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.
keywords
MAGNESIUM ALUMINOSILICATE MELTS; IRON PYROELECTROLYSIS; SI-O; TEMPERATURE; CONDUCTIVITY; STABILITY; MAGNETITE; SPINELS; THERMOPOWER; ANODE
subject category
Materials Science
authors
Ferreira, NM; Ferro, MC; Fagg, DP; Costa, FM; Frade, JR; Kovalevsky, AV
our authors
Andrei Kavaleuski
Principal Researcher
Jorge Ribeiro Frade
Retired Professor
Marta Ascenção Carmona Ferro
Laboratory Officer
Nuno Miguel Freitas Ferreira
Post-Doc FellowshipProjects
Cellular oxide catalysts for emission lean combustion in porous media (LEANCOMB)
CICECO - Aveiro Institute of Materials (UID/CTM/50011/2013)
RMNE-UA-National Network of Electron Microscopy (REDE/1509/RME/2005 )
acknowledgements
This work was developed within the scope of projects LEANCOMB (refs. 04/SAICT/2015 and PTDC/CTMENE/2942/2014) and CICECO-Aveiro Institute of Materials (refs. POCI-01-0145FEDER-007679 and UID/CTM/50011/2013) and i3N (FCT Ref: UID/CTM/50025/2013), financed by FCT/MEC and FEDER under the PT2020 Partnership Agreement. The support from FCT, Portugal (grants SFREI/BPD/111460/2015, IF/00302/2012, IF/01344/2014, PTDC/CTM-ENE 6319 2014) is also acknowledged. M.C. Ferro acknowledges support from RNME - Pole University of Aveiro and FCT project REDE/1509/RME/2005.