Ultrafast firing effects in Y-doped zirconia nanoparticles: Heating rate matters even under “Conventional” conditions

The development of firing technologies like flash sintering and ultrafast high-temperature sintering has renewed interest in how heating rates influence microstructural evolution during sintering. Herein, we observe an exceptional heating-rate effect during conventional consolidation of 3YSZ nanopowder (20 nm). Increasing the heating rate from 2.5 to 50°C min−1 accelerates sintering by a factor of ∼1000, reversing the positions of the sintering curves in dilatometric analysis: the material sinters at a lower temperature when heated faster. We attribute this behavior to “microstructural separation” in which high-density regions of the green body draw mass from lower-density ones via surface-mediated transport, causing the formation of pores significantly larger than the grain size. This observation highlights the importance of the green shaping procedure: sintering of more homogeneous green bodies is less sensitive to the heating rate because the driving force for surface transport between differently packed regions is reduced.