Reaction kinetics in a coarse equimolar powder mixture were slow enough to allow for the different stages to be identified, notably in the lower and higher temperature ranges, respectively. In the former (T≤ 1600 K), Al2TiO5nucleation was hindered by the strain energy contribution to the overall driving force. The setting up of metastable layer sequences Al2TiO5/TiO2/Al2O3was found to occur generally during subsequent growth. The high Al mobility in the TiO2provided a rapid aluminum transport from the metastable Al2O3/TiO2interface to the TiO2/Al2TiO5front. At temperatures above ∼1700 K the Al2O3/TiO2interface was very rapidly sealed off by Al2TiO5formation. Reactant transport across the Al2TiO5was slow because of the low mobilities in the product phase. Therefore, much lower product growth velocities were observed at higher temperatures than at lower temperatu