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摘要751价铬钝化是目前应用最广泛的镀锌层钝化工艺，但是751价铬钝化液中的751价铬化合物具有高毒性和致癌性，对环境污染严重，对工人的身体影响很大，在实际生产过程中，以及后续的废水、废渣处理过程中都会产生极大的不安全因素。因此必须寻找一种毒性低、性能上与751价铬钝化液接近的钝化工艺来替代751价铬钝化工艺。三价铬钝化在许多方面具有与751价铬钝化相似的性质，而毒性却只有751价铬的 1％，是751价铬钝化最有可能被接受的替代品，得到了研究者的广泛关注。6208
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本课题的目的在于研究出一种对环境毒性低的三价铬钝化工艺，用以取代毒性高的751价铬钝化工艺。该工艺要求能够在镀锌层上形成一层致密的三价铬钝化膜，该工艺以CrCl3•6H2O为主成膜剂；NaF为配位剂；HNO3为氧化剂；Co2+为活化金属离子，活化钝化液及增加钝化膜的耐蚀性；SO42-为金属溶解的促进剂，通过加速阳极溶解使膜的生成速度加快，缩短钝化时间；实验中还探讨了pH值、钝化时间、不同的稀土和耐蚀性的关系，并对钝化膜的成膜机理进行了简要的讨论。6208
按照国家标准的检验方法检验了这种三价铬钝化膜的性能，结果表明，该钝化膜具有满意的附着力，钝化膜呈浅蓝色。但与751价铬钝化膜相比，还存在一定的差距，有待于进一步改进。
关键词：镀锌 三价铬 钝化 稀土
Study of trivalent chromium passivation solution
Abstract
The Cr(Ⅵ) passivation is applying very widely in passivation technics on zinc and zinc alloys. But the Cr(Ⅵ) has great toxicity with the environment and can bring cancer to the workers. It is very dangerous in the producing process and the dispose process of waste water and residue. So, to find a Cr(Ⅵ)-free passivation technics which not only can protect the environment but has the analogous capability to the Cr(Ⅵ) passivation. Cr(Ⅲ) passivation possesses as good performance as Cr(Ⅵ) passivation, but the toxicity realated to Cr(Ⅲ) passivation is only one percent of the latter one, thus Cr(Ⅲ) passivation will be the most acceptable technics instead of Cr(Ⅵ) passivation and attracts many researchers’attention.
A new Cr(Ⅲ) passivation technics is found which can protect the environment and be the good substitute of Cr(Ⅵ) passivation. The new technics can form a Cr(Ⅲ) conversion layer。In this processing solution, Cr(Ⅲ) which is offered by CrCl3•6H2O is the main element of the conversion layer; Sodium fluoride can form awater-soluble complex with Cr(Ⅲ); HNO3 is the oxidant; Co2+ present in an amount effective to activate the bath and improve the corrosion resistance of the passivate film; SO42- is the accelerant of metal deliquescence which quicks the formation of passivate film and shorts the passivation time by accelerating anode’s deliquescence; The correlation among the passivating parameters and the morphology and corrosion resistance of the electroplated zinc coating were explored. The formation mechanism of passivate film were also discussed.
According to national standard method, we test the capability of the passivate film. The result indicate that the capability of the film is a satisfactory. The Passivation film is the light blue. But the chroma and corrosion resistance of the Cr(Ⅲ) passivate film are inferior to Cr(Ⅵ) passivate film, so it should be improved more.
Keywords: zinc plating Cr(Ⅲ) passivation REES
一．前言
1.2镀锌层表面的钝化技术
金属材料长期以来一直广泛应用于社会生产和生活的各个方面。为了改善性能，．提高表面质量和延长使用寿命，金属制品一般都要进行适当的表面处理。钝化处理作为一种重要的表面防蚀处理手段，普遍运用在许多金属，尤其是锌、铝、镉、锡、镁等金属及其合金材料上。钢铁锌镀层是廉价镀层，由于锌的电位比铁负，当镀锌钢铁件受到腐蚀介质侵蚀时，锌作为阳极首先腐蚀，保护铁基。因而镀锌是提高钢铁抗腐蚀性的有效方法。但是，在潮湿的环境中储存或运输的过程中，锌层容易腐蚀，使锌层表面形成一层白色疏松的腐蚀产物，或者变成灰暗的颜色，影响镀层外观及使用寿命，因而必须进行钝化处理。