Microbiologically influenced corrosion and titanate conversion coatings on aluminum alloy 2024-T3
Due to its poor corrosion resistance, Aluminum alloy 2024-T3 has been targeted to study corrosion mechanisms and protection strategies. The present study has two areas of focus: (1) the effects of aquatic microorganisms on corrosion, and (2) the surface-cleaning step in the conversion coating process. ^ Microorganisms and biofilms on solid surface can be found almost in any natural aqueous environments. So far, microbiologically influenced corrosion (MIC), or biocorrosion, has been poorly understood. A comparative study on the corrosion of aluminum alloy 2024-T3 was conducted in either plain seawater or nutrient-rich ZoBell 2216 medium, and with or without the marine bacterium Pseudoalteromonas atlantica by electrochemical impedance spectroscopy (EIS). Results indicated that the presence of P. atlantica in seawater decreased the corrosion rate of aluminum alloy 2024-T3. Nutrients such as yeast extract and peptone in ZoBell 2216 medium also reduced the corrosion rate of aluminum alloy 2024-T3 in the absence of the bacterium. Examination of attached P. atlantica on the surface of aluminum alloy 2024-T3, in different media, suggested that, in low nutrient-concentration environments, more bacteria adhered to the solid surface; in high nutrient-concentration environments, bacterial cells tended to distribute in the aqueous media. ^ Health and environmental concerns call for the development of a non-toxic conversion coating with comparable corrosion protection and paint adhesion properties, to replace excellent chromate conversion coatings on aluminum alloys, due to the toxicity of chromates. A titanate conversion coating has been already developed towards this end; the main focus of this study was on improving the surface-cleaning step that precedes coating. Impedance measurements showed that in surface-cleaning step, proper mechanical abrasion and efficient chemical cleaning improved the surface uniformity of aluminum alloy 2024-T3 before immersion in the titanate conversion solution; the surface's uniformity then contributed to the formation of a high-quality titanate conversion coating. The pH of the conversion coating solution was important to the formation of the titanate conversion coating and its anticorrosive properties: the corrosion inhibition of aluminum alloy 2024-T3 with titanate conversion coating developed at pH = 5 was better than that at pH = 2. ^
"Microbiologically influenced corrosion and titanate conversion coatings on aluminum alloy 2024-T3"
Dissertations and Master's Theses (Campus Access).