PHASE-EQUILIBRIUM RELATIONSHIPS IN THE SYSTEM AL2O3-TIO2-MNO, RELEVANT TO THE LOW-TEMPERATURE SINTERING OF ALUMINA

A great deal of research work has been devoted to lowering the sinteri ng temperature of ceramic powders of varied nature, to fulfil a variet y of purposes. Both experimentation and theory show that the sintering temperature of alumina can be lowered to 1400 degrees C and below by using small particle sizes and certain additives like TiO2 and/or MnO. The general idea is that sintering is aided by the development of a l iquid phase at this low temperature, due to the presence of the additi ves. However, there is no phase diagram available to throw light on th is matter. I;br this reason, the present work was aimed at investigati ng the phase equilibrium relationships in the ternary, non-condensed s ystem Al2O3-TiO2-MnO, in air. Selected compositions in this system wer e prepared from reagent-grade oxides, uniaxially pressed into 6 mm cyl indrical pellets, fired at temperatures between 1000 and 1650 degrees C for 2 to 22 h, water-quenched, and observed by X-ray diffraction and scanning electron microscopy, the composition of some of the phases i dentified being evaluated by energy-dispersive spectroscopy. These exp eriments led to the definition of the compatibility triangles and a te ntative location of the boundary curves between primary phase fields i s presented. (C) 1996 Elsevier Science Limited.