Direct and Indirect Microwave Heating of SnO 2 -ZnO ceramics
Résumé
Microwave (MW-) sintering is a rapid sintering technique, where the material interacts directly with the electromagnetic radiation. This leads to volumetric heating, which enables high heating rates and a uniform temperature distribution in the sample. Materials based on SnO2, ZnO and Zn2SnO4 are due to its unique properties used in various applications such as gas sensors, varistors, electrodes, photoelectric devices, and others. Therefore, the investigation of their processing is important. In this contribution we present results on MW-sintered SnO2-ZnO based ceramics prepared either by direct or indirect MW-heating (i.e. without or with SiC as a susceptor). The samples were prepared by uniaxial pressing from pure SnO2 and ZnO powders and their mixtures. The as-pressed samples were sintered at 1200 °C (ZnO at 1000 °C) with heating rate of 50 °C/min and a dwell time of 5 min. It was possible to heat all the samples directly by MW-heating. In the case of pure SnO2 the heating initiation was faster compared to pure ZnO but on the other hand it was difficult to keep the set heating rate (compared to ZnO). In the case of the composite the behavior was a combination of these two binary oxides. Different behavior was observed on the power vs temperature curves for direct and indirect MW-heating. It is shown that the presence of SiC enhances the densification and grain growth
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