Zirconia spacer electrodes improve microstructural uniformity of flash sintered zirconia ceramics

Abstract

The sample-electrode contact often represents the most problematic part of the flash sintering circuit. We demonstrate that adding 3 mol% yttria-stabilized zirconia (3YSZ) spacer electrodes between a 3YSZ powder compact and steel electrodes positively impacts the final density and microstructure in AC flash sintering. The 3YSZ spacer electrodes, with intrinsically low thermal conductivity, were also heated by Joule heating alongside the 3YSZ sample, reducing the temperature gradient at the specimen-electrode interface and limiting heat loss from the specimen. A reference 3YSZ sample, which was sintered with stainless steel electrodes only, reached 98.2% of relative density with a notable grain size difference between the central (∼290 nm) and near-electrode parts (∼160 nm). The addition of 3YSZ spacer electrodes improved the final density to 98.9 % and reduced the grain size difference between the central (∼300 nm) and near-electrode parts (∼220 nm) almost by half compared to the reference sample.