交、直流交替氧化对3005铝合金电解着色的影响

采用交、直流交替氧化的方法,改变3005铝合金在硫酸介质中阳极氧化膜的结构与组成,探讨其对膜层电解着色性能的影响。结果表明,交、直流氧化的顺序及相关电解着色参数对电解着色膜性能产生明显的影响。最佳氧化及着色工艺条件为:直流氧化电流密度1～2A/dm2,交流氧化电压15～20V,着色电压5～7V,着色温度20～30℃,着色时间2～7min。由此可获得浅茶色、桃红色、朱红色、紫黑色等一系列具有高装饰性的铝阳极氧化着色膜。     

Modeling of the Current Distribution in Aluminum Anodization

The growth of porous anodic Al₂O₃ films, formed potentiostatically in continuously stirred 15 wt.% H₂SO₄ electrolyte was studied as a function of the anodization voltage (14–18 V), bath temperature (15–25 °C) and anodization time (15–35 min). The variation of the anodic surface overpotential with the current density was measured experimentally. The film thickness at the more accessible portions of the anode was observed to increase with the anodization voltage and the bath temperature. However, the film thickness on the less accessible portions of the anode did not significantly change with the voltage or the bath temperature. This indicates that the anodization process at the more accessible regions is more strongly influenced by the surface processes than by the electric migration within the electrolyte. Furthermore, analysis confirms that the major portion of the film resistivity resides within a thin sub-layer that does not vary with the anodization time, and the growing anodic layer contributes only marginally to the overall film resistance. Computer aided design software was employed to simulate the current density distribution. For the range of process parameters studied, the electrochemical CAD software predicts accurately the measured thickness distribution along the anode.     

关于氧化铝膜着色层的研究

本研究结果指出阻挡层的厚度与电解氧化的时间无关，在较大的电流密度下进行阳极氧化时，阻挡层的厚度增大，但氧化铝膜的溶解速度亦随之增大，生成的Ａｌ２（ＳＯ４）３共沉积于氧化铝膜中，致使氧化铝膜变得松散。     

Galvanostatic anodization of pure Al in some aqueous acid solutions Part I: Growth kinetics, composition and morphological structure of porous and barrier-type anodic alumina films

The growth kinetics of anodic films formed on the surface of high purity Al by anodization under galvanostatic conditions at current densities in the range 5–75 mA cm^–2 in thermostatically controlled and vigorously stirred solutions of chromic, sulfuric, phosphoric, citric, tartaric and oxalic acids at different temperatures, were studied. It has been shown that chromic acid solution produces a typical barrier type oxide growth at any given temperature, while the specific kinetic curve representing the combined barrier/porous type film growth is observed when the anodization process is carried out in a nonstirred chromic acid solution. The oxide growth in the rest of the anodizing solutions occurs in different ways depending on the bath temperature. Barrier oxide growth is observed at temperatures lower than 30 °C. Above this temperature, combined barrier/porous oxide growth is observed. In all cases, the slope of the linear part of the potential against time curves, and therefore the rate of barrier oxide growth, increases with increasing anodizing current density and acid concentration, while it decreases with increase in temperature. The composition and surface morphology of the anodic films have been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM).     

电压施加方式在阳极氧化钛薄膜形成过程中的作用

采用阳极氧化的方法,通过改变电压的施加方式制备了具有不同形貌的氧化钛薄膜。使用扫描电子显微镜考察了氧化钛薄膜的形貌,结合实验现象探讨了阳极氧化钛薄膜纳米孔的形成机制。研究结果表明,采用一步施加电压和连续施加电压的方法,氧化钛薄膜纳米孔的形成过程由电压、阻挡层的厚度决定;采用两步施加电压的方法,氧化钛薄膜纳米孔的形成过程由放电电压、阻挡层的厚度和阻挡层/电解液的边界条件协同控制。在相同工艺条件下,采用两步施加电压法能够扩展阳极氧化钛薄膜纳米孔孔径和孔密度的范围。     

Preparation of nanoporous tin oxide by electrochemical anodization in alkaline electrolytes

This paper reports the creation of a porous tin oxide structure by means of anodization of pure tin foil in alkaline NaOH solutions. The tin oxide film formed is polycrystalline and possesses an irregular nanoporous structure with a porosity of ∼50%. The average pore size is ∼37 nm with a size distribution from 10 to 60 nm irrespective of anodization conditions, including the applied voltage (5–15 V) and NaOH concentration (0.125–1 M). The BET specific surface area of this porous structure is 79.6 m²/g. Linear relationships are observed for the dependence of tin oxide layer thickness on anodization time, applied voltage, and NaOH concentration. A thermodynamic model is established to explain the pore growth mechanism in the anodization process.     

