Synthesis of anodic films in the presence of aniline and TiO2 nanoparticles on AA2024-T3 aluminium alloy

Coatings, comprising an inner porous anodic alumina film and an outer polyaniline/TiO₂ nanoparticle layer, were electrochemically synthesised on an AA2024-T3 aluminium alloy by single-step, anodic polarisation in an oxalic acid-based electrolyte. The morphology and composition of the coatings were examined by TEM, SEM and XPS, with the size and zeta-potential of the TiO₂ nanoparticles in the oxalic acid solution also measured. Observation of the growth of the coating during of anodic polarisation revealed that a distinct, two-layered coating is formed from the early stages of polarisation, with the anodic film forming at a constant rate and the outer layer developing at a rate that decreases markedly with times beyond about 30 min. Nanoparticles, agglomerated in the electrolyte, migrate to the anode due to the negative zeta-potential and form the nanoparticle-containing layer at the surface of anodic film. Such particles are not incorporated in the pores due to agglomeration and disordered film porosity at the outer layer of the anodic film.     

高度有序多孔阳极氧化铝模板的制备

为了得到纳米孔排列高度有序的多孔阳极氧化铝模板,以0.3 mol·L-1的草酸为电解液研究了模板的制备工艺.采用场发射扫描电子显微镜(FE-SEM)对多孔氧化铝模板的表面形貌进行表征,X射线衍射分析高纯铝及氧化膜的结构.实验结果表明,铝基体不经过高温退火处理,同样能够得到高度有序的氧化铝膜,简化了多孔氧化铝膜的制备工艺.分别讨论了阳极氧化电压和电解液温度对多孔阳极氧化铝膜的形貌及孔径的影响,并对一步法和两步法制得的多孔氧化铝膜进行比较,结果表明,两步阳极氧化法制备的多孔氧化铝模板的有序性优于一步氧化法.XRD分析证实,多孔氧化铝膜由非晶态的Al2O3组成.     

Combined kinetic and X-ray electron probe microanalysis characterization of local porosity variation and pore shape across anodic alumina films

Porous anodic alumina films on Al were prepared by anodic oxidation of Al in H₂SO₄ electrolyte at a constant temperature and current density and different thicknesses, up to ≈ 41 μm. Their cross section was examined by EPMA for revealing the variation of local porosity across the films and shape of pores while a kinetic model for film growth was developed describing the variation of pore diameter. It was found that the pores open, and local porosity increases, towards the film surface, predicting a conical pore shape, while the results coincided with those obtained by kinetic study. The EPMA analysis combined with kinetic results emerges as a promising tool for studying structural features of these films.     

Comparative study of porous anodic alumina: effects of aluminium deposition methods

This article reports on the comparative study of the fabrication of porous anodic alumina films by anodisation of the aluminium films on glass substrates which were deposited by direct current sputtering and electron beam evaporation methods. The relationship between surface morphology of the deposited aluminum films and porous anodic alumina films was investigated. A more uniform and ordered porous anodic alumina was obtained by fabricating from electron beam evaporation deposited aluminium film with smaller and compact grains. Two-step anodisation was used to further improve the quality of porous anodic alumina compared to one-step anodisation. The optical transmittance spectra within wavelength of 370–800 nm were obtained and the optical properties were studied.     

Titanium oxide films produced on commercially pure titanium by anodic oxidation with different voltages

Titanium oxide films produced on commercially pure Ti by anodic oxidation with different voltages were analyzed. Anodic oxidation was carried out at room temperature using 1.4 M H₃PO₄ electrolyte and a platinum counter-electrode, in potentiostatic mode under the following conditions: 50 V, 100 V, 150 V, 200 V and 250 V. It was observed that porous titanium layers were formed at all voltage values but morphological differences were observed. Initially, the film was thin but with increasing voltage it broke down locally and porous regions became evident due to the dielectric breakdown. The porosity and the pore size increased with the increasing voltage. The surface morphology in samples formed with 200 V had substantially different porous structures than those formed with other voltage values. The anodic film surface displayed pores and craters formed on the relatively flat ground oxide surface. AFM images showed that higher voltages produced thicker titanium oxide films.     

