A tracer investigation of chromic acid anodizing of aluminium

A tungsten tracer introduced into a sputtering‐deposited aluminium substrate was employed to investigate pore development in anodic films formed at 3 mA cm^?2 in 0.25 M chromic acid electrolyte at 313 K. The anodized specimens were observed by transmission electron microscopy (TEM), with compositions of films determined by Rutherford backscattering spectroscopy (RBS). The anodic films were found to be similar in thickness to that of the aluminium layer consumed during anodizing and revealed the feathered pore morphology that is a characteristic of the electrolyte. The anodizing efficiency was ～45–48%, with tungsten tracer species, in addition to aluminium species, being lost to the electrolyte at the pore base. These findings, together with the relatively uniform distribution of tungsten species within the film, are consistent with field‐assisted dissolution of the alumina playing a major role in the development of pores. The films contrast with those formed in phosphoric and sulphuric acid electrolytes, for which feathering of pores is absent, the tracer distribution is inverted and the film thickness exceeds that of the consumed metal, features indicative of the influence of material flow in pore development. Copyright © 2007 John Wiley & Sons, Ltd.     

Discovery by kinetic studies of the latent physicochemical processes and their mechanisms during the growth of porous anodic alumina films in sulfate electrolytes

The kinetics of growth of porous anodic alumina films in pure H₂SO₄, in mixtures of H₂SO₄ and Al₂(SO₄)₃ and in Al(HSO₄)₃, NaHSO₄ and KHSO₄ electrolytes were studied. The latent physicochemical processes at the pore base surface/electrolyte interface, across the barrier layer, inside the metal/oxide interface and at the pore wall surface/electrolyte interface and their mechanisms were revealed. High field strength equations were formulated describing the ionic migrations from the pore base surface. These showed that, at constant current density and temperature, the inverse of the pore base square diameter depends linearly on the inverse of the H⁺ activity in the anodizing solution and that this diameter increases with H⁺ activity, in agreement with the experimental results. The mechanism of electrolyte anion incorporation inside the barrier layer and the real distribution of the anion concentration across both the barrier layer and pore walls were deduced. The effects of the different kinds and concentrations of the electrolyte anions and cations on both the above processes and their mechanisms were also examined. Electronic Publication     

Solid surface and field catalysed interface formation of colloidal Al<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> during Al anodizing affecting the kinetics and mechanism of development and structure of porous oxides

Overall kinetic and potentiometric studies of the growth of porous anodic alumina films in saturated H₂SO₄+Al₂(SO₄)₃ electrolyte showed non-saturation conditions inside the pores and supersaturation conditions at the pore surface/electrolyte interface where the field and the solid surface catalyse the formation of colloidal Al₂(SO₄)₃ micelles. Suitable high-strength field thermodynamically sustained electrochemical and chemical kinetic equations were formulated. It was shown that the diameter and surface fraction of charge exchange at the pore bases, the real pore wall surface fraction where oxide dissolution occurs, and its rate are strongly affected by the conditions. The mechanism of growth and structure of the films are quite different from those in H₂SO₄. A mechanism of regular film growth is imposed and the critical current density, above which pitting appears, strongly increases. The formulated theory may predict improved or new Al anodizing technologies. Electronic Publication     

Development of the local proton concentration during pulse anodizing

The literature describes various beneficial effects of the pulse anodizing of aluminum related to the corrosion resistance, hardness, and electronic properties of the oxide layer, the thermal impact during the anodizing process as well as reduced energy consumption. In spite of the considerable improvements, the understanding of basic mechanisms and the specific impact of the applied pulse parameters are still under discussion. Herein, the local development of the electrolyte concentration during pulse anodizing in sulfuric acid is investigated by means of finite element computations. The impact of the thickness of the porous oxide, the applied current density, and the pulse frequency are examined systematically. The results suggest that the electrolyte concentration at the oxide/electrolyte interface can be effectively controlled by applying tailored pulse parameters.     

