无铬达克罗涂液的制备与性能研究

【作者】 高节明；

【导师】 朱晓云；

【作者基本信息】 昆明理工大学 ， 材料学， 2007， 硕士

【摘要】 达克罗技术是一项高耐蚀、无氢脆和对环境污染小的金属表面防腐新技术,自其问世以来便得到了极广泛的应用。然而它还存在一定的缺点和不足,需要进一步研究和改进。从环保方面讲,六价铬是最大的问题,因为它的毒性强而且具有致癌作用,所以世界上工业发达国家的汽车行业中许多名牌车辆都率先制定了采用无铬涂层的技术标准,在其它行业中达克罗的应用也都开始向低铬和无铬方向发展,寻找各方面的性能都较优的无铬替代品是达克罗技术必然发展方向。本论文研究目的是通过试验寻找一种不含铬的酸体系,代替有铬达克罗涂液中的铬酸,制备出一种水溶性无铬达克罗涂液,使用此涂液制取的涂层具有一定防腐性能。本论文主要研究内容是无铬酸体系的选择研究和无铬达克罗涂液的制备。无铬酸体系的选择研究是以铬同类族的酸或盐为基础,加入有机酸或无机酸配制成不含铬的酸体系。通过对酸体系的自身相容性和稳定性试验研究,确定酸体系组成;采用正交试验法确定酸体系的配方。结果表明,无铬酸体系为由钼酸钠、硼酸、甲酸组成的水溶液。其最佳配方是钼酸钠10wt%,硼酸1wt%,甲酸8wt%。酸体系中钼酸钠对涂层性能影响最大,硼酸次之,甲酸最小。采用正交试验研究无铬达克罗涂液配方和工艺。以酸体系、锌粉、铝粉、聚乙二醇和烧结温度与时间作为因素考虑,涂层的外观、附着力和5%NaCl浸泡试验作为指标。选择设计了正交试验表L₂₇(3¹³)进行试验,确定无铬达克罗涂液的配方和工艺。通过正交试验研究涂液组分与涂层烧结工艺,以及通过对涂层性能进行检测、无铬涂层和有铬涂层进行对比的研究,结果表明,制备无铬达克罗涂液的最优值为:锌粉300g/L,铝粉70g/L,混合酸40g/L,聚乙二醇为180g/L,工艺是烧结温度300℃,烧结时间30分钟。制取的无铬涂层的5%NaCl浸泡出红锈时间为1500h,中性盐雾试验720h。采用金相显微镜和扫描电镜分析涂层表面形貌和截面形貌,结果表明,涂层均匀、连续,与基体结合紧密。通过能谱分析仪和X射线衍射仪对涂层元素组成和相组成进行了分析,结果表明:涂层中存在大量的Zn和Al,其总量超过70%,它们对涂层起着牺牲阳极保护作用,其中Zn的耐蚀作用最大。涂层中还存在质量百分比为20%左右的氧元素,它与Zn、Al之间形成的氧化物起到了有效的钝化作用。综上所述,本实验制得了不含铬的酸体系和水溶性无铬达克罗涂液,用此涂液制取的涂层具有一定的耐蚀性能。通过本文研究,为无铬达克罗涂液的制备提供一种新方法,对进一步研究和改进无铬达克罗涂液有一定的参考价值。更多还原

【Abstract】 Dacromet technology is a new metal surface anti-corrosion technology which has many advantages such as high corrosion resistance, no hydrogen embrittlement and small environmental pollution, it has been widely applied since it came out. However, it has some shortcomings and deficiencies need to be further studied and improved. From the environmental point of view, hexavalent chromium is the biggest problem for its high toxicity and carcinogenic effect. In the auto-industry of developed industrialized countries in the world, many famous brand vehicles have adopted chromium-free coating technical standard. In other industries adopting the low chromium and chromium-free standard is also the trend of the application of dacromet. Looking for the chromium-free substitutes which have superior performance in all aspects is an inevitable developmental direction of dacromet technology.The purpose of this paper is through experiment to find a chromium-free acid system which could instead of the chromic acid in the chromium dacromet liquid, and prepare a new kind of chromium-free dacromet liquid which has anti-corrosion performance.The main contents of this paper are to research the selection of chromium-free acid system and prepare chromium-free dacromet dope liquid. The selection of chromium-free acid system is basicd of acid or salt being similar to chromium, and is prepared by adding organic acids or inorganic acid. Through researching the compatibility and stability of acid system, we determined its composition, Through orthogonal testing ,we determine the composition of acid system. The results show that the chromium-free acid system is composed of Sodium molybdate and boracic acid and methanoic acid. The best composition is that the percentage of Sodium molybdate is 10%, the percentage of boracic acid is 1%, and the percentage of methanoic acid is 8%. Sodium molybdate has the greatest impact on the coating, the second is boracic acid and the third is methanoic acid.Adopting the orthogonal experiment to study the composition and craft of chromium-free dacromet dope liquid. The acid system, zinc powder, aluminum powder, polyethylene glycol, the sintering temperature and time as a factor to consider, the coating appearance, adhesion and 5% NaCl immersion testing as a factor to indicate, and using the orthogonal experiment by the table of L₂₇ ( 3¹³) to design the chromium-free dacromet dope liquid composition and craft. According to studying the dope liquid composition by orthogonal experiment and coating sinter craft, and examining the coating performance, and contrasting the chromium-free dacromet coating with the chromium daromet coating, all of analysis results indicate that the excellent composition of preparing the chromium-free decromet dope liquid is as follow, Zinc powder is 300g/L, Aluminium powder is 70g/L, the mixed acid is 40g/L, assemble glycol is 180g/L, technics agglomeration temperature is 300°C and time is 30 minute. The time of appearancing red rust is 1500h in 5%NaCl liquid and is 720h in the neutral salt mist.Using the metallographic microscope and scan electricity mirror to analyzing coating surface appearance and section appearance, the results show that the coating is uniformity and continuum, and which is tight combined with radicle object. Using the power spectrum analyzer and X beam diffraction instrument to analyzing coating element composition and appearance composition, the results show that costing consisted of a mass of Zn and Al, and the gross of Zn and Al is more than 70%, and the quality percentage of oxygen is about 20%, three substances form the oxide which has effective passivation action. In summary, those experiments made a chromium-free acid system and water-solubility chromium-free dacromet dope liquid, and the coating has excellent anti-corrosion performance. The study in this paper provides a new method of preparing chromium-free dacromet dope liquid, and has a reference value of researching and improving chromium-free dacromet dope liquid.更多还原