摘要采用电化学沉积方法，将不溶性固体纳米颗粒（1～100 nm）加入镀液中，可与 金属离子共沉积而形成纳米复合镀层。基于此，本课题采用新型超声辅助双脉冲电沉 积工艺制备纳米晶纯镍和 Ni-CeO2 复合镀层。采用优化电沉积工艺参数：脉冲频率 1500 Hz，电流密度 1。5 A/dm2，占空比 1: 5，交变超声震荡频率 45+80 kHz，CeO2 添 加量 12~15 g/L 制备出的纳米晶镀层结构致密且性能优越。分析指出：在超声震荡场 作用下，织构择优生长方向由 Ni（111）向 Ni（200）（311）等多方向转变。超声窄 化作用所产生冲击波作用迫使优先生长的粗大 Ni 晶粒破碎，并改变 Ni 结晶表面 Gibbs 自由能，粗大晶粒被破碎成许多细小的新晶核，可诱发“形核增殖”作用。81238
借助 FE-SEM、XRD 及 TEM 等手段对比研究添加纳米 CeO2 纳米颗粒前后对纳 米晶 Ni 镀层的组织结构影响。发现：在机械搅拌与超声冲击波和微射流共同作用下， 纳米 CeO2 颗粒吸附在晶界微孔等高能缺陷区，不仅改变了 Ni 晶生长的表面能，还起 到弥散强化与微合金化等作用，能显著提高镀层的致密度；Ni 晶粒尺寸由未添加纳 米 CeO2 颗粒前的~250 nm（纯镍）细化至 Ni-CeO2 复合镀层中 Ni 晶粒的~80 nm，Ni 结晶取向也由择优取向随机多方向性生长转变。这主要归功于稀土纳米颗粒或其微量 Ce4+离子优先吸附于 Ni 晶尖端，并同时演变成 Ni 晶催化形核的中心，从而提高 Ni 晶形核率，降低临界形核半径，促使细化晶粒。
分别对纯镍和 Ni-CeO2 复合镀层，在酸性 10wt。% H2SO4 腐蚀介质中进行电化学 耐腐蚀性能研究。电化学阻抗谱（EIS）测试表明：纯镍与 Ni-CeO2 试样呈现类似 EIS 特征，均由单一的容抗弧构成，而后者的相位角在更宽的频率范围内接近～75º，从 而表现出更为优异的耐腐蚀性能。静态浸泡腐蚀形貌显示：纯镍试样腐蚀表面出现了 严重的点蚀现象，而 Ni-CeO2 镀层试样表面则被团絮状的微溶腐蚀产物物所覆盖，呈 现轻微均匀化腐蚀，这主要归功于稀土复合相的弥散效应提高了镀层的致密度，在镀 层表面形成富 Ce 弥散型氧化膜，可屏蔽并减少金属 Ni 镀层在腐蚀溶液中接触面积， 由此显著减缓点蚀进程和金属 Ni 基体的电化学溶解。
毕业论文关键词：电沉积；超声震荡；Ni-CeO2纳米复合镀层；表面形貌；耐蚀性
Abstract Nanocomposite coating can be produced by electrolytic or electroless codeposition, which inert nanoparticles (1~100 nm) suspended in the bath are codeposited with the metal to form the composite coating。 In this paper, an effective method of ultrasonic-assisted double pulse electro deposition was used to prepare nanocrystalline nickel coatings incorporated with CeO2 nanoparticels。 According to a great amount of our comparative tests, the optimization of processing parameters were therefore obtained such as 1500 Hz pulsed frequency, 1。5 A/dm2 current density, 1: 5 duty cycle, a periodic variation of ultrasonic frequency at 45 + 80 kHz, and an appropriate amount of 12~15 g/L CeO2 nanoparticles。 Under these optimizing conditions, it displayed a fully denser microstructure and superior properties for measured speciemns。 Based on the observations of surface morphologies and phase determination by FE-SEM and XRD analysis, surface features of Ni grains were rounded by the addition of ultrasonic oscillations and then turned from irregular diamond into the elliptical shape, also emerging the persified directions for Ni growth along Ni (111), (200), (311), etc。 It showed an available of grain refinement based
on a broadening XRD diffraction peaks’ integral widths and the drastically decreasing of its relative intensity。 This was mainly attributed to that coarse grains were pided into smaller-sized ones by ultrasonic oscillations, thereby modifying surface free energy and achieving more crystal nucleus sites for better recrystallization and structural integrity。 添加纳米CeO2颗粒对电沉积Ni镀层的表面形貌及其耐蚀机理研究:http://www.youerw.com/cailiao/lunwen_94806.html