ALUMINUM-ALLOY COMPATIBILITY WITH GELLED INHIBITED RED FUMING NITRIC-ACID

Gelled inhibited red fuming nitric acid (IRFNA) is being considered as the oxidizer for advanced propulsion systems for the next generation U.S. Army missiles. The advanced systems have strict weight and volume limitations. Therefore, the desire is to use the strongest, lightest- weight materials for construction that are also compatible with the pr opellant ingredients. Aluminum alloys have traditionally been used to contain IRFNA. However, a minimum amount of quantitative corrosion rat e data is available on the standard alloys, and less on the aluminum a lloys being considered for advanced missile systems. This article prov ides data and information on the compatibility and corrosion rate of I RFNA gels of various compositions with several different aluminum allo ys. Oxidizer composition changes included the addition of inhibitors s uch as P4O10 to replace and/or supplement the hydrogen fluoride alread y present in the IRFNA. Low corrosion rates were obtained in certain g elled systems. Data were obtained by 1) electrochemical methods, 2) su rface analytical methods, and 3) weight loss/change methods. The combi nation of methods provides useful data and is applicable to a variety of systems. The combined methods provide useful corrosion rates and lo ng-term storage data for metals in contact with corrosive materials. T he techniques and procedures are suitable for a variety of systems. Th e corrosion rate was found to decrease with time and stabilize quickly because of the formation of a protective film on the metal surface. T he corrosion rates measured in neat IRFNA and gelled IRFNA were compar able.