Peculiarities of Aluminum Anodization in AHAs-Based Electrolytes: Case Study of the Anodization in Glycolic Acid Solution

The anodization of aluminum (Al) in three alpha-hydroxy acids (AHAs): glycolic (GC), malic (MC), and citric (CC), was analyzed. Highly ordered pores in GC were obtained for the first time. However, the hexagonal cells were characterized by a non-uniform size distribution. Although common features of current density behavior are visible, the anodization in AHAs demonstrates some peculiarities. The electric conductivity (σ) of 0.5 M GC, MC, and CC electrolytes was in the following order: σ(CC) > σ(MC) > σ(GC), in accordance with the acid strength pKa(CC) < pKa(MC) < pKa(GC). However, the anodization voltage, under which a self-organized pore formation in anodic alumina (AAO) was observed (Umax), decreased with increasing pKa: Umax(CC) > Umax(MC) ≥ Umax(GC). This unusual behavior is most probably linked with the facility of acid ions to complex Al and the active participation of the Al complexes in the AAO formation. Depending on the AHA, its tendency and different modes to coordinate Al ions, the contribution of stable Al complexes to the AAO growth is different. It can be concluded that the structure of Al complexes, their molecular mass, and the ability to lose electrons play more important roles in the AAO formation than pKa values of AHAs.

Synthesis and Photoelectrocatalytic Activity of Anodic Nanostructured TiO₂ Films

Nanostructured titanium dioxide films were prepared by electrochemical oxidation technique, anodization voltage effect on structure morphology, optical and photoelectrocatalytic performances of the nanotubes were studied. The anodization voltage is shown to significantly affect structure of nanofilms and, accordingly, their photoelectrocatalytic activity. An active heterojunction photoanode was synthesised with electrodeposition of Cu₂O onanodized TiO₂. The anode photoelectroact ivityunder bias 1V (Ag/AgCl/3,5M KCl) is found to be 15 % higher than that of the original nanostructured TiO₂ film

Well-defined nanostructuring with programmable anodic aluminium oxide template

Well-defined nanostructuring over size, shape, spatial configuration, and multi-combination is a feasible concept to reach unique properties of nanostructure arrays, while satisfying such broad and stringent requirements with conventional techniques is challenging. Here, we report programmable anodic aluminium oxide templates to address this challenge by achieving well-defined pore features within templates in terms of in-plane and out-of-plane shape, size, spatial configuration, and pore combination. The structural programmability of template pores arises from broad-range anodization voltage adjusting together with uneven aluminium anodization rate designing, and further relies on a systematic blueprint guiding pore diversification. Starting from the programmable templates, we realize a series of nanostructures that inherit equal structural controllability relative to their template counterparts. Proof-of-concept applications based on such nanostructures demonstrate boosted performance. In light of the broad selectivity and high controllability, programmable templates will provide an all-in-one platform for well-defined nanostructuring.

Low-Cost Nanostructured Coating of Anodic Aluminium Oxide Synthesized in Sulphuric Acid as Electrolyte

The anodic oxidation of aluminium is an electrochemical technique that allows obtaining nanostructures with easily adjustable morphology depending on the synthesis variables, for its application in medicine, engineering, biotechnology, electronics, etc. In this work, low-cost aluminium oxide nanostructured films were synthesized and morphologically characterized using two anodization steps in sulphuric acid, varying the concentration and temperature of the electrolyte and anodization voltage. The order of the porous matrix, pore diameter, interpore distance, pore density, thickness, and porosity were measured and statistically analyzed. The results showed that under the proposed conditions it is possible to synthesize low-cost nanoporous aluminium oxide films, with a short-range ordering, being the best ordering conditions 10 °C and 0.3 M sulphuric acid at 20 V and 5 °C and 2 M sulphuric acid at 15 V. Furthermore, it was determined that the pore diameter and the interpore distance vary proportionally with the voltage, that the pore density decreases with the voltage and increases with the concentration of the electrolyte, and that the thickness of the oxide film increases with electrolyte concentration, temperature, and anodization voltage.

Study on the photoelectrical performance of anodized titanium sheets

Anodization is a widely used method to obtain multicoloured oxidized titanium sheets. However, most researchers paid great attention to the colour-related properties instead of photoelectrical properties of titanium oxide film obtained by anodization. In this work, to study their photoelectrical properties, a series of multicoloured oxidized titanium sheets were prepared by anodization method, and UV–vis absorption and photocurrents were tested. The relationship between anodization voltages/anodization durations and photocurrents of titanium sheets was studied. Results show that titanium sheets have excellent photoelectrical performance. With the increase of anodization voltage, the number of UV–vis absorption peaks increased under visible light which means increasing absorption. When anodization duration increased, absorption band edge also increased in the visible light region, which means the band gap needed to produce charge transfer transition decreased. Under simulated sunlight and applied voltage of +0.4 V, photocurrent increased with the increase of either anodization voltage or anodization duration, and can be expressed by linear equations. In addition, anodization currents were recorded during anodization. Morphology, crystal structure and photoelectrical properties of anodized titanium sheets were characterized. The anodized titanium sheets can not only be used as decorative material in jewellery and architecture fields etc. but also are supposed to be used as photoelectrical catalyst in further work.

Surface Modification of Ti-6Al-4V Alloy By Anodization Technique at Low Potential to Produce Oxide Layer

Due to their excellent biocompatibility, titanium alloys are tremendously as implants used, since relatively low modulus, corrosion resistance, and good fatigue strength. The biocompatibility, comes from the formation of natural Titanium dioxide (TiO2) layer. Therefore, TiO2 layer growth surface alteration is frequently applied to improve biological, chemical , and mechanical properties. TiO2 nanostructures are obtained under self-organization conditions by electrochemical anodization of Ti-6Al-4V. Parameters of anodization such as anodization time, voltage and addition of thiourea were evaluated in the composition of the H3PO4+NH4F solution. The morphology and elements of the Ti alloys surface were analyzed by Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS), whereas potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to evaluate the TiO2 layer in corrosion resistance. The results showed that the anodized Ti-6Al-4V alloy E-corr imcreased as the anodization voltage increased. Titanium alloy anodized using 12 V during 2 hours with H3PO4 + NH4F without thiourea solution had the thickest of oxide layer and highest corrosion resistance. Higher applied voltages have been shown to increase the deposition rate and coating thickness. Addition of thiourea has a definite effect on the inhibition of oxide layer of titanium. In order to produce the optimum titanium surface, the required applied anodization voltage and addition of volume thiourea is necessary.

Tailoring the Anodic Hafnium Oxide Morphology Using Different Organic Solvent Electrolytes

Highly ordered anodic hafnium oxide (AHO) nanoporous or nanotubes were synthesized by electrochemical anodization of Hf foils. The growth of self-ordered AHO was investigated by optimizing a key electrochemical anodization parameter, the solvent-based electrolyte using: Ethylene glycol, dimethyl sulfoxide, formamide and N-methylformamide organic solvents. The electrolyte solvent is here shown to highly affect the morphological properties of the AHO, namely the self-ordering, growth rate and length. As a result, AHO nanoporous and nanotubes arrays were obtained, as well as other different shapes and morphologies, such as nanoneedles, nanoflakes and nanowires-agglomerations. The intrinsic chemical-physical properties of the electrolyte solvents (solvent type, dielectric constant and viscosity) are at the base of the properties that mainly affect the AHO morphology shape, growth rate, final thickness and porosity, for the same anodization voltage and time. We found that the interplay between the dielectric and viscosity constants of the solvent electrolyte is able to tailor the anodic oxide growth from continuous-to-nanoporous-to-nanotubes.