铝合金氧化膜上沉积铈的椭圆法研究

用现场椭圆法和电化学方法研究了LD10铝合金铈电化学转化膜的成膜过程，并通过EDAX方法对膜表面成分进行了分析，结果表明：通过阴极极化步骤，可使铈在氧化膜表面发生沉积；阴极极化液的PH值，会影响氧化膜上铈的沉积量，PH值越高，沉积上去的铈越多，根据实验结果，提出了铈在氧化膜上沉积的可能机理。     

铝表面防护性稀土铈转化膜的研究

采用阴极电沉积法在铝阳极氧化膜上制备出稀土铈转化膜;通过SEM和EDS表征了阳极氧化膜、阴极电沉积铈转化膜的形貌和组成成分;用极化曲线法、EIS交流阻抗法等电化学方法对这两种膜进行了耐蚀性评估.结果表明,在铝阳极氧化膜上经过阴极电沉积可制备稀土铈转化膜,其耐蚀性比铝阳极氧化膜的耐蚀性显著提高.     

铝箔阳极氧化后2种铈转化膜的沉积机理

为探讨铝阳极氧化沉积铈转化膜形成机理,分别用化学沉积和电沉积法在铝阳极氧化膜上制备了铈转化膜._用SEM和EDS表征了阳极氧化膜、化学沉积铈转化膜和阴极电沉积铈转化膜的形貌和组分,测试了膜层厚度和膜的耐腐蚀性.结果表明:平均孔径89 nm的铝阳极氧化膜经阴极电沉积、化学沉积铈后平均孔径分别减小为38 nm和32nm,2种沉积分别可得到含铈52.10%和20.39%的铈转化膜.2种铈转化膜的平均膜厚分别比铝阳极氧化膜的大1.96 μm和1.23 μm,极化电阻均是铝阳极氧化膜的近3倍.2种铈转化膜形成机理不同是造成它们性质不同的原因.     

铝合金表面铈基转化膜研究进展

铝合金具有成本低、强度质量比高、可加工性能良好等优点,被广泛应用于航空、交通、建筑等领域.但铝合金表面易发生小孔腐蚀和晶间腐蚀,需要进行防腐处理才能满足应用要求.稀土元素铈因具有特有的电子层结构和物理化学特性,是制备铝合金稀土转化膜最具优越性的元素,以此为防腐基材开发的稀土转化膜技术被认为是最有可能替代铬酸盐钝化的技术.目前所报道的铈基转化膜工艺有化学浸泡法、溶胶-凝胶法、电化学法、磁控溅射法等.其中,化学浸泡法制备过程简单,但铈离子的转化和沉积速率较难控制一致,膜层微米级裂纹较多;溶胶-凝胶法制备的膜层与基体结合强度高,耐蚀性好,但需要大量铈盐,且产生较多废酸、碱液,成本高,环境污染大;电化学法在低温下实现性能可控的铈基转化膜,成本低,但成膜有大量晶间裂纹,结构疏松,成膜质量差;磁控溅射法制备的涂层均匀,成分可控,但靶材的利用率低,难以实现强磁性材料的低温高速溅射.总体来看,目前所报道的铈基转化膜工艺存在溶液体系稳定性差,所制备的转化膜层不稳定、容易开裂,以及制备成本较高的问题,难以满足工业化应用的要求.铈基转化膜成膜机理被普遍认为是阴极成膜理论,即铝合金表面形成了氧化还原微电池.溶液中的溶解氧以及加入的H2 O2可作为羟基的供体,通过改变溶液局部pH值、物质、电子和电荷浓度来影响稀土元素的氧化反应和在基体表面的沉积.铈基转化膜的耐蚀机理是阴极抑制机理,即在铝合金表面形成的铈基转化膜阻止了氧的传输和电子的转移和传递,从而阻止了阴极微区上的还原反应,防止了铝合金表面的腐蚀溶解.但该机制只强调了阴极抑制,而忽略了也可能发生的阳极抑制.同时,由于涉及到电化学动力学抑制,因此铈基转化膜有"自愈能力".本文综述了国内外铝合金铈基转化膜制备工艺的研究进展,指出了各工艺的优点和缺点,阐述了铈基转化膜主流成膜和耐蚀理论的研究,并对制备工艺的改进方向及未来理论的研究方向进行了展望.     

