Effect of compact density on phase transition kinetics from anatase phase to rutile phase during sintering of ultrafine titania powder compacts

The effect of compact density on the phase transition from anatase phase to rutile phase during sintering of ultrafine TiO2 powder compacts has been investigated. The compact densities are varied using different compaction pressures. The shrinkage behaviors of compacts are monitored in;situ at the condition of uniform heating rate by dilatometric measurement and subsequently related to the phase transition kinetics in the respective compact densities. A phase transition behavior of the compacts (59.3% of theoretical density (TD)) made with 65 MPa pressure is compared either with that of the compacts (86.9% TD) made with 4.5 GPa pressure or with that of loose powder pack without compaction. The phase transition kinetics is proved to be affected strongly by the density of green compacts. The compact with high green density exhibits lower transition temperature than those with loll, green density. The occurrence of anatase-->rutile phase transition at the lower temperature in the high density compacts is attributed to the relatively large coordination number compared with the low density compacts. (C) 1998 Acta Metallurgica Inc.