铂微电极位点上氧化铝纳米孔的制备

金属微电极表面的纳米级处理可以大大提高电极的性能。本文基于微加工及电化学技术在铂微电极位点上制备了一致性良好的氧化铝纳米结构。通过对基片铂层表面等离子体处理,使铝膜与铂层之间粘附力明显增强。利用二次阳极氧化法,在铂微电极位点上制备出纳米孔。结果表明,30V是该条件下比较理想的氧化电压。同时,通过对氧化过程中电流的监测,发现当铝膜完全氧化后电流大幅上升,可将此现象作为终止阳极氧化的标志。这种微电极位点处的氧化铝模板可进一步用于不同材料纳米微电极的制备。     

钛的阳极氧化过程与TiO_2纳米管的形成机理

阳极氧化法制备的TiO_2纳米管因其独特的结构和优异的性能在多个领域获得广泛应用。阳极氧化TiO_2的生长机理也成为本领域的研究热点,最近几年有关生长机理的文章屡见报端。本文从两种阳极氧化钛膜对比的角度,综述了阳极氧化钛纳米管生长机理的最新研究进展和研究意义。首先介绍了Ti的阳极氧化过程,综述了两种阳极氧化钛膜(致密膜和多孔膜)的区别和联系。随后阐述了TiO_2纳米管的形成过程,重点综述了TiO_2纳米管的几种生长机理。分析表明,传统的"场致溶解"理论在解释纳米管结构和形成过程时存在很多局限性,而黏性流动模型和两电流模型相结合能较全面地解释TiO_2纳米管的形成过程,但电子电流的产生机制和纳米孔道中的氧气气泡还有待进一步的实验验证。     

纳米多孔阳极氧化铁膜的形成及其形貌演变

阳极氧化法制备具有纳米多孔结构的阳极氧化铁膜因其潜在的应用价值而倍受关注。然而,在阳极氧化过程中多孔结构的形成机制至今尚不清楚。本文结合电流密度-电位响应（I-V曲线）及法拉第定律的推导,分析了形成纳米多孔阳极氧化铁膜的过程中阳极电流的组成。结果表明,离子电流（导致离子迁移形成氧化物）和电子电流（导致析出氧气）共同组成阳极电流,并且纳米多孔阳极氧化铁膜的形成与两种电流的占比相关。分段式氧化物之间的空腔以及在阳极氧化初期纳米孔道上覆盖的致密膜,表明氧气泡可能是从氧化膜内部析出。此时,阳离子和阴离子绕过作为模具的氧气泡实现传质,最终导致纳米多孔结构的形成。此外,在阳极氧化铁膜形貌演变过程中,氧气泡不断向外溢出会使表面氧化物被冲破,导致表面孔径不断增大。     

铝的多孔阳极氧化自组织过程结晶度依赖特性

电子束蒸发在硅衬底上的多晶铝膜多孔型阳极氧化得到的多孔列阵排布与体材料单晶铝氧化结果比较,有序度存在很大差异,导致这种差异的原因,除了氧化时间、应用电压、电解液等电化学参数外,新引入的结晶度将作为一重要因数影响自组织过程.结晶度的影响主要反映在晶粒间界区域相比于晶粒内部存在的铝原子浓度和阳极氧化反应速度涨落,这种涨落将通过干扰孔底电场的分布,对自组织过程产生微扰,由于微扰具有实时和随机性质,将使铝膜阳极氧化不再象体材铝那样,可以通过单一延长时间来最终改善孔排布的有序度.     

含镓、锡的铝合金在碱性溶液中的活化机理

镓锡合金沉积于铝阳极表面 ,形成活化点 ,是铝阳极活化的根本原因 .简单的Al_Sn、Al_Ga二元合金在碱性介质中不能活化 .Al_Sn_Ga多元合金阳极溶解时 ,Ga、Sn溶解进入溶液 .锡离子首先还原沉积于铝阳极表面 ,镓离子又在沉积的锡上沉积 ,在铝合金阳极表面不断形成Ga_Sn合金活性点 .低溶点的合金由于其良好的流动性 ,以单个或多个原子的形式嵌入氧化膜 ,形成活性点 ,起到了局部分离氧化膜的作用 ,是铝合金阳极活化的关键     

