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.

Спектры электролюминесценции и структура анодного оксида алюминия при его формировании в химически чистой воде и спиртах

For a film of aluminum oxide (Al2O3) formed in distilled water (H2O), a linear growth was revealed during the high-voltage anodization time of 2000 s, and it was found that its electroluminescence (EL) is reliably recorded at an Al2O3 thickness of about 120 nm. It is shown that in DV and its deuterium-containing analogue, deuterium water (D2O), the electrolysis formation of Al2O3 is possible. cellular-nanoporous structure, identical to that formed in aqueous solutions of electrolytes. It was found that the presence of such a structure in the oxide is not a prerequisite for the generation of its EL. The EL spectrum of Al2O3 in H2O and D2O, as well as in “water-like” electrolytes: ethylene glycol, N, N-dimethylethanolamine, and isopentanol, was recorded for the first time. In the investigated range of 400–700 nm, significant differences in the luminescence in water and the above alcohols are revealed. For EL, the short-wavelength component with a wavelength of the order of 440 nm dominates in water, and in alcohols, the long-wavelength component with a maximum at 625 nm. In this case, nonstationarity of luminescence is observed both in the spectral composition and in the intensity of individual parts of the spectrum for the entire time of aluminum anodization.

A hydrogen evolution catalyst lowering energy consumption in aluminum anodization

Aluminum anodization process requires a lot of electric energy for ions migration in barrier-type oxide film, in which the electrode polarization leads the massive energy consumption. The cathodes are considered...

The Sealing Step in Aluminum Anodizing: A Focus on Sustainable Strategies for Enhancing Both Energy Efficiency and Corrosion Resistance

Increasing demands for environmental accountability and energy efficiency in industrial practice necessitates significant modification(s) of existing technologies and development of new ones to meet the stringent sustainability demands of the future. Generally, development of required new technologies and appropriate modifications of existing ones need to be premised on in-depth appreciation of existing technologies, their limitations, and desired ideal products or processes. In the light of these, published literature mostly in the past 30 years on the sealing process; the second highest energy consuming step in aluminum anodization and a step with significant environmental impacts has been critical reviewed in this systematic review. Emphasis have been placed on the need to reduce both the energy input in the anodization process and environmental implications. The implications of the nano-porous structure of the anodic oxide on mass transport and chemical reactivity of relevant species during the sealing process is highlighted with a focus on exploiting these peculiarities, in improving the quality of sealed products. In addition, perspective is provided on plausible approaches and important factors to be considered in developing sealing procedures that can minimize the energy input and environmental impact of the sealing step, and ensure a more sustainable aluminum anodization process/industry.

Determination of the field strength and realization of the high-field anodization of aluminum

The electric field strength during aluminum anodization was clarified, and this work can shed some light on the self-ordering mechanism of porous anodic alumina.