Porous WO3 formed by anodization in oxalic acid

This work reports the investigation of the anodic growth of porous tungsten oxide (WO₃) in oxalic acid. It was found that pore diameter increases from approximately 50 to 90 nm while the layer thickness of porous structures increases from approximately 100 to 400 nm as the voltage varies from 40 to 100 V. Extended anodization duration improves the homogeneity of the porous structure at 40 V but it has no effect on the pore layer thickness. During the pore formation process, nucleation of small pores in the existing pore is observed while several layers of pores with voids underneath the surface layer are formed especially at high anodization voltage. A possible growth mechanism of the pores is proposed.     

Modelling and simulation of self-ordering in anodic porous alumina

Real-time evolution of pre-textured anodic porous alumina growth during anodization is numerically simulated in two-dimensional cases based on a kinetic model involving the Laplacian electric field potential distribution and a continuity equation for current density within the oxide body. Ion current densities governed by the Cabrera–Mott equation in high electric field theory are formed by ion migration within the oxide as well as across the metal/oxide (m/o) and oxide/electrolyte (o/e) interfaces, and the movements of the m/o and o/e interfaces due to oxidation and electric field assisted oxide decomposition, respectively, are governed by Faraday's law. Typical experimental results, such as linear voltage dependence of the barrier layer thickness and pore diameter, time evolution of the current density, scalloped shape of the barrier layer, and the extreme difference in the reaction rates between pore bottoms and pore walls, are successfully predicted. Our simulations revealed the existence of a domain of model parameters within which pre-textured porous structures which do not satisfy self-ordering configurations are driven into self-ordering configurations through a self-adjustment process. Our experimental results also verify the existence of the self-adjustment process during anodization.     

应用多孔阳极氧化电流—时间曲线比较壁垒膜厚

在有壁垒膜存在的表面,多孔膜的生长在氧化初期受到延迟阻碍,这一现象在直流恒压多孔阳极氧化电流一时间曲线上反映出来。电流达到稳态氧化的时间愈长,壁垒膜愈厚。文中应用此法判断了0.5MH_3BO_3介质的pH值、温度对壁垒阳极氧化膜厚的影响,并应用记录同一介质环境壁垒恒流阳极氧化的槽压一时间曲线得到验证。     

电压对7N01铝合金阳极氧化膜结构及耐蚀性的影响

采用160 g/L硫酸溶液在17℃下对7N01铝合金阳极氧化30 min,氧化电压分别选取14、15、16、17和18 V。用扫描电镜观察所得阳极氧化膜的形貌,用能谱仪和电化学测量分析了它的成分、厚度和耐蚀性。结果表明,7N01铝合金经过不同电压下的阳极氧化处理后,表面均能形成凹凸不平并有孔洞的阳极氧化膜,电压为17 V时所制膜层致密、均匀,厚度约为7.6μm,耐蚀性最佳,在3.5%NaCl溶液中浸泡1 440 h后没有明显的腐蚀。     

铝合金直流电阳极氧化膜电解着色的研究

以工业纯铝L2为实验材料,采用硫酸直流电阳极氧化-电解着色工艺在铝合金表面制备黑色膜层.着重分析着色电压对黑色膜层表观颜色、厚度、硬度的影响.通过SEM表征、EDS测试及性能测试表明:在优化后的电解着色工艺条件下可以获得与工业纯铝L2基体结合力良好,且耐蚀性、耐热性、吸光性均较好的黑色膜层.     

Nucleation and growth of anodic oxide films on bismuth—II

The rate of nucleation of the anodic oxide film on bismuth in 0.1 M NaOH is limited by electrochemical reaction at the uncovered metal surface or surface diffusion to the periphery of a spreading oxide patch, not by incorporation into the growing lattice. Anodic oxide layers grown on bismuth consist of a thin barrier layer overlaid by a much thicker cracked and porous layer. Discrepancies between previous workers are thus resolved. The growth kinetics of the barrier layer are satisfactory described by the simple model of high field ion transport. Galvanostatic and potentiostatic techniques, and microscopic examination of the metal surface, including scanning electron microscopy, were employed.     

Tailoring the nanostructure of anodic aluminum oxide cladding on optical fiber

We report a comprehensive investigation of fabricating nanostructured anodic aluminum oxide (AAO) cladding on optical fiber. We show that the pore size and interpore distance in the AAO cladding with pore channels vertically aligned to fiber surface can be readily controlled by applied voltage, the type, and concentration of electrolytic acid during anodization of aluminum‐coated optical fiber. The structural characteristics of the AAO cladding were examined by scanning electron microscopy (SEM) and analyzed using ImageJ software. Processing maps correlating AAO growth and anodization parameters were established. Compared to planar AAO growth on aluminum foil, higher growth rate as well as larger pore diameter and interpore distance were observed for AAO cladding formation on optical fiber under identical anodization conditions due to circumferential tensile stress in the AAO growth front at the convex AAO/aluminum interface. This tensile stress also contributed to radial cracking of the AAO cladding upon exceeding some threshold thickness.     

