Process Development Of Metals' Surface Treatment With Silane Solution

Silane surface treatment is a new technology in the field of corrosion control of metals, which has great advantages such as environment-protecting, low cost, wide application and excellent adhesive strength to organic coating, compared with mature industrial phosphating process. Therefore silane surface treatment has wide applications and market value.In this paper, silane solution for surface pretreatment of ordinary low carbon steel was prepared by mixing silane A and silane B, and LaNO₃ nanoparticles as additive is added. The time of corrosion resistance of silane film is 25min in pitting corrosion test of 3% CuSO₄ solution.In the preparation process of silane solution, hydrolysis methods and conditions were studied. Then the optimum conditions were obtained by using single factor experiments & orthogonal experiments, which were showed as: volume ratio between silane A and silane B, 5:1; hydrolysis solvent, distill water; pH, natural pH; hydrolysis temperature, room temperature; hydrolysis time, 48h; silane concentration, 5%. Under the optimum conditions, the time of corrosion resistance can be up to 25min by pitting experiments with 3% CuSO₄ solution.LaNO₃ nanoparticles are as additive, which can improve the corrosion resistance of silane film and have no influence on the stability of silane solution. The optimum concentration of La(NO₃)3 is 0.3g/L by single factor experiments & orthogonal experiments.In the low-carbon steel pretreatment process, the effects of the different treatments and conditions on the substrate microstructure and corrosion resistance of silane film were studied by using scanning electron microscopy and the pitting corrosion test of 3% CuSO₄ solution. The result demonstrate that the best pretreatment methods and conditions of the low-carbon steel before it was impregnated in the silane solution are as follows orderly: cleaning with hydrochloric acid; polishing with 800 mesh sandpaper; ultrasonic cleaning 20 min in the 60℃degreasing solution; washing clearly with a deionized water; ultrasonic cleaning 5 min in the mixture alkali solution and repeating twice; washing clearly with a deionized water.In the forming-film experiments, the corrosion resistance of silane film in the different drying temperatures and drying times were investigated. From the perspective of feasibility and saving energy, the optimal drying temperature (℃) and drying time (min) are 120 and 20 respectively.The prepared silane films under different conditions were characterized by scanning electron microscopy, infrared spectroscopy, salt spray test, electrochemical test an adhesion test. The result demonstrate that the corrosion resistance of the prepared silane films under the optimal conditions increased several times than the prepared film in phosphating process, the paint films and silane films have a strong adhesion with the surface of the substrate and the waste does not contain residues.