| A molybdate non-chromate cathodic treatment for tinplate has been systematically developed in this paper, and the composition and properties of molybdate passivation coating were also studied. The effects of the concentration of molybdate and phytic acid, pH, cathodic current density, treatment time and temperature on the properties of passivation coating have been analyzed. Besides, the mechanisms of molybdate passivation coating formation and enhancing corrosion resistance were also discussed in this paper.The optimum composition of the passivation solution was gained by orthogonal test as follows: Na2MoO4 20 ~ 30 g·L–1,phytic acid 5 ~ 8 g·L–1. This passivation solution has good adaptability and 1ong life of service. The best process conditions ware gained by single factor change once time test: cathodic current density 0.5 ~ 2.0 mA·cm–2, pH 3.5 ~ 5.0, treatment temperature 30 ~ 50℃and treatment time 30 ~ 60 seconds. A corrosion-protecting and finely attached thin film is formed on the surface of tinplate by this molybadate non-chromate treatment.The effects of the cathodic current density, treatment temperature, pH and treatment time on the properties of passivation coating have been studied using 3wt% CuSO4 spot test. The corrosion resistances of passive film and tin-plating film were studied by dipping in salt solution and periodic wet-dry test. Waste production could not be found on the surface of tin-plating film passivated by Na2MoO4 dipping in salt solution after one week. The weight-loss of Na2MoO4 passive film is one or one and half times the chromate film and 75% of the tin-plating film. So Na2MoO4 passive film improved the corrosion resistance and ability of anti-waste production of tin-plating film.The surface appearance of the film and the mechanism of passivate procession were investigated by SEM and EDAX analysis.Potential–time curve, polarization curve, galvanostatic charging curve and electrochemical impedance spectroscopy on passive films and tin-plating film were investigated. The electrochemical parameters of electrochemistry were gained by computer fitting. Using the parameters of Rp, icorr, Ecorr, the corrosion resistance and anti-corrosin mechanisms of Na2MoO4 passive film and chromate film was compared and analysised.Integrating the results from experiments, passivation coating became thickening with treatment time increasing, the cracking easily occurs when the passivation coating over definite thicken during the passivation coating growth process. It is possible that the incidence of cracking acted as means of stress relief. It can be concluded that Na2MoO4 passive film greatly improved the corrosion resistance and the anti-ability of waste production by inhibit the cathodic and anodic process on the tin-plating film.
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