Influence of particle contact on flash sintering of ZnO and 8YSZ: Microstructure and electrical conductivity

Abstract

The flash phenomenon in flash sintering of ceramic materials is closely related to electrical conductivity of the material. However, our understanding of how particle-to-particle contact of ceramic powders affects this phenomenon and, consequently, the microstructure and electrical properties of flash-sintered materials remains limited. To address this, we utilized “pseudo-in-situ” impedance spectroscopy to investigate the effect of particle-to-particle contact in nanometric powders of ZnO and 8YSZ, both before and after flash sintering. The powders were prepared using two different procedures, either grinding with a binder or employing multiple milling and calcining steps. After compacting into pellets, the samples were characterized before and after flash sintering, either with current-to-voltage control or with the application of current density ramps until the flash event occurred. Pseudo-in-situ impedance was employed to demonstrate that preparing powders using multiple milling and calcining steps improved charge-carrier mobility paths, facilitated homogeneous passage of electric current, reduced thermal gradients, and consequently resulted in better microstructural homogeneity and electrical conductivity. In addition, the use of the electric-current ramp control retained microstructural homogeneity to a greater degree.