二次阳极氧化技术的理论依据及其局限性

二次阳极氧化技术在多孔阳极氧化铝和氧化钛纳米管的制备过程中得到广泛应用,但其理论依据还不清楚。本文详细综述了二次阳极氧化和预压印技术的由来及其理论依据,阐明了二次阳极氧化过程中传统“场致助溶”理论无法解释的实验事实,分析了二次阳极氧化和预压印技术在多孔阳极氧化铝制备中的局限性和前提条件,并用氧气气泡模型对文献中报道的一些特殊孔道的形成机制进行了诠释,揭示了气泡模具和氧化物的黏性流动对圆柱形、规则有序孔道的形成的重要影响,展望了电子电流和氧气气泡模具对多孔氧化铝、氧化钛纳米管的制备和结构调控的指导作用。本综述对阳极氧化钛纳米管的制备和机理的深入研究,促进其在光催化和太阳能电池领域的应用有重要的意义。     

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。     

特殊型纳米多孔阳极氧化铝模板的制备

多孔阳极氧化铝(PAA)模板具有六角有序排列的柱形孔,且孔径均匀可调,加之其良好的机械和热稳定性,在纳米材料领域得到了广泛研究和应用。近年来,人们通过改变铝阳极氧化条件制备出了多种特殊型纳米PAA模板,并利用这些模板结合物理或化学方法成功地合成了多种新型纳米功能材料。本文在简要介绍常规纳米PAA模板制备的基础上,较全面地综述了诸如孔道呈分叉形、锯齿形、骨形、倒圆锥形,孔洞呈菱形、三角形、正方形,孔道或孔壁结构呈周期性变化等特殊型纳米PAA模板的制备,揭示了电场强度和电解液种类、温度在PAA孔洞形貌尺寸调控方面的重要性,并展望了这类模板的发展方向及应用前景。     

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。     

氧化钴纳米管的制备和模板剂多孔氧化铝的孔洞结构

以草酸电解液制备的多孔氧化铝作为模板,采用硝酸钴溶液浸润法,合成出氧化钴纳米管．通过对分叉氧化钴纳米管成因研究,指出氧气气泡的作用是形成多孔氧化铝纳米孔洞结构的主要驱动力．     

用AFM研究阳极氧化铝的不稳定生长

用原子力显微镜(AFM)研究了多孔阳极氧化铝(AAO)模板的不稳定生长. 结果表明:AAO模板的不稳定生长导致了纳米孔道结构有序度的降低.在H₃PO₄溶液中生长的AAO模板孔道结构稳定性较差;而在H₂C₂O₄溶液中生长的AAO模板稳定性依赖于氧化电压和电流密度,在低电压和电流密度下稳定性较好,高电压和电流密度下稳定性较差. 充分利用这种不稳定生长特性,通过控制AAO模板的阳极氧化条件,可得到具有分枝孔道结构的特殊模板,这为利用模板法制备各种Y形或T形纳米线、管提供了新的发展空间.     

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.     

多孔阳极氧化铝膜的制备研究

在直流恒压下,在不同的酸性溶液中对铝片实施两步阳极氧化制备多孔氧化铝膜,在磷酸溶液中制得的模板孔径大,并且电解时间缩短,加快了制备模板的过程。同时利用阳极氧化初期电流密度的变化,分析了多孔氧化铝膜的形成机理。     

二次阳极氧化方法制备有序多孔氧化铝膜

通过二次阳极氧化方法制备多孔氧化铝膜与一次阳极氧化方法制备多孔氧化铝膜孔排布规律性的对比,结果发现,二次阳极氧化方法制取的多孔氧化铝膜孔排布规律性明显好于一次阳极氧化法制取的多孔膜.在几个微米范围内,孔呈理想的六角排布.去除一次阳极氧化膜后,二次阳极氧化得以在更良好的表面进行,制取的氧化铝膜孔规律性和有序度更高.有序区域的尺寸与晶粒内的亚晶大小有一定关系.     

