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

COMPATIBILITY STUDIES OF ALUMINUM 313 interaction between ethyl alcohol and fluorocarbon 11 has been studied (12), and the identified products seem to indicate a free radical mechanism for the reaction under ambient or slightly above ambient temperature conditions. Several studies have been reported with aluminum aerosol cans. One study included 31 combinations of chemicals packed in uncoated aluminum cans (13). Among the combinations were ethyl or isopropyl alcohol combined with fluorocarbon 12 and various levels of water. Pitting and perforation of the aluminum was common in the presence of ethyl alcohol combinations. The isopropyl alcohol containing mixtures showed signif- icantly less tendency to cause pitting. In another study (14) tests were conducted with ethyl alcohol and fluorocarbons 11 or 114 with the result that there was significantly more pitting and perforations where fluoro- carbon 11 was used. The effect of variable moisture content was studied in these same tests and it was concluded that there did not appear to be any water concentration that satisfactorily reduced the corrosion to a safe level. SCOPE OF INVESTIGATION While it had been previously recognized in unpublished data that some unusual reactions can occur between certain aluminum alloys and mixtures of carbon tetrachloride and methyl alcohol, no systematic study had been made involving other alcohols and other halogenated hydrocarbons. Because aerosol solutions often include halogenated hydrocarbons (i.e., fiuorinated-chlorinated propellants) and ethyl alcohol, compatibility studies were pertinent. Initial studies were concerned with the exposure of aluminum sheet specimens to the individual effects of the commonly employed propellant fiuorocarbons 11 and 12 with and without various additions of water. Similarly, it was necessary to establish the separate effect of ethyl alcohol in various concentrations in water. For this study it was assumed that 95% ethyl alcohol would be most conveniently employed and would be the minimum water content ethyl alcohol solution. A number of combinations of propellant, alcohol and water in contact with aluminum must then be studied to evaluate properly their interactions. If any corrosion occurred, then it was proposed to study the retardation effect of certain inorganic and organic chemical additives. In order that conclusions of practical significance could be drawn, it was believed that exposure times of up to three years should be included. Other alcohols were also substituted for ethyl alcohol in the basic aerosol mixtures of propellant and alcohol to determine if there was any pattern of similar behavior among the different alcohols.