Densification, microstructure and elastic properties of microwave-sintered SnO2, ZnO and Zn2SnO4
Résumé
Tin oxide (SnO2) and zinc oxide (ZnO) are functional ceramics used for applications as varistors, electrodes, gas sensors or catalysts. SnO2 has a very poor sinterability because the main sintering mechanism is nondensifying: surface diffusion at temperatures below 1000°C and evaporation-condensation at temperatures above 1300°C. This specific sintering behaviour can be used to study the effect of the microstructural evolution on some properties, such as elastic properties [1,2]. On the other hand, ZnO can be densified easily. ZnO and SnO2 can be mixed to create a composite containing the Zn2SnO4 spinel phase. The aim of this study was to investigate the properties of SnO2, ZnO and their composites sintered by conventional (CV) and microwave (MW) sintering. For this purpose, different samples were prepared from commercial powders: pure SnO2, pure ZnO and SnO2/ZnO mixtures with different weight ratios (8:2, 2:8 and 1:1). Pellets were pressed and sintered with various thermal cycles. MW sintering was performed in a multimode cavity, with and without a silicon carbide susceptor [3]. Then the sintered samples were characterized: linear shrinkage, bulk density, phase composition, microstructures and elastic properties. The samples were also heated in a single-mode cavity to understand better its behaviour under MW. All the samples were densified by MW with and without SiC, which proves that all the compositions had a high MW coupling ability. MW powers vs temperature curves show variations of powers, which can be related to the evolution of material’s dielectric and electric properties. In the case of pure SnO2, the porosity and bulk density remained constant and no shrinkage occurred even at 1400 °C, but the elastic properties significantly changed for the samples sintered at high temperatures. This can be related to the non-densifying sintering mechanisms of this material. The final properties were similar for CV and MW-sintered samples for pure SnO2 and ZnO. But in the case of composites, significant differences were observed between CV and MW sintering. The spinel phase was detected above 900°C for both CV and MW sintering. However, the porosity and bulk density were different for both types of sintering. Référence [
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