Cold‐Sintering Pretreatment for Energy‐Efficient Densification of 3YSZ via Macropore‐to‐Mesopore Transformation

ABSTRACT

Yttria‐stabilized zirconia ceramic (3YSZ) was densified to only 60% relative density (RD) by cold‐sintering process (500 MPa pressure, 180°C temperature) but yielded majority of the pores in nano‐scale range. In contrast, 3YSZ conventionally sintered at low temperature of 1200°C yields a high RD of ∼97% with large macro pores ∼2 µm size. To explore further, cold sintering was done as a pretreatment followed by conventional low‐temperature sintering at 1200°C. This method yielded exceptional properties with a majority of tetragonal phases and a complete densification with a remarkably minimal pore size of ∼0.01 µm having Vickers hardness of 12.6 ± 0.3 GPa and flexural strength of 450 ± 40 MPa. The ceramic specimens obtained by combined cold and conventional sintering (CS) were thoroughly characterized using mercury porosimetry, x‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman, confocal Raman, impedance spectroscopy, and AFM. The evolution of pore size during the combined cold and CS stages closely mirrors the behavior seen in the well‐known two‐step sintering process. The combined cold and CS process provides an energy‐efficient two‐step sintering route for densification of micron‐sized 3YSZ ceramics, which are important in ceramic industry from a sustainability point of view.