Electronic and structural characterization of cerium-based corrosion inhibitors

Chromate conversion coating has been the corrosion inhibitor of choice for aluminum alloys. However, chromate based systems face restriction in their use due to the toxic and carcinogenic natures of hexavalent chromium.; Cerium salts have been shown to be effective inhibitors of aluminum corrosion, tending to produce stable oxide coatings over the reactive metal surface. Therefore, cerium-based coatings of aluminum surfaces are a promising system to replace chromate-based coatings. The research work in this dissertation is divided into two parts, which characterize the environment around cerium compounds that are used as corrosion preventive compounds, e.g., in a conversion coating or within an organic matrix coating. High-energy spectroscopic absorption techniques, i.e., X-ray absorption and X-ray photoelectron spectroscopies, have been used to elucidate the predominant local atomic structure and valence of otherwise amorphous cerium species.; The first investigation measures the cerium valence and local structure around cerium ions found in cerium oxide powders. The powders were precipitated under conditions similar to those used in the preparation of cerium oxide films on aluminum alloys, i.e., conversion coatings. The effect of precipitation conditions on the local atomic structure around cerium was measured using X-ray absorption spectroscopy and modeled using the FEFF 8.20 software.; Amine reactions with cerium inhibitors were observed when synthesizing the polyamide-containing coatings. The second part of the dissertation thus presents a model study of the effect of the pKa of aliphatic amines on the cerium valence in cerium-amine complexes.