Influence of the Ti microstructure on anodic self-organized TiO2 nanotube layers produced in ethylene glycol electrolytes

Abstract

The relationship between the microstructure of Ti substrates and the anodic growth of selforganized TiO2 nanotube layers obtained upon their anodization in the ethylene glycol based electrolytes on these substrates is reported for the first time. Polished Ti sheets with mirror-like surface as well as unpolished Ti foils were considered in this work. Grains with a wide range of crystallographic orientations and sizes were revealed by Electron Backscatter Diffraction (EBSD) and correlated with nanotube growth on both types of substrates. A preferred grain orientation with (0001) axis perpendicular to the surface was observed on all substrates. Surfaces of all substrates were anodized for 18 hours in ethylene glycol electrolytes containing 88 mM NH4F and 1.5% water and thoroughly inspected by SEM. By a precise comparison of Ti substrates before and after anodization, the uniformity of produced self-organized TiO2 nanotube layers was evaluated in regard to the specific orientation of individual grains. Grains with (0001) axis perpendicular to the surface turned out to be the most growth-promoting orientation on polished substrates. No orientation was found to be strictly growth-retarding, but sufficient This postprint version is available from http://hdl.handle.net/10195/61977 Publisher's version is available from http://www.sciencedirect.com/science/article/pii/S0169433216304482 DOI: 10.1016DOI: 10. /j.apsusc.2016 This document is licenced under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0.International. ______________________________________________________________________________________________________ 2 anodization time (24 hours) was needed to obtain uniform nanotube layers on all grains without remnant porous initial oxide. In contrast with polished Ti sheets, no specific orientation was found to significantly promote or retard the nanotube growth in the case of unpolished Ti foils.Finally, the difference between the average nanotube diameters of nanotubes grown on various grains was investigated showing non-negligible differences in the diameter for different grain orientations and substrates.

Ideally Hexagonally Ordered TiO2 Nanotube Arrays

“…Other methods include mechanical, chemical, or electro‐polishing of the Ti substrates before the anodization to reduce the surface roughness or the use of high‐purity Ti substrates . However, owing to the grain microstructure of Ti, the nanotube layers are usually just locally ordered, limited by the grain boundaries …”

“…[12,18] However,o wing to the grain microstructure of Ti,t he nanotube layers are usually just locally ordered, limitedb ythe grain boundaries. [18,19] Therefore, pre-texturing of the Ti substrate surface with nanoimprints before anodization,a si sa lso known for porous alumina, [5][6][7] was used to receive ideally ordered nanotube or nanopore arrays. Alreadyi n2 004, Choi et al [20] anodized nanoimprinted Ti.T hey used a1 1cm 2 master stamp consistingo f Si 3 N 4 pyramids (hexagonally arranged with ad istance of 500 nm to the nearest neighboringp yramid) that they imprinted ontot he Ti surface.…”

Characterization of the morphology, structure and wettability of phase dependent lamellar and nanotube oxides on anodized Ti-10Nb alloy

“…Different factors and their influence on nanotubes have been investigated with details, such as pH, fluoride content, ageing of the electrolyte, anodizing potential and time, current density and temperature; which were summarized by several review [10]. Some authors investigated the effect of Ti crystalline orientation/ microstructure on morphology nanotubes [11][12][13][14][15][16][17] and others for porous films obtained by anodic process [18][19][20][21][22][23].…”

Self-organized double-wall oxide nanotube layers on glass-forming Ti-Zr-Si(-Nb) alloys

“…As the alloys have an amorphous structure, they have naturally no grain structure. This is especially interesting since for the anodization of crystalline Ti, the grain structure plays an important role regarding the nanotube uniformity [27,28]. The dimensions of the obtained nanotubes were compared with those obtained on reference Ti substrates, and differences in the current transients were analysed.…”