还原剂对多孔阳极氧化铝纳米孔道结构的影响

多孔阳极氧化铝(PAA)和多孔阳极氧化钛纳米管(PATNT)的结构调控近年来倍受关注. 在形成机理尚不清楚的情况下, 对PAA和PATNT的结构调控很难避免盲目性. 为验证“氧气气泡模具”可以形成纳米孔道这个新观点, 本文采用化学方法对PAA的结构进行调控, 成功地引入了一种还原剂来吸收纳米孔道中的氧气气泡. 在添加还原剂的草酸溶液中得到了一种特殊的阳极氧化铝膜. 研究了还原剂的含量对磷酸溶液中形成PAA孔道结构的影响, 结果表明随着还原剂含量的增加, PAA的孔道直径逐渐减小, 有序性降低. 对比了添加还原剂前后阳极氧化过程的电压-时间曲线的差异, 结果表明, 在含有还原剂溶液中制备的阳极氧化铝膜的导电性明显提高. 在密封的条件下, 还原剂能吸收掉孔道中的氧气, 使气泡模具效应消失, 得到完全的致密型氧化膜. 这些实验事实充分证明PAA中有序孔道的形成是氧气气泡模具效应的结果.     

铝膜腔体内高度有序的介孔硅SBA-16的合成

在阳极铝膜腔体内, 以三嵌段聚合物F127为表面活性剂合成出一维纳米介孔二氧化硅材料. 采用压力诱导合成方法能使纳米纤维沿着铝膜腔体有序生长排列, 并且只存在于铝膜的腔体内, 在铝膜表面没有残留. 在纳米纤维的两侧可以清楚地观察到具有六边形结构的孔道, 直径为12 nm. 考察了正硅酸乙酯的水解时间以及化合物的不同配比对材料形貌的影响.     

铈、锂盐对铝阳极氧化膜的协同封闭作用

研究了铈、锂盐在铝阳极氧化膜封闭处理中的协同作用.场发射扫描电镜和X射线衍射谱对铈、锂盐协同封闭前后铝阳极氧化膜形貌和结构的研究结果表明，封闭后膜表面的孔洞消失，封闭产物分布均匀，封闭后膜仍然以非晶态形式存在.根据X射线光电子能谱的结果，封闭后的膜主要由含结晶水的Al2O3及铈、锂的混合氢氧化物组成，同时膜中还含有及封闭溶液组分中的一些阴离子.电化学阻抗谱的研究结果表明铈、锂盐协同封闭能够显著提高膜的耐蚀性能.在实验结果基础上，初步认为铈、锂盐封闭是通过生成结构紧密的封闭产物填充、覆盖膜孔，从而显著提高铝阳极氧化膜的耐蚀性能.     

阳极氧化物纳米孔道和TiO2纳米管形成机理的研究进展

自组织有序的TiO2纳米管和多孔型阳极氧化膜(PAO)因其潜在的应用价值而倍受关注.阀金属的阳极氧化研究了80多年,但是六棱柱元胞结构和多孔纳米管的形成机理至今尚不清楚.本文不是简单地综述PAO的形成机理,而是从更宽的视角综述了致密型阳极氧化膜与PAO的本质联系和形貌差异.对比两种膜的形貌差异和生长过程有助于孔洞形成本质的认识.简要综述了PAO的传统"场致助溶(FAD)"理论和局限性,重点综述了PAO形成机理的最新研究进展,包括粘性流动模型、阻挡层击穿模型、氧气气泡成孔模型、等电场强度模型等.在充分对比分析最新成果的基础上,对PAO机理研究的发展趋势进行了展望:采用超声氧化、真空或高压条件下氧化以及对电解液中添加碳酸钠或还原剂等方法,对揭示孔洞形成和自组织的本质将会有很大帮助;从电流和阳极氧化效率角度入手,是探究传统FAD理论的物理本质的有效途径.     

