【作者】 杨洋；

【导师】 张昭；

【作者基本信息】 浙江大学 ， 化学， 2015， 博士

【摘要】 萤石型结构CeO2及其固溶体具有较强的储氧和释放氧能力以及良好的高温离子导电率等特性,在汽车尾气处理、光催化、紫外吸收、抛光材料和金属防护等诸多领域具有广阔的应用前景。由于电化学沉积方法可通过对电解液的选择以及电极电位、镀液温度、镀液pH和添加剂等因素调控,选择性地得到具有各种化学组成、相组成和微观结构的材料。因而,相对于纳米结构CeO2薄膜的其它制备方法(目前主要采用化学气相沉积、溶胶-凝胶和磁控溅射等方法来制备Ce02薄膜)具有独特之处。迄今为止,国内外通过阳极或阴极电沉积技术所获得的CeO2薄膜的厚度一般较薄,其主要归因于Ce02的较低导电性能。Ce02是常见的半导体材料,一定波长(能量)的紫外光照可以大幅度地提高其导电性能,从而提高薄膜的生长厚度。此外,Ce3+可通过阳极直接氧化为Ce4+,因此阳极直接电沉积方法相较于阴极间接沉积方法可制备得到纯度更高的Ce02薄膜。为了制备纯度较高、厚度较大的Ce02薄膜,本论文对纳米结构Ce02薄膜的阳极电沉积及其光辅助沉积工艺、沉积机理、Ce02薄膜颜色与其结构和化学组成的关系、CeO2薄膜沉积过程的电化学噪声与其结构的关系、纳米结构CeO2薄膜的耐蚀性能等问题进行系统研究。论文第三章主要探索了暗态(未光照)下纳米结构CeO2薄膜的阳极电沉积工艺。主要研究了沉积电位、镀液温度、镀液pH、镀液冲脱02以及镀液中添加不同乙醇含量等因素对Ce02薄膜的致密性、组成、结构和耐蚀性能等的影响规律,优化得到了最佳的沉积工艺条件：0.8V.50℃、pH6.2.10%(V/V)乙醇的自然充02镀液。发现镀液中的乙醇含量是影响Ce02薄膜致密性的关键因素之一：乙醇的添加可降低镀液的导电性,增加薄膜沉积的阳极极化,因而镀液中过高的乙醇含量反而不利于Ce02薄膜的沉积。此外,分析了Ce02薄膜具有耐蚀性能的几个原因：(a)Ce02对氧具有较高的吸引力,导致Ce02薄膜附近的溶解氧的浓度降低、阻止了氧向不锈钢的扩散；(b)不锈钢在NaCl溶液中的腐蚀为电化学腐蚀,发生电化学腐蚀反应需要阳极和阴极电子交换,具有半导体性质的Ce02能够阻止电子转移到不锈钢电极表面,导致氧和质子的阴极还原需要更高的过电位；(c)腐蚀阴极反应产生的OH"使电极表面pH偏向弱碱性,提高了薄膜的稳定性；(d)CeO2和Ce3+的氧化还原电位远大于1.26rV(CeO2(s)+4H+e-→Ce3++2H2O),因而使CeO2薄膜在较宽的电位范围内稳定。论文第四章主要分析了阳极电沉积方法在316L不锈钢电极表面沉积的铈氧化物薄膜的颜色与薄膜组成和结构之间的关系。随着沉积时间的延长铈氧化物薄膜的颜色经历了黄色(1.5)、紫色(3h)、蓝色(5h)、灰绿色(7h)、最后回到黄色(12h)的变化规律,且带颜色的薄膜均能在空气中保持长期稳定不变色。薄膜颜色的变化主要取决于薄膜中Ce(Ⅲ)和氢氧化物含量及其引起的薄膜结构变化。当沉积时间由40mmin增至7h,薄膜中Ce(Ⅲ)的相对含量由20.09%增至27.57%,当沉积12h,减至22.93%。此外,薄膜中氢氧化物的含量与Ce(Ⅲ)含量的变化趋势保持一致。论文第五章主要探索了光照下镀液中添加不同乙醇含量沉积的Ce02薄膜的耐蚀性能以及不同波长(能量)紫外光对沉积CeO2薄膜的影响。结果显示：随着乙醇含量的增加,光助沉积的Ce02薄膜的耐蚀性能逐渐增强；当镀液中添加70%V/V乙醇时,沉积薄膜的耐蚀性最佳。光照有助于提高薄膜的生长厚度,入射光照波长越短(光能增加)越有助于CeO2薄膜的沉积,且薄膜的结晶性随着光能的增强而逐渐增强。论文第六章分析了阳极电沉积Ce02薄膜的成核/生长信息,同时建立了基于电化学沉积噪声技术所获得的成核能量/生长能量的相对大小与CeO2薄膜晶粒大小之间的关系。结果表明Ce02薄膜阳极电沉积受电荷转移控制,Ce02的阳极成膜遵循二维(2D)层状生长机制；成核相对能量越大则薄膜晶粒越细小。更多还原

