Incorporation of Ions into Nanostructured Anodic Oxides—Mechanism and Functionalities

Abstract

Anodic oxidation of metals leads to the formation of ordered nanoporous or nanotubular oxide layers that contribute to numerous existing and emerging applications. However, there are still numerous fundamental aspects of anodizing that have to be well understood and require deeper understanding. Anodization of metals is accompanied by the inevitable phenomenon of anion incorporation, which is discussed in detail in this review. Additionally, the influence of anion incorporation into anodic alumina and its impact on various properties is elaborated. The literature reports on the impact of the incorporated electrolyte anions on photoluminescence, galvanoluminescence and refractive index of anodic alumina are analyzed. Additionally, the influence of the type and amount of the incorporated anions on the chemical properties of anodic alumina, based on the literature data, was also shown to be important. The role of fluoride anions in d-electronic metal anodizing is shown to be important in the formation of nanostructured morphology. Additionally, the impact of incorporated anionic species, such as ruthenites, and their influence on anodic oxides formation, such as titania, reveals how the phenomenon of anion incorporation can be beneficial.

Nanoporous anodic alumina-based iontronics: fundamentals and applications

“…50 Typically, the amount of anionic contaminants decrease in the anodic Al 2 O 3 formed in electrolytes follows the order of H 2 SO 4 4 H 3 PO 4 4 H 2 C 2 O 4 . 88,97 The photoluminescence spectra acquired by Yamamoto et al revealed three layers in the chemical composition of NAA, with a decrease of impurities across the outer, middle and inner region of oxide pore walls (Fig. 5a-ii).…”

“…Due to their larger ionic radii and lower mobility, electrolytic anions migrate across the BOL at lower velocity during the electric field-assisted growth of anodic oxide. [88][89][90][91][92][93] This results in a duplex structure of anodic oxide: inner layers composed of pure Al 2 O 3 and outer layers that are contaminated with electrolytic anions. [94][95][96] pure alumina in porous anodic oxide layer to the strength of electric field applied during anodization and their transmission electron microscopy analysis of ion-beam thinned porous anodic films revealed the existence of cell boundary bands in the pore wall oxide produced in different electrolytes.…”

Nanostructure Analysis of Anodic Films Formed on Aluminum-Focusing on the Effects of Electric Field Strength and Electrolyte Anions

“…The anion content of porous anodic films linearly increases with the increasing log of the current density, i.e., electric field strength [ 15 ], similar to the case of barrier-type films [ 17 , 19 , 59 ]. It is shown that the anion content and species significantly affect the film properties [ 23 , 36 , 68 , 71 , 72 , 73 ]. In barrier-type films, the anion species and the content of anions have a significant impact on the permittivity, as well as the leakage current, due to the formation of defects [ 17 , 18 , 19 , 74 , 75 ].…”

Biofunctionalization of Porous Titanium Oxide through Amino Acid Coupling for Biomaterial Design

“…Over the years, numerous studies have been conducted to optimize the properties of the surface oxide layer to promote implant osseointegration. Anodic oxidation is a widely used method for this purpose because it allows, through appropriate choice of anodizing conditions, to improve the passivation of the metal by growing thick oxide films enriched in osteoconductive elements, such as Ca and P, with a highly porous structure, which favors osseointegration [ 1 , 2 , 3 , 4 , 5 , 6 ].…”