氯化胆碱-尿素离子液体中电沉积高耐蚀Ni/Ni-Zn纳米多层膜的研究

The electrodeposition of Ni and it's alloy are widely used in protection and decoration field due to their good corrosion-resistance, high hardness combined with being well decorative.However, the hydrogen evolution reaction often occurs in the course of electrodeposition of Ni in aqueous solutions, and which will result in pinholes in coatings and low current efficiency. Fortunately, coatings with good quality can be electroplated from ionic liquid with high current efficiency since side reaction can be avoided owing to its wide electrochemical window. Furthermore, it's easier to electroplate high corrosion-resistant coatings which have amorphous and nano-crystallline structure. Hence, electrodeposition of Ni/Ni-Zn nano-multilayers from Choline-urea ionic liquid single bath, and which is stable, easy to prepare, of low cost, environment friendly, was carried out in air. The corrosion resiatance can be further improved by Ni/Ni-Zn nano-multilayers due to multi-electrochemical protection effect. Deposition and dynamical mechanism of Ni/Ni-Zn nano-multilayers was studied. The effect of additives, such as nicotinic acid, EDTA and ethanediamine on deposition mechanism was explored. The relationship between the deposition parameters and coating properties was found. The micro-structure and protection machanism of Ni/Ni-Zn nano-multilayers was revealed. The project is meaningful for offering a guidance to electroplating coatings with high quality from ionic liquid.

电沉积镍和镍合金层耐腐蚀性能好，硬度高，同时具有装饰性能，在防护装饰性领域有着广泛的应用。然而水溶液中电沉积镍时往往存在阴极析氢副反应，导致镀层存在针孔，阴极电流效率低。而离子液体电化学窗口宽，可避免类似阴极析氢等副反应，制备的镀层致密性好，阴极效率高。此外，离子液体中更易于沉积具有非晶或纳米晶等特殊结构的镀层，更利于高耐蚀镀层的制备。本项目采用稳定性好、制备简单、成本低、绿色环保且可在大气环境中电沉积的第三代化胆碱-尿素离子液体配置电解液，采用单槽法电沉积Ni/Ni-Zn纳米多层膜，使镀层具有多重电化学保护作用，进一步提高镀层耐腐蚀性能。同时研究Ni/Ni-Zn纳米多层膜阴极沉积机理和动力学机制；探索添加剂烟酸、EDTA、乙二胺和"水"对沉积机理的影响机制；建立沉积工艺与镀层性能之间的联系，揭示Ni/Ni-Zn纳米多层膜的微观结构和防护机理，为离子液体中高性能镀层的制备提供指导。

电沉积镍及镍合金镀层耐腐蚀性能优异，硬度高，兼具装饰和防护效果，因此在相关领域应用广泛。目前一般采用水溶液电沉积镍镀层，不可避免存在阴极析氢副反应，所以镀层往往存在针孔、氢脆等缺陷，且阴极电流效率较低。而离子液体电化学窗口宽，可避免类似阴极析氢等副反应，沉积的镀层致密性好，阴极效率高。我们在前期研究中发现，胆碱类离子液体是电沉积镍及镍合金镀层优良的溶剂：相对于其他离子液体来说，胆碱类离子液体虽然电化学窗口相对较窄，但电沉积金属Ni时，阴极极限电位远比金属还原电位负，电沉积时阴极效率高，可以达到100%。电沉积的镀层致密，为纳米晶体结构，晶粒尺寸<10纳米，具有高的硬度和好的耐腐蚀性能。进一步地，还对氯化胆碱-尿素离子液体中电沉积的金属Ni、Ni-Zn合金镀层的电化学性能进行了研究，发现Ni-10%Zn合金的腐蚀性能可与金属Ni相当，但腐蚀电位比金属Ni负200-300 mV左右。基于此，本项目设计了Ni/Ni-Zn多层膜，除了镀层致密性好外，使镀层具有多重电化学保护作用，为活泼金属如镁合金等提供有效防护。氯化胆碱-尿素离子液体吸湿性非常强，吸水后会失去离子液体的特性，因此本项目还重点探索了水、含结晶水的镍盐对离子液体性质、电沉积机理和镀层性能的影响，并系统研究了电沉积工艺对镀层的结构和性能的影响规律，最后研发了一种水合氯化胆碱-尿素离子液体电解液，并成功在镁合金表面实现电沉积Ni/Ni-Zn镀层，为镁合金提供可靠保护。本项目的实施对实现离子液体中电沉积的拓展及规模化应用具有重要的意义。