| Autor: |
Egorov, S. V., Eremeev, A. G., Kholoptsev, V. V., Plotnikov, I. V., Kirill Rybakov, Sorokin, A. A., Bykov, Yu V. |
| Rok vydání: |
2021 |
| Předmět: |
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| Zdroj: |
Scopus-Elsevier |
| DOI: |
10.5281/zenodo.5562314 |
| Popis: |
This paper describes a study of rapid microwave sintering of zinc-oxide based varistor ceramics undertaken with the goal to elucidate the mechanisms that underlie fast densification of these materials and compare them with those acting in other oxide ceramic materials in which ultra-rapid microwave sintering has been demonstrated previously. The samples used in the experiments were compacted from a commercial powder mixture with a nominal composition ZnO + 1.5 mol. % Bi2O3 + 1 mol. % Sb2O3. The microwave sintering was carried out on gyrotron systems for high-temperature processing of materials, operating at a frequency of 24 GHz with a maximum output power of 5 kW [1]. The samples were heated at a constant heating rate, selected in the range of 10 – 130 °C/min, up to a temperature of 1100 – 1300 °C with no isothermal hold. The temperature of the center and periphery of the samples, the automatically regulated microwave power and the shrinkage determined using an optical dilatometry systems were recorded throughout all experiments. To isolate the influence of the temperature non-uniformity arising during volumetric microwave heating, some heating runs were carried out with the sample enclosed in a SiC susceptor ring. In addition, dc electric conductivity of the samples was assessed in situ during microwave heating. In all processes carried out without the SiC susceptor ring a pronounced decrease in microwave power occurred at a temperature of about 600 °C. Simultaneously, an abrupt increase in the densification rate was observed. These are manifestations of the thermal instability associated with the liquid phase formation, which has been previously demonstrated to be a possible reason for ultra-rapid densification during microwave sintering of different ceramic materials [2–4]. In the presence of the SiC susceptor the thermal instability was not observed, and the maximum of the densification rate shifted towards higher temperatures. The temperature difference between the center and the periphery of the samples heated without the susceptor reached 200 °C due to a significant amount of microwave power absorbed in them volumetrically. However, the final sintered density of these samples, 95 – 96 % of the theoretical value, was not lower than the density of the samples heated uniformly using the susceptor to the same center temperature. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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