电镀锌钢板黑变机理的动力学

Kinetic study of black patina on electrogalvanized steel sheets

为探索铬酸盐钝化膜提高锌镀层耐蚀性的机理和研究其发生黑变的初期腐蚀现象， 对电镀锌钢板黑变的动力学规律进行了研究。以湿热实验中镀锌层表面明度差随时间变化的关系来表征钝化和未钝化试片腐蚀的速度， 发现钝化后的镀锌层的腐蚀规律符合Ｗａｇｎｅｒ 方程， 未钝化的镀锌层的腐蚀规律符合对数方程， 并求出了相应的腐蚀反应的活化能。钝化使腐蚀反应的活化能提高了一个数量级以上。实验结果表明该腐蚀是由于氧的向内扩散和锌离子的向外扩散， 钝化膜的存在影响了腐蚀的历程。

In order to make clear the mechanism of that the chromate passivation film increases the corrosion resistance of the zinc coating and to study the black patina which is a kind of prime corrosion phenomenon, the dynamic regulation about the black patina of electrogalvanized steel sheets has been studied. The corrosion rate of zinc coating is characterized by the relationships of surface lightness differences of chromated and unchromated sheets with test time in humidity cabinet test (HCT). It is found that corrosion regulation of chromated zinc coating conforms to Wagner equation and that of unchromated zinc coating conforms to logarithm equation,and the corresponding activity energy of the corrosion reaction was figured out. It is also found that the passivation makes the activity energy raise more than one order of magnitude. These experimental results show that the corrosion is caused by the diffusion of oxygen towards inner and the diffusion of zinc ion towards external in passivating film, and the existence of the passivating film affects the corrosion mechanism.