Preparation Of The Superhydrophobic Composite Coatings On The Carbon Steel Surface And Their Anti-corrosion Properties In Seawater

Nowadays, the types of protection coating on the metal are various. However,there exits limitation on the characteristic and preparation of the monolayer coating,which leads to the monolayer couldn’t protect the metal substrate well. In this paper, itdesigns a composite coating on the carbon steel aiming to the limitation of themonolayer on the metal. And the bionic superhydrophobic film is applied to thecomposite coating to improve the corrosion of carbon steel.First, Ni-P coating, TiO2/ZnO coating are prepared successively on the carbonsteel by electroless deposition technique and sol-gel technique. And rough surfacewith different roughness on the (Ni-P)/(TiO2/ZnO) composite coating is preparedusing cetyl trimethyl ammonium bromide (CTAB), which is easy to decompose whenheated under certain temperature. Then the low surface energy material is used tomodify the rough surface to get the superhydrophobic composite coating. The contactwater angle (WCA), phase, chemical composition, morphology and anticorrosionperformance of the composite coating samples are investigated by differentmeasurements. The result shows that the composite coatings improve theanticorrosion of carbon steel greatly. The obtained composite coatings showsuperhydrophobicity for the samples with Ti to CTAB molar ratio of1/2,1/1, and2/1except for the4/1sample, where the measured WCA is120±3o. However, theelectrochemical results show that the coated sample with Ti to CTAB molar ratio of2/1and4/1have the better anticorrosion performance. This suggests thatsuperhydrophobicity does not definitely mean better anticorrosion. Meanwhile, thecorrosion mechanism of the superhydrophobic composite coating in sterilizedseawater is investigated in this paper.On the basic of the obtained the superhydrophobic composite, the dynamicanticorrosion behavior in seawater is studied. The durability of superhydrophobicity, chemical composition, morphology and anticorrosion of the composite coating afterimmersed in the sterilized seawater for different time are investigated. The resultsshow that the composite coating has excellent long-term stability onsuperhydrophobicity in air. However, when the coated samples are immersed in theseawater for24h, the superhydrophobicity becomes lower and the WCA valuesdecrease with the immersion time. The results of micro-morphology and chemicalcomposition suggest that there are damage and hydrolyzation on the coated samplesurface after immersion in the seawater. However, the electrochemical results showthat the coated samples still have good anticorrosion property even after immersion inseawater for168h. Subsequent corrosion mechanism analysis suggests that the TiO2and/or ZnO sealed inner Ni–P coating may play an important role on anticorrosion forthe composite coating.The investigation results above show the anticorrosion property ofsuperhydrophobic samples are not definitely better than that of hydrophobic samples.Therefore, the anti-corrosion performance of several composite coatings withsuperhydrophobic and hydrophobic surfaces is studied in this paper. The results showthat superhydrophobicity does not definitely mean better anti-corrosion thanhydrophobicity again. The Lotus and immersion experiments demonstrate that theadvantage of the superhydrophobicity is effective when its rolling characteristicmaintains. The analysis on anti-corrosion mechanism reveals that the rough surface inthe composite coating may play a double-acting role.