Anodic oxide film growth on thin magnetron sputter-deposited titanium layer

A ~ 100 nm thick sputter-deposited titanium layer on electropolished aluminium is used for the investigation of anodic film growth in 1 M H₃PO₄. It is found that the thin titanium layer could not provide sufficient current efficiency for titanium anodic film growth when anodized to the voltage over 80 V due to the occurrence of oxygen evolution. The ruptures of titanium anodic film and the sputtering layer are induced by the development of oxygen bubbles. The penetrated phosphoric acid electrolyte in the ruptured regions of sputtering titanium layer contacts with the aluminium substrate, which is leading to the anodic oxide growth of aluminium. The thickness of the titanium anodic film increases from 10 to 100 V, however, it is reduced from 100 to 150 V due to the thinning of titanium layer. Over 80 V, the sputtering layer at some regions where it is completely ruptured, the anodic film growth of titanium could not be created. A thicker aluminium anodic film is formed on such regions due to the direct connection with the electrolyte.     

Increased growth rate of anodic porous alumina by use of ionic liquid as electrolyte additive

The use of ionic liquids 1-Butyl-3-methylimidazolium 2-(2-methoxyethoxy) ethyl sulfate and 1-Butyl-3-methylimidazolium tetrafluoborate has been tested in the fabrication of anodic porous alumina. The anodizations of the aluminium substrate have been carried out in oxalic acid in galvanostatic mode. During anodization with 1-Butyl-3-methylimidazolium tetrafluoborate added electrolyte, proper tuning of the current density and of the additive concentration resulted in a three-fold increase of the growth rate as compared to the bare acidic solution with the same acid concentration. This did not cause cracks in the film during growth, and did not affect the regular structure of the pores at the interface with the substrate.     

Formation of complex anodic films on porous alumina matrices

The kinetics of growth of complex anodic alumina films was investigated. These films were formed by filling porous oxide films (matrices) having deep pores. The porous films (matrices) were obtained voltastatically in (COOH)₂ aqueous solution under various voltages. The filling was done by reanodization in an electrolyte solution not dissolving the film. Data about the kinetics of reanodization depending on the porosity of the matrices were obtained. On the other hand, the slopes of the kinetic curves during re-anodization were calculated by two equations expressing the dependence of these slopes on the ionic current density. A discrepancy was ascertained between the values of the calculated slopes and those experimentally found. For this discrepancy a possible explanation is proposed, related to the temperature increase in the film, because of that the real current density significantly increases during re-anodization.     

How structure changes in fabrication of large size ordered anodic alumina film?

Large size anodic alumina film has not been used in the industry due to that the fabrication parameters are very difficult to control, but the fabrication of large size anodic alumina is exigent as a template in the fabrication of diverse nano-devices oriented to the industrialization. In this paper, large size (width length = 80 mm × 80 mm) porous ordered anodic alumina film was fabricated by using two-step anodization process as compared to the small size (diameter = 40 mm) anodic alumina film in the structures. Pore size and film thickness of anodic alumina film are strongly related to the size of the anodization film. The large size anodic alumina film has an ideally ordered pattern by applying low voltage. However, with the increase of voltage, the ordered pattern of the PAA films was gradually disrupted, especially in the 70 V due to the local thermal imbalance.     

Behaviour of hydrogen impurity in aluminium alloys during anodizing

The present study examines the behaviour of hydrogen impurity in an Al-6.5 at.% W alloy during anodizing, using elastic recoil detection and nuclear reaction analyses. Increased concentrations of hydrogen are found near the alloy/anodic film interface, amounting to ∼2×10¹⁵ H atoms cm⁻² for the particular alloy, containing 0.1-0.3 at.% hydrogen in the bulk regions, and conditions of anodizing. The enrichment arises from hydrogen in the alloy (i) diffusing to the interface, which acts as a trap, or (ii) accumulating at the interface, due to the growth of the anodic film, or a combination of both processes. Diffusion is consistent with the known mobility of hydrogen in aluminium near ambient temperature. Further, accumulation, and subsequent oxidation, of hydrogen are expected based on the general behaviour of alloying elements in anodized aluminium. The anodic films contained ∼0.1-0.3 at.% hydrogen, originating from either the electrolyte or the alloy.     