Fabrication of self-ordered nanoporous alumina with 500–750 nm interpore distances using hard anodization in phosphoric/oxalic acid mixtures

A hard anodization (HA) technique is employed using different mixtures of phosphoric/oxalic acid for fast fabrication of alumina nanopore arrays in voltages higher than 200 V. The mixtures enable to avoid the breakdown of porous anodic alumina (PAA) in the high voltages. It is revealed for the first time that continuously tunable pore intervals (D_int) from 500 to 750 nm can be controlled by varying the concentrations of oxalic acid at anodization voltages (U_anod) from 230 to 360 V, far beyond the U_anod in the single electrolyte of phosphoric acid or oxalic acid. The ratios of interpore distance, pore diameter and barrier layer thickness to anodization voltage are in the range of conventional HA process for each acid mixture. In this approach, the PAA film growth rate is 26 µm/h, being 7 times larger than that in typical mild anodization.     

Surfactant-assisted growth of anodic nanoporous niobium oxide with a grained surface

Nanoporous niobium oxide film with a maximum thickness of 520 nm was prepared by anodizing niobium in a mixture of 1 wt% HF, 1 M H₃PO₄, and a small amount of Sodium Dodecyl Sulfate (SDS) surfactant. The porosity of the anodic niobium oxide prepared without SDS is irregular with the surface of the oxide suggesting a grained surface pattern rather than an ordered porous structure. A proper amount of SDS addition can prepare a pore arrangement with stripe patterns. The pore depth and surface pattern were strongly affected by the concentration of SDS and bath temperature. We found that the addition of SDS surfactant facilitated improvement in the chemical resistance of niobium oxide, leading to the formation of pores with a longer length compared to those prepared without a SDS surfactant. This can be in part ascribed to the protection of the surface by the physical adsorption of SDS on the surface due to a charge-charge interaction and be in part attributed to the formation of NbO bonding on the outermost oxide layer by SDS. When anodization was carried out for 4 h, the surface dissolution of niobium oxide was observed, which means that the maximum tolerance time against chemical dissolution was less than 4 h.     

Electrochemical impedance spectroscopic study of barrier layer thinning in nanostructured aluminium

The electrochemical behaviour of electropolished and anodised aluminium was studied by electrochemical impedance spectroscopy (EIS). Freshly electropolished aluminium behaves as a pure capacitor exhibiting Warburg impedance at low frequencies. Storage of the electropolished aluminium, even in an air-tight bottle, results in the reconstruction of a uniform compact barrier layer. The impedance response of a stored electropolished aluminium as well as anodised aluminium after oxide removal, done by chemical etching, exhibits only a capacitive loop in the complex plane. The effect of the oxide layer thickness on the impedance data was investigated for layers formed during anodising at a cell potential of 15 or 23 V. Impedance measurements carried out over a wide range of frequencies gave useful information on the efficiency of the thinning of the barrier layer at the bottom of porous aluminium oxide layers. The rate of thinning of the barrier layer was estimated for samples anodised at different voltage.     

Embedded space charge in porous alumina films formed in phosphoric acid

The embedded charge in the barrier layers of porous alumina, formed potentiostatically in phosphoric acid was studied as a function of anodizing voltage (30-57 V) and bath temperature (18 and 21 °C). For that, the polarization measurements of as-grown and annealed alumina/Al samples were conducted in the same anodizing bath by anodic potential sweep at a scan rate of 2.6 V/min. The plane capacitor model was used for the assessment of the charge density in the barrier layers of as-grown porous alumina. For the barrier layers of films formed at 18 °C this value equals to 0.747 μC cm⁻² and does not depend on the anodizing voltage. Increase in electrolyte temperature rises the embedded charge density. Polarization measurements carried out in this paper clearly present that the barriers of phosphoric acid films grown at the anodizing voltages lower than 39 V contain a layer of virtual cathode while at higher voltages this layer disappers. The obtained results allow speaking about promising opportunities of potentiodynamic polarization measurements of alumina films in the same anodizing solution before and after annealing for the studies of charges embedded within the alumina barriers and for the regularities of ion transport.     

Impact of ac/dc spark anodizing on the corrosion resistance of Al–Cu alloys

An ac/dc spark anodization method was used to deposit an oxide film (6 ± 3 μm in thickness) on the Al–Cu alloy AA2219. The oxide films were formed at 10 mA/cm² for 30 min in an alkaline silicate solution, showing three main stages of growth. Scanning electron microscopy and electron microprobe analysis revealed that the oxide films are not uniform and consist of three main layers, an inner Al-rich barrier layer (∼1 μm), an intermediate Al–Si mixed oxide layer (∼2 ± 1 μm), and an outer porous Si-rich layer (∼3 ± 3 μm). In addition, microscopic analysis showed that the Al₂Cu intermetallics present in the alloy have not been excessively oxidized during the anodization process and thus are retained beneath the oxide film, as desired. The coating passivity and corrosion resistance, evaluated using linear sweep voltammetry (LSV) in pH 7 borate buffer solution and electrochemical impedance spectroscopy (EIS) in 0.86 M NaCl solution, respectively, were both significantly improved after spark-anodization.