High-temperature conductivity,stability and redox properties of Fe3?xAlxO4 spinel-type materials |
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| Authors: | Andrei V Kovalevsky Eugene N Naumovich Aleksey A Yaremchenko Jorge R Frade |
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| Affiliation: | 1. Department of Bioscience and Oral Diagnosis, Institute of Science and Technology, UNESP — Univ Estadual Paulista, São José dos Campos (SP), School of Dentistry, Av. Engenheiro Francisco José Longo, 777, São José dos Campos 12245-000, SP, Brazil;2. Department of Diagnosis and Surgery Institute of Science and Technology, UNESP — Univ Estadual Paulista, São José dos Campos (SP), School of Dentistry, Av. Engenheiro Francisco José Longo, 777, São José dos Campos 12245-000, SP, Brazil;3. Division of Materials, Air and Space Institute, CTA, Praça Mal. do Ar Eduardo Gomes, 14, São José dos Campos 12904-000, SP, Brazil |
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| Abstract: | Iron-based oxides are considered as promising consumable anode materials for high temperature pyroelectrolysis. Phase relationships, redox stability and electrical conductivity of Fe3?xAlxO4 spinels were studied at 300–1773 K and p(O2) from 10?5 to 0.21 atm. Thermogravimetry/XRD analysis revealed metastability of the sintered ceramics at 300–1300 K. Low tolerance against oxidation leads to dimensional changes of ceramics upon thermal cycling. Activation energies of the total conductivity corresponded to the range of 16–26 kJ/mol at 1450–1773 K in Ar atmosphere. At 1573–1773 K and p(O2) ranging from 10?5 to 0.03 atm, the total conductivity of Fe3?xAlxO4 is nearly independent of the oxygen partial pressure. The conductivity values of Fe3?xAlxO4 (0.1 ≤ x ≤ 0.4) at 1773 K and p(O2) ～10?5 to 10?4 atm were found to be only 1.1–1.5 times lower than for Fe3O4, showing high potential of moderate aluminium additions as a strategy for improvement of refractoriness for magnetite without significant deterioration of electronic transport. |
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