The surface characterization of the early stages of the oxidation of titanium

Abstract

In order to study the early stages of oxidation of pure titanium surface nanoscale characterisation has been carried out using different surface sensitive techniques. Metal surfaces have been prepared so as to study the effects of different surface finishes such as buffing (BP), chemical (CP), electrical (EP) and mechano-chemical (MCP) treatments. Characterisation of the oxide layers has been carried out using scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). These measurements have shown that the BP and MCP surfaces have thick modified layers whereas only very thin oxide layers are formed on the CP and EP surfaces. The influence of hydrogen on the titanium oxidation during the surface treatments has been estimated by obtaining the depth profiles of hydrogen, as measured using elastic recoil detection analysis (ERDA). High concentrations of hydrogen have been found in the surface regions especially for MCP and BP treatments. An α-titanium single crystal has been used to investigate the initial stages of the oxidation processes using grazing incidence reflection high energy electron diffraction and Auger electron spectroscopy (RHEED-AES). This method has demonstrated the time dependence of the titanium oxidation during the early stages with the RHEED intensities from the α-titanium single crystal surface, TiO being observed in the oxide layer. We discuss the characteristics of the oxidised surface on a sub-micro scale in relation to parameters such as the thickness of the oxide layer, crystalline state, chemical state, compactness of the oxide layer and hydrides of titanium.