Chromium compounds

The electronic spectrum of Cu(II)(L-His)2 has been measured in the visible-near IR and UV regions. By assigning ligand field bands and by fitting the band maxima with calculated energies using angular overlap model, the structure of the complex has been deduced to be five-coordinate C4v1 The observed bands in the UV spectrum have been assigned as due to ligand-to-metal charge transfer transitions. Electronic spectra of Cu(II)(diphenylcarbazide)2 and Cr(II)(diphenylcarbazone)(H2O)4 complexes have also been measured. By interpretation of the ligand field bands in these spectra, tentative structures of these complexes in solution have been proposed.

This research investigates the influence of chromate, as a conversion coating and as an inhibitor pigment, on the adhesion of epoxy coatings to an aluminum substrate. Epoxy coatings, with and without strontium chromate (SrCrO4) inhibitor pigment, are prepared according to manufacturers' specifications on AA2024-T3 substrates, with and without chromate conversion coatings. Specimens are exposed in an environmental chamber, cycling between high and low humidity conditions. After exposure, specimens are evaluated using Electrochemical Impedance Spectroscopy (EIS), ASTM D3359 cross-cut tape test, and an Environmental Scanning Electron Microscope. From the evaluation it was determined that under these exposure conditions chromate does not increase the adhesive strength between the aluminum substrate and the epoxy coating system, but does provide corrosion inhibition. Regardless of the pretreatment or the coating system, the coating fails at the interface between the substrate and the coating.