Premium
Porous‐Alumina‐Assisted Growth of Nanostructured Anodic Films on Ti−Nb Alloys
Author(s) -
Bendova Maria,
Kolar Jakub,
GispertGuirado Francesc,
Mozalev Alexander
Publication year - 2018
Publication title -
chemelectrochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.182
H-Index - 59
ISSN - 2196-0216
DOI - 10.1002/celc.201800785
Subject(s) - anodizing , materials science , oxide , amorphous solid , alloy , anode , chemical engineering , crystallization , porosity , metallurgy , composite material , electrode , crystallography , aluminium , chemistry , engineering
Porous‐anodic‐alumina (PAA)‐assisted anodizing is employed, for the first time, for growing arrays of oxide nanocolumns on Ti−Nb alloy films with up to 58 at% Nb. Beyond about 24 at% Nb in the alloy, the system allows for high formation potentials of 250–420 V, giving columns that are 500–700 nm long, which are 100 % stable during the PAA etch. The stability worsens when lowering the Nb content in the alloy, owing to contamination of the column roots by alumina, which arises from the amorphous‐to‐crystalline transition of the anodic oxide, oxygen evolution, formation of O 2 ‐filled nanobubbles within the roots, and development of bigger voids. The voids force the roots to regrow and spread laterally along with anodizing the surrounding Al residues, which increases alumina content in the titania‐based nanoroots. The incorporation of sufficient amounts of Nb 2 O 5 in the anodic TiO 2 hinders oxide crystallization and lowers alumina content in the roots, which stabilizes the columns. The two oxides are distributed uniformly along the columns, indicating comparable migration rates of Ti 4+ and Nb 5+ ions in the mixed anodic oxide. This uniform distribution, combined with possibly mixing the oxides at atomic level, is expected to narrow the band gap of the material, which is of vast importance for solar energy conversion applications.