Preparation Of Silane Films On The Surface Of Metal And Study On Corrosion Protection

The silane films is one of environmental techniques of metal surface pretreatment in resent years. It is a technology to apply silane coupling agents in metal pretreatments, which has great advantages such as no pollution, low cost, wide application and excellent corrosion resistance, therefore attracts many experts'attention. This dissertation paid attention to the following work: selecting dodecyltrimethoxysilane(DTMS) andγ-aminopropyltriethoxysilane(γ-APS) silanes, studying their processes of hydrolysis and the preparation of silane films and testing corrosion properties of metals pretreated by them. As a result, many important and applied conclusions were obtained.The hydrolysis degree of silanes was reflected by using the conductivity testing method online not disturbing and destroying the solution system. It was found out that the stability of silane solution was related to the constitution of hydrolysis solution, hydrolysis time, pH value, temperature. The results indicated that the stability of silane solution decreased with hydrolysis time and concentration increasing during hydrolyzing in mixing solvent with ethanol and water. The two silanes hydrolyzed had the best constitution of hydrolysis solution.High pH value contributed to hydrolyze and low pH value helped to condense. The optimum hydrolysis temperature was between 20℃to 40℃.The optimum process conditions of prepared DTMS silane film on the 6063 aluminum alloys surface was studied by orthogonal experiment. The corrosion resistance of the silane films was investigated in 3.50%NaCl solution, using the open circuit potential, Tafel curves, Linear sweep voltammetry testings and electrochemical impedance spectroscopy (EIS). The equivalent circuit was obtained by EIS. Coating time, curing time and curing temperature were studied for corrosion resistance. The results indicated that the optimum process conditions for DTMS was got by orthogonal experiment. Silane films had a very good corrosion resistance for alloys in 3.50%NaCl solution and coating time had more influence in the optimum process conditions.The optimum process conditions of preparedγ-APS silane film on cold rolled steel was studied by orthogonal experiment. The corrosion resistance of the silane films was investigated in 3.50%NaCl solution, using the Tafel curves, anode polarization curve testings and electrochemical impedance spectroscopy (EIS). The uniform and compact silane film could be formed or not on the CRS when the surface of CRS was pretreated in CeCl3 or NaOH. The results indicated that the optimum process conditions forγ-APS was obtained by orthogonal experiment. The prepared films led to the large increase in polarization resistance and therefore the evident decrease in corrosion current density. The uniform and compact silane film could be formed when the surface of CRS was pretreated especially in CeCl3.The chemical structure and the morphologies of silane films were characterized by FI-IR and SEM. The results indicated that silanes hydrolyzed to produce silanol. The surface of metals was formed a uniform and compact silane films nearly unchanged before and after corrosion.