Pressureless Sintering Kinetics of NiFe 2 O 4 Ceramic Fabricated by Slip Casting
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JMEPEG (2020) 29:7899–7907 https://doi.org/10.1007/s11665-020-05313-8
Pressureless Sintering Kinetics of NiFe2O4 Ceramic Fabricated by Slip Casting Zhigang Zhang, Zhuokun Cao, Guoyin Zu, and Jianrong Xu Submitted: 30 June 2020 / Revised: 21 October 2020 / Accepted: 1 November 2020 / Published online: 16 November 2020 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 mol21, 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. Keywords
activation energy, densification, kinetics, nickel ferrite
grain
growth,
1. Introduction NiFe2O4 is a typical mixed valence metal oxide with an inverse spinel structure, where the tetrahedral sites are occupied by Fe3+ cations, and the octahedral sites are equivalently occupied by Fe3+ and Ni2+ cations (Ref 1-3). Due to the superior and unique structure of this material, NiFe2O4 has been widely applied in magnetic materials (Ref 4, 5), catalyst (Ref 6, 7), high sensitive gas sensors (Ref 8, 9), microwave devices (Ref 10), supercapacitors (Ref 11, 12) and high temperature electrode material (Ref 13, 14). Production of nickel ferrite bulk ceramics with high performances gained increasing interests on account of the prospective applications. It has been well-known that the microstructure (mainly density and grain size) is an essential ingredient of ceramic materials, therefore the microstructure plays a precedence role in the properties of NiFe2O4 ceramics (Ref 15). In the process of preparing ceramics by powder metallurgy, sintering is the crucial stage that determines the final microstructure of the dense NiFe2O4 ceramics bec
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