铝合金表面稀土转化膜工艺研究

为了全面取代铬酸盐，开发无污染铝合金防蚀处理新工艺，采用了正交试验得出以Ce(NO3)3为主盐的铝合金富铈转化膜工艺，膜的耐蚀性略高于铬酸盐处理膜，比铝合金的自然氧化膜耐蚀性高出约20倍，并以成膜均匀性、溶液稳定性和在0.1mol／L NaCl溶液中的极化阻力Rp为依据，研究了适合工业化应用的工艺范围，对几种富铈转化膜工艺进行了比较研究，结果表明，氧化剂的选择及其在溶液中的稳定性对成膜性能起重要作用。     

AAO样膜法电沉积镍纳米线表征及电化学行为研究

采用AAO样模法在多孔阳极氧化铝膜上电沉积镍金属微粒,从而制备出一维镍纳米线阵列.多孔阳极氧化铝膜的制备是采用直流阳极氧化的方法,在EG&G PARC公司的M175型恒电位仪上直流电沉积镍金属微粒,获得镍纳米线和阳极氧化铝膜的组装体系.本实验采用日本电子公司JEM-5600LV扫描式电子显微镜SEM观察阳极氧化铝膜的尺寸和形态;利用X射线衍射仪XRD和电子探针对纳米线的结构和组分进行分析.在EG&G PARC公司的M175型恒电位仪上通过阴极极化曲线测试技术,考察了镍盐溶液中的电沉积过程.由阴极极化曲线分析得出,沉积电流在0.5～3 mA/cm2为最佳范围.电沉积过程中要控制沉积温度,一般25～30℃左右较为合适.     

铝合金上铈氧化膜形成的电化学研究

研究了ＬＣ４铝合金在静置的、充氧或充氮的ＣｅＣｌ３（０．１％）／ＮａＣｌ（０．１ｍｏｌ／Ｌ）溶液中长时间浸泡形成的铈氧化物膜。在０．１ｍｏｌ／ＬＮａＣｌ中测得的极化数据表明，自上述三种浸泡体系所形成的铈氧化物膜在对铝合金的抗腐蚀特性上没有差别，这种膜是合金表面先前存在的自然铝氧化膜直接转化而成的，浸泡溶液中的溶液中的溶解氧对成膜速度并无贡献。提出了膜的形成机理。     

硝酸铈封闭对2A12铝合金己二酸-硫酸阳极氧化膜耐蚀性的影响

研究了硝酸铈溶液封闭对2A12铝合金己二酸-硫酸阳极氧化膜耐蚀性的影响,通过盐雾腐蚀实验、电化学动电位极化扫描法和电化学阻抗谱法(EIS)对阳极氧化膜的耐蚀性进行研究,采用场发射扫描电镜(FE-SEM)观察试样封闭前后的表面微观形貌,并与稀铬酸封闭、沸水封闭传统工艺进行比较。结果表明:采用硝酸铈溶液封闭的2A12铝合金阳极氧化膜腐蚀电流减小,阻抗值增大,耐腐蚀性增强。阳极氧化膜表面呈致密的花瓣状,多孔层内及氧化膜表面附着一层致密铈的氧化物或氢氧化物,其耐蚀性优于沸水封闭,与稀铬酸封闭相当。     

甘油对阳极氧化铝纳米孔形成过程的影响

电解电压、电解质种类以及添加剂等因素对氧化铝多孔膜的形成过程有显著影响.在电解液中加入甘油作为添加剂,不但可以增加阳极氧化形成的多孔膜的厚度,而且有利于增强氧化膜的韧性.采用高纯铝作阳极,铂网作为阴极,在草酸溶液中进行恒压阳极氧化.研究了在3%(质量分数)草酸溶液中,添加甘油对氧化铝多孔膜形成过程的影响.结果发现,添加甘油并不会改变氧化铝多孔膜的形成过程,也不会改变形成氧化铝多孔膜中Al2O3的非晶态结构,但甘油的加入将降低阳极氧化时多孔氧化铝膜的生长速度以及氧化铝阻挡层的形成速度,同时增加了纳米孔阻挡层的厚度,因此增加阻挡层的形成时间.在阳极氧化电解液中加入甘油还有利于减小氧化铝多孔膜的纳米孔孔径.     

