Corrosion Protection Mechanisms of Rare-Earth Compounds Based on Cerium and Praseodymium

Abstract

This report is approved for public release; distribution is unlimited The mechanisms by which rare-earth compounds provide corrosion protection were investigated. A variety of environmentally benign corrosion inhibitors, including rare-earth compounds, are potential replacements for carcinogenic chromate-based inhibitors in conversion coatings and primers. Chromates are robust inhibitors that provide protection to a multitude of metal alloys from a variety of different types of coatings, whereas most alternative inhibitors only protect a limited number of alloys or can only be used in a specific type of coating. Understanding protection mechanisms could allow for extension of protection to other alloys or coating types. For cerium-based conversion coatings, protection was accompanied by the formation of an interfacial reaction layer between the coating and the substrate. Praseodymium-based inhibitors in epoxy-polyamide primers provided protection by dissolving from the primer and forming precipitates in damaged areas. Both inhibitors are capable of providing corrosion protection on high strength aluminum alloys that is comparable to chromates when a suitable phase is incorporated into an appropriate coating. Corrosion protection mechanisms; non-chromate corrosion inhibitors; cerium; praseodymium; cerium-based conversion coatings, epoxy-polyamide primers;