复合稀土铝阳极氧化膜的耐蚀性研究

用金属氧化物前驱体法,在前处理阶段添加稀土再进行阳极氧化,获得了Nd和Ce改性的铝阳极氧化膜.稀土含量在靠近氧化膜/基体界面处达到0.9%左右,由内向外逐渐降低,氧化膜外表面处的含量约为0.5%.稀土前处理后制备得到的阳极氧化膜耐蚀性能比普通硫酸阳极氧化膜有明显提高,其中Ce改性的氧化膜作用尤为明显;经过NaCl溶液浸泡15 d以后,经稀土改性的阳极氧化膜仍然保持良好的耐腐蚀性.稀土引入后,阳极氧化膜的孔径变小,膜更加致密,显微硬度提高.XPS测试表明氧化膜中的稀土Ce以CeO2和Ce2O3形式存在,而Nd以Nd2O3形式存在.阻抗测试表明氧化膜阻挡层的阻抗值增大,说明稀土除了改变氧化膜生长机制外,也可能通过掺杂作用改变氧化膜结构.     

硅基超薄多孔氧化铝膜的制备

将二次阳极氧化法应用于硅基铝膜的制备, 在草酸溶液中得到了厚度可控的硅基超薄多孔氧化铝膜(PAM), 厚度小于100 nm. 实验中记录了氧化电流随时间的实时变化曲线, 发现硅衬底的氧化电流在大幅下降前有一小幅波动. 对应于Al/Si界面的氧化过程中, 孔洞底部之间的残留铝岛被优先氧化, 可将此作为终止铝氧化的标志. 扫描电镜(SEM)观察表明, 二次氧化提高了孔洞分布的均匀性, 使得孔在一定的区域内呈现有序六角分布.这种模板可进一步用于硅基纳米器件和纳米结构的制备.     

The effect of anode surface area on nanoporous oxide formation during anodizing of low purity aluminum (AA1050 alloy)

Porous anodic alumina layers were obtained by a simple two-step anodization of low purity aluminum (99.5 % Al, AA1050 alloy) in a 0.3 M oxalic acid electrolyte at 45 V and 20 °C. The effect of anode surface area on structural features of nanoporous oxide and process of oxide formation was investigated. An ordered structure composed of nanostripes or nanopores was formed on the Al surface during electrochemical polishing in a mixture of perchloric acid and ethanol. This nanopattern is then replicated during the anodic oxide formation. It was found that the pore diameter, interpore distance, and porosity increase slightly with increasing surface area of the aluminum sample exposed to the anodizing electrolyte. On the other hand, a slight decrease in pore density and cell wall thickness was observed with increasing surface area of the sample. The detailed inspection of current density vs. time curves was also performed. The obtained results revealed that the higher surface area of the anode, the local current density minimum, was reached faster during first step of anodization and the increase in current density corresponding to the pore rearrangement process was observed earlier. Finally, a dense array of Pd nanowires (～90 nm in diameter) was synthesized by simple electrodeposition of metal inside the channels of through-hole nanoporous anodic alumina templates with relatively large surface areas (4 cm²).     

Fabrication of ideally ordered anodic porous TiO2 by anodization of pretextured two-layered metals

Ideally ordered anodic porous TiO₂ was fabricated by anodizing an Al/Ti layered specimen. A two-layered specimen composed of an Al top layer and a Ti underlying layer was prepared and then processed by nanoimprinting. The Al top layer was easily pretextured by nanoimprinting owing to its softness and it was straightforward to introduce an ideally ordered pore arrangement by anodization. This pore arrangement was transferred to the underlying Ti layer, resulting in ideally ordered porous structures in TiO₂. This process can be applied to the high-throughput fabrication of ideally ordered anodic porous oxides other than TiO₂ and also to other metals with high hardness.     

Anodic alumina membranes with defined pore diameters and thicknesses obtained by adjusting the anodizing duration and pore opening/widening time

The through-hole porous anodic aluminum oxide (AAO) membranes were fabricated by a simple two-step anodization of aluminum in 0.3?M oxalic acid, 0.3?M sulfuric acid, and 2?wt.% phosphoric acid solutions under different operating conditions followed by the removal of the remaining Al substrate and the pore opening/widening process. The effect of duration of the second anodizing step on the thickness of the porous oxide layer and the influence of other anodizing conditions such as applied voltage, type of electrolyte, and purity of the substrate on the rate of porous oxide growth were discussed in detail. The pore opening procedure for all synthesized membranes was optimized, and the influence of the duration of chemical etching on structural features of AAO membranes, especially pore diameter, was studied. The rate of pore widening was established for AAO membranes formed in various anodizing electrolytes and for different temperatures of 5?wt.% H₃PO₄ used for alumina dissolution.     

