Oxidation kinetics of commercially pure titanium

The aim of this work was to perform thermal characterization of commercially pure titanium in dry air to determine its oxidation kinetics and the structure of the oxide. The oxidation kinetics were determined thermogravimetrically under isothermal conditions in the temperature range 300 to 750 oC for 48 hours and the structure of the oxides was determined by differential thermal analyses and X-ray diffraction in the temperature range room temperature - 1000 oC. The oxidation rate of titanium increased with increase in temperature. It was high in the initial stages of oxidation and then decreased rapidly with time, especially up to 600 oC. The kinetic laws varied between inverse logarithmic at the lower temperatures (300 and 400 oC) and parabolic at the higher temperatures (650, 700 and 750 oC). Evidences from X-ray diffraction and differential thermal analyses data revealed that the passive oxide film formed at room temperature crystallized into anatase at about 276 oC. The crystallized oxide formed in the range 276 - 457 oC consisted of anatase, in the range 457 - 718 oC consisted of anatase and rutile sublayers, and at temperatures beyond 718 oC consisted of a layer of pure rutile. Scanning electron microscopy observations reveled that the oxidized surfaces were crack-free and the surface roughness increased steadily with oxidation temperature.