Pressureless Sintering Kinetics of NiFe₂O₄ Ceramic Fabricated by Slip Casting

In this work, a systematic research is carried out to investigate the sintering kinetics of NiFe₂O₄ ceramic obtained by slip casting and pressureless sintering. The sintering shrinkage behaviors showed the linear shrinkage and linear shrinkage rate of the green body in the axial and radial directions, both increased with increasing sintering temperature, though the maximum linear shrinkage rate in the radial direction was acquired at a lower temperature (1280.7°C) than that in the axial direction (1305.4°C) for a denser compact. The temperature related to the maximum densification rate was about 1316.5°C while the relative density was around 72%. The characteristic sintering kinetics window exhibited that the sintering process could be typically divided into three stages. The sintering activation energy of the initial stage was 268.34 kJ mol⁻¹, and the initial stage of the sintering process was controlled by both grain boundary diffusion and volume diffusion mechanisms. The grain growth kinetic analysis illustrated the grain growth exponent (n) reduced from 2.959 to 2.169 when the sintering temperature increased from 1300 to 1375°C, while the activation energy for grain growth decreased with both the increasing of sintering temperature and the shortening of holding time. It implied that the atomic diffusion process controlled the grain growth. In addition, it was observed that increases in the bending strength and elastic modulus reached its maximum value of 70.36 ± 1.03 MPa and 3.44 ± 0.53 GPa, respectively, mainly associated with the relatively dense microstructure.