Prepare TiO₂ Composite Films On The Surface Of Aluminum Alloy And Carbon Steel Based On Electrochemical Method

Using electrochemical method to prepare TiO₂ films on the conductive material has many advantages, such as low-cost, simple process, easy to operate, applicable to workpieces with different shapes. By this method, films could be prepared with good uniformity; in addition, their thickness could be controlled in certain deposition time and under a range of voltage. In a word, electrochemical method illustrated a good prospect of application and extension. On the basis of electrochemical methods, two improved approaches were drew out, one is preparing Al₂O₃/TiO₂ composite films on aluminum surface, and the other was preparing NiP/ TiO₂ composite films on the surface of the carbon steel. Due to these two kinds of substrate metal cheap and widely used, no treatment involved, promotion of these two methods to prepare TiO₂ composite films are of great realistic significance.Al₂O₃/TiO₂ composite films were prepared on LY-12 Aluminum alloy sample surface in TiPO₄ electrolyte under D.C. voltage increased at a constant speed, by anode oxidizing and depositing TiO₂ at one time. The surface microstructure of composite films was observed by SEM, and composition was characterized by EDS. The results showed that the surface microstructure is different to porous anode alumina film (PAA), no micropore structure existing; and contained Ti atoms. The corrosion behavior of Aluminum alloy electrodes coated respectively by Al₂O₃/TiO₂ composite films and PAA films in 3.5% NaCl solution at room temperature were compared and studied by the measurements to corrosion potential changes over time, electrochemical impedance spectroscopy (EIS), and polarization curves. The results indicated that the corrosion mechanism of those two electrodes was different in this solution under natural condition; corrosion resistant in Al₂O₃/TiO₂ composite films was higher than that in PAA films; the same property in the electrode covered by Al₂O₃/TiO₂ composite films (EDTA : Ti³⁺=4 : 1, by molar ratio) was higher than that in PAA electrode, and pitting corrosion resistant in both electrodes was much more better than that in Aluminum alloy.TiO₂ films were formed on NiP transition layers of Q235 carbon steel in TiPO₄ solution by anode deposition with constant potential. The surface microstructure of TiO₂ films was observed by environmental scanning electron microscopy (ESEM), and surface composition was analyzed by EDS. The results showed that: there was little difference between NiP/TiO₂ composite films and NiP coating layers in the microstructure when the pH value of the electrolyte was around 2, however, micro-cracks generated when pH value reached 3; and contained Ti atoms. The corrosion behavior of Q235 carbon steel electrodes coated respectively by NiP/TiO₂ composite films and NiP coating layers were investigated and compared by measurements to EIS and polarization curves in 3.5% NaCl solution at room temperature. The results showed that their mechanisms of corrosion were different in the corrosive media, corrosion resistance of the former was higher than that in the latter. The paper introduced a new electrochemical approach to deposit TiO₂ film on the NiP coating to replace sol-gel method. The new method simplified technique, reduced costs; in addition, TiPO₄ electrolyte replaced TiCl₃ solution, avoided the introduction of Cl^- which could cause pitting corrosion easily on carbon steel.