【作者】 周新莉；

【导师】 何湘柱；

【作者基本信息】 广东工业大学 ， 应用化学， 2011， 硕士

【摘要】 随着现代工业对材料表面性能要求的提高,多功能合金镀层的研究和应用日愈广泛。铬及其合金镀层不仅外观漂亮,还具有硬度高、耐磨性好、耐蚀性好等优点,已得到广泛的研究和应用。为了取代重污染的六价铬电镀,国内外学者致力于研究环保、低毒的三价铬体系电镀,但三价铬体系的电镀还存在镀液不稳定、镀层难增厚等问题。二氧化锆是一种具有高熔点、热膨胀系数大、导热系数小、耐磨性及耐腐蚀性能优良的无机非金属材料,已被广泛应用于各种领域。本文将纳米ZrO2粉末加入镀液中,通过复合电沉积使纳米ZrO2与铬、镍发生共沉积生成性能良好的Cr-Ni-ZrO2复合镀层。研究了在低电流密度区,低浓度的Ni2+对三价铬电沉积的影响。探讨了镀液中各成分及工艺条件对电沉积Cr-Ni-ZrO2复合镀层的影响。采用SEM、EDS及XRD分别测定了镀层的表面形貌、组成及组织结构,检测了镀层的结合力、耐蚀性、孔隙率和硬度等性能。研究结果和结论如下：(1)在低电流密度区,往三价铬镀液中加入低浓度的Ni2+,所得镀层外观明显好于不含Ni2+的镀液,电沉积25min,镀层厚度为0.46～0.93μm,基本上满足工业生产装饰铬的要求。三价铬电沉积的阴极极化曲线表明,三价铬镀液中低浓度Ni2+的存在,使Cr3+电沉积总反应的极化曲线位于更负的区域,说明Ni2+使Cr3+电沉积总反应的阴极极化增强,更有利于三价铬电沉积形成蓝膜,证明了往三价铬镀液中加Ni2+能够促进三价铬的电沉积。(2)通过单因素实验研究了镀液中各组分如辅助络合剂、主盐、纳米Zr02等浓度对电沉积Cr-Ni-ZrO2复合镀层的影响,采用正交实验对镀液配方进行优化。研究了镀液温度、pH值、电流密度、电沉积时间和搅拌速率对电沉积Cr-Ni-ZrO2复合镀层的影响。在最佳工艺条件下,采用最优的镀液配方电沉积所得镀层,外观光亮,厚度达到8.50μm。SEM和EDS检测结果表明,镀层表面光滑细致,纳米ZrO2粒子均匀分散于镀层中,但不足的是有少许ZrO2粒子发生团聚。镀层中主要含有Cr、Ni、O和Zr四种元素,其质量分数分别为：82.6%、0.41%、9.34%、7.65%,纳米Zr02与Cr、Ni实现了共沉积。(3)与Cr-Ni合金镀层的表面形貌相比,Cr-Ni-ZrO2复合镀层的表面较为平整、微裂纹减细。另外XRD检测结果表明所得Cr-Ni-ZrO2复合镀层为非晶态结构。结合力试验表明Cr-Ni-ZrO2复合镀层的与铜基体的结合力良好。孔隙率试验表明Cr-Ni-ZrO2复合镀层比Cr-Ni合金镀层的结晶更为致密,孔隙率减小。硬度测试表明,镀层中纳米ZrO2粒子的存在,使镀层硬度提高达664.6HV。对镀层的交流阻抗试验和Tafel试验表明,在酸性和碱性介质中,Cr-Ni-ZrO2复合镀层的耐蚀性能优于Cr-Ni合金镀层；在中性介质中,Cr-Ni合金镀层的耐蚀性能略优于Cr-Ni-ZrO2复合镀层。(4)Cr3+电沉积的循环伏安曲线和阴极极化曲线表明,Cr3+电沉积还原反应有两个明显的反应平台,具体发生何反应还有待研究。镀液的阴极极化曲线表明,Cr3+镀液中的Ni2+主要用于促进Cr3+的电沉积,极少用于与Cr3+发生共沉积而生成Cr-Ni合金镀层；辅助络合剂B能够提高镀液的分散能力；添加剂A有利于镀层晶粒的细化,提高镀层光亮度；镀液中加入纳米ZrO2,使Cr3+电沉积的阴极极化增强,加快电沉积反应。更多还原

