【作者】 杜艳娜；

【导师】 李国希；

【作者基本信息】 湖南大学 ， 应用化学， 2007， 硕士

【摘要】 本文研究了镀锡钢板的钼酸盐阴极钝化处理工艺,测量了钝化液中钼酸盐钝化液的组成与阴极电流密度等工艺条件对钝化膜耐腐蚀性能的影响,分析了钼酸盐钝化膜的组织结构和耐腐蚀性能,探讨了钼酸盐钝化膜成膜过程及其耐腐蚀机理。采用正交实验确定的钼酸盐钝化液的组成为:钼酸盐20 ~ 30 g·L–1,植酸5 ~ 8 g·L–1。通过单因素实验确定的最佳工艺条件是:阴极电流密度0.5 ~ 2.0 mA·cm–2,温度30 ~ 50℃,pH 3.5 ~ 5.0,时间30 ~ 60 s。钝化液稳定性好,使用寿命长。采用3wt%硫酸铜点滴实验研究了钝化处理时间、温度、阴极电流密度、pH等因素对钝化膜耐腐蚀性的影响;并用盐水浸泡实验和干湿交替实验对钼酸盐钝化膜和铬酸盐钝化膜的耐腐蚀性进行了对比测定。在盐水浸泡实验中,未钝化试样在第4天出现黑斑,钼酸盐钝化后,浸泡7天也没有出现黑斑;钼酸盐钝化试样的腐蚀失重是铬酸盐钝化试样的1 ~ 1.5倍,是未钝化试样的75%。这些都说明钼酸盐钝化显著提高了锡镀层的耐蚀性能和抗黑斑的能力。采用扫描电子显微镜和能量散射谱对钝化和未钝化锡镀层进行了表面形貌观察和成分分析。测量了钝化和未钝化镀锡电极在3.5wt%NaCl溶液中的电位–时间曲线、极化曲线、恒电流充电曲线和电化学阻抗谱。根据腐蚀电化学参数Rp、icorr、Ecorr等分析了钼酸盐钝化膜和铬酸盐钝化膜的耐蚀性能及其作用机理。结果表明,钼酸盐钝化膜随着钝化时间增加而不断增厚,但膜层较厚时容易发生开裂。开裂的原因可能是膜层较厚时产生了比较大的内应力。钼酸盐钝化膜同时抑制了锡镀层腐蚀的阳极和阴极过程。更多还原

【Abstract】 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.更多还原