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 sintering temperature of ceramic powders of varied nature, to fulfil a variety 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 liquid phase at this low temperature, due to the presence of the additives. However, there is no phase diagram available to throw light on this matter. I;br this reason, the present work was aimed at investigating the phase equilibrium relationships in the ternary, non-condensed system Al2O3-TiO2-MnO, in air. Selected compositions in this system were prepared from reagent-grade oxides, uniaxially pressed into 6 mm cylindrical 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 identified being evaluated by energy-dispersive spectroscopy. These experiments led to the definition of the compatibility triangles and a tentative location of the boundary curves between primary phase fields is presented. (C) 1996 Elsevier Science Limited.