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Abstract  

Kinetics of oxidation of Fe-Cr steel containing 25 wt.-percent Cr was studied as a function of temperature (1023–1173 K) for up to 480 h in flowing air, which corresponds to SOFC cathode environment operating conditions. The oxidation process was found to be a parabolic, suggesting that the diffusion of ionic defects in the scale is the slowest, rate determining step and it occurs predominantly by short-circuit diffusion paths. Comparison of the determined activation energy of oxidation of the studied steel with literature data indicates that at 1098–1173 K the chromia scale grows by the outward solid-state diffusion of chromium interstitials, whereas at 1023–1098 K — through a significant contribution of counter-current oxygen/chromium diffusion along Cr2O3 grain boundaries. The oxide scales were composed mainly of Cr2O3 with a continuous thin Mn1.5Cr1.5O4 spinel layer on top of the chromia scale. The oxidation test results on Fe-25Cr steel demonstrate the applicability of the commercial type DIN 50049 stainless steel as interconnect for SOFC.

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Introduction The spinel ferrites, MeFe 2 O 4 (where Me is a metallic element or a group of metallic elements), are from decades in the centre of many researches all over the world due to the different and interesting

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–zinc ferrite phases with x Zn = 0, 0.2, 0.4, 0.6, and 0.8 was included in the program of full-profile analysis. The given set reflected quasi-continuous distribution of Li 0.5(1– x ) Zn x Fe 2.5–0.5 x O 4 type spinel phases that could be formed in different

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Introduction Development of spinel ferrite nanoparticles has been intensively pursued because of their technological and fundamental scientific importance. Ferrites have received great attention as a result of their magnetic

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Thermal decomposition of pure basic zinc carbonate (BZC) and doped or mixed with iron ions were studied using TG, DTA and kinetics of isothermal decomposition. The TG and DTA investigations revealed that, the presence of iron ions retards the decomposition processes of (BZC). Also, the retardation effect increases on increasing of iron concentration up to 50 at.%. The curves of isothermal decomposition show the usual sigmoidal character. The decomposition velocity contsant (K) values are plotted vs. 1/T according to Arrhenius equation gave a plot of good straight lines with activation energies of 43.7, 48.2, 53.2 and 57.1 kJ mol−1 for pure (BZC) and incorporated with 1, 10, 30 and 50 at.% Fe2+ respectively. The products of the thermal decomposition of pure BZC and mixed with iron ions are characterized using X-ray diffraction, IR spectroscopy, surface area determination and the surface porosity. These investigations showed that iron ions are effectively incorporated into zinc oxide lattice in the range of 30–50 at.%, which gave a ZnFe2O4 spinel.

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Journal of Thermal Analysis and Calorimetry
Authors: Lucjan Chmielarz, Małgorzata Rutkowska, Piotr Kuśtrowski, Marek Drozdek, Zofia Piwowarska, Barbara Dudek, Roman Dziembaj, and Marek Michalik

high surface mixed metal oxides, with a high dispersion of introduced transition metals oxide species [ 2 – 6 ]. An increase in the calcination temperature results in the aggregation of these species and formation of the spinel phases [ 2 – 6

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The morphology of kaolinite thermally processed to 1600° in a thermoanalyzer was studied and related to DTA/TG/DTG data. The results show that DTA/TG/DTG data refined with scanning electron microscopic information offers insight into some of the controversies concerning the kaolinite-mullite transformation. In particular, the study supports the hypothesis that a spinel phase forms in the 950–1000° region. Further, the study shows that during dehyroxylation in the 450–700° region, water escapes by a process opposite to that generally supposed.

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Solid state reactivity and mechanisms in oxide systems

IX. Formation and decomposition of NiMn2O4, Ni1.5Mn1.5O4 and Mg2TiO4 in the metastable state

Journal of Thermal Analysis and Calorimetry
Authors: A. Feltz, J. Töpfer, and U. Schulz

Starting from oxalate mixed crystals NixMn3−x(C2O4)3·6H2O thermal decomposition at reduced oxygen partial pressure (po2= 2%) leads to the formation of NiMn2O4 (x = 1) at metastable conditions. Ni1.5Mn1.5O4 (x = 1.5) existing in the metastable state only has been also prepared. The spinel compounds both are of the highly inversed type. Following a sol-gel preparation route Mg2TiO4 has been also found to be formed in the metastable state. Annealing results in decomposition of the compounds providing NiMnO3 and 1/2α-Mn2O3 or NiMnO3 only or MgTiO3 and MgO, respectively. The reaction rates observed are lower for NiMn2O4 and Ni1.5Mn1.5O4 than for Mg2TiO4 decomposition. The reverse reaction of NiMn2O4 formation above 730°C shows an endothermic enthalpy of +61 kJ·mol−1. For Mg2TiO4 formation above 1050°C an endothermic enthalpy of +19.3 kJ·mol−1 is found. The results are discussed in terms of structural features of the oxides.

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Introduction Lithium pentaferrite (LPF) (LiFe 5 O 8 or Li 0.5 Fe 2.5 O 4 ) is the simplest basic material for a variety of chemical compositions of lithium ferrospinels. LPF has the structure of inverted spinel. Its crystal

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lithium–zinc ferrites under conditions of heating the reaction mixtures by a pulsed beam of accelerated electrons. In order to reveal the radiation effects, the lithium–zinc ferrite spinel was synthesized from the same stock reagents by the conventional

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