COMPATIBILITY OF GELLED INHIBITED RED FUMING NITRIC-ACID WITH ALUMINUM-ALLOYS

This paper presents data obtained from electrochemical methods, weight loss studies, and surface studies to determine compatibility of gelle d inhibited red fuming nitric acid (IRFNA) with aluminum alloys. Compa risons are presented between liquid IRFNA and gelled IRFNA with and wi thout added inhibitor (P4O10). The 1100 and 2014 aluminum alloys behav e in a similar fashion when exposed to gelled IRFNA, based upon the we ight loss investigations. The addition of phosphoric oxide is benefici al with the 1100 Al systems according to the electrochemical results. However, the weight loss data suggest that the gels are satisfactory w ithout added P4O10, especially when compared to a liquid IRFNA system, The x-ray photoelectron spectroscopy shows that the fluorine from the hydrofluoric acid inhibitor in IRFNA is not consumed entirely by the silica gelling agent, and is available to the metal surface as in gel systems without P4O10. Aluminum, silicon, and phosphorous will compete for the fluorine present in the systems with added inhibitor. In gene ral, all corrosion rates are small and decrease with time. These rates appear acceptable for long-term storage of gelled IRFNA; they are con sistent with the storage of IRFNA in the field.