Synthesis and Pressureless Sintering of Zirconium Phosphate Ceramics

Abstract

Zirconium phosphate (ZrP2O7) powder is synthesized by direct reaction between ZrO2 and H3PO4 and is used to prepare ZrP2O7 ceramics with MgO and Al2O3 as the sintering additives by pressureless sintering technique. The mechanism of reaction between ZrO2 and H3PO4 is analyzed. The results suggest that the reaction between ZrO2 and H3PO4 is completed at 250°C and ZrP2O7 is stable up to ∼1200°C. At temperatures above ∼1200°C, decomposition starts to occur, resulting in the formation of Zr2O(PO4)2. After exposure to temperatures as high as 1500°C, decomposition is still not complete. The pure ZrP2O7 ceramic, however, is difficult to sinter to high density. In contrast, ZrP2O7 ceramics with MgO and Al2O3 sintering additives can be liquid‐phase sintered to relative densities of 90%–96% at sintering temperatures of 1250°–1500°C, without significant decomposition. The microstructure is observed by scanning electron microscopy. The effect of density, phosphate glass phase, and grain growth on bending strength is analyzed. Because of the abnormal grain growth and microcracking of ZrP2O7 ceramics, the bending strength first increases and then decreases as a function of the sintering temperature.