Oxidation behavior of high-purity nonstoichiometric Ti2AlC powders in flowing air

The oxidation behavior of nonstoichiometric Ti2AlCx (x = 0.69) powders synthesized by combustion synthesis was investigated in flowing air by means of simultaneous thermal gravimetric analysis-differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope/energy dispersive spectroscopy, with an effect of powder size. The oxidation of the fine Ti2AlC powders with the size of about 1 mu m starts at 300 degrees C and completes at 980 degrees C, while with increasing the powder size around 10 mu m the corresponding temperature increases to 400 and 1040 degrees C, respectively. The oxidation of nonstoichiometric Ti2AlCx (x = 0.69) powders is controlled by surface reaction in 400-600 degrees C, and mainly diffusion in 600-900 degrees C, with the corresponding oxidation activation energy of 2.35 eV and 0.12 eV, respectively. In other words, the critical temperature of changing oxidation controlling step is around 600 degrees C. The oxidation products were mainly rutile-TiO2 and alpha-Al2O3. The tiny white flocculent particles of alpha-Al2O3 appeared on the surface of fine Ti2AlC powders and increased with increasing the oxidation temperature.