Anodic oxidation of foil copper on fiber-glass plastic in sulfate-chloride electrolyte

The effect of the conditions of galvanostatic anodizing of copper foil at fiber-glass plastic on growth kinetic parameters of Cu₂O films is studied. It is shown that the anodic treatment current density in the sulfate-chloride electrolyte features a logarithmic dependence on the electric field strength in the anodic Cu₂O film, which is probably caused by the presence of either a p-n-transition, or an inversion layer of electronic conductivity at the Cu/Cu₂O interface. It is found that the dependence of the film thickness on the formation time at different current densities is nonlinear.     

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.     

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。     

Fast migration of fluoride ions in growing anodic titanium oxide

The rapid inward migration of fluoride ions in growing anodic titanium oxide under a high electric field has been elucidated by anodizing a Ti–12 at% silicon alloy, where film growth proceeds at nearly 100% efficiency in selected electrolytes. Further, incorporated silicon species in the anodic film are immobile, acting as marker species. The migration rate of fluoride ions is determined precisely by three-stage anodizing, consisting of initial anodic film formation at a constant current density to 50 V in ammonium pentaborate electrolyte, subsequent incorporation of fluoride ions by reanodizing to 55 V in ammonium fluoride electrolyte and, finally, anodizing again in ammonium pentaborate electrolyte at high current efficiency. The resultant films were analyzed by glow discharge optical emission spectroscopy to reveal the depth distribution of fluoride ions and the location of the silicon marker species. The fluoride ions migrate inward at twice the rate of O²⁻ ions. Consequently, anodizing of titanium in fluoride-containing electrolytes develops a fluoride-rich layer that separates the alloy substrate from the anodic oxide, with eventual detachment of the film from the substrate.     

Factors influencing the growth behaviour of nanoporous anodic films on iron under galvanostatic anodizing

The growth behaviour of nanoporous anodic films on iron during galvanostatic anodizing in ethylene glycol electrolytes containing NH₄F and H₂O is examined at various current densities, H₂O concentrations in electrolytes and temperatures. The film morphology is mainly controlled by the formation voltage, regardless of anodizing conditions. Relatively regular cylindrical pores are formed at formation voltages less than 50 V, while rather disordered pores are formed above 100 V. The decrease in the H₂O concentration suppresses chemical dissolution of anodic films in addition to the increased growth efficiency, resulting in the formation of anodic films with a steady thickness of ～7 μm. The cell size of the anodic films depends upon the H₂O concentration as well as the formation voltage, but not upon the current density. Findings in this study will be useful for controlled growth of the anodic films on iron.     

Porous cobalt hydroxide film electrodeposited on nickel foam with excellent electrochemical capacitive behavior

A new porous cobalt hydroxide film has been successfully electrodeposited on nickel foam from 0.1?M cobalt nitrate electrolyte at ?1.0?V vs. SCE without adding any surfactant. The microstructure and surface morphology of prepared cobalt hydroxide films were physically characterized by X-ray diffraction analysis and scanning electron microscopy. The results indicate that an interlaced network structure was obtained. The effects of electrodeposition time, deposition potential, and different substrates on the specific capacitance and microstructure of prepared porous ??-Co(OH)₂ thin film were systematically studied. The results indicate that the film deposited on nickel foam at ?1.0?V has excellent electrochemical properties. A maximum specific capacitance of 1473?F?g^?1 could be achieved at a current density of 2?A?g^?1.     

稀土盐对铝合金阳极化过程的影响

在阳极化溶液中添加稀土盐得到的铝合金氧化膜在腐蚀试验中表现出优良的耐蚀性能,现场椭圆法对阳极氧化过程的研究结果表明,稀土盐的加入,对椭圆编振参数的振荡方式没有显著影响,但却使振荡的周期和振幅发生了一些变化,由此可以推知,稀土盐的加入并未改变氧化膜的组成,但却在一定程度上影响了成膜过程,使膜的结构发生了变化。对椭圆数据进行定量分析的结果进一步表明：加入稀土盐后,氧化膜多孔层生长速率加快,阻挡层厚度增加,多孔部分变得更加致密,这种结构上的变化是阳极化膜耐蚀性能得以提高的主要原因,EDAX和TEM分析结果也证实了椭圆法研究的结果。     

Surface characteristics of anodic oxide films fabricated in acid and neutral electrolytes on Ti–10V–2Fe–3Al alloy