Anodic alumina membranes with defined pore diameters and thicknesses obtained by adjusting the anodizing duration and pore opening/widening time

The through-hole porous anodic aluminum oxide (AAO) membranes were fabricated by a simple two-step anodization of aluminum in 0.3 M oxalic acid, 0.3 M sulfuric acid, and 2 wt.% phosphoric acid solutions under different operating conditions followed by the removal of the remaining Al substrate and the pore opening/widening process. The effect of duration of the second anodizing step on the thickness of the porous oxide layer and the influence of other anodizing conditions such as applied voltage, type of electrolyte, and purity of the substrate on the rate of porous oxide growth were discussed in detail. The pore opening procedure for all synthesized membranes was optimized, and the influence of the duration of chemical etching on structural features of AAO membranes, especially pore diameter, was studied. The rate of pore widening was established for AAO membranes formed in various anodizing electrolytes and for different temperatures of 5 wt.% H₃PO₄ used for alumina dissolution.

     

二氧化钛纳米管的制备与光催化活性

用阳极氧化法,室温条件下在含NH4F和H2O的电解液(丙三醇+NH4F+H2O;乙二醇+NH4F+H2O)中制备了TiO2纳米管阵列。用环境扫描电子显微镜(SEM)、X射线衍射仪(XRD)表征二氧化钛纳米管阵列的微观形貌和物相结构。在丙三醇电解液中,电压为60 V,65 V,70 V,75 V制备的纳米管直径依次为160、170、190、220 nm。对甲基橙(10 mg/L)降解测试TiO2纳米管阵列的光催化性能。研究结果表明:在100 V阳极电压制备经过500℃退火处理后的TiO2纳米管阵列的光催化效果最好,其光催化降解率在光照时间120 min时达到89.2%。     

Nanoporous oxide formation by anodic oxidation of Nb in sulphate–fluoride electrolytes

The influence of hydrofluoric acid (HF) concentration and applied potential on the processes of anodic oxidation of Nb in sulphuric acid solution was studied by chronoamperometry, electrochemical impedance spectroscopy and scanning electron microscopy. During the first stage of the process, a compact barrier film is formed. On top of this film, a porous overlayer starts to form, then the nanopores grow into an ordered nanostructure. Subsequently, secondary 3D flower-shaped structures begin to form. These structures gradually spread all over the surface as an irregular multilayer film. The rates of the process of porous overlayer formation and subsequent growth of nanopore arrays increase with applied potential as well as with the HF concentration. The films have been characterised ex situ by electrochemical impedance spectroscopy at open circuit potential and capacitance vs. potential measurements to follow the different stages of nanoporous film formation with electrochemical methods. The impedance spectra and capacitance vs. potential curves have been interpreted using previously proposed models for the amorphous semiconductor/electrolyte interface. An attempt to rationalise the mechanism of nanoporous layer growth is presented by using the conceptual views of the mixed-conduction model and recent ideas for porous film formation on valve metals.     

Highly increased breakdown potential of anodic films on aluminum using a sealed porous layer

The growth of a uniform barrier-type anodic film on aluminum is usually terminated by electric breakdown, which is controlled by the resistance of electrolyte or anion concentration. In this study, highly resistive porous layers have been introduced by anodizing aluminum in sulfuric acid electrolyte followed by boiling water treatment to examine their influence on the electric breakdown potential. The pores of the porous alumina film are sealed by forming hydrated alumina (pseudo-boehmite) after the boiling water treatment. The breakdown potential increases to over 1500 V for the pore-sealed aluminum specimens on anodizing in sodium tungstate electrolyte. The electrochemical impedance spectroscopy measurements revealed an increased resistance of the porous layer after the pore-sealing treatment. GDOES depth profile analysis disclosed that the sealed porous layer impedes the incorporation of tungsten species into the barrier layer. The introduction of a highly resistive layer that also suppresses the anion incorporation on aluminum is effective in increasing the breakdown potential of anodic films.