Nearly stoichiometric iron monoxide formed as a metastable intermediate in a two-stage disproportionation of quenched wüstite. Thermodynamic and kinetic aspects

-The possibility of the incorporation of solar energy by solar thermochemical water-splitting with WOstite, which is the 2nd step H2 production in Fe30Jcoal redox process for solar/fossil energy mixing, was studied kinetically. The reaction formed efficiently molecular hydrogen and cation-excess magnetite. The reaction rate was greatly dependent on reaction temperature and H20 steam flow rate. The H2 volume generated by the reaction gave the maximum value (76 % of theoretical value) at 873K. I . INTRODUCTIONSolar thermochemical process has been the current subjects for introducing the solar energy into the primary energy system. Several thermochemical systems have been studied for harnessing the concentrated sun light as the process heat. They include carbothermal redox process by Steinfeld et al. [1][2], methane reforming with CO 2 producing the syngas [3], and ammonia decomposition [4].The carbothermal redox process uses fossil fuels such as coal and natural gas.Coal will be primarily important from long-term strategy consideration instead of relatively high-quality natural gas, i.e., C~.Coal-magnetite redox process is the first step of the overall solar carbothermal process:where x is the mole ratio of hydrogen to carbon content in the coal. This is highly endothermic and involves the mixing [5][6][7] offossil energy (coal) and solar energy as a process heat.Solar reactor experiments using a high-flux irradiation of 300W/cm 2 using a PSI solar system showed that the carbon decreased rapidly within only 1 sec of exposure, suggesting efficient heat transfer and chemical conversion by direct absorption of concentrated solar energy at the reaction site. The water-splitting is thesecond solar step, producing Hl and Fe304. The latter material is recycled to the first solar process. The proposed solar thermochemical process offers the possibility of performing simultaneously gasification of coal and reduction of iron oxide and also producing a fuel with an upgraded calorific value. The above process needs to be fast enough to follow the first step (1) to perform effectively the overall solar gasification and water-splitting. Thus, the objective of the present study was to investigate the reaction kinetics ofEq.(2). . EXPERIMENTAL A. SpecimensThe non-stoichiometric wiistites used in this investigation were prepared from Fe304. The samples prepared and reacted with water were identified by X-ray diffractometry with FeKa. radiation (Rigaku X-ray diffractometer, model RAD-2A). Thermogravimetry (TG) was used to determine the oxygen content of the wiistite samples. B. Water splitting by H 2 0-wustite systemThe reaction cell was set in an infrared furnace (Shinku-Riko, model RHL-E45P). The sample feeder was fixed on the top of the reaction cell via a flexible silicone tube connector. H 2 01 Ar diluent gases were introduced through the sample feeder and the reaction cell. The concentrations of the H2 gas in the outlet gases were determined by gas chromatography with thermal conductivity detector(GC-TCD) (Shimadzu G...

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“…The chemical composition and the observed lattice constants of all prepared samples were in good agreement with reported values [8].…”

Section: A Kinetics Of Water Splitting By H 2 0-wustite Systemsupporting

confidence: 78%

Study of Water-splitting on Carbothermally Reduced Wüstite for Solar/Chemical Energy Conversion

et al. 1998

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“…This is in a good agreement with the theoretical instability of wüstite below this temperature (570°C). [35,[43][44][45][46] The idea of formation of FeO as the principal conversion product is also supported by the weight loss of 67.22 % observed in the TG curve discussed earlier.…”

Section: Decomposition Under Dynamic Inert Conditionsmentioning

confidence: 57%

“…The presence of iron-deficient wüstite in the sample above 570°C is supported by its conversion to iron-richer wüstite and magnetite with time, [44,48] which was observed in the in situ XRD pattern measured after 120 min of the isothermal treatment at 700°C (Figure 4, c). Hence, an observed decrease in the content of α-iron in this sample can be explained by its partial reaction in forming magnetite.…”

Section: Decomposition Under Dynamic Inert Conditionsmentioning

confidence: 77%

“…It should be mentioned that the temperature of 577°C is presented as the Curie temperature of magnetite [42] and a very close value of 570°C represents a temperature below which FeO is unstable and disproportionates to Fe 3 O 4 and α-Fe. [35,[43][44][45][46] The total weight loss of 67.22 % is only a little bit lower than a theoretical mass loss expected for the formation of FeO (67.91 %). The above-mentioned conclusions are supported well by evolved gas analysis.…”