【Abstract】 Cerium oxides, particularly ceria (CeO2), have a wide range of applications due to their ability to store and release oxygen as well as good high-temperature ionic conductivity. For example, they have been used in automobile exhaust treatment, photocatalysis, ultraviolet absorption, polishing materials and metal protection, etc. Since the chemical composition, phase composition and microstructure of the materials can selectively obtained using electrochemical deposition method by changing electrolyte, potential, bath temperature, pH and additives, etc. Thus, the electrochemical method has its own advantages to produce the CeO2film comparing with the other preparation methods (mainly using chemical vapor deposition, sol-gel and magnetron sputtering deposition methods).So far, the thickness of the CeO2films obtained by anodic or cathodic electrodeposition technique is thin due to CeO2has a lower conductivity. Since Ce3+can be directly oxidized to soluble Ce(OH)22+, therefore, it is believed that anodic deposition is more appropriate than cathodic to fabricate pure CeO2film. In addition, it is well known that CeO2is a common semiconductor material, a cerain wavelength (energy) of photo illumination can greatly improve the conductivity, therefore, enhancing the film thickness.This dissertation systematicly investigated the processes, growth mechanisms of anodic electrodeposition and photo assisting anodic electrodeposition of nanostructured CeO2thin film, the relationship between the film color and film structure and composition, the relationship between the electrochemical potential noise and the fil, structure, the corrosion resistance of the as-deposited nanostructured CeO2thin films.The third chapter mainly explores the processes of anodic electrodeposition of nanostructured CeO2thin film under dark condition (without photo illumination).The influences of deposition potential, bath temperature, bath pH, oxygen and ethanol content on the compact, structure and corrosion resistance of CeO2film have been investigeted. The optimized deposition parameters are0.8V,50℃, pH6.2,10%V/V ethanol, natural aeration. Under dark state, ethanol content plays a significant role on deposition of CeO2films. The addition of ethanol can reduce the bath conductivity and increase the anodic polarization of the film deposition, result in a higher content of ethanol is not appropriate for anodic deposition of ceria film. In addition, the beneficial effects of cerium oxides on the corrosion behavior of stainless steel may be mainly attributed to the following synergistic factors.(a) The high affinity of ceria towards oxygen can possibly decrease the oxygen content adjacent to the film and also inhibits oxygen diffusion towards steel.(b) The corrosion of stainless steel in NaCl solution is electrochemical in nature, which involves electron exchange between the anodic and cathodic sites, the semiconductor or even the insulator characteristic of CeO2makes the electron diffusion onto the stainless steel surface be inhibited, and also makes the cathodic reduction of oxygen and protons take place at a higher overvoltage;(c) The product of cathodic reaction (OH") will generate a slight alkaline state adjacent to the electrode surface, and consequently further stabilize the cerium oxidant in the coatings,(d) The standard redox potential of the reaction between CeO2and Ce3+(CeO2(s)+4H++e"→Ce3++2H2O) is more than1.26V, which makes the deposited CeO2stable on the specimen surface in a wide potential range.The fourth chapter analyzes the composition-depended color evolution of anodic electrodeposited cerium oxide thin film. Cerium oxide thin films with various colors were deposited onto316L stainless steel using anodic electrodeposition approach. Results show that the film color evolves from golden yellow (1.5h), purple (3h), blue (5h), grey-green (7h) and turns back to yellow (12h) again, and all these colored films are stable in the ambient conditions. The film color is related to both the contents of Ce(Ⅲ) and hydroxide species in the films. The relative content of Ce(Ⅲ) increases from21.19%to27.57%with increasing the deposition time from1.5h to7 h, and then decreases to22.93%for the film deposited at12h. The content of hydroxide species shows the same variation trend as Ce(Ⅲ) with the deposition time.The fifth chapter explores the effect of ethanol contents and photo energies on photo assisting anodic electrochemical deposition of CeO2film. Results show that light illumination favors the film growth and improves their crystallinity. Shortening the incident wavelength (increase photo energy) favors the deposition of CeO2thin film and enhances the crystallinity of the film. With ethanol content increases from0%V/V to70%V/V in the depositon bath solution, the corrosion resistance of the deposited CeO2thin film increased.The sixth chapter analyzes the nucleation/growth information of anodic electrochemical deposition of CeO2film. Results show that the anodic deposition of CeO2film is limited by electrochemical process and following the two-dimensional (2D) layered growth mechanism. In addition, the relationship between EEN characteristics and CeO2structure has been eastablished. The energy of nucleation and growth of CeO2thin film deposition process have been analyzed, and the relationship between nucleation energy/growth energy and the corresponding film structure have established using glancing angle XRD.更多还原