热镀锌层硅酸盐钝化膜的耐蚀性

Corrosion Resistance of Silicate Passivation Film on Hot Dipped Galvanizing Coating

热镀锌层的硅酸盐钝化体系无毒无污染、成本低,且使用方便、寿命长,但pH值不稳定,易形成凝胶。研制了一种pH值易于控制的硅酸盐钝化体系对热镀锌层钝化,采用扫描电镜(SEM)和能谱仪分析了镀锌层硅酸盐钝化前后的形貌和成分,通过中性盐雾试验、5%NaCl浸泡试验和极化曲线测试研究了镀锌层、硅酸盐钝化试样、铬酸盐钝化试样的耐蚀性,并分析了硅酸盐钝化膜的耐蚀机理。结果表明:镀锌层表面的硅酸盐钝化膜可抑制镀锌层腐蚀的阳极和阴极过程,阻碍腐蚀反应的进行,同时可对镀锌层机械隔离,提高镀锌层的自腐蚀电位,从而显著改善了镀锌层的耐蚀性能,其防腐蚀效果与铬酸盐钝化膜的相当。

A kind of silicate-based passivation fluid with well controllable pH value was formulated and used for passivation of hot-dipped galvanizing coating.The morphology and composition of the hot-dipped galvanizing coating before and after passivation with the silicate based passivation fluid were analyzed with a scanning electron microscope and an energy dispersive spectrometer.The corrosion resistance of the hot-dipped galvanizing coating,silicate passivated specimen and chromate passivated specimen was comparatively evaluated based on neutral salt-spray tests and immersion tests in 5% NaCl as well as measurement of polarization curves.Moreover,the anticorrosion mechanism of the silicate passivation film was discussed.It was found that the silicate passivation film on hot-dipped galvanizing coating was able to significantly delay the anodic and cathodic process of the galvanizing coating subjected to corrosion,thereby retarding the corrosion reaction.In the meantime,the silicate passivation film was able to mechanically keep off the hot-dipped galvanizing coating and increase its corrosion potential,thereby significantly improving the corrosion resis tance of the hot-dipped galvanizing coating.In one word,the anticorrosion effectiveness of the silicate passivation film on hot dipped galvanizing coating was comparable to that of chromate passivation film.