In this work, a trivalent chromium conversion coating applied on AA2024-T351 alloy has been optimized for corrosion protection in sodium chloride solutions. Scanning electron microscopy, energy dispersive X-ray spectroscopy and electrochemical measurements were employed to characterize the coating. An immersion post-treatment of the coated alloy in 40 • C deionized water for 120 s considerably enhanced the corrosion protection properties, compared with a post treatment at 20 • C, or the absence of a post-treatment. Electrochemical noise measurements, combined with real time imaging, and potentiodynamic polarization experiments indicated a conversion treatment for 300 or 600 s provides optimal corrosion protection. Relatively long conversion treatments decreased the corrosion protection due to an increase in coating defects and cracks, especially around the second-phase particles.

In the present work, modified copper-containing trivalent chromium conversion (TCC) coating processes for aluminum were investigated. The copper addition to the TCC bath was made for the purposes of reducing the generation of hydrogen peroxide and chromium (VI) species during the coating growth. The morphologies and compositions of the coatings were examined using highresolution electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. UV photometric measurements were employed to determine the amount of hydrogen peroxide in the TCC solution. The resultant coatings contained zirconium oxides, chromium hydroxide and fluorides and sulfate constituents, as well as copper oxides and copper-rich deposits that were preferred cathodic sites for oxygen reduction. Of most significance, no chromium (VI) species were detected in the coatings by Raman spectra. It is suggested that this results from reduced generation of hydrogen peroxide, as disclosed by photometric measurements, at the cathodic copper-rich particles, due to favoring of the four electron oxygen reduction reaction. Trivalent chromium conversion (TCC) coatings are promising ecofriendly alternatives to chromate conversion coatings due to the lower toxicity of trivalent chromium species compared with hexavalent chromium.1 The TCC coating solution can be regarded as a modified Zr-based conversion coating solution with addition of small amounts of trivalent chromium salts.2,3 Our previous work used scanning electron microscopy and atomic force microscopy to reveal cracking and spalling of the coating formed on superpure aluminum, especially after a prolonged conversion treatment. 4 This was associated with the fast kinetics of aluminum dissolution due to the attack by fluorine ions in the reaction solution and the stress in the coating. 5 In contrast, the TCC coating formed on AA2024 alloy suppressed the oxygen reduction reaction, due to the physical barrier created by the Zr-/Cr-rich coatings, 1,6,7 and the coating displayed improved adhesion, although the coating was significantly thinner than that formed on superpure aluminum.With respect to the effect of copper alloying, George et al. 8 investigated binary alloys containing 1, 5, and 25 at.% Cu prepared by magnetron sputtering and revealed a decrease in the coating growth rate of zirconium-based coatings with increase of the Cu/Al ratio. This was suggested to be due to the copper species present in the coating impeding the cation transport to the coating base. Furthermore, a layer of corrosion products formed at the coating base. Cerezo et al.9-11 modified the Zr-based conversion coating solution by adding a small amount of copper salts (30-50 ppm). The copper components, which had a high deposition tendency, formed copper and/or copper oxide agglomerates on the substrate, which created local alkalinity that supported the coating formation. As a consequence, the coating thickness on the multi-metal substrate (AA6014, cold rolled steel and hot dip galvanized steel) was increased.One conc...

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Surfactant is mainly responsible for the stability of oil droplets in surfactant/polymer flooding waste water compared with polymer, decreasing oil-water interfacial tension, and zeta potential on the surface of the oil droplets. Flocculation and demulsification were conducted to remove the stable oil droplets. Demulsifier reverse phase demulsifer-E (RPDE) together with flocculant cationic polyacrylamide is effective in accelerating the coalescence of small oil droplets in surfactant/polymer flooding waste water due to synergistic effect of demulsification and flocculation.

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