The effect of beta-spodumene additions on the in situ phase formation and abundances in an Al2O3-Al2TiO5 system in the temperature range 1000-1400 degrees C has been studied by neutron diffraction and differential thermal analysis. Results show that beta-spodumene began to decompose by phase separation and partial melting at 1290 degrees C, followed by complete melting at 1330 degrees C. Formation of Al2TiO5 was observed to occur at 1310 degrees C and its abundance increased with temperature. The addition of beta-spodumene as a sintering aid did not cause its reaction with alumina or rutile to form additional phases. Addition of beta-spodumene in excess of 5 wt% resulted in pronounced vitrification, which partly recrystallised when cooled to room temperature. The temperatures of Al2TiO5 formation and melting of beta-spodumene are consistent with the results of differential thermal analysis. Crown Copyright (C) 2005 Published by Elsevier Ltd. All rights reserved.