Abstract
Aluminum is an important subject of research because it is very abundant and easy to handle. In addition, aluminum is provided with low price, low density and high strength. However, its application scopes are restricted by the defects of its high chemical activity and poor corrosion resistance. Sea water is the most natural corrosive medium in the world, because of chloride ion, pH, halobios and corrosive organic. With the development of the activities and extending applied range of Al in the ocean, it is urgent to develop effective, eco-friendly and functional anticorrosion coatings. Moreover, the application of new coatings technology also has been beneficial in other areas (e.g., the automotive and aerospace industries, treating the copper with the aluminum).
Three novel functional anti-corrosive coatings are prepared by anodized pretreatment on aluminum substrates, including super-hydrophobic coatings,nano-TiO2 coatings, self-healing coatings.The effect of anodic voltage, current, number of times, time, electrolyte systems,chemical polishing technology on the pore size and ordered performance are studied systemically. It is found that the formation and growth mechanism of the porous membrane are observed using SEM. Two efficient and controlled anodic oxide processes, that comprised one–step constant current anodic treatment in sulfuric acid and two-step constant current anodic treatment in oxalic acid, are confirmed by comparison and analysis. The porous structure is characterized by means of atomic force microscope (AFM), and scanning electron microscopy (SEM).
A super-hydrophobic anticorrosion coating is prepared by self-assembly dipping method on porous aluminum anodizing film. The surface structure and super-hydrophobic performance are characterized by means of water contact angle measurement, scanning electron microscopy (SEM), atomic force microscope (AFM).The electrochemical measurements show that the super- hydrophobic coatings significantly decrease the corrosion rate. In addition, the preponderant bacterium is obtained from the surfaces of aluminum which are statically hung in natural sea water.
The preponderant bacterium is identified as Pseudomonas lindanilytica strain IPL-1 through analysis of the sequences of S16 rRNA gene segment. In addition, the electrochemical results and SEM show that the super-hydrophobic coatings significantly reduce the corrosion rate of aluminum, which is accelerated by the presence of Pseudomonas lindanilytica strain IPL-1.
A compact nano-TiO2 coating on aluminum is successfully generated by anodization and vacuum dip-coating process. The morphology of the coatings and chemical composition are studied by SEM and XRD. The analysis of potentiodynamic polarization, EIS and equivalent circuit models reveal that the coatings effectively inhibit the aluminum corrosion in sterile seawater. The anodization and vacuum dip-coating are ideal for the formation of the stable nano-TiO2 coatings better than conventional dip-coating on fresh Al. UV reflection spectroscopy was used to determine and analyze that the "spike" structure nano-TiO2 coatings could improve the light photo catalytic activity which made the bactericidal performance of the coatings increase.
A novel method of self-healing anticorrosion protection is developed including the Al substrates pretreatment by anodized and deposition of inhibitors and polyelectrolytes. This method results in the formation of a smart porous carrier for environmentally friendly organic inhibitors. Release of the inhibitor is stimulated by mechanical damage and corrosion products. Therefore, the self-healing coating enables prolonged anticorrosion activity. The coatings’ formation and structure are characterized by means of atomic force microscope (AFM) and scanning electron microscopy (SEM). This self-healing system can provide new insight for design and prepare different functional coatings.
Keywords: Aluminum; anodized pretreatment; coatings; marine corrosion;microbial corrosion
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