Section: Decomposition Under Dynamic Inert Conditionsmentioning

confidence: 91%

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Thermal Decomposition of Ferric Oxalate Tetrahydrate in Oxidative and Inert Atmospheres: The Role of Ferrous Oxalate as an Intermediate

2010

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The thermal decomposition of ferric oxalate tetrahydrate Fe2(C2O4)3·4H2O was studied in dynamic oxidative and inert atmospheres by using a simultaneous thermogravimetric (TG) and differential scanning calorimetric (DSC) analytical device equipped with an evolved gas analyzer (EGA). Solid‐state decomposition products formed during the decomposition were analyzed by 57Fe Mössbauer spectroscopy, in situ and ex situ X‐ray powder diffraction, and magnetic measurements. In the dynamic inert atmosphere, we observed the formation of a tiny amount of superparamagnetic iron oxide (most likely Fe3O4) together with a majority of ferrous oxalate (FeC2O4) and remains of undecomposed Fe2(C2O4)3 after the first decomposition step, which finished at 210 °C. The astonishing presence of the oxidic phase at such low temperatures is a highly probable side effect of the main reduction action of the electrons on the FeIII cations in the ferric oxalate structure, thus resulting in the creation of intermediate FeC2O4. The final product of decomposition of the FeC2O4 intermediate in a dynamic inert atmosphere is a mixture of wüstite (FexO), α‐iron (α‐Fe), and magnetite (Fe3O4). Their proportion accurately reflects actual disproportionation/synproportionation/redisproportionation processes likely encouraged by the preserved size and morphology of the initial ferric oxalate crystals and that are dependent on temperature. In the oxidative atmosphere, the decomposition proceeds in the three overlapped stages that include dehydration, the astonishing reductive formation of FeC2O4 as an intermediate, and final decarboxylation to hematite (α‐Fe2O3). The principal effect of the experimental conditions on the amount of intermediate formation of FeC2O4 in the oxidative atmosphere is also discussed and evaluated from the isothermal experiments carried out at 180 °C.

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“…FeO-wiistite is a nonstoichiometric compound with NaCl-type structure and is decomposed into magnetite (Fe304, spinel-type structure) and a-Fe by disproportionation at the temperatures below S7SoC [1,2]. Replacement of the Fe(II) ions in the FeO-wiistite with foreign cations will cause a change in the crystal parameters.…”

Section: Introductionmentioning

confidence: 99%

Stabilized Wüstite Formed from Zn(II)-and Mn(II)-Wüstite below 575°C

et al. 1998

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Nearly stoichiometric iron monoxide formed as a metastable intermediate in a two-stage disproportionation of quenched wüstite. Thermodynamic and kinetic aspects

Cited by 38 publications

References 20 publications

Study of Water-splitting on Carbothermally Reduced Wüstite for Solar/Chemical Energy Conversion

Study of Water-splitting on Carbothermally Reduced Wüstite for Solar/Chemical Energy Conversion

Thermal Decomposition of Ferric Oxalate Tetrahydrate in Oxidative and Inert Atmospheres: The Role of Ferrous Oxalate as an Intermediate

Stabilized Wüstite Formed from Zn(II)-and Mn(II)-Wüstite below 575°C

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Nearly stoichiometric iron monoxide formed as a metastable intermediate in a two-stage disproportionation of quenched wüstite. Thermodynamic and kinetic aspects

Cited by 38 publications

References 20 publications

Study of Water-splitting on Carbothermally Reduced W&uuml;stite for Solar/Chemical Energy Conversion

Study of Water-splitting on Carbothermally Reduced W&uuml;stite for Solar/Chemical Energy Conversion

Thermal Decomposition of Ferric Oxalate Tetrahydrate in Oxidative and Inert Atmospheres: The Role of Ferrous Oxalate as an Intermediate

Stabilized W&uuml;stite Formed from Zn(II)-and Mn(II)-W&uuml;stite below 575&deg;C

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Study of Water-splitting on Carbothermally Reduced Wüstite for Solar/Chemical Energy Conversion

Study of Water-splitting on Carbothermally Reduced Wüstite for Solar/Chemical Energy Conversion

Stabilized Wüstite Formed from Zn(II)-and Mn(II)-Wüstite below 575°C