【作者】 黄先球；

【导师】 张鉴清； 张昭；

【作者基本信息】 浙江大学 ， 化学， 2013， 博士

【摘要】 电镀锡板广泛应用于各种形态物品如化工、油漆、喷雾剂、食品、饮料的包装和各种器皿的制造。一直以来,锡板的电沉积和耐蚀性能一直是生产企业特别关心的问题。电沉积成核与生长机理对镀层的结构、相组成具有十分重大的影响,进一步影响镀层的耐蚀性能及其使用条件。采用电化学手段和技术(计时安培法、循环伏安法、电化学阻抗谱,电化学噪声等)开展锡电沉积过程的成核／生长机制方面的研究,对于探索和深入理解金属电沉积的电化学理论,开发新型电镀添加剂,提高电镀锡板的耐蚀能力等,具有极其重要的理论和实际指导意义。同时,镀层的软熔和钝化是提高镀锡板耐蚀性能的两个重要方法,研究其工艺参数并加以优化,有助于得到耐蚀性能更优的镀锡板。本论文主要分为两部分,第一部分研究了镀锡板电沉积成核与生长机理,采用电化学方法分别建立了相关的机理模型；第二部分研究了镀锡板的两种防护技术：软熔及钝化,并以镀层的耐蚀性能为指标优化出最佳的工艺参数。论文首先研究了镀锡板的电沉积成核与生长机制。以镀锡板的耐蚀性能为指标,主要通过电化学阻抗谱评价不同工艺(主盐浓度、镀液pH值、温度、电流密度等)得到的镀锡板的耐蚀性能,从而优化得到最佳电沉积工艺。通过循环伏安方法判断出在此电沉积条件下,锡的电沉积行为为三维成核与生长机理,且主要受扩散控制。采用电势阶跃的方法研究了不同过电位下瞬时成核与连续成核类型,成核与生长速率常数等。结果表明,镀锡板电沉积随着过电位的增大,成核与生长机制由连续成核转变为瞬时成核。考虑到沉积过程伴随着析氢反应,基于成核与析氢过程总电流建立了新的电流—时间曲线模型,并以此计算出镀锡板真实的成核与生长速率常数。阶跃结果表明,较低恒电位沉积时,沉积总电流主要由锡的成核与生长电流和基底表面的析氢反应电流,以及锡核表面的析氢反应电流三部分组成；较高恒电位沉积时,沉积总电流主要由锡的成核与生长电流和锡核表面的析氢反应电流组成。同时采用电化学阻抗研究了镀锡板电沉积机理。结果表明,镀锡板电沉积过程的电荷转移电阻与沉积过电位间存在着指数衰减的关系。进一步采用电化学电位噪声的方法探讨了电位噪声特征与镀层结构间的对应关系。当镀锡板结晶颗粒较大或有枝晶时,电位噪声波动幅动较大且电位出现正移,而当镀锡板表面平整致密时,电位噪声波动幅动较小且电位正移值很小。相对能量分布谱得到的沉积过程中的生长能量与X射线衍射测得的镀锡板的晶粒尺寸具有随恒电流变化相同的变化趋势。其次,论文研究了镀锡板的软熔工艺与性能。利用电化学测试和表面分析手段研究了软熔处理温度和时间对镀锡钢板中合金层及其在3.5%NaCl溶液中腐蚀电化学行为的影响。结果显示,软熔处理温度和时间增加,镀锡钢板的合金层数量增多,且腐蚀电位正移,对应腐蚀速率下降。与锡偶接后,脱锡处理后的镀锡钢板初始阶段作为阴极而锡作为阳极。然而经过一段时间后,电偶对的极性反转。而且,软熔处理温度和时间增加,电偶电流下降。最后,论文探讨了镀锡板的钝化工艺与性能。以镀锡板的耐蚀性能为指标,采用极化曲线和电化学阻抗谱的方法研究了不同工艺下的钝化镀锡板的耐蚀性能。结果表明,钝化镀锡板耐蚀性能随着浓度、时间以及温度呈现出先上升而下降的趋势,这是钝化膜的生成与氧化膜的溶解共同作用的结果。更多还原

