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Materials (Basel). 2018 Jul 14;11(7). pii: E1214. doi: 10.3390/ma11071214.

Investigation of Electrochemical, Optical and Thermal Effects during Flash Sintering of 8YSZ.

Author information

1
Department of Industrial Engineering, University of Trento, Trento 38123, Italy. mattia.biesuz@unitn.it.
2
Department of Industrial Engineering, University of Trento, Trento 38123, Italy. lorenzo.pinter@alumni.unitn.it.
3
School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, UK. saunders.theo@gmail.com.
4
School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, UK. m.j.reece@qmul.ac.uk.
5
School of Metallurgy and Materials, University of Birmingham, Birmingham B15 2TT, UK. J.Binner@bham.ac.uk.
6
Department of Industrial Engineering, University of Trento, Trento 38123, Italy. vincenzo.sglavo@unitn.it.
7
School of Engineering and Material Science, Queen Mary University of London, London E1 4NS, UK. s.grasso@swjtu.edu.cn.
8
Key Laboratory of Advanced Technologies of Materials, Ministry of Education, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China. s.grasso@swjtu.edu.cn.

Abstract

This paper reports the electrochemical, optical and thermal effects occurring during flash sintering of 8 mol % yttria-stabilized zirconia (8YSZ). In-situ observations of polycrystalline and single crystal specimens revealed electrochemical blackening/darkening during an incubation period prior to flash sintering. The phenomenon is induced by cathodic partial reduction under DC fields. When using a low frequency AC field (0.1⁻10 Hz) the blackening is reversible, following the imposed polarity switching. Thermal imaging combined with sample colour changes and electrical conductivity mapping give a complete picture of the multi-physical phenomena occurring during each stage of the flash sintering event. The partial reduction at the cathode causes a modification of the electrical properties in the sample and the blackened regions, which are close to the cathode, are more conductive than the remainder of the sample. The asymmetrical nature of the electrochemical reactions follows the field polarity and causes an asymmetry in the temperature between the anode and cathode, with the positive electrode tending to overheat. It is also observed that the phenomena are influenced by the quality of the electrical contacts and by the atmosphere used.

KEYWORDS:

electrochemical blackening; electrochemistry; electronic conductivity; flash sintering; yttria stabilized zirconia

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