Preparation of Dense Negative-Thermal-Expansion Oxide by Rapid Quenching of ZrW₂O₈ Melt

Abstract

By rapid quenching of ZrW₂O₈ melt from 1300°C, dense specimens with few inner pores were successfully prepared. Dilatometry experiments were performed and an abrupt thermal expansion was observed in the range 120-160°C, probably due to removal of internal stress upon the first heating measurement from room temperature to 300°C. The specimen annealed at 200°C for removal of internal stress exhibited a negative average thermal expansion coefficient of -(4-5)×10^-6K^-1 from room temperature to 250°C, which was smaller than that of sintered ceramic ZrW₂O₈, (-(6-10)×10^-6K^-1). X-ray diffraction and secondary electron microscopy measurements revealed that the obtained specimen was a hybrid of ZrO₂ and/or WO₃ grains with -1μm diameter and ZrW₂O₈ grains with 10-25μm diameter. The smaller negative thermal expansion could be attributed to this hybridization due to decomposition of ZrW₂O₈ during the quenching process.