J. soc. cos. CHEM. 15, 311-326 (1964) COMPATIBILITY STUDIES OF ALUMINUM WITH PROPELLANT AND SOLVENTS FOR USE IN AEROSOLS By J. DE^N M:[NlVORD, PH.D.* Presented September 24-25, 1963, Seminar, Boston, Mass. ABSTRACT Exposure of aluminum alloy 1100-HI4 to fluorocarbons 11 or 12 or 95% ethyl alcohol for one year caused only very minor corrosion. A signif- icant increase in corrosion occurred when the alcohol was combtned with either fluorocarbon or a combination of both fluorocarbons. The addition of 5% water increased the corrosivity of the alcohol-fluoro- carbon mixture, whereas lar•er amounts of water appeared to have an initial retardin• effect. Inorllanic additives were found that effectively retarded the corrosion. Substitution of hi•her homolo•ue alcohols such as propyl, butyl, allyl, amyl and capryl formed noncorrosive solu- tions with fluorocarbon 11. INTRODUCTION The tremendous growth of the American aerosol industry in recent years has prompted a continuing search for new materials of construction for aerosol containers. The outstanding features of aluminum, such as light-weight, attractive design and ease of formability, have already gained public acceptance in the field of general packaging. Other out- standing advantages which aluminum can provide are directly related to its surface chemistry. It is both odorless and tasteless as well as hygienic, nontoxic and substantially sterile. Furthermore, its freedom from rust- ing, even under humid conditions, assures a continuing attractive ap- pearance and protects other contacting surfaces from rust staining. These same advantages could be of the same significant value in aerosol cans if aluminum was compatible with most aerosol formulations. Some corrosion was anticipated as a result of extensive studies in these laboratories on the compatibility of aluminum with various halogenated hydrocarbons. The possibility that some unusual aluminum reaction * Alcoa Research Laboratories, Chemical Metallurgy Div., New Kensington, Pa. 311

312 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS would result from combining ethyl alcohol with halogenated propellants was of specific concern. In earlier studies (1) the combination of methyl alcohol with carbon tetrachloride had shown an unexpected and unusual reactivity with several aluminum alloys. The very complicated nature of this reaction was further indicated by studies of the mechanism of the reaction of aluminum with the simple carbon tetrachloride molecule itself (2, 3). This paper is actually an extension of some of these earlier investigations in which the individual and combination effects of fiuorocarbons, alcohols and moisture level on aluminum had been studied. HISTORICAL BACKGROUND Many literature reports of the outstanding resistance of aluminum to a wide variety of environmental conditions can be cited. General excellent atmospheric weathering resistance has been demonstrated both for in- dustrial and marine environments (4-7). In 1953 further evidence was gathered to support the fact that aluminum alloys performed well in many organic and inorganic chemically contaminated atmospheres (8). The further use of aluminum for storing and processing foods, cosmetics, essential oils, microbiologicals, plastics and pharmaceuticals was reported in 1956 (9, 10). The reactions of fiuorocarbons with aluminum alloys have been extensively studied. i'..: o=r laboratories for a number of years both at ambient and elevated temperatures and in the absence and presence of contaminating moisture. In genera], the added presence of fluorine in the molecule reduces the general level of reactivity below that shown by anal- ogous compounds having only carbon to chlorine bonds. There is so little tendency for the pure fiuorocarbons to react chemically in any way with aluminum that long exposure times at temperatures up to 200øC failed to show any significant chemical reaction. Reactions can occur, however, if conditions for hydrolysis of the fiuorocarbon exist or high temperature pyrolysis of the fiuorocarbon can occur. It was concluded in a recent paper (11) that the reactions between aluminum and fiuoro- carbons at high temperature are quite dif}•rent in nature from those at low temperature. While the first effect of raising the temperature may be acceleration of the low temperature reactions, new reactions take place at elevated temperatures which were not detectable at the lower temperature. The combination of ethyl alcohol with fiuorocarbons is rather unique because some chemical reactivity with aluminum is noted in contact with these combined solutions under conditions which cannot be basically classified as being promoted by hydrolysis or pyrolysis mechanisms. The