aluminum and tinplated steel containers with different types of formulas. A hair mousse formula with a pH of four is usually compatible with aluminum containers, but is usually not compatible with steel containers (in the early 1990s most of us unsuccessfully attempted to find a coated steel aerosol container for hair mousse formulas) An aluminum container is usually not compatible with a high pH oven cleaner, while steel containers are typically used for aerosol oven cleaners. There are also many formulas, such as hair sprays, air fresheners and insecticides that can be packaged in either aluminum containers, or steel containers, depending on the formula’s chemical composition. There are a few rules-of-thumb about formula pH as a guide for when to use aluminum or steel containers. These are: • Aluminum containers with internal coatings are most likely more corrosion resistant with low pH formulas (around 4–6) • Steel containers are most likely more corrosion resistant when formula pH is above 10 • Aluminum and steel containers could be compatible with formulas whose pH is around seven However, other formula ingredients could invalidate these pH rules-of-thumb. For example, organic halogens (most notably carbon tetrachloride) could violently react with aluminum. (Please don’t confuse chloro-organic molecules with inorganic chloride ions.) Ultimately corrosion testing is needed for both types of spray package metals to determine if they are compatible with a given type of formula. In addition, a properly optimized corrosion inhibitor system will significantly increase the corrosion resistance of either aluminum, or steel. However, different types of corrosion inhibitors are typically needed for aluminum and for steel. Please send your questions/comments/suggestions to rustdr@pairodocspro.com. Back issues of Corrosion Corner are available on CD from ST&M. Thanks for your interest and I’ll see you in June. SPRAY May 2013 Spray 41
Spray May 2013
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