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Ultra-high voltage SnO2 based varistors prepared at low temperature by two-step sintering

Maleki Shahraki, M ; Sharif University of Technology | 2019

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  1. Type of Document: Article
  2. DOI: 10.1016/j.jallcom.2019.07.138
  3. Publisher: Elsevier Ltd , 2019
  4. Abstract:
  5. In this research, full density, single phase microstructure (in the XRD and SEM detection limits), and fine-grained SnO2 varistors with an average grain size of 0.65 μm was acquired at low temperature by the two-step sintering technique. The sintering temperature was successfully decreased from 1300 °C in the normal sintering to 1150 °C and 1100 °C of respectively the first and the second stage in the two-step sintering. The mechanism of grain growth suppression of the two-step sintered samples was discussed and it was suggested that in addition to triple point junction, solute drag and/or nano-secondary phases contribute to cease the grain growth. These SnO2 varistors exhibited ultra-high breakdown electric field of 26 kV/cm with a nonlinear coefficient of about 120 in the 1–10 mA/cm2 standard. The exact evaluation showed that this high value of the nonlinear coefficient is artificial and was the result of joule-self heating phenomenon. The true value of the nonlinear coefficient (28) is measured within the 0.1–1 mA/cm2 standard. Due to the joule self-heating phenomenon, the thermal runaway was observed for ultra-high voltage SnO2 varistors in DC-accelerated aging test conditions (0.85 E1mA/cm2 and room temperature). By changing DC-accelerated aging electric field to 0.85 E0.1 mA/cm2, TSS3-20h presented excellent stability after 10 h from room temperature to 75 ᵒC. © 2019 Elsevier B.V
  6. Keywords:
  7. Low temperature sintering ; SnO2 ; Ultra-high voltage ; Varistor ; Electric fields ; Grain growth ; HVDC power transmission ; Temperature ; Testing ; Varistors ; Accelerated aging test ; Low-temperature sintering ; Single phase microstructure ; Sintering temperatures ; Triple point junctions ; Two-step sintering ; Ultra high voltage ; Sintering
  8. Source: Journal of Alloys and Compounds ; Volume 805 , 2019 , Pages 794-801 ; 09258388 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/abs/pii/S0925838819326416