ABSTRACT
Due to the advantages such as self-cleaning, antifriction, hydrophobic, resistance to pollution, inhibition of surface corrosion and oxidation, super-hydrophobic surfaces have a bright prospect in self-cleaning materials, drag reduction materials, industrial and agricultural fields, the building up of national defense and biomedical materials. There are two methods which produce traditional super-hydrophobic surfaces, such as the improvement of surface roughness of the hydrophobic surfaces and the modification of rough surface by low-surface-energy materials. Up to now, artificial super-hydrophobic surfaces have been fabricated by tailoring surface topography and using techniques such as template method, self-assembly techniques, chemical vapor deposition,electrochemical deposition, sol-gel, and others. However, either special equipment or complex process control is required in most cases which are lack of large-scale preparation operation. Therefore it is important and meaningful to make the fabrication of transparent superhydrophobic surface controllable, low-cost and applicable in large-scale.
In this dissertation, we reported on three simple and convenient techniques for fabricatiing super-hydrophobic coating which was developed based on the combination of theoretical and experimental reasearch. Using these techniques, we have succeeded in the preparation of super-hydrophobic coating on the two light alloy substrates including magnesium alloy and aluminium alloy, FE-SEM、CA、XPS、Polarization Curve were used for coating characterizations, and the main results are as follow:
1. A new technique combined chemical etching with surface modification was developed to produce super-hydrophobic coating on magnesium alloy. The results show that the magnesium alloy surface is rather rough and covered by a relatively uniform micro- and nano-porous structure. The coatings fabricated possess high water static CAs of 157.3 ± 0.5°, small sliding angles of less than 10°. The electrochemical measurement show that the corrosion potential of the super-hydrophobic sample is slightly more positive than that of the untreated sample, and as compared to the corrosion current density of the untreated sample, that of the super-hydrophobic sample decreased by more than three orders of magnitude. These results indicate that the super-hydrophobic coating on magnesium alloy has better corrosion resistance. Besides,the effects of etchant, etching time on CA were researched. Furthemore, the formation mechanism of the magnesium alloy surface was investigated, and a better processing parameter was obtained.
2. A simple technique combined chemical etching with surface modification was developed to produce super-hydrophobic coating on aluminium alloy. We find out that the aluminium alloy surface is configured in a labyrinthic structure with cuboid plateaus and caves of micro-and nano structure. The coatings fabricated possess high water static CAs of 161.2 ± 1.7°, small sliding angles of less than 8°. The electrochemical measurement show that the corrosion potential of the super-hydrophobic sample is slightly more positive than that of the untreated sample, and as compared to the corrosion current density of the untreated sample, that of the super-hydrophobic sample decreased by more than four orders of magnitude. These results indicate that the super-hydrophobic coating on aluminium alloy has better corrosion resistance. The orthogonal design was taken for the optimization. The content of etching time and etching concentration were measured for fixing on the optimum conditions. Furthemore,the formation mechanism of the magnesium alloy surface was investigated, and a better processing parameter was obtained.
3. A novel technique combined anodic oxidation、chemical etching with surface modification was developed to produce super-hydrophobic coating on aluminium alloy.The results show that the aluminium alloy surface is rather rough and covered by a regularly ordered leaf-like structure, and many cracks and venations were observed. The coatings fabricated possess high water static CAs of 167.7 ± 1.2°, small sliding angles of less than 5°. The electrochemical measurement show that the corrosion potential of the super-hydrophobic sample is slightly more positive than that of the untreated sample,and as compared to the corrosion current density of the untreated sample, that of the super-hydrophobic sample decreased by more than four orders of magnitude. These results indicate that the super-hydrophobic coating on magnesium alloy has better corrosion resistance.
Keywords: Super-hydrophobie; Light alloy; Chemical etching; Anodic oxidation;Coating
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