镀锌层上单宁酸钝化膜的耐腐蚀性能

Corrosion Resistance of Tannic Acid Passivation Coating on Zinc Coating

为提高镀锌板的耐蚀性,以硝酸、氟化铵、氧氯化锆为辅助成分,配制了单宁酸钝化液,并用其对镀锌板进行钝化处理。通过浸泡试验确定了最佳钝化工艺,通过扫描电镜(SEM)、Tafel曲线和交流阻抗谱研究了不同条件制备的钝化膜的形貌、耐蚀性。结果表明:镀锌层经1 mol/L氢氧化钾溶液于65℃活化30 s后再在含10 g/L氧氯化锆的钝化液中钝化,所得钝化膜致密,出白锈时间可达100 h;单宁酸钝化膜有效抑制了镀锌层腐蚀的阳极过程,提高了镀锌板耐蚀性;钝化前对镀锌板活化以及在钝化液中添加氧氯化锆均能提高钝化膜的致密度及耐蚀性。

Tannic acid passivating solution containing HNO3,NH4F and ZrOCl2 as the auxiliary ingredients was formulated and used to prepare tannic acid conversion coating on galvanized steel sheet.The optimized passivation process was established based on immersion tests.The morphology of the conversion coating was observed using a scanning electron microscope.The corrosion resistance of the conversion coating was evaluated using Tafel curve and electrochemical impedance spectrum.It was found that compact tannic acid conversion coating could be obtained by activating the galvanized steel sheet in 1 mol/L KOH solution at 65 ℃ for 30 s in association with passivation in the passivation fluid containing 10 g/L ZrOCl2.Resultant tannic acid conversion coating was free of white rust for up to 100 h.In one word,as-prepared tannic acid conversion coating was able to effectively retard the anodic process of galvanizing coating and increase the corrosion resistance of the galvanized steel.Activation of the galvanized steel sheet before passivation and introduction of ZrOCl2 into the passivation fluid could both improve the compactness and corrosion resistance of the passivation coating.