Growth of porous anodic films on FVS0812 aluminium alloy

The formation of porous anodic films on FVS0812 aluminium alloy has been examined by transmission electron microscopy in order to elucidate the processes of film growth. A complex morphology of film material is revealed containing relatively tortuous, branched and terminated porosity and relatively large cavities. The morphology is associated with the differing anodic oxidation behaviour of the aluminium matrix and silicide dispersion regions of the alloy and the differing chemical stabilities of the resultant film regions. The anodic oxidation of the silicide proceeds more slowly than that of the aluminium matrix, with the production of film material of much finer morphology. The reduced rate of oxidation of the silicide is attributed to the effects of alloying element species in the anodic film material and pore solution. The rate of oxidation of the silicide is sufficient for most of the particles to be oxidized completely during anodizing. However, the resultant film material subsequently dissolves in the pore solution leaving relatively large cavities in the film. The differing oxidation rates of the alloy components, coupled with locally differing film properties, leads to a relatively rough alloy/film interface.© 1998 Kluwer Academic Publishers     

Room-temperature photoluminescence from porous anodic alumina films with embedded terbium and europium species

Strong room-temperature terbium and europium photoluminescence, with well-resolved optical bands corresponding to electron transitions ⁵D₄→⁷F_j (j = 3–6) for Tb³⁺, and ⁵D₀→⁷F_j (j = 1–4) for Eu³⁺, was observed from porous anodic alumina films of 5–55 µm thickness after immersion in solutions of terbium or europium nitrates and subsequent heat treatment. GDOES and TEM examinations of the specimens treated with terbium ions revealed a uniform distribution of terbium across the porous anodic film thickness of 55 µm, with an increased terbium concentration toward the pore bases. Europium- and terbium-doped specimens displayed anisotropic indicatrix of luminescence for the emission wavelength of 613 nm for europium and 545 nm for terbium, with a maximum intensity in the direction along the channels of the pores that is typical for porous anodic alumina with lanthanide ions within the pores. The potential applications of porous anodic alumina doped with lanthanides through immersion in the absence of xerogel are discussed.     

Surface morphology, composition and thermal behavior of tungsten-containing anodic spark coatings on aluminium alloy

Anodic spark coatings on aluminium alloy were prepared in aqueous electrolytes with sodium tungstate. The influence of boric acid addition in the electrolyte on the surface morphology, elemental and phase composition of the coatings was investigated. In both cases the coatings contained O, Al and W. The coatings obtained in electrolyte with boric acid and sodium tungstate contain also B at approximately 1 at.%. Scanning electron microscopy indicated that the coatings had three layers: the grey underlayer of anodic alumina, the second black layer of crystalline or amorphous aluminium tungstate agglomerated into fibers and the outer green layer of WO₃. It was proposed that isopoly- and heteropolyanions in the electrolyte used take part in the coating growth.     

Anodic oxide growth on aluminium surfaces modified by cathodic deposition of Ni and Co

Surface conditions similar to those found in aluminium alloys of practical use were assessed by cathodic deposition of transitions metals (Ni and Co) from different electrolytes. Fundamental aspects concerning with the growth of anodic oxide films at potentials lower than 10 V in neutral acetate buffer solution on these modified surfaces were analysed by common electrochemical techniques complemented with scanning electron microscopy and transmission electron microscopy. In both potentiodynamic and galvanostatic modes, the growth of aluminium oxide competes with the dissolution of deposited metal particles. The formation of a thin aluminium barrier oxide film beneath them shifts the dissolution potential over to 1.5 V towards more positive values. Some particles get progressively embedded in the matrix of the growing alumina and act as cation sources, increasing the film conductivity and diminishing the established electric field in the oxide. This effect is more pronounced with Co deposits due to its high active dissolution rate, before passivation occurs. Then, the generation of a two-layer film is explained in terms of the precipitation of metal hydroxide at the solution side on the oxide barrier film.     

