Environmentally Benign Corrosion Inhibitors

Period of Performance: 08/29/1996 - 08/29/1998

$749K

Phase 2 SBIR

Recipient Firm

EIC Laboratories, Inc.
NORWOOD, MA 02062
Principal Investigator

Research Topics

Abstract

The development of a corrosion protection system for Al-based aerospace alloys that avoids the use of hexavalent chromium and other heavy metal constituents that pose environmental and health hazards is proposed. The corrosion protection system involves the replacement of conventional chromate conversion coatings with analogs of the CrO42- oxyanion and synergistic cathodic inhibitors which retard oxygen (02) or proton (H+) reduction. In combination with the conversion coating, a new class of corrosion inhibitors based on reduction-oxidation (redox) active, electrically conductive oxides is proposed. When galvanically coupled to the conversion coated Al alloy, the redox active inhibitors maintain the potential of the couple within the passive range of the alloy preventing active corrosion. Further, the inhibitors poise the potential of the alloy sufficiently positive that the nonchromate oxyanions, in either the conversion coating or from primer pigments, are actively reduced at exposed Al sites to promote repassivation at defects in the coatings. The metal oxide inhibitors autocatytically reduce 02 diffusing through the topcoat and primer paint binders to sustain the anodic protection without themselves being consumed in the protection process. In Phase I, nonchromate conversion coatings and redox-active inhibitor coatings on electrochemically inert carrier pigments were demonstrated. The objective of the Phase II program is the refinement of the conversion coating/inhibitor system and the demonstration of corrosion protection in accelerated tests using Al aerospace alloys with commercially available primer and topcoat resins.