Achieving homogeneous anodic TiO2 nanotube layers through grain refinement of the titanium substrate

Abstract

In this work we used two-step electrochemical anodization to produce self-assembled layers of titanium dioxide nanotubes (TNT) on commercially pure titanium substrates with various grain sizes between 140 nm to 35 µm. The refined grain sizes were obtained using high pressure torsion (HPT). Optical microscopy, transmission electron microscopy, scanning electron microscopy and wettability testing showed that the homogeneity, morphology, thickness and wettability of TNT layers are critically dependent on the substrate grain size. With HPT processing up to ten turns, significant grain refinement was achieved with increasing dislocation density, leading to gradually thicker TNT layers up to 2 µm and improved homogeneity with decreasing standard deviation from 10 to 5 nm. HPT processing also changed the dissolution rate of oxide during anodization, which resulted in a different top morphology as well as an increased aqueous contact angle of TNT layers.

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