Cr(VI) and Cr(III)-Based Conversion Coatings on Zinc-猫眼课题宝

DOI：

10.1016/j.surfcoat.2004.12.002

发表时间：

2005-02

期刊：

影响因子：

通讯作者：

中科院分区：

其他

文献类型：

作者：

X. Zhang;C. V. D. Bos;W. G. Sloof;A. Hovestad;H. Terryn;J. Wit

研究并比较了Cr（VI）和Cr（III）处理中锌转化膜的形貌、组成和腐蚀性能。通过椭偏光谱测定，在1分钟的浸泡时间下，Cr（VI）镀液中生成的涂层厚度约为400 nm，而在商业Cr（III）镀液中生成的涂层厚度约为90 nm。通过XPS分析发现，在Cr（VI）液中生成的涂层最外层中，约40%的铬处于Cr（VI）氧化态，约60%的铬处于Cr（III）态。在Cr（III）镀液中制备的涂层中未检测到Cr（VI）。采用直流极化和交流阻抗技术研究了锌在0.01 M NaCl溶液（pH=6）中两种表面处理后的腐蚀行为。还研究了未经处理的锌表面在含不同重铬酸盐浓度的去氧0.01 M NaCl溶液中的行为。在Cr（III）液中生成的涂层在很大程度上抑制了锌的腐蚀，但效果不如在Cr（VI）液中形成的涂层。两种涂层在防腐性能上的差异主要是由于涂层厚度的不同以及可再钝化缺陷的流动Cr（VI）的可用性。

The morphology, composition and corrosion performance of conversion coatings generated on zinc in Cr(VI) and Cr(III) treatments have been studied and compared. With an immersion time of 1 min, the coatings produced in a Cr(VI) bath were about 400 nm thick, whereas the coatings produced in a commercial Cr(III) bath were about 90 nm thick, determined by spectroscopic ellipsometry. By means of XPS, it was found that about 40% of the chromium in the outermost layer of the coating generated in the Cr(VI) bath was in the Cr(VI) oxidation state, while about 60% was in the Cr(III) state. No Cr(VI) was detected in the coating produced in the Cr(III) bath. The corrosion behaviour of zinc in 0.01 M NaCl solution (pH=6) after both types of surface treatment was studied using d.c. polarisation and a.c. impedance techniques. The behaviour of untreated zinc surfaces in de-aerated 0.01 M NaCl solutions containing different concentrations of dichromate was also studied. The coatings generated in the Cr(III) bath inhibited the corrosion of zinc to a significant degree, but less effectively than the coatings formed in the Cr(VI) bath. The difference in the corrosion protection given by the two coating types was attributed to the difference in the coating thickness and to the availability of mobile Cr(VI) species which can repassivate flaws.

Cr(VI) and Cr(III)-Based Conversion Coatings on Zinc

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