【作者】 毕四富；

【导师】 李宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 硕士

【摘要】 六价铬黑色钝化工艺通常用于提高锌及锌铁合金镀层的耐蚀性能和装饰性能。由于六价铬有毒,具有致癌性,对人体和环境均有很大的危害;而三价铬钝化工艺无毒,所得膜层具有与六价铬钝化膜层相似的性能,是最有可能替代六价铬钝化的工艺。本论文研究了锌及锌铁合金镀层的三价铬黑色钝化工艺,并对其成膜过程与耐蚀机制进行了初步探讨。通过初选、单因素和正交试验,分别获得了镀锌层和锌铁合金镀层三价铬黑色钝化的基础工艺。采用此两种工艺均可获得均匀黑亮,结合力良好的黑色膜层。膜层耐蚀性相对较差,耐醋酸铅点滴时间仅有5~8 s,中性盐雾试验(NSS)出白锈时间仅有24 h。为提高膜层耐蚀性,采用醋酸铅点滴、NSS试验以及Tafel、EIS电化学测试研究了钝化封闭一步法,并与商品化封闭剂进行了对比。结果表明向钝化液中添加合适的添加剂能够提高膜层耐蚀性。在基础工艺的基础上得到了比较理想的镀锌层和锌铁合金镀层三价铬黑色钝化工艺;该钝化液含有添加剂A,所得膜层均匀黑亮,结合力良好,具有良好的耐蚀性能,NSS试验出白锈时间超过96 h;该膜层耐蚀性能与增加后封闭工序相当。还考察了烘烤对膜层耐蚀性能的影响,结果表明在适当的温度下进行充分老化能够一定程度上提高耐蚀性能。运用AFM、SEM、XRF、XPS以及Tafel、EIS电化学测试手段研究了不同钝化时间和不同温度的三价铬黑色钝化膜层性能。确定了三价铬黑色钝化膜层的形成过程。试验结果表明所得钝化膜主要由Cr、Zn、P、O等元素组成,存在形式为Cr2O3、Zn(OH)2和磷酸盐。试验结果也说明三价铬黑色钝化膜的耐蚀性主要由锌、铬氧化膜的机械隔离作用产生;耐蚀性较差的膜层具有许多微裂纹,破坏了膜层完整性,降低了锌、铬氧化膜的机械隔离作用,影响了耐蚀性。更多还原

【Abstract】 Black chromate passivation films on zinc and zinc-iron alloy coating have been used to improve the corrosion resistance, and the decorative properties of the substrates. The Cr(VI) is toxic and carcinogenic, which is hazardous to man or the environment. A nontoxic trivalent chrome passivation film has similar functional properties, and becomes a viable Cr(VI)-free conversion coating as the most adequate alternative to date. In the present paper, trivalent chrome black passivation technologes on zinc and zinc-iron alloy coating were investigated. The forming process and the corrosion mechanism of the black trivalent passivation film were also discussed.In this paper, the primary trivalent chromium black passivation technologies on Zn and zinc-iron alloy coating were confirmed by single factor and orthogonal test methods. The passivation films obtained from the two passivation baths have bright black surface with uniform color, good adhesion to the coating. However, the corrosion resistance of the black passivation film is poor for that the Pb(Ac)2 corrosion time was only 5~8 s, and the presence of white rust on the passivation after exposure in Neutral Salt Spray (NSS) was only 24 h.A one-step of passivation process on zinc and zinc-iron alloy coating was investigated by Pb(Ac)2 corrosion, NSS, Tafel polarization and electrochemical impedance spectrum. The effects of this passivation process on the film corrosion resistance were compared with the commercial sealing agent. The results show that the appropriate additive agent can improve the corrosion resistance of passivating film. The optimal passivation technologies of trivalent chrome black passivation on zinc and zinc-iron alloy were confirmed based on the primary passivation technologies by the above experiments. These two passivation baths include chromium (III) ions, nitrate ions, cobalt (II) ions, nickel (II) ions, phosphate, organic acid and additive agent A. As the results, the passivation film obtained from the optimal technology has bright black surface with uniform color, good adhesion to the electroplated zinc and zinc-iron alloy coating. The passivation film has preferable corrosion resistance, and no white rust was generated on the passivated zinc and zinc-iron alloy coating after exposure in NSS for 96h, which is equivalent to that after sealing process. The performance of corrosion resistance is studied in the different temperature of roasting. The results show that full aging under some appropriate temperature can improve the characteristic of anti-corrosion to some extend.The properties of trivalent chromium passivation film at different time and temperature were studied by measuring the Tafel polarization, EIS in combination with atomic force microscopy, scanning electron microscope, X-ray fluorescence spectrometer and X-ray photoelectron spectroscopy surface analysis. A model for understanding the trivalent chromium black passivation process was proposed based on the experimental data. The results show that the Cr, Zn, P and O were the main components of the coating. These elements of the coating were in the form of Cr2O3, Zn(OH)2 and phosphate. It also demonstrates that the trivalent chromium black passivation film acts as a barrier, which prevents the contact of substrate Zn with corrosive environment. The many small cracks on the black coating surface damage the integrality of the coating and decrease the corrosion resistance.更多还原