| The annual costs of metal corrosion amount to 4% of the GDP of our country. The employment of aluminum is the largest quantity and broadest use in color metal, however, aluminum is so easy to be eroded because of its high chemical activity. Especially under the conditions of moist air, sulfuric atmosphere and oceanic aerosphere, the electrochemical corrosion would occur on the surface of aluminum. At present the protection of a film or coating is one of the most widely and effective one of all the corrosion-resistant methods. Chromate conversion coating provides highly effective corrosion protection, but hexavalent chromium presents an environmental hazard due to its carcinogenic properties. Self-assembled monolayres (SAMs) is a greatly promising coating to protect metal from corrosion, whereas the defect and weak adheresion of the coating depress their anti-corrosion ability. Thus it is emergent to develop a novel, effective, and contaminative-free anti-corrosion material. In this study the super-hydrophobic layered double hydroxides (LDHs) film prepared was used to the protection of aluminum and aluminum alloy in this study. At first, LDH films were prepared on aluminum and aluminum alloy. Based on the variant interlayer anions in LDHs, the lautate anions occupied the space between the LDH layers leading to super-hydrophobic ability of ZnAl-LDH-La film. And the corrosion-resistance of LDH film was evaluated to investigate the relationship of corrosion-resistance and hydrophobic ability. The results obtained are as following.Firstly, ZnAl-LDH films were prepared in situ on aluminum substrates which were first coated with a layer of porous anodic alumina (PA0/A1) by conventional anodization. Then super-hydrophobic ZnAl-LDH-La films, whose water contact angle was 160°, were observed by a simple chemical process. DC polarization measurement showed that the ZnAl-LDH-La films gave current densities as low as 10-9A/cm2, which was much lower than the value of inorganic material reported in previous literatures, indicating the superior corrosion resistance of super-hydrophobic LDH film. Moreover, there was no defect or disfigurement on super-hydrophobic ZnAl-LDH-La film after long-term immersion (as long as 21 days). X-ray powder diffraction (XRD) demonstrated that the structure of ZnAl-LDH-La film before and after immersion remained unchaiged. The contact angle value of the film after immersion was 142°. The good adheresion of the film on aluminum was tested according to ASTM Standard D 3359-02. It is concluded that the super-hydrophobic ZnAl-LDH-La film could insulate the corrosive ions (CT) from the surface of aluminum so as to effectively protect mental from corrosion.Secondly, taking into account that aluminum alloy has more application and worse anti-corrosion than aluminum, aluminum alloy (AA2024) was studied in this work. The ZnAl-LDH film was in-situ synthesized, and laurate anions were exchanged to the interlays by simple chemical process leading to hydrophobic ZnAl-LDH-La film. The observed ZnAl-LDH-La film was also a good and potential protective coating for aluminum alloy.Thirdly, ZnAl-LDH-NO3- film was also synthesized directly on aluminum by in situ crystallization method in order to simplify the preparation of LDH film. XRD demonstrated that good orientation was observed on the LDH film which was impact and uniform showed in its SEM images. The current density of the film was about 10-8Amps/cm2 by polarization curve test, and no defect or disfigurement occured on the ZnAl-LDH film after long-term immersion, demonstrating that the LDH film was a good anti-corrosion material. The results of XRD, FT-IR and EDX showed that the anions were Cl- after immersion tests, so we presumed that the corrosion resistance of ZnAl-LDH-NO3- films depended on their ion-exchange reaction between NO3-and Cl- in corrosive solution.
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