Mixed Rare Earth - Sodium Tripolyphosphate Synergy Passivation Process And Mechanism Research

Galvanize is one of the most important anti-corrosion technology in steel field. Galvanizing steel is widely used in the field of the automotive, appliances, construction, aviation and other fields, because of its good protection against corrosion. But the galvanized steel suffering from corrosion and Generates white corrosion products in wet environment, Seriously affecting the ability of anti-corrosion of galvanized steel. Chromate passivation can significantly improve the ability of anti-corrosion of galvanized steel and chromate paassivation process is simple and inexpensive. But many countries adopted a strict restrictions to the chromate passivating. So it’s received widely attentions which the development of technology of chromium-free passivation and environment-friendly passivation. The article is actively involved in research on nonpoisonous pollution-free coating process of rare earths and the corrosion resistance and composition of the films has been tested by a series of tests. The forming mechanism of films has discussed by summary of test results.First determine the main amount of salt, Oxidants, buffering, additives and scope by the single factor experiments. And determine the best technology by orthogonal test. the single factor test as follows:Rare earth25g/L, Na2SiO37g/L, H2O215ml/L, H3BO330g/L,Na5P3O1015g/L, additives0.8g/L, K2S2O80.3g/L, the pH of Na5P3O10is8, Temperature is room temperature.Study on corrosion resistant properties of composite films by neutral salt spray test, Experiment of copper sulphate and salt water immersion experiment. Test results shows that the composite films has a very strong anti-white embroidery and pitting corrosion resistance, Corrosion-resistant properties of composite films better than low chromate films, polyphosphate films, Single rare earth films. So the effection of collaborative passivation is existed between the rare-earth and phosphate.Research on electrochemical properties of complex films by Potentiodynamic Polarization curves and Electrochemical impedance curves, And contrast with the low chromate films, Single rare earth films and more than a polyphosphate films. Test results shows that the composite films can reduce the corrosion potentials and corrosion currents of the basements. Comparative experiments indicated that the corrosion potentials of composite films higher than the low chromate films, rare earth films and more than a polyphosphate films, the corrosion currents lower than other films.Determination of composition of complex films and elements in valance by XPS, SEM and EDS. Test results shows that the components of composite films is Ce, P,O, Si, Zn and others elements. And the valence of the elements exists in the film are as follows: Ce mainly exists as Ce4+, the specific forms of Ce is phosphate; P mainly exists as P5+, the specific forms of P is phosphate and ZnP3O103-; O mainly exists as O2-, the specific forms of P is phosphate and ZnP3O103-.The morphology of composite films is observed by SEM. The results shows that the composite films surface is smooth and tight.In conclusion, the technology of composite films with the advantages of Non-toxic, pollution-free and simple operation, Composite films has good corrosion resistance. The passivation solution with the advantages of stable and low cost, Having broad application prospects.