【Abstract】 Electrolytic tinplate is widely used in various forms of items such as chemical, paint, spray, food and beverage packaging and manufacturing of various kinds of vessels. For a long time, electroplating mechanism and corrosion resistant properties of tin plate has been the special concern of the production enterprises. Nucleation and growth mechanism has the very big impact on the electrodeposition of coating structure, phase composition, further influence on the performance of the coating corrosion resistance and its wide application. The study on electrodeposition nucleation/growth mechanism by electrochemical methods and technology (chronoamperometry, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), electrochemical noise (EN)) is beneficial to explore and understand metal electrodeposition of electrochemical theory, development of new type electroplating additives, improve the corrosion resistant ability of electrolytic tinplate, etc., which also has extremely important theoretical and practical significance. Meanwhile, reflowing and passivation are two important ways to improve the corrosion resistance of tinplate. The study on the effect of different technological parameters on the corrosion resistance helps to optimize these parameters to get the best corrosion resistance of tinplate.This paper was mainly divided into two parts, one of the works on the nucleation and growth mechanism of tinplate electrodeposition. New mechanism models are established using some electrochemical methods; the other one mainly on the two protection technology:tinplate reflowing and passivation, where the corrosion resistant was used as the target to optimize the related process parameters.This paper first studied the nucleation and growth mechanism of tinplate electrodeposition. The effect of the electrodeposition parameters (main salt concentration, solution pH, temperature, current density, etc.) on the corrosion resistance of tinplate was evaluated mainly by electrochemical impedance spectroscopy to optimize these parameters.Tin electrodeposition behavior follows three-dimensional nucleation and growth mechanism, and mainly controlled by the diffusion, which was confirmed by cyclic voltammetric method. Chronoamperometry was used to differentiate the instantaneous nucleation or progressive nucleation type under different overpotentials, nucleation and growth rate constant, etc. The results show that with the increment of overpotentials, nucleation and growth mechanism changes from progressive nucleation into instantaneous nucleation. New current-time model was established based on both the tin nucleation/growth and the simultaneous hydrogen evolution reaction, which was used to analyze the real nucleation and growth rate constant. Chronoamperometry results show that under the lower deposition overpotentials, the total current is composed of tin nucleation/growth current and current of hydrogen evolution reaction on the substrate, as well as on the tin growth centres; while under the higher deposition overpotentials, the total current is composed of tin nucleation/growth current and current of hydrogen evolution reaction on the tin growth centres.Meanwhile, EIS was also used to study the electrodeposition mechanism of tinplate. Results reveal that the charge transfer resistance of the deposition process decreases exponentially with the applied potential bias. Furthermore, electrochemical potential noise was carried out to explore the relationship between the potential noise features and the tinplate structure. EEN generated during the electroplating of dentritic or large conglomerate zinc deposit has large potential oscillation amplitude and positive potential drift while the compact zinc deposit possesses small noise amplitude and little potential drift. The variation trend of the growth energy obtained from the relative energy distribution plot is the same as the tin crystal size from XRD with variation of deposition current density.Secondly, the paper studied the tinplate reflowing process and performance. Effects of reflowing temperature and time on the alloy layer of tinplate and its electrochemical behavior was investigated in3.5%NaCl solution by electrochemical measurements and surface characterization. It is found that with increase of reflowing temperature and time, the amount of alloy layer increases. Then the corrosion potential of detinned tinplate shifts positively and the corrosion rate decreases. After coupled with tin, detinned tinplate is as cathode initially. However, after exposed for some time, the potential shifts of both detinned tinplate and tin reverse polarity of coupling system. The galvanic current density decreases with increase of reflowing temperature and time.Finally, the paper discusses the passivation process of tinplate. The corrosion resistance was used as the target to evaluate the effect of different passivation parameters, mainly by the method of polarization curve and EIS. The results show that the variation trend of the corrosion resistance with the passivation parameters, is initially rise and then drop, which is the result from the joint action of both the growth of passive film and dissolvation of oxidation film.更多还原