镀锌层单宁酸钝化膜的耐蚀性

为提高镀锌层的耐蚀性,以氟钛酸钾、双氧水、硝酸为辅助成分,制备了单宁酸钝化液,并对低碳钢上的碱性镀锌层进行了钝化处理.通过质量分数为5%的NaCl溶液浸泡试验,确定了最佳钝化液组成和钝化工艺条件为:单宁酸40 g/L,HNO3 5 mL/L,氟钛酸钾10g/L,H2O2 60 mL/L,温度25℃,时间20～30 s....

Corrosion resistance of passive film converted on zinc coating from tannic acid system

To improve the corrosion resistance of zinc coating,low-carbon steel substrate coated by alkaline zinc plating process was passivated in tannic acid system using potassium fluotitanate,hydrogen peroxide and nitric acid as the auxiliary agents. The composition of passivation bath and process parameters of passivation were optimized by immersion test in 5wt% NaCl solution. The optimal bath composition and process parameters are as follows:tannic acid 40 g/L,HNO3 5 mL/L,potassium fluotitanate 10 g/L,H2O2 60 mL/L,temperature 25 °C,and time 20-30 s. The surface morphology of passive film was analyzed by scanning electron microscopy,and the corrosion resistance was studied by Tafel polarization and electrochemical impendence spectroscopy. The results showed that no white rust appears on the surface of passivated zinc coating within 120 h and the obtained passive film is compact. The passive film is characterized with lower corrosion current,higher corrosion voltage and better corrosion resistance thanthe zinc coating,implying that the passive film prepared from tannic acid can effectively inhibit the anodic process of zinc coating corrosion.