Oxidation of nanometer-sized titanium nitride and micrometer-sized titanium particles with titanium nitride traces up to 1473K in air

This study compares the oxidation behaviour of TiN particles (nanometer-sized to micrometer-sized) to titanium particles with traces of titanium nitride (micrometer-sized) regarding the similarities of the formation of the products. These particles were investigated between 323 K and 1473 K in air using high-temperature X-ray diffraction, SEM, and the methods of thermal analysis (TG and DSC). The oxidation of the nanometer-sized TiN particles forms anatase and rutile in two partially overlapping successive steps, whereas the anatase transforms completely to rutile at higher temperatures. The investigated titanium particles directly transform to rutile. Traces of TiN in titanium particles induce the formation of traces of anatase phase which similar to the oxidation of TiN particles transforms to rutile phase. A Jander model for three-dimensional diffusion was utilized for describing the oxidation kinetics of the both oxidation steps occurring with TiN. A least squares fit procedure gives good agreement of the calculated curves to measured TG and DSC curves and adequate approximation to intensities of X-ray measurements. The amount of TiN oxidized to anatase was found to be about 46%. The kinetic parameters were determined: for the first step of TiN oxidation, the pre-exponential factor was 1.33 . 106 mu m(2)/s and the activation energy was 180.5 kJ/mol as well as for the second step 5.51 . 103 mu m(2)/s and 197.6 kJ/mol, respectively