超声辅助电化学合成形貌可控的三维铂催化剂

在室温条件下, 采用超声辅助电化学方法合成了几种三维铂纳米电催化剂. 利用透射电子显微镜(TEM)、X射线粉末衍射(XRD)以及电化学测试对该三维铂纳米电催化剂进行了表征. 结果表明, 这些铂纳米电催化剂的形貌、结构可以通过添加不同的形貌控制剂来调控, 在水溶液、聚乙烯吡咯烷酮(PVP)溶液和十六烷基三甲基氯化铵(CTAC)溶液中分别得到了立方海绵状铂、分枝状铂和球形多孔状铂. 其中, 球形多孔状铂纳米电催化剂由于其多孔的结构, 因此具有更高的电化学活性面积, 对氧气还原和甲醇氧化反应具有更好的催化作用.     

Influence of anodizing voltage mode on the nanostructure of TiO2 nanotubes

The nanostructure of self-ordered porous anodic TiO₂ nanotubes (PATNTs) has extraordinary influence on their physical and chemical properties. For this reason, extensive attention has been paid on pulse anodization to regulate the nanostructure of PATNT. However, the relationships between the nanostructures and current curves still remain unclear. Based on the traditional potentiostatic and pulse anodizations, five different modes (i.e., potentiostatic, pulse, triangle wave, decrease, and increase step by step) of applied voltage and their influences on the nanostructures of PATNT have been investigated in detail. The growing rates of the nanotubes anodized under five different modes were compared for the first time. The results show that the growing rate of pulse voltage anodization is the fastest, reaching 116.4 nm min^?1. The slowest is triangle wave voltage anodization, only 59.3 nm min^?1. When the applied voltage decreases step-by-step, branched nanotubes can be formed in the bottom of PATNT. Yet, when the applied voltage increases step-by-step, triple-layer nanotubes with different diameters are formed, and the forming mechanism of this special nanostructure is discussed. The present results may be helpful to understand the mechanism of PATNT and facilitate the assembling diverse nanostructures for extensive applications in photocatalysis, dye-sensitized solar cells, and biomedical devices.     

Size Effects on the Luminescence Properties of Polymer Nanowires简

Poly（3-（2-methoxyphenyl）thiophene） （PMP-Th） nanowires were fabricated using porous anodic alumina （PAA） as template through electrochemical polymerization by cyclic voltammetry. The control on the size of nanowires was confirmed by electron microscopy. The results indicated that the luminescence spectra of PMP-Th nanowires in PAA nanochannels were blue-shifted and emission intensity was enhanced compared to the emission of the PMP-Th film. Moreover, the luminescent spectra of PMP-Th nanowires were size dependent, which may result from the change in the degree of confinement of nanowires in PAA. F6rster energy transfer from PAA to PMP-Th molecules is considered to be responsible for the enhancement of luminescence from PMP-Th nanowires in PAA. The results show that the emission properties of polymers with nanostructures can be tuned by controlling their size.     

Oxygen bubble mould effect: serrated nanopore formation and porous alumina growth

We discovered a unique formation of serrated nanopore in porous anodic alumina (PAA). A new growth model is proposed for the formation mechanism of PAA. The model emphasizes the close relationship between pore generation and oxygen evolution. The initial pore formation is ascribed to oxygen bubble mould effect. Our model provides a satisfactory explanation for the growth process of PAA, alleviating the difficulties encountered in existing theories. These findings represent a decisive new step towards the full understanding of the nature of PAA films. The serrated nanopore arrays in PAA could also be used in a wide range of future nanostructure fabrications. Correspondence: Ye Song, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.     

Growth of porous anodic alumina films in hot phosphate–glycerol electrolyte

Growth of porous anodic alumina films has been examined at 10 V in hot phosphate-containing glycerol electrolyte containing 0.1 to 0.57 mass% water. The growth rate of the films is highly dependent upon the water content of the electrolyte, reducing markedly at a water content of 0.1 mass%, an opposite trend to that found previously for the formation of porous films on titanium and niobium. Chemical dissolution of the anodic alumina is also suppressed in electrolyte of low water content. GDOES depth profiles revealed that an increased water content of the electrolyte promoted the incorporation of phosphorus species into the films, although chemical dissolution reduced the amounts of phosphorus in the outer regions. Carbon species also appeared to be present in films, particularly at lower water content. Using a niobium oxide outer layer to suppress chemical dissolution resulted in films that were about 1.2 times the thickness of the consumed aluminium for an electrolyte containing 0.25 mass% water. The expansion suggests a possible contribution of field-assisted flow of film material in the growth of the porous anodic film.     