Anodic oxide films were fabricated on Ti–10V–2Fe–3Al alloy in acid (H₂SO₄/H₃PO₄) and neutral environmental friendly (C₄H₄O₆Na₂) electrolytes. The morphology, roughness, crystalline structure of the anodic oxide film were characterized by using scanning electron microscopy, atomic force microscopy, Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The results showed that the oxide film fabricated in H₂SO₄/H₃PO₄ electrolyte had a porous structure and the thickness of the film was 3.5 µm. The oxide film fabricated in C₄H₄O₆Na₂ electrolyte presented a nonporous structure that sustained the evident microstructure of the substrate, and the thickness of the film was 6.0 µm. The surface average roughness values of the two types of films were 245 nm and 166 nm, respectively. The phase of the anodic oxide films consisted mainly of anatase and rutile. EIS results showed that the film fabricated in C₄H₄O₆Na₂ electrolyte had higher impedance of the outer layer, while the film fabricated in H₂SO₄/H₃PO₄ electrolyte had higher impedance of the inner layer. Moreover, we attempt to explain the differences in the anodizing kinetics, structure and electrochemical impedance of anodic oxide films by the different films growth processes in the two types of electrolytes. Copyright © 2012 John Wiley & Sons, Ltd.     

硼砂-对苯二甲酸电解液中AZ91D镁合金的阳极氧化处理

研究了硼砂-对苯二甲酸环保型电解液中AZ91D镁合金的阳极氧化.考察了对苯二甲酸对镁合金阳极氧化过程及其氧化膜性能的影响,并利用扫描电镜(SEM)、X射线衍射(XRD)、能量散射谱(EDS)、动电化极化和电化学交流阻抗谱(EIS)等进行了分析表征.结果表明,对苯二甲酸的浓度对阳极氧化成膜过程、氧化膜的表面形貌、厚度、相结构和耐腐蚀性能都有重要影响.在硼酸盐电解液中加入适量的对苯二甲酸后,氧化电流密度降低,过度放电现象受到了明显的抑制,所制得的阳极氧化膜的质量也有了显著改善.氧化膜表面变得光滑、致密,膜厚度略有降低.氧化膜与镁合金基底的结合更紧密,而且其耐腐蚀性能也得到了明显增强.该研究对于镁合金阳极氧化处理工艺的环保化及阳极氧化膜质量的提高都具有积极意义.     

脉冲激光沉积LiNi0.5Mn0.5O2薄膜正极性能

高能量密度、功率密度和高温度稳定性的全固态薄膜锂离子电池是微电子器件的理想电源.开发新型的大比容量正极薄膜材料是解决问题的关键之一.与LiCoO2正极相比,层状结构的LiNi0.5Mn0.5O2有更高的可逆比容量和结构稳定性.本文应用脉冲激光沉积法制备LiNi0.5Mn0.5O2沉积薄膜,研究了衬底材料、温度对薄膜的微观结构、表面形貌及组分的影响.由LiNi0.5Mn0.5O2电极组装半电池,研究了薄膜的电化学性能与晶体结构、表面形貌及组分间的关系,表征了LiNi0.5Mn0.5O2沉积薄膜于不同充电截止电压的循环稳定性及倍率性能,并讨论了LiNi0.5Mn0.5O2薄膜的结构特点.     

CuInSe2 thin-film deposition on flexible plastic substrate: electrolyte recirculation rate and deposition potential effects

Copper indium diselenide (CuInSe₂; CIS) layer was electrolytically plated from an aqueous medium at room temperature onto electroless nickel deposited on flexible plastic (Kapton). The CIS depositions were carried out under constant deposition potentials (−0.5 to −1.1 V vs. Ag/AgCl) and at various electrolyte flow rates (0.3 to 1.5 ml/s) under constant applied current. The resulting thin films were characterized using atomic force microscopy, energy-dispersive X-ray spectroscopy, environmental scanning electron microscopy, and X-ray diffraction. The surface morphology and the atomic composition of the deposited CIS film were found to be influenced by the deposition potential under potential control and the electrolyte recirculation rate under current control. Low electrolyte flow rates under constant current control and high cathodic deposition potential under voltage control favor the deposition of indium. CIS films of uniform deposit, smoother surfaces, and with better adhesion properties are favored by moderate electrolyte recirculation rate. At a current density of 0.6 mA/cm², the electrolyte recirculation rate required to achieve ideal CIS atomic composition was found to be 1.0 ml/s in such a setting. The crystallinity of the film improved after annealing for 2 h at 390 °C under argon atmosphere.     

