Mechanism of TiO₂ Nanotubes Formation on the Surface of Pure Ti and Ti-6Al-4V Alloy

Abstract

The present paper deals with the investigation of the mechanisms of TiO2 nanotubes formation on titanium surfaces during anodization process. The samples were made of pure Ti Grade-2 and Ti-6Al-4V alloy. They were grinded, etched with 0,5 wt. % HF acid and anodized. The anodization was done in electrolyte containing 0,5 wt. % HF acid using DC power supply with graphite electrode as cathode. The samples were investigated by SEM, EDAX and XRD analysis. The results show two different mechanisms of formation of TiO2 nanotubes on the surfaces of both materials. During the anodization process the oxide formations, obtained on the pure Ti surface after etching, are oxidized to nanorods; the area between them is also oxidized and connects them. This thin oxide layer grows in the metal depth while the nanorods are dissolved thus forming the porous sponge-like structure which is further transformed in tubular. While on the surface of Ti-6Al-4V alloy oxide nanonuclei originate which transform their shape from nanoseed to bowl-like with clearly pronounced bottom and walls, growing in tubular structures. The type of the material defines the surface morphology after etching. Thus obtained morphology influences on the processes running rate in different micro-regions determining origination of the titanium nanotubes on different stage as well as by different mechanism. The field-enhanced oxidation and field-enhanced dissolution are the main processes for formation of TiO2 nanotubes during anodization. In the regions with prevalent oxidation processes the TiO2 nanotubes are formed earlier while in the regions with dominant dissolution processes the TiO2 nanotubes are formed on the later stage.

A Novel Methodology for Economical Scale-Up of TiO2 Nanotubes Fabricated on Ti and Ti Alloys

“…e data presented above were proportional to the previously reported studies [48,69,80]. e nanotube dimensions, morphology, and EDS analysis of the anodised Ti-6Al-4V titanium alloy specimens showed a similar trend to those reported in previous publications [79,[89][90][91][92]. e EDS analysis revealed that the anodic layer was composed of titanium, aluminium, vanadium, oxygen, and traces of carbon and fluorine.…”

“…It could be due to the different electrolyte and base material composition used, as well as the effect of the additional pickling process before the anodisation is carried out to remove the naturally occurred oxide layer. ese phenomena have been previously demonstrated in other comparable studies [90,93,94]. In addition to that, the literature has also shown that changes in nanotube length are the least significant for the modulation of cellular behaviour [50], unlike the pore size and interpore distance, which are important.…”

Mixed oxide nanotubes in nanomedicine: A dead-end or a bridge to the future?

“…One of the pioneering efforts to utilize electrochemical anodization as an innovative approach for the surface modification of Ti-based alloys was performed by Dunn et al [ 221 , 222 ], where porous surface coatings are formed by anodization and incorporating antibiotics onto the oxide surface. Zwilling et al [ 223 ] also reported that anodization on Ti and Ti–6Al–4V alloys in the F − ion solution is an effective approach to attain tunable tubular oxide layers under different anodization conditions [ 16 , 17 , 65 , 133 , [224] , [225] , [226] , [227] , [228] , [229] , [230] , [231] , [232] , [233] , [234] , [235] , [236] , [237] , [238] , [239] , [240] , [241] , [242] , [243] , [244] , [245] , [246] , [247] , [248] , [249] , [250] , [251] , [252] , [253] , [254] , [255] , [256] , [257] , [258] , [259] , [260] , [261] , [262] ]. Since the Ti–6Al–4V alloy is a dual-phase alloy, the development kinetics of nanotubes are dissimilar for the α and β phases [ 69 ].…”

The Effect of Initial Etching Sites on the Morphology of TiO2Nanotubes on Ti-6Al-4V Alloy

“…The anodisation started with randomly arranged porous structures and ended with uniformly arranged nanotubes. Meanwhile, Dikova and colleagues defined the mechanism behind the growth of nanotube on the surface of Ti-6Al-4V with the surface of their samples being coated up to 80% with nanotubes in 7 hours [26]. During the process, where they used just hydrofluoric acid (HF), the synthesis of the nanotubes started with the presence of nano-seeds.…”

“…The process as to why the nanotubes are uniformly arranged had been described by different groups [26] [27]. The group of Dikova performed a step by step analysis of the nanotube formation in hydrofluoric acid at 25 V and provided microscopic images of the different structures at different intervals.…”