Sintering Behavior and Fracture Morphology of NiFe 2 O 4 /Nano-TiN Ceramics Synthesized under Argon Atmosphere
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JMEPEG (2020) 29:7971–7980 https://doi.org/10.1007/s11665-020-05009-z
Sintering Behavior and Fracture Morphology of NiFe2O4/ Nano-TiN Ceramics Synthesized under Argon Atmosphere Bin Wang, Jinjing Du, Shoukun Gao, Meng Zhou, Erhu Li, and Linbo Li Submitted: 6 August 2019 / Revised: 19 June 2020 / Published online: 16 November 2020 NiFe2O4/nano-TiN ceramics were synthesized by a two-step cold-pressing sintering process. Sintering behavior, fracture morphology, mechanical performance and high-temperature conductivity were investigated. The results indicated that besides NiO and NiFe2O4, new Ni3TiO5 and metallic phases (iron and nickel) formed in the sintered samples. TiN accelerated the grain growth along with considerable quantity of micro-pores in the sintered samples. Compared to the un-doped samples, the temperature for the onset of sintering of the NiO-Fe2O3-2.0 wt.% TiN system decreased from 1093 to 985 °C. TiN addition changed the sintering mechanism of the NiO-Fe2O3 from grain boundary diffusion to volume diffusion. TiN additions reduce the apparent sintering activation energy and porosities and improve the density, bending strength, and pyroconductivity. Three-dimensional fracture morphology of the composite ceramics synthesized under argon atmosphere, exhibits self-similarity characteristics and the fractal dimension for NiFe2O4-1.0 wt.% TiN ceramics is 2.0813. Keywords
conductivity, fracture morphology, mechanical performance, nano-TiN, NiFe2O4 ferrite, phase transformation, sintering mechanism
1. Introduction For modern aluminum electrolysis industry, the current efficiency of aluminum electrolysis is 96%, but consumable carbon anodes are used with generating hydrogen fluoride, carbon dioxide, carbon monoxide and fluorocarbons (Ref 1), which is an obstacle to sustainable economic development and environmentally friendly industrial production. Much attention has been paid to development of novel techniques to apply inert anodes in aluminum electrolysis for many years (Ref 2, 3). Nickel ferrite (NiFe2O4) with cubic inverse spinel structure provides a better chemical stability in the molten cryolite– alumina bath, so it provides a possibility to be used as inert anode material (Ref 4, 5). Moreover, NiFe2O4 spinel shows good semiconducting nature at 600 °C, and when temperature is higher than 650 °C, the conductivity can jump from a mere value of 20– 275 S/cm (Ref 6, 7). So nickel ferrite (NiFe2O4) can be employed as promising materials with producing environmentfriendly O2 gas instead of greenhouse gases. Solid-phase synthesis is mainly applied to prepare NiFe2O4 ceramics with Fe2O3 and NiO powders for its simple preparation technology and lower cost (Ref 8). However, lower sintering activity among solid particles and poorer electric conductivity of the
Bin Wang, Jinjing Du, Meng Zhou, Erhu Li, and Linbo Li, School of Metallurgy Engineering, XiÕan University of Architecture and Technology, 4, Box, 710055 XiÕan, China; and Shoukun Gao, Lanzhou Engineering and Research Institute of Nonferrous Metallurgy Co. L
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