Sintering kinetics and properties of NiFe₂O₄‐based ceramics inert anodes doped with TiN nanoparticles

Abstract

Sintering kinetics of NiFe 2 O 4 -based ceramics inert anodes for aluminum electrolysis doped 7 wt% TiN nanoparticles were conducted to investigate densification and grain growth behaviors. The linear shrinkage increased gradually with the increasing sintering temperature between 1000 and 1450 • C, whereas the linear shrinkage rate exhibited a broad peak. The maximum linear shrinkage rate was obtained at 1189.4 • C, and the highest densification rate was achieved at the relative density of 75.20%. Based on the pressureless sintering kinetics window, the sintering process was divided into the initial stage, the intermediate stage, and the final stage. The grain growth exponent reduced with increased sintering temperature, whereas the grain growth activation energy decreased by increasing sintering temperature and shortening dwelling time. The grain growth was mainly controlled by atomic diffusion. NiFe 2 O 4 -based ceramics possessed hightemperature semiconductor essential characteristics. The electrical conductivity of NiFe 2 O 4 -based ceramics first increased and then decreased with increasing sintering temperature, reached their maximum value (960 • C) of 33.45 S/cm under 1300 • C, mainly attributed to the relatively dense and uniform microstructure. The thermal shock resistance of NiFe 2 O 4 -based ceramic was improved by a stronger grain boundary bonding strength and lower coefficient of linear thermal expansion.

Review—Primary Production of Aluminium with Oxygen Evolving Anodes

“…51 Zhang and Xu also reported that addition of TiN to NiFe 2 O 4 could improve the electrical conductivity of the ceramic. 52 The maximum relative density and bending strength were achieved when TiN content was 7 wt% in the NiFe 2 O 4 -TiN composite. The electric conductivity of NiFe 2 O 4 -(7 wt%) TiN composite below 960 °C was 31.68 S cm −1 , which is nearly 10 times larger than that of undoped NiFe 2 O 4 material (3.36 S cm −1 ).…”

Anode Process on Platinum in Low Temperature KF-AlF3-Al2O3 Based Melts: An Update

“…[1][2][3] Significant progress has been made in the field of creating oxygen-evolving anodes and aluminum-wetted cathodes over the past two decades. [4][5][6][7][8][9] However, even the most corrosion-resistant materials cannot withstand the simultaneous effects of high temperature and aggressive electrolyte. The situation changes when the cryolite-alumina melt is replaced with a KF-AlF 3 -Al 2 O 3 based molten electrolyte offering an operating temperature in the range of 750 °C-850 °C.…”

“…For the KF-AlF 3 -Al 2 O 3 based melts, the regularities of the cathode process on tungsten and glassy carbon, 24,25 as well as those of the anode process on glassy carbon, 26,27 and the anode behavior of various candidate materials of oxygen-evolving anodes (Cu, Ni, Cu-Al, Cu-Fe-Ni, Cu-Fe-Ni-Al, NiFe 2 O 4 et al) were studied earlier. [4][5][6][7][28][29][30] The interpretation of the mechanism and determination of anode process parameters according to the available results is challenging due to the superposition of chemical and electrochemical dissolution of the above oxygen-evolving anode materials, as well as the variability of the electrical resistance of the surface layer of the anode. To obtain new fundamental results for the purpose of their practical application, it is necessary to study the anode process on more stable materials (e.g., Pt, Au, Ir).…”