Flash Sintering of Nanograin Zirconia in <5 s at 850°C

We show that yttrium-stabilized zirconia can be sintered in a few seconds at similar to 850 degrees C to full density, starting from a green density of 0.5, by the application of a dc electrical field (nominally, several hours at 1450 degrees C are needed to complete the sintering process). This finding is explained by the local Joule heating at grain boundaries, which, on the one hand, promotes grain-boundary diffusion (a kinetic effect), while at the same time restricts grain growth (a thermodynamic effect). The smaller grain size and the higher temperature at grain boundaries can then act synergistically to enhance the rate of sintering. These results have a bearing in explaining the widespread spark plasma and microwave-assisted techniques for enhanced sintering.