多孔阳极氧化铝形成机理的研究综述

铝阳极氧化已经研究了五十多年,涉及铝阳极氧化膜的实验数据十分丰富,然而阳极氧化过程的本质特别是多孔氧化膜的生长机制迄今为止还远未认识清楚。近些年,随着纳米技术的兴起,多孔氧化铝膜作为理想的纳米结构模板材料倍受国内外学者的关注,对多孔氧化铝膜形成机理的研究显得尤为重要。本文对多孔阳极氧化铝的结构、形成机制方面的历史发展和现状进行了综述。指出了大多数学者认同的“酸性场致溶解”理论的缺陷。作者认为铝多孔氧化膜形成机理的研究具有重大的理论意义和实际应用价值,同时也会促进其他多孔阳极氧化物形成机理的认识。     

干涉着色阳极氧化铝

本文主要介绍了利用光干涉效应原理的工艺着色阳极氧化铝,并对干涉色涂层的微观结构进行了初步分析。将经过常规硫酸阳极氧化后的铝试样,在磷酸溶液中作短时间的阳极氧化扩孔处理,再置于普通电解着色液中进行电解着色,即可获得性能优异的干涉色涂层。阳极氧化铝中的干涉着色效应,来源于沉积金属层表面和阳极膜/铝基体界面的两束散射光的相互作用。     

预处理工艺对制备多孔阳极氧化铝膜的影响

对铝的预处理工艺进行了研究,详细探讨了高温退火、除油及电化学抛光等对多孔阳极氧化铝形貌的影响.实验结果表明,采用丙酮除油效果最好,不经高温退火和电化学抛光仍能得到高度有序的多孔阳极氧化铝膜,使制备工艺得到了简化.其原因是两步阳极氧化法可以消除铝的内部结构及表面缺陷对多孔氧化铝膜有序性的影响.     

Morphological instability leading to formation of porous anodic oxide films

Electrochemical oxidation of metals, in solutions where the oxide is somewhat soluble, produces anodic oxides with highly regular arrangements of pores. Although porous aluminium and titanium oxides have found extensive use in functional nanostructures, pore initiation and self-ordering are not yet understood. Here we present an analysis that examines the roles of oxide dissolution and ionic conduction in the morphological stability of anodic films. We show that patterns of pores with a minimum spacing are possible only within a narrow range of the oxide formation efficiency (the fraction of oxidized metal atoms retained in the film), which should exist when the metal ion charge exceeds two. Experimentally measured efficiencies, over diverse anodizing conditions on both aluminium and titanium, lie within the different ranges predicted for each metal. On the basis of these results, the relationship between dissolution chemistry and the conditions for pore initiation can now be understood in quantitative terms.     

Highly ordered hexagonally arranged nanostructures on silicon through a self-assembled silicon-integrated porous anodic alumina masking layer

A combined process of electrochemical formation of self-assembled porous anodic alumina thin films on a Si substrate and Si etching through the pores was used to fabricate ideally ordered nanostructures on the silicon surface with a long-range, two-dimensional arrangement in a hexagonal close-packed lattice. Pore arrangement in the alumina film was achieved without any pre-patterning of the film surface before anodization. Perfect pattern transfer was achieved by an initial dry etching step, followed by wet or electrochemical etching of Si at the pore bottoms. Anisotropic wet etching using tetramethyl ammonium hydroxide (TMAH) solution resulted in pits in the form of inverted pyramids, while electrochemical etching using a hydrofluoric acid (HF) solution resulted in concave nanopits in the form of semi-spheres. Nanopatterns with lateral size in the range 12-200?nm, depth in the range 50-300?nm and periodicity in the range 30-200?nm were achieved either on large Si areas or on pre-selected confined areas on the Si substrate. The pore size and periodicity were tuned by changing the electrolyte for porous anodic alumina formation and the alumina pore widening time. This parallel large-area nanopatterning technique shows significant potential for use in Si technology and devices.     

Composition and density of non-thickness-limited anodic films on aluminium and tantalum

The unusual occurrence of anodic films of unlimited thickness has been recently reported for anodizing of tantalum in certain dehydrated, high-temperature electrolytes with organic solvents. The precise nature of these films is still uncertain. In the present work, non-thickness-limited (NTL) anodic films were formed at 0.1 mA cm⁻² on aluminium and tantalum in glycerol/phosphate electrolyte at 453 K and then examined by Rutherford backscattering spectroscopy (RBS). The results disclosed films composed of alumina and tantala, free of phosphorus species at the resolution of the measurements. Most notably, the densities of the NTL alumina and tantala were about 2.4 and 3.6 g cm⁻³, respectively. These values are less than those of compact anodic films of the type usually grown at high efficiency in aqueous electrolytes by respective factors of about 1.3 and 2.2. This difference in density is attributed primarily to the morphology and structure of NTL film materials, which incorporate significant porosity.