The Fabrication Of Alkoxy Silane Superhydrophobic Coatings On Iron Surface And The Studies Of Their Anti-corrosive Performance

Iron was widely used in every walk of life because of its many excellent properties.However,iron is an active metal and can be corroded easily in aqueous solution or a humid atmosphere,leading huge economic losses every year.Therefore,the study on metal corrosion and protection is of great significance.The presence of surface coatings can protect the metal base from corrosion.Though Chromate-and phosphate-based coatings are extensively applied in surface pretreatment of metals before coatings,their use has been restricted due to the high toxicity of Cr? and the serious phosphorus pollution.Superhydrophobic coating(water contact angle larger than 150° and sliding angle less than 10°)as a protective coating has attracted great attention.Water-repellent nature of lotus leaf is a typical superhydrophobic phenomenon.The fabrication of superhydropbic coating usually requires two key factors,namely,rough microstructure and low surface energy.Herein rough micro-and nano-structures were fabricated by chemical etching and electrodeposition respectively,and then further modified with a long alkyl chain silane by means of self-assembly method.Hydrolyzed silane molecules could adsorb on the metal surface by the condensation of silicon hydroxyl groups,forming the thin films that protect the metal base from corrosion.Moreover,silane coatings may reduce the surface energy of a solid substrate,which contributes to the superhydrophobicity.The main contents of this paper include:(1)The surface roughness was manipulated by etching method and the rough iron surface was then modified with surface functionalized silica sol to fabricate the SH coating.The surface roughness and surface morphology of the coatings on the treated iron were observed by employing atom force microscopy(AFM)and scanning electron microscopy(SEM).Further analysis of the functional groups in the as-fabricated films could be carried out by Fourier Transform Infrared Spectroscope(FTIR).The element analysis of the chemical compositions contributing to the superhydrophobicity was examined using X-ray Photoelectron Spectroscopy(XPS).To get the static Contact Angles,an optical angle meter with a computer-controlled liquid dispensing system was applied to make accurate measurements.The surface of etched iron exhibited the rough micro-/nano-structures as shown by SEM images.Contact angle measurements and SEM observations have demonstrated the superhydrophobic properties after being treated with a long alkyl chain silane.The WCA of SH coating was 155° and the sliding angle was less than 10°;The results of XPS demonstrate that self-assembly of OTES molecules onto the rough iron surfaces through the formation of Si-O-Si bonds;Polarization curve and EIS results show the excellent anticorrosion properties of the as-fabricated SH coatings.(2)The surface roughness was created by etching method and the rough surface was then treated with ODTMS which was added into the modified silica solution.The surface morphology and wettability were characterized by SEM and WCA measurements respectively.The corrosion resistance was determined by electrochemical tests.SEM showed that rough micro-/nano-scale structures appeared on the iron surface after electrodeposition.The superhydrophobic coatings exhibited the water contact angle of 160° as well as the sliding angle of less than 5°.According to the XPS survey spectrum,superhydrophobic coating modified iron surface showed that the content of O decreased while the content of C increased because of self-assembly of ODTMS molecules onto the ZnO surfaces.Corrosion current density and charge transfer resistance were obtained by carrying out polarization curve and EIS measurements.These results showed the lower current density and the higher corrosion protection efficiencies.Moreover,the charge transfer resistance greatly increased because of the presence of SH coatings.Electrochemical test results indicated that superhydrophobic membranes prepared through constructing the micro/nano hierarchical structures on steel surface presented the outstanding corrosion resistance.