摘要
镀锌钢板经过铬酸盐钝化处理后，可获得具有良好外观和极佳耐蚀性的钝化膜。但六价铬是剧毒性物质，对人体和环境有极大的危害。为了消除六价铬的不利影响，须找到一种锌层铬酸盐钝化的替代工艺。
本文通过SEM、XPS、钝化膜极化电阻率测定、耐盐雾实验等方法研究了SiO_2、Ce~(1-)、Cl~-、Fe~(2-)等对锌电镀层三价铬钝化膜的影响。
SiO_2在钝化处理液中以胶体颗粒的形式存在，其含量须与主要成膜剂三价铬盐成一定比例，才能保持溶液的稳定，形成光亮透明、颜色鲜艳、耐蚀性好的三价铬钝化膜。
Cl~-是金属溶解的促进剂，通过加速阳极溶解使膜的生成速度加快，缩短钝化时间。另外，Cl~-通过“阴离子效应”使胶体沉淀反应匀速进行，生成均匀细小的沉淀颗粒，充分地填充在钝化膜的孔隙中，提高膜的耐蚀性。
Ce~(4-)在酸性溶液中有很强的氧化性，可通过消除阴极反应的极化提高电化学反应速度，使Cr~(3-)钝化膜的厚度增加。Ce~(4-)离子及其还原产物与溶液中的阴离子形成复杂的不溶性化合物沉积在钝化膜的孔隙中，使钝化膜更加致密。这两个方面对钝化膜耐蚀性的提高均有显著作用。Ce~(4+)还可加深钝化膜的颜色。
Fe~(2-)主要是通过与Ce~(4-)的协同效应改善钝化膜的颜色，对钝化膜的耐蚀性贡献不大。
经正交实验研究出FS-3配方，并确立了FS-3配方的工艺流程和工艺参数。FS-3钝化膜的外观及耐蚀性可与六价铬钝化膜相媲美，其耐热性优于六价铬钝化膜。
对锌电镀层FS-3钝化膜生成机理的讨论说明，FS-3钝化膜生成过程是一个电化学反应、胶体聚沉、沉淀等反应相互交织的复杂过程。XPS分析表明，钝化膜中含Zn、Cr、Si、O、F、Ce、Cl、Fe、S等元素，由多种金属化合物及其水合物构成。
Through surface passivating treatment with chromate, Zinc electrodeposited sheet can get passivation film with good external appearance and corrosion resistance. But being toxic, Cr6* has great poisonousness to human body and environment. To avoid the disadvantageous influence of Cr6+, it' s needed to find alternatives to chromate passivation.
This paper studys the effect of SiO Ce1+ CTand Fe2+ to Cr3+ passivation film by means of SEM. XPS. measurement in polarization resistance rate and salt spray test.
Existing in the passivation liquid as colloid granule, SiO2 s content must be in proportion to trivalent chromium, so as to retain the passivation liquid' s stabilization and get transparent trivalent chromating film with bright color and better corrosion-resistance.
OF is the accelerant of metal deliquescence. It quickens the formation of passivation film, shortens passivation time by accelerating anode' s deliquescence. In addition, by "anion effect" , CT makes the reaction of colloid precipitation go along at even speed so as to get even fine granule. The granules fill in the holes of passivation film richly and advance the film' s corrosion-resistance.
Ce'1+ has very strong oxidbillity in the acidity liquor and can accelerate electrochemistry reaction by reducing polarization of cathode reaction to increase the thickness of film. Ce'4+ and its deoxidization productions together with all kinds of anions in liquid form complicated infusibility compounds. The compounds settle into the holes of passivation film to make the film more compact. These two aspects improve the film' s corrosion resistance obviously.
Fe2+ chiefly polishes up the film's color in coordination with Ce4+, doesn' t function much to corrosion resistance.
Through orthogonal experiment , FS-3 passivation composition , the process and parameters are studied and established. FS-3 passivation film ' s external appearance and corrosion-resistance can compare with that of chromating. Moreover, the peformance of heat tolerance is more excellent.
Above Discussion about the formation machanism of FS-3 passivation film illustrates that the formation process is a complex process composed of electrochemistry reaction . colloid polymerized . precipitation reaction, etc. Through XPS analysis, FS-3 passivation film contains multiple elements such as Zn. Cr. Si. 0. F. Ce. Cl. Fe. S, etc, composed of many metal compounds and their hydrates.
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