Fabrication of ordered Ni nanocones using a porous anodic alumina template

Hexagonally ordered Ni nanocones have been produced using an electroless Ni deposition technique on a porous anodic alumina (PAA) template, where the pores are of a cone shape. The conical PAA film was found to exhibit hexagonal order with a period of 100 nm. The aspect ratio (cone height vs. the diameter of the base of the cone) of the conical pores on the PAA film was found to be one. The Ni nanocones and the surface morphology of the nano-conical film exhibit the same periodic structure of the template. A significant advantage of the fabrication process employed in this work is that it utilizes existing techniques.     

纳米晶状磷酸钙盐/Al2O3-Ti生物复合材料的制备与结构表征

0引言众所周知,钛及其合金具有优良的机械力学性能,但其生物活性不足。因此,在金属基体上涂敷一层生物活性涂层,结合金属与生物活性材料的各自优势,已成为世界各国学者研究最为活跃的生物复合材料体系之一。该体系可用于临床医学,作为人体硬组织等的修复替换材料。目前,已开发出多种在金属基体上制备生物活性涂层的工艺和方法。如:等离子沉积法[1]、离子束溅射法[2]、激光熔覆法[3]、溶胶鄄凝胶法[4]、电化学沉积与水热处理合成法[5]、电泳沉积[6]、电结晶[7]等多种方法。但现有涂层材料尚存在一些问题:(1)由于替换材料的高硬度而导致其周围硬组织坏死[8];(2)由于疲劳磨损或热膨胀不匹配引起涂层脱落[9];(3)由于异质相导致生物活性降解[10]。因此,研究新的制备工艺,开发新的生物复合材料体系就显得十分重要。考虑到Al2O3具有优异的抗磨损、耐腐蚀等性能,以及较好的生物相容性,常作为临床选用的人造硬组织承载材料[11],故在本研究工作中,我们首次采用阳极氧化与水热处理复合工艺研制酸式磷酸钙/Al2O3鄄Ti生物复合材料体系。该体系不同于由日本Ishizawa等研制的HAp/TiO2鄄Ti复合体系[12]。主要体现在两...     

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.     

离子液体中电沉积制备钴纳米线阵列

Porous anodic alumina (PAA) was used as a template to prepare Co nanowires array from 1-ethyl-3-methylimidazolium chloride ionic liquid by direct current method. The surface morphology of porous anodic alumina template was observed by field emission-scanning tunneling microscopy (FE-SEM) before and after the electrodeposition of Co nanowires. The electrodeposition of Co nanowires was characterized by transmission electron microscopy (TEM) and X-ray powder diffraction (XRD). TEM results indicate that the Co nanowire surface is coarse and porous when aqueous solution was used as electrolyte， and the Co nanowire deposited from the ionic liquid is uniform and smooth. XRD results show that the electrodeposition of Co is a mixture of crystal and microcrystal phase.     

Oxygen evolution: the mechanism of formation of porous anodic alumina

Abstract  Aluminium anodization behavior in ammonium sebacate solution (w = 4%) in ethylene glycol, and in several H₃PO₄-containing electrolytes, has been investigated. A new mechanism is proposed for the formation of porous anodic films. The model emphasizes the close relationship between pore generation and oxygen evolution. PO₄ ³⁻ ions incorporated in the anodic films behave as the primary source of avalanche electrons. It is the avalanche electronic current through the barrier film that causes oxygen evolution during anodization. When growth of anodic oxide and oxygen evolution occur simultaneously at the aluminium anode, cavities or pores are formed in the resulting films. Accordingly, the mechanisms of growth of barrier and porous films are not very different in nature. These findings are a decisive new step towards full understanding of the nature of anodic alumina films. Graphical abstract