Processing effects on the microstructure observed during densification of the NTE-compound ZrW2O8

The crystal structure of zirconium tungstate exhibits large isotropic negative thermal expansion. As a result, zirconium tungstate might find use in applications which require tailored thermal expansion properties. In this work, the sintering ability of commercially available ZrW₂O₈ and the reactive sintering of an oxide mixture was studied. The microstructure obtained when sintering oxide mixtures on porous alumina based refractory fibre-boards is characterised by large pores and clear grain boundaries, arising from a liquid phase sintering mechanism due to chemical interaction of the oxide mixture with the fibre-board. Although this interaction is avoided when using commercially available zirconium tungstate its sintering ability is very poor. When reactive sintering of oxide mixtures was performed in sealed quartz tubes in air, dense zirconium tungstate was obtained. The reactivity of the oxide mixtures using quartz tubes as support, is dependent on the homogeneity and particle size of the precursor oxide mixture.