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

TLDR

This paper reports the electrochemical, optical and thermal effects occurring during flash sintering of 8 mol % yttria‑stabilized zirconia (8YSZ). The study attributes the observed effects to cathodic partial reduction under DC fields and employs thermal imaging, colour changes, and conductivity mapping to capture the multi‑physical phenomena throughout flash sintering. In‑situ observations show that cathodic partial reduction causes reversible blackening under low‑frequency AC, increases conductivity near the cathode, creates temperature asymmetry with the anode overheating, and that these effects depend on contact quality and atmosphere.

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.