Preparation and characterisation of TiO2 thick films fabricated by anodic oxidation in sulphuric acid

Abstract

Anodic oxidation is an electrochemical method for the production of oxide films on metallic substrates. It involves the application of an electrical bias at relatively low currents while the substrate is immersed in an acid bath. The resultant oxide films can be very dense and stable, showing a variety of colours and microstructural characteristics. In the present work, thick films of the anatase and rutile polymorphs of TiO2 were formed on highpurity Ti foil (50 m thickness) using sulphuric acid solutions (1.5 M H2SO4). The conditions of oxidation involved the application of potentials (5 to 350 V) and current densities (5 to 60 mA.cm-2) for 10 min at room temperature. The films were characterised using a digital photography, laser Raman microspectroscopy, and field emission scanning electron microscopy (FESEM). The thicknesses of the oxide films on Ti were measured using a thin film analyser based on optical spectroscopy principles. The phase formation, colours, thicknesses, and microstructures of the films depended strongly on the applied voltage and current density. At a standard bias of 150 V, single-phase anatase was observed to form on Ti at low current density (5 mA.cm- 2) but, at higher current densities (up to 60 mA.cm-2), increasing rutile formation was observed.