Non-isothermal and isothermal kinetics of high temperature oxidation of micrometer-sized titanium particles in air

The oxidation behaviour of micrometer-sized titanium particles was investigated in the temperature range from 323 to 1473 K in air using high-temperature X-ray diffraction and thermogravimetric (TG) analysis with multiple heating rates (2, 5, and 10 K/min). The investigated titanium particles were directly transformed to rutile without the formation of other polymorphic crystalline phases. Moreover, only traces of titanium nitride were observed below 700 K. Assuming mono-modal particles, a Jander model for three-dimensional diffusion was applied to derive the kinetic parameters of the oxidation of titanium particles (5 and 20 μm) from fitting the TG measurements using a least squares fit procedure. The model described reasonably well the oxidation process when all the TG experiments (multiple heating rates and two different particle sizes) were simultaneously used for the fitting. For titanium particles the oxidation occurs by a three-dimensional diffusion through a dense rutile layer and differs from the one-dimensional diffusion in a stratified structure of bulky materials. The derived diffusion coefficients ranged from 10−14 to 10−7 cm2/s in the temperature interval 700–1400 K.