314 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS EXPERIMENTAL PROCEDURE The procedure employed in these tests was based on earlier inves- tigations into the compatibility of aluminum with fluorocarbons. Heavy walled Pyrex glass ampules were formed by closing one end of an 18-in. length of tubing which could accommodate a 0.25 X 1 X 0.064 in. alumi- num specimen. Alloy 1100-H14 was used in most of the tests because this alloy has been considered a good compromise of strength, corrosion resistance and cost for aerosol containers. A few tests were conducted with 5052-H34 alloy, which is a representative higher strength alloy. One specimen was slipped into the bottom of the ampule and a con- striction was placed in the ampule sidewall several inches above the specimen. This constriction allowed free flow of liquid and vapor between the two parts of the ampule but would not permit passage of the aluminum specimen. SufFicient solution was then measured into the ampule to establish the liquid-vapor interface slightly below the glass constriction. A second specimen was inserted in the area above the constriction which would subsequently be exposed to the vapor phase of the solution Where a low boiling fluorinated hydrocarbon was employed, it was necessary to cool the ampule and its contents with dry ice in order to add the solution and seal the ampule. The open end of the ampule was now sealed by melting. The ampules and their contents were then exposed to ambient tem- perature laboratory conditions in order to minimize any significant contri- bution of hydrolytic effects or temperature degradation. Periodic ob- servations were made and the presence or absence of corrosion effects was readily identifiable. When significant corrosion was apparent, the ampules were broken and the weight losses of the specimens determined. Where no corrosion was evident, the tests were often continued for periods up to three years before the tests were terminated and final weight changes were measured. INTERPRETATION OF RESULTS It is necessary to consider the design and construction of an aerosol container to interpret these experimental results properly. There are three main areas of concern in projecting the service life of an aerosol container. They are: 1. An adequate metal thickness to hold the internal pressure exerted by the propellant and solution. 2. Maintenance of intact seals at all can joints. 3. Maintenance of controlled valve release of the can contents for a reasonable service life.

COMPATIBILITY STUDIES OF ALUMINUM 315 A combination of economic considerations and internal pressure require- ments has dictated a wall thickness of 0.008--0.010 in. for aluminum aerosol containers. By contrast, architectural and chemical applications involving aluminum may employ sheet, plate or pipe from 0.020--0.250 in. thick. This means that penetration of the sidewall of an aerosol container can result from pitting corrosion that would be considered insignificant in many other chemical applications. Relatively small corrosion weight losses could also result in a can seam leak or restriction of flow through an atomizing valve. For these reasons, the actual weight losses rather than calculated corrosion rates are employed in this paper. Visual observations as to the type of corrosion could also be important in predicting service life and are, therefore, included. ALUMINUM COMPATIBILITY STUDIES WITH FLUOROCARBONS AND ETHYL ALCOHOL Periods of exposure up to three years are recorded in Table I, and selected values are compared in Fig. 1. In individual solutions of fluorocarbons 11 or 12 or ethyl alcohol (95%), no corrosion was evident in any solutions for periods of approximately two months. After two months exposure, however, slight turbidity began appearing in the fluorocarbon 11 solution, indicating some very minor aluminum corrosion. Even after one year of exposure the actual weight losses were insignificant. No corrosion or turbidity was noticed in fluorocarbon 12 solution exposures, even after 80 A- 100% F-II (414 DAYS) B - 100% F- 12 (1049 DAYS ) • 70 C - 95% ETHYL ALCOHOL (414 DAYS ) D - [50% F-II, 50% (95% ETHYL ALCOHOL)] (67 DAYS ) • E- [50•, F-12, 50•,(95• ETHYL ALCOHOL)I(67 DAYS) o 60 F- [50% F-IZ, 50% (95% ETHYL ALCOHOL)I(387 DAYS) • 6 - [25% F-II,Z5% F-IZ,50•(95D% ETHYL ALCOHOL)] (107 DAYS) so I ß L,OU,D o, 40 [] VA•,O. o • 3o • zo •o •o Figure 1.--Comparison of corrosion weight losses of aluminum in solutions of propellants and ethyl alcohol.