CHARACTERIZATION OF GREEN MATERIALS Densification Kinetics of CeO 2 Reinforced 8 Mol.% Y 2 O 3 Stabilized ZrO 2 Ceramics ALKA GUPTA, 1 AMBREEN NISAR, 1 SHOBIT OMAR, 1 and KANTESH BALANI 1,2 1.—High Temperature Fuel Cell Laboratory, Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, U.P. 208016, India. 2.—e-mail: kbalani@iitk.ac.in The grain growth kinetics of 8YSZ ceramics processed using spark plasma sintering (SPS) has been investigated in the temperature ranging from 1100°C to 1500°C. The activation energy during SPS densification was obtained as 332 kJ/mol with grain boundary diffusion as a dominant mechanism. Further, the effect of CeO 2 on the densification kinetics of 8YSZ ceramic processed via SPS and conventional sintering (CS) has been delineated. The lower grain boundary mobility of CS-processed composites (an order of magnitude lower than SPS) is attributed to the solute drag and lattice distortion mechanism. However, no significant change in the grain boundary mobility was observed with CeO 2 addition ( 14.7–43.9 9 10 18 m 3 /N/s for CS and 107.2– 116.7 9 10 18 m 3 /N/s for SPS) revealing that the defect concentration is nearly constant in 8YSZ. The study highlights the effect of sintering tech- niques (SPS and CS) and reinforcement (CeO 2 ) on engineering the desired microstructure of 8YSZ ceramic. INTRODUCTION Over the past decade, ceramic matrix composites have gained interest because of their excellent thermo-mechanical properties for high-temperature applications such as a thermal protection system (TPS), solid oxide fuel cells (SOFCs) and armor applications. 1–3 The 8 mol.% yttria-stabilized zirco- nia (8YSZ) is a conventionally used electrolyte mate- rial for SOFCs operating at high temperatures ( 800–1000°C). Adequate ionic conductivity ( 0.1 S/cm), a high ionic transference number (close to unity) and excellent mechanical properties (hard- ness  12 GPa, fracture toughness  3–7 MPam 1/2 and flexural strength  300 MPa) qualify 8YSZ as a good candidate for such extreme conditions. 4–8 For attaining enhanced ionic conductivity, the electrolyte must possess a nearly complete densification ( 99%) and a homogeneous microstructure, as the porosity in the material impedes the effective conductance path- ways between the grains, thus, decreasing its ionic conductivity. 9,10 Other than densification, the influence of grain boundaries and the grain size on the ionic conductivity of electro-ceramics has also been recognized. 11–13 8YSZ ceramic is a potential material for thermal barrier coating (TBC), where sufficient mechanical strength is required to prevent failure during cyclic oxidation. 11,12 Nevertheless, the fabrication of dense 8YSZ ceramic with fine grain size ( < 1 lm) while maintaining the cubic structure is a concern. The densification behavior is greatly influenced by the sintering method, sintering parameters and rein- forcements such as yttria (Y 2 O 3 ), ceria (CeO 2 ), tantalum (Ta), lanthanum (La) and carbon nan- otubes (CNT), etc. 2,14–16 Recently, spark plasma sintering (SPS) has emerged as a novel pressure- assisted technique for a rapid densification of ceramic powder compacts at low sintering temper- atures (by  100–500°C) and short dwell times ( 5–10 min) compared with other conventional sintering (CS) techniques (1500–1600°C, 10–15 h) for zirconia-based ceramics. 17–20 The SPS method has been widely used for the sintering of diverse new and traditional bulk ceramics with grains in the nanometric regime including zirconia. 7,21–25 During SPS processing, a very fast heat and mass transfer lead to suppressed grain growth and high Alka Gupta and Ambreen Nisar Have contributed equally as first authors. JOM https://doi.org/10.1007/s11837-018-3001-2 Ó 2018 The Minerals, Metals & Materials Society