封闭对铝合金微弧氧化膜在酸性溶液中耐蚀性的影响

为了提高7A85铝合金的耐蚀性, 采用单极性正脉冲微弧氧化(MAO)技术在其表面制备了陶瓷膜层, 并采用稀土铈盐、铬酸盐和SiO₂溶胶对MAO膜进行封闭处理。采用扫描电子显微镜(SEM)、X射线衍射仪和电化学工作站研究了封闭处理对膜层表面形貌、结构和在酸性NaCl溶液中腐蚀行为的影响。实验发现, MAO膜在酸性NaCl溶液中不能有效地保护铝合金基体。稀土铈盐和铬酸盐封闭处理通过沉积水合氢氧化物封闭孔隙, 可以提高MAO膜的耐蚀性。但在酸性溶液中, 封孔物质会和H⁺发生反应而溶解, 故经封闭的MAO试样也会发生腐蚀失效。SiO₂溶胶封闭处理后MAO膜表面覆盖一层凝胶, 使膜层成为完整的致密层, 可以保护铝合金基体在酸性NaCl溶液中免受腐蚀。     

高纯铝阳极氧化膜的电化学行为研究

为考察氧化膜状态对其电化学性能的影响,采用电化学方法研究了高纯铝阳极氧化膜在磷酸二氢钠缓冲溶液中的电化学性能.测试结果表明,高纯铝氧化膜的阴极极化过程分为3个阶段:1)电流密度变化较小而电位迅速负移,系克服氧化膜阻挡层电阻阶段;2)电流密度迅速增大而电位变化较小的析氢阶段;3)电流密度变化较小而电位迅速负移的氢离子扩散...     

Synergistic effect of rare earth salt and organic acid in the anodization of aluminum in phosphoric acid

The effect of rare-earth element (cerium salt) and organic acid (citric acid) on the anodic oxide film obtained in phosphoric acid and their synergistic mechanism in the anodizing process were studied. The results show that the synergistic effect of cerium salt and citric acid in anodization of phosphoric acid can reduce surface defects, improve its microstructure and properties of the anodic oxide film. With the analysis of EDAX and XPS, the hydroxide of cerium salt was deposited on the film surface. It is deduced that cerium salt takes part in the formation of oxide film directly on the synergistic effect of citric acid.     

An approach to the effect of hydrogen loading on the anodic behaviour of Ti in NaOH solutions

The voltammetric behaviour of titanium electrode in 0.5 M NaOH solution was investigated. The I-E curves revealed the presence of a well-defined O₂ evolution peak. The peak current density decreases to a great extent by pre-loading the metal with hydrogen by cathodic polarization, indicating that pre-loading the metal with hydrogen suppresses the O₂ evolution. The oxidation of hydrogen loaded inside the metal was suggested to be responsible for reducing the O₂ evolution peak current density during Ti anodization. The charge consumed during the anodic polarization of Ti, below O₂ evolution potential, was used to estimate the anodization coefficient and capacitance measurement was conducted for measuring the dielectric constant of the oxide film. Pre-loading the metal with hydrogen was found to decrease the oxide film formation rate as well as the dielectric constant.     

铝金属基复合材料Al6061/SiCP表面稀土转化膜的研究

利用电化学方法评价了铝金属基复合材料A l6061/SiC_P表面稀土转化膜的抗腐蚀性能, 膜的存在使腐蚀过程中的阴极反应和阳极反应同时减弱, 腐蚀速率降低。利用扫描电镜(SEM ) 观察了稀土转化膜的表观形貌, 膜是以球团状结构层层向外生长, 最后完全覆盖基体表面。利用X 射线衍射(XRD) 研究了膜的微观形态, 膜是以非晶态形式存在。利用X 射线光电子能谱(XPS) 分析了膜的成分, 膜是由铈的氧化物和氢氧化物组成。      

Charge transfer reactions on oxide-covered Ti Electrodes: Effect of dielectric constant variation and oxide stabilization

The electron transfer kinetics of the Fe³⁺/Fe²⁺ redox couple on the oxide covered Ti electrodes were investigated as a function of the film thickness, film stabilization, and concentration of the redox species. The oxides were formed potentiodynamically in acidic solution of pH=3 (Na₂SO₄+H₂SO₄) at a scan rate of 1 mV s⁻¹. The cathodic and anodic Tafel lines were also measured at the same scan rate. The logarithm of the exchange current density i₀ shows an exponential decrease with the oxide film thickness. Direct tunnelling may explain the kinetics of the reaction across thin Ti0₂ (oxide formed at the potential region before the O₂-evolution). Values of the cathodic and anodic transfer coefficients are tabulated. It was found that, the stabilization of the oxide could possibly increase its conductivity. The electron transfer reaction showed a first order dependence on the redox species concentration, independent of the conditions of oxide film formation.     

