Effect of Sintering Atmosphere on the Synthesis Process, Electrical and Mechanical Properties of NiFe 2 O 4 /Nano-TiN Ce
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Effect of Sintering Atmosphere on the Synthesis Process, Electrical and Mechanical Properties of NiFe2O4/Nano-TiN Ceramics Bin Wang, Jinjing Du, Shoukun Gao, Zhao Fang, Jun Zhu, and Linbo Li (Submitted June 5, 2018; in revised form November 1, 2018; published online December 10, 2018) NiFe2O4/nano-TiN ceramics were fabricated by a two-step cold-pressing sintering process. Effect of sintering atmosphere (air, nitrogen, argon) on the synthesis process of NiFe2O4/nano-TiN ceramics was investigated. The DSC-TG and XRD analysis results indicated that besides principal phases of NiO and NiFe2O4, new-phase Ni3TiO5 formed in the sintered ceramics under the three sintering atmospheres, and metallic phase including iron and nickel appeared in the sintered samples with inert gas (nitrogen, argon) sintering condition. Microstructure analysis results showed that considerable quantity of micropores appeared in the ceramic samples sintered under inert gases (argon, nitrogen), but lower porosity (3.0, 3.6%) and higher densities (4.78 g/cm3, 4.51 g/cm3) can be obtained, comparing to the both values (14.4%, 4.17 g/ cm3) for the ceramic samples sintered under air atmosphere. Besides, the average bending strength and elastic modulus of the samples sintered under argon is 113.75 MPa and 7.13GPa, which is higher than that of 75.12 MPa, 5.42GPa and 91.96 MPa, 6.26GPa for the samples synthesized under air and nitrogen, separately. When changing sintering atmosphere from air to inert gases (argon, nitrogen), the fracture model of the 4 wt.%nano-TiN/NiFe2O4 ceramics synthesized at 1400 °C for 4 h transformed from intergranular fracture to intergranular-transgranular fracture. Keywords
mechanical performance, microstructure, nano-size titanium nitride, NiFe2O4 ferrite, phase transformation, sintering atmosphere
1. Introduction At present, carbon anodes are mainly applied to aluminum electrolysis industry with a high current efficiency of 96%, and the anode products are mainly CO2, CO and fluorocarbons. In recent years, inert anodes have attracted great interests and activities due to low carbon consumption and production of environment-friendly O2 gas during aluminum electrolysis (Ref 1, 2). Among these materials, NiFe2O4 with cubic inverse spinel structure could provide a better chemical stability in the molten cryolite-alumina bath (Ref 3). So NiFe2O4 spinel can be applied as a promising candidate for green inert anodes. For its high initial electrical resistivity at room temperatures, pure NiFe2O4 spinel as semiconductor-natured polycrystalline spinel ferrite was seldom employed to serve as electrode material (Ref 4). Solid-phase synthesis has the advantages of simple process and low cost; it is mainly applied to prepare NiFe2O4 ceramics with Fe2O3 and NiO powders (Ref 5). However, low sintering ability of solid particles and poor electrical properties of the synthesized samples limit its use in aluminum electrolysis as inert
Bin Wang, Jinjing Du, Shoukun Gao, Zhao Fang, Jun Zhu, and Linbo Li, School of
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