at the same order of magnitude as those for SS and EP_SS CFVAs (12 days).…”