Formation of Al₂O₃ during heating of an Al/TiO₂ nanocomposite powder

The solid-state reactions between Al and TiO₂ that occur during heating an Al/TiO₂ nanocomposite powder produced using high-energy mechanical milling have been studied using thermal analysis, x-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in combination with compositional microanalysis. It has been found that Al and TiO₂ react in the temperature range from 650 to 800 °C, forming Al₃Ti, but XRD analysis, SEM examination, and detailed TEM characterization of the powder particles heated to 800 °C show that the expected Al₂O₃ does not form. However, α–Al₂O₃ particles form during heating from 800 to 1000 °C. The possible reasons for the time gap between formation of Al₃Ti and Al₂O₃ are discussed.