Oxide density distribution across the barrier layer during the steady state growth of porous anodic alumina films: chronopotentiometry, kinetics of mass and thickness evolution and a high field ionic migration model

The steady state growth of porous anodic alumina films in oxalate solutions at various conditions was studied by chronopotentiometry, mass balance and optical microscopy methods enabling determination of consumed Al, film mass and thickness, current efficiencies, Al³⁺ and O²⁻ transport numbers across barrier layer, etc. The film thickness growth rate was found to be proportional to O²⁻ anionic current. A high field ionic migration model was developed. It predicted that, during anodising, the local oxide density across barrier layer rises from 2.6 in Al|oxide to 4.59–5.22 g cm⁻³ in oxide|electrolyte interface with mean value ≈3.21–3.52 g cm⁻³. The field strength rises from the first to second interface. The mechanism of Al oxidation near the Al|oxide interface embraces the transformation of the Al lattice to a transient, rare oxide one sustained by field with comparable Al³⁺ spacing parameter. The oxide near the Al|oxide interface and around the density maximum in the oxide|electrolyte interface are under different levels of electro-restriction stresses. During relaxation, the oxide behaves like a solid-fluid material suppressing the initial density distribution.     

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%。     

Fabrication and characterization of porous Si-Al films anode with different macroporous substrates for lithium-ion batteries

Porous Si-Al films were fabricated by magnetron sputtering (co-sputtering) using three different copper substrates as current collectors, respectively. The morphology, compositions, structure, and crystallinity of the porous Si-Al films anodes were examined by using SEM, EDX, TEM, XRD, and Raman spectroscopy. The electrochemical properties of the porous Si-Al films anodes were evaluated by galvanostatic cycling. The Si-Al film deposited on copper foam showed higher insertion/extraction capacity, capacity retention, and longer cycle life in comparison to the Si-Al films deposited on expanded copper mesh and even copper mesh grid, which could be attributed to its unique three-dimensional macroporous structure. The three-dimensional macroporous structure could offer larger materials/electrolyte contact area, a much better adhesion, lower electrical resistance (i.e., well conductive), and stress-alleviated environment to partly accommodate volume expansion that leads to exfoliation during cycling.     

Thermal phenomena during anodizing of aluminium in sulfuric acid

The heat developing at the oxide-aluminium interface during anodizing in sulfuric acid has been measured. The temperature of the aluminium anode increases rapidly to attain a steady value after a few minutes, and drops sharply upon current interruption. The rise in temperature increases linearly with the current density. The effects of the concentration and temperature of the electrolyte and the anodizing voltage on the heat developed in aluminium have been examined. The results are discussed with regard to the dispute concerning the conditions necessary at the base of the pores for the relatively high local dissolution.     

The effect of electrolyte-controlled growth morphology on the charge transport properties of poly(3-methylthiophene)

Poly(3-methylthiophene) films were potentiostatically and galvanostatically synthesized on platinum electrodes in acetonitrile using lithium perchlorate, lithium tetrafluoroborate, tetra-n-butylammonium perchlorate, and tetra-n-butylammonium tetrafluoroborate as supporting electrolytes. Cyclic voltammetric analyses of the polymer films indicate the synthesis is polymerization process dependent. Constant potential syntheses, which resulted in a higher current density and were carried out at higher potentials, yielded polymer films with a higher charge capacity. Chronocoulometric results show that the charge transport rates of the films were electrolyte dependent and that tetra-n-butylammonium tetrafluoroborate yielded poly(3-methyl-thiophene) with the highest charge transport rate. The charge transport rate was found to be electric field dependent for all cases, suggesting that the films resemble a porous electrode. Scanning electron microscope analyses of the films, prepared under various conditions, indicate that the synthesis method used, and the nature of the electrolyte, strongly influence morphology and charge transport.