Self-organized Anodic TiO2 Nanotube Layers: Influence of the Ti substrate on Nanotube Growth and Dimensions

Abstract

In this contribution, various Ti thin substrates were explored and compared for the anodic growth of self-organized TiO 2 nanotube layers for the first time. In order to evaluate differences in the electrochemical anodization characteristics and the tube dimensions, five different Ti substrates from four established suppliers were anodized in the widely used ethylene glycol electrolytes containing 88 mM NH 4 F and 1,5 vol.% water. Two anodizations were carried out to elucidate an influence of the pre-anodized substrates used for the second anodization. By thorough evaluation of the nanotube dimensions, large variations between the dimensions of the nanotubes were found for the different substrates, ranging from ~32 µm to ~50 µm for the nanotube length and from ~109 nm to ~127 nm for the nanotube diameter after the second anodization. Upon AFM measurements, Goodfellow Ti substrates (99.99 % purity), yielded the smoothest surface and the highest degree of ordering from all substrates.Moreover, considerably different consumption of Ti substrates via anodization was revealed by profilometric measurements between the original non-anodized part of the Ti substrates, and the anodized part after the removal of the nanotube layer. Orientation imaging 2 microscopy revealed considerable differences in the size and orientation of the substrate grains.

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

“…Such finding can be advantageous for the preparation of the nanotubes in the ethylene glycol electrolytes over other electrolytes, because Ti substrates prepared usually by rolling often exhibit texture in which (0001) axis of the grains in Ti sheets tend to be oriented perpendicular to the sheet plane [13]. Although exact reasons for preferential nanotube growth in (0001) direction remain unclear, the results can be specific for anodization in ethylene glycol electrolytes.…”

Ideally Hexagonally Ordered TiO2 Nanotube Arrays

“…A simple way to increase the ordering of the nanotube layers is, to a certain extent, a two‐step or three‐step anodization of the Ti substrates . 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][13][14] Other methods include mechanical, chemical, or electro-polishing of the Ti substrates before the anodization to reduce the surface roughness [15][16][17] or the use of high-purityT is ubstrates. [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.…”

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.…”