Cerium-based coating for enhancing the corrosion resistance of bio-degradable Mg implants

Recently there has been interest in employing degradable metallic implants for internal fixation in bone fracture healing. The major purpose of using degradable implants is to avoid a second surgery for implant removal when bone healing has completed. However, the corrosion rate of Mg in vivo is too high. Thus increasing the corrosion resistance of Mg is the key problem to address in the development of degradable Mg implants. One possible route is by way of surface treatment, which would lower the corrosion rate at the initial phase of bone healing, the period during which the implant provides mechanical support for the broken bone. In the present study cerium oxide coating was prepared on pure Mg by cathodic deposition in cerium nitrate solution followed by hydrothermal treatment. The coated samples were characterized by SEM, EDS and XRD. The corrosion resistance in Hanks’ solution (a simulated body fluid) was studied using polarization method and electrochemical impedance spectroscopy (EIS). The corrosion resistance of cerium oxide coated Mg in Hanks’ solution at 37 °C and pH 7.4 was higher than that of bare Mg by about two orders of magnitude.     

海水介质中碳钢"绿色"缓蚀剂缓蚀过程的研究

采用电化学方法研究了自制的高效、绿色复合缓蚀剂（葡萄糖酸钙、硫酸锌和具有多个配位基团的酯类物质——OCTA）在海水介质中对碳钢的缓蚀作用过程．结果表明,单一的硫酸锌是阴极型缓蚀剂,葡萄糖酸钙和OCTA是阳极型缓蚀剂,复配的缓蚀剂是混合型缓蚀剂．复合缓蚀剂在碳钢表面的成膜过程初步认为是OCTA与葡萄糖酸根离子协同与溶液中金属阳离子发生络合反应,生成三维吸附膜,锌离子在阴极形成氢氧化锌沉淀膜,使得两种缓蚀剂膜优势互补,提高了膜的保护性能．     

Corrosion inhibition of AA6063 alloy by vanadates in alkaline media

Vanadium aqueous compounds are considered as promising environmentally friendly inhibitors for heterogeneous aluminium alloys. In this study, mechanism of corrosion inhibition of AA6063 in alkaline media by vanadate inhibitors is presented. A combination of weight loss and open circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy was used to compare corrosion behavior of AA6063 alloy in aerated pH 10 0.05 M sodium chloride solutions in the absence and presence of 0.003 mol/l sodium orthovanadate. Tetrahedrally coordinated mono‐ and polyvanadates, that are main forms in such solutions, cause a decrease in corrosion current density and significantly increase amplitude of impedance spectra and impedance modulus |Z| values due to mixed cathodic‐anodic inhibition effect mainly associated with the formation of adherent surface film on cathodic and anodic intermetallic particles of alloy.     

Effect of pH on the formation-dissolution processes of anodic films on bismuth

Interrupted polarization measurements indicate that among Na₂SO₄, buffer (pH 7) and NaOH, the most passivating anodic film is formed on bismuth in the buffer solution. Under opencircuit conditions, film growth occurs on the metal surface in buffer solutions of pH 1.81 to 11.25. The rate of growth increases with decrease in pH. The passive metal undergoes dissolution in buffer solutions according to a zero-order mechanism; the most effective pH values for film dissolution lie between 8 and 10. The results indicate the simultaneous importance of the anion type and pH of the electrolyte in determining anodic film stability.     

用阴极电解法沉积铝合金铈转化膜

在铈盐溶液中阴电极解的方法沉积铝合金铈转化膜,用电化测试,腐蚀实验,ＳＥＭ和ＥＤＡＸ等分析手段研究了转化膜的性能,结果表明,钪转化膜的形貌垢形貌组成和耐蚀与铝合金表面状态和阴极是否发生析氢反应关系密切,要想获得性能良好的转化膜必须抑制氢气在阴极上析出。