Grain Growth of ZnO in ZnO‐Bi2O3 Ceramics with TiO2 Additions

Abstract

Grain growth of ZnO in liquid‐phase‐sintered ZnO‐Bi2O3ceramics containing systematic additions of TiO2 to the 0.55 wt% level has been studied for flring in air from 900° to 1400°C. The Bi2O3 melts during flring, and then the TiO2dissolves into the Bi2O3‐rich liquid. The TiO2 initially reacts with the Bi2O3 to form the compound Bi4Ti3Oi2. Above ∼1050°C, the Bi4Ti3O12 reacts with ZnO to form the Zn2TiO4 spinel phase. This results in two distinct regions of ZnO grain growth in this System; one below 1050°C, where the Bi4Ti3O12 affects the process, and the other above 1050°C, where the Zn2TiO4 spinel dominates. The exponent for ZnO grain growth decreases from 5 for TiO2‐free ZnO‐Bi2O3 to 3 for ZnO‐Bi2O3‐TiO2 at temperatures below 1050°C, but increases to 6 at temperatures above 1050°C. The exponents are related to the presence of Bi4Ti3O12 in the Bi2O3‐rich liquid phase below 1050°C and the Zn2TiO4particles that are present above 1050°C. The activation energy for grain growth of the ZnO is ∼300 kJ/mol below 1050°C, but 360 kj/mol above 1050°C. It is suggested that diffusion of ZnO through the Bi2O3‐rich liquid phase is the rate‐controlling mechanisrn for ZnO grain growth below 1050°C and that grain‐boundary drag by the pores and Zn2TiO4 spinel particles is the rate‐controlling mechanism above 1050°C.