Guidelines to design multicomponent ferrospinels for high-temperature applications

Abstract

This work explores the possibilities to design magnetite-based spinels through multiple simultaneous co-substitutions with transition metal cations, with emphasis on redox behavior and electronic transport. For the first time this approach was assesses for high-temperature applications, being of particular interest for the development of consumable anodes for pyroelectrolysis, an alternative carbon-lean steelmaking process. A Taguchi plan was used to assess the impact of the concentration of substituting chromium, titanium, manganese and nickel cations on the lattice parameter and electrical conductivity of the multicomponent ferrospinels. The results revealed comparable decrease in the electrical conductivity, provided by Cr 3+ , Mn 3+/2+ and Ni 2+ cations. The impact of Ti 4+ was found to be less negative, contributing by the formation of Fe 2+ cations and increased hopping probability. Strongest structural impacts, exerted by manganese cations, are likely to affect the mobility of polarons, as revealed by the analysis of correlation factors for combined effects. Ferrospinels, containing various transition metal cations, are more susceptible to oxidation and phase decomposition, which often result in sudden conductivity drop and significant dimensional changes in ceramics. The observed trends for redox behavior suggest that the potential applications of multicomponent ferrospinels in oxidizing conditions are limited at 1000-1400 K due to insufficient stability, while higher temperature applications, requiring significant electronic conductivity, are rather suitable.

Effect of Ni, Bi and Se on the tetrahedrite formation

“…The Taguchi method has been recently implemented with success in several Materials Science studies. [27][28][29][30][31] Studies as distinct as the optimization of the fabrication of TiO 2 -Nb 2 O 5 -Al 2 O 3 mixed oxide nanotube arrays on Ti-6Al-7Nb, 27 the design of multicomponent ferrospinels for high-temperature purposes, 28 the densi-cation of ZrB 2 -based composites by reactive hot pressing with changes in ZrO 2 /SiC ratio and sintering conditions, 29 the bond strength optimization of Ti/Cu/Ti clad composites produced by roll-bonding, 30 or the synthesis of minimal-size ZnO nanoparticles through sol-gel method 31 were recently made using the Taguchi method. In these works, L-9 and L-32 orthogonal arrays 26 were used, allowing a strong decrease in the number of experiences needed to determine the optimal conditions.…”

Oxidation and electrical properties of chromium–iron alloys in a corrosive molten electrolyte environment

“…The ceramic-based anodes adopt a radically different approach. They include using magnetite (Fe 3 O 4 , the stable form of iron oxide at 1,535 °C in presence of > 7.2 × 10 –10 atm of oxygen 45 ) or ferrospinel-based ceramics such as Fe 3−x Mg x O 4 46 , Fe 3−x Al x O 4 47 , (Fe,Mg,Al) 3 O 4 42 , 48 , (Fe,Mg,X) 3 O 4 (X = Si and Zr) 43 , 49 . Those approaches rely on the limited solubility of the ceramics in the electrolyte, which is obviously a challenge in an electrolyte designed to dissolve sufficient amount of iron oxide for electrolysis.…”

Oxidation and electrical properties of chromium-iron binary alloys in a corrosive molten electrolyte environment

“…The ceramic-based anodes adopt a radically different approach. They include using magnetite (Fe3O4, the stable form of iron oxide at 1535°C in presence of >7.2 × 10 -10 atm of oxygen [46]) or ferrospinelbased ceramics such as Fe3−xMgxO4 [47], Fe3−xAlxO4 [48], (Fe,Mg,Al)3O4 [43,49], (Fe,Mg,X)3O4…”