In order to evaluate beneficial effect of CeO2 addition on managing textural develoment of Ni grains, FE-SEM, XRD and TEM observations were carried out。 Results indicated that nano-sized CeO2 particles where adsorbed along high-energy grain boundaries or defective interfaces was likely to make inpidual contributions to both of dispersion strengthening and micro alloying for signficant improvements of vacancies condensation。 As a result, the crystal size of Ni grains was refined from ~200 nm (pure nickel) into ~100 nm (Ni-CeO2 coatings), also appearing the persified directions instead of exclusively preferential growth for Ni growth。 This is mainly due to the existence of CeO2 nanoparticles or its small amount of Ce3+/4+ ions that could be acted as an increasing catalytic site ofnucleation and growth for thereby achieving the effects of grain refinement。 Finally, a comparative study of corrosion resistance for pure nickel and Ni-CeO2 coatings was carried out in an acid 10 wt。 % H2SO4 corroding solution。 Results obtained from electrochemical measurements shown that Bode plots of pure nickel was contained of

a capacitive reactance arc at high frequency。 Wereas similar electrochemical characteristics were observed for the Ni-CeO2 coatings also exhibited a larger capacitive arc and the largest phase angle close to ~ 75°, as indictative of an improved corrosion resistance。 According to observations of their corroded surfaces, it exhibited the selectively pitting corrosion for pure nickel, most probbaly due to pinholes or micro cracks existing on the coating’s surface to be induced as active sites for initiations of localized corrosion。 Within the addition of CeO2 particles, an uniform corrosion surface that covered by the slightly soluble corrosion productions was detected for the Ni-CeO2 coatings, which was attributed to the inert CeO2  phase that adsorbed onto the coating’s surface and acted as dielectric

phase in order to reduce  the short-circuit  diffusion penetration by both  H+  ions and    free

charges occurred at the corroded surface, and therefore inhibiting the pitting corrosion and electrochemical dissolution of metal Ni coatings。

Keywords: Pulsed electrodeposition; Ultrasonic oscillations; Ni-CeO2 nanocomposite coatings; Surface morphology; Corrosion resistance

目 录

第一章 绪 论 1

1。1  纳米复合电沉积 1

1。1。1  纳米复合镀层研究进展 1

1。1。2  纳米颗粒分散预处理技术 2

1。2  脉冲电沉积 3

1。2。1  脉冲电沉积与直流电沉积的优缺点比较 3

1。2。2  双脉冲电沉积电流特性 4

1。3  纳米颗粒添加对电沉积过程的影响机理 6

1。4 稀土 CeO2 纳米颗粒及其他纳米颗粒增强 Ni 基复合镀层 7

1。5  本课题选题依据及主要研究内容 9

第二章 实验部分 11

2。1  实验材料与仪器 11

2。2  实验方法 12

2。2。1  表面预处理 12

2。2。2  电镀液的配制 12

2。2。3 稀土纳米颗粒均匀化分散 13

2。2。4  纳米复合镀层试样的制备 14

2。3  镀层试样的测试与表征