【Abstract】 Due to its favorable properties such as desirable appearance, high hardness, resistance to wear and corrosive environments etc., Cr-Ni alloy coatings especially obtained by electrodeposition have been being the subject of investigation by numbers of researchers. Environment-friendly and low-toxic trivalent chromium electrodeposition has been being widely studied to replace the heavy-polluting hexavalent chromium electrodeposition both at home and abroad. However, it is of some disadvantage like unstable plating bath, difficult to get thick coatings and so on for trivalent chromium deposition. Owing to its superior properties such as high strength, high melting point, desirable heat stability and wear resistance, nano-ZrO2 particles have been widely used to modify the hardness, abrasive and wear resistance of metal deposits currently. In this work, nano-ZrO2 particles were added to the Cr-Ni plating bath in order to prepare the Cr-Ni-ZrO2 composite coatings with desirable properties by means of co-electrodeposition. Effect of little amount of Ni ions in the bath on trivalent chromium electrodeposition under the condition of low current density was studied. The influence of bath component and process parameters on the co-electrodeposition of Cr-Ni-ZrO2 were also studied. Properties of Cr-Ni-ZrO2 coatings such as surface morphology, composite, organizational structure, corrosion resistance, void fraction and hardness were characterized by means of SEM, EDS, XRD, Tafel plots and electrochemical impedance spectroscopy (EIS) separately. Analyses of the results are as follows:(1) Cr coatings obtained from the plating bath with little amount of nickel ions are of better appearance than that of without nickel ions. The thickness of the coatings obtained from the plating bath with little amount of nickel ions are 0.46～0.93μm, which meets the industrial requirement. Results of cathodic polarization cures show that the LSV of the plating bath shift towards positive side when nickel is added to the bath. That is to say, nickel ions can strengthen cathodic polarization of trivalent chromium and promoting the forming of blue film. It is demonstrated that the addition of little amount of nickel ions has a catalytic effect on chromium deposition.(2) Effects of concentration of auxiliary complexing agent, main salt, nano-ZrO2 particles and additive A on the thickness and appearance of Cr-Ni-ZrO2 coatings were studied by single-factor experiments, and the bath formula was optimized by orthonormal experiments. Effects of tempture, pH, current density, deposition time and stirring speed on the thickness and appearance of Cr-Ni-ZrO2 coatings were studied. The Cr-Ni-ZrO2 composite coatings obtained under the optimum process condition are bright and are of the thickness of 8.5μm. Results of SEM and EDS show that nano-ZrO2 particles are well distributed in the coatings and the surface morphology of Cr-Ni-ZrO2 composite coatings is homogeneous and finely crystallized. However, some ZrO2 particles in the coatings have lager diameter (100nm) than before (30nm), given some of them agglomerate. Mass fractions of the main element in the coating are as follows:Cr 82.6%, Ni 0.41%, Zr 7.65%, and O 9.34%.(3) Compared with Cr-Ni alloy coatings, Cr-Ni-ZrO2 composite coatings take more even and more compact surface. Analysis of XRD demonstrates that structure of Cr-Ni-ZrO2 composite coatings is amorphous. Kinds of performance test show that Cr-Ni-ZrO2 composite coatings possess good adhesion, low void fraction and high hardness (664.6HV). Tafel plots and EIS of Cr-Ni-ZrO2 composite coatings and Cr-Ni-alloy coatings demonstrate that Cr-Ni-ZrO2 composite coatings have much better corrosion resistance than Cr-Ni alloy coatings in both acid and alkaline corrosive medium. However, Cr-Ni-ZrO2 composite coatings are more easily corroded than Cr-Ni-alloy coatings in neutral corrosive medium.(4) Analyses of cyclic voltammogram curves and cathodic polarization cures show that trivalent chromium ions are deposited by a two-step reduction, but the detaied reductions are remaied to study further. Conclusions are made by analyzing cathodic polarization as follows: the nickel ions in the bath barely co-deposited with trivalent chromium ions but tend to boost the deposition of trivalent chromium ions; addition of auxiliary complexing agent A is good for dispersion of the plating bath; the additive A in the bath refines grains of the coatings and brightening the coatings; the addition of nano-ZrO2 particles strengthens the cathodic polarization of trivalent chromium and boosting the deposition rate.更多还原