Date of Award
MS in Polymers and Coatings
Chemistry & Biochemistry
Dr. Chad Immoos
Eight fluorescent indicators were evaluated for their ability to detect the corrosion of aluminum metal substrates. The fluorophore Rhodamine-salicylaldehyde (RSA) was selected as a candidate for further study based on its ability to bind and detect aluminum ions at low concentrations, its selectivity for aluminum ions, its long-term stability, its solubility in our solvent-based epoxy formulation, and its compatibility with our testing method.
A recent publication suggested that an alternative method of fluorescence activation was possible—an acid-promoted ring opening that occurred in the absence of metal ions. To prove the capability of RSA to bind aluminum ions, thorough 1H and 27Al nuclear magnetic resonance spectroscopy, mass spectrometry, and fluorescence analysis was conducted. It was found that RSA bound aluminum ions, with a preferred binding stoichiometry of 2:1 RSA/Al.
Long-term immersion and salt spray corrosion studies were conducted to investigate the ability of RSA to detect corrosion on aluminum substrates. Aluminum panels were coated with epoxy coatings that contained the fluorescent indicator. Following optimization, a linear relationship between corroded area and time of immersion/exposure to salt fog was observed.