Exploring the effects of silica and zirconia additives on electrical and redox properties of ferrospinels

authors	Ferreira, NM; Ferro, MC; Fagg, DP; Costa, FM; Frade, JR; Kovalevsky, AV
nationality	International
journal	JOURNAL OF THE EUROPEAN CERAMIC SOCIETY
author keywords	Ferrospinel; Magnetite; Electrical conductivity; Thermal expansion; Redox stability
keywords	MAGNESIUM ALUMINOSILICATE MELTS; IRON PYROELECTROLYSIS; SI-O; TEMPERATURE; CONDUCTIVITY; STABILITY; MAGNETITE; SPINELS; THERMOPOWER; ANODE
abstract	The interplay of unique cation arrangement and redox coupling in ferrospinels offers a wide range of magnetic and catalytic properties, evaluated mostly for low and intermediate temperature applications. This work focuses on high-temperature properties of magnesium-substituted magnetite, for prospective high temperature applications such as electrodes for pyroelectrolysis, energy conversion, catalysis, etc. The effects of silica and zirconia additions to (Fe,Mg)(3)O-4 are studied, with emphasis on structural, electronic transport and redox properties. Up to at least 2% Zr4+ can be dissolved in the spinel lattice by sintering in inert atmosphere at 1773 K, resulting in a moderate conductivity decrease and lower tolerance against oxidative decomposition. Silica additions are accommodated by magnesium exsolution and formation of (Fe,Mg)(2)SiO4 and (Mg,Fe)O phase impurities rather than by the substitution in spinel lattice, as confirmed by combined structural, microstructural and electrical conductivity studies. Minor amounts of silica in ferrospinels do not result in the conductivity decrease and apparently provide more stable thermo-chemical expansion behaviour, being favourable for prospective high-temperature applications, including anode materials in silicate-based melts. (C) 2017 Elsevier Ltd. All rights reserved.
publisher	ELSEVIER SCI LTD
issn	0955-2219
isbn	1873-619X
year published	2017
volume	37
issue	7
beginning page	2621
ending page	2628
digital object identifier (doi)	10.1016/j.jeurceramsoc.2017.02.037
web of science category	Materials Science, Ceramics
subject category	Materials Science
unique article identifier	WOS:000398753400009