Protection of Aluminum against Corrosion by Incorporation of Organic Inhibitors into Paints and Primers.
MARTIN MARIETTA LABS BALTIMORE MD
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Selected organic compounds have been further evaluated on the basis of their ability to inhibit corrosion of aluminum and their bonding compatibility with specified metal-adhesive systems. Organic amino phosphonate and silane inhibitors were applied to sulfuric acid-anodized SAA or Forest Products Laboratories FPL prepared 7075-T6 aluminum either by adsorption from aqueous solution or by spraying the specified formulation containing the dissolved inhibitor compound. Wedge test results indicate that in both epoxy-aluminum systems studied, certain organosilanes i.e. mercapto, epoxy derivatives tend to both increase the epoxy-metal bond durability and maintain hydration resistance. The results of the salt fog and anodic polarization experiments further suggest that these silane films are effective against localized pitting. The adsorption of NTMP exhibits a pH-dependent surface coverage, which includes a region characterized by a multilayer of hydrogen-bonded phosphonate molecules. These thick layers are weak and fail to provide good bond durability in a humid environment. NTMP monolayers are protective against hydration and are compatible with a nitrile-modified epoxy adhesive, but not with an epoxy-polamide primer topcoat. In constrast, hydrolyzed silane compounds are adsorbed as olingomeric films, and confer corrosion resistance in both hydrating and Cl- environments. These inhibitors can also couple with applied epoxy primer or organosilanes and do not appear to affect the curing process, e.g., crosslinking, of the polymeric epoxy systems.
- Coatings, Colorants and Finishes
- Properties of Metals and Alloys