Influence of Temperature and Duration of α-Fe2O3 Calcination on Reactivity in Hydrogen Oxidation

Исследовано влияние температуры и продолжительности прокаливания однофазных образцов гематита со структурой α-Fe2O3 на окислительную способность в отношении водорода в режиме температурно-программируемой реакции в интервале 40–900 °C. Показано, что температура прокаливания является существенным фактором, влияющим на реакционную способность решеточного кислорода в окислении водорода. Образцы α-Fe2O3, прокаленные при 800–900 °C, проявляют наибольшую активность, процесс восстановления α-Fe2O3 в этих образцах протекает через стадию восстановления до магнетита, с последующим полным восстановлением до металла через совмещение стадий восстановления оксидов. Прокаливание образцов α-Fe2O3 при 1000–1100 °C приводит к существенному снижению окислительной способности, восстановление α-Fe2O3 начинается при температурах на 50–100 °C выше, идет без выделения отдельных стадий восстановления, полное восстановление α-Fe2O3 до металла в исследованных условиях не происходит. Установлено, что с увеличением температуры прокаливания образцов возрастает рентгенографическая плотность α-Fe2O3, что свидетельствует о снижении степени разупорядочения кристаллической решетки, которое приводит к росту энергии связи решеточного кислорода и существенному снижению реакционной способности α-Fe2O3 в окислении водородаThe effect of temperature and duration of calcination of single-phase samples of hematite with the α-Fe2O3 structure on the oxidizing ability with respect to hydrogen in the temperature-programmed reaction mode in the temperature range of 40–900 °C was studied. It is shown that the calcination temperature is a significant factor affecting the reactivity of lattice oxygen in the oxidation of hydrogen. Samples of α-Fe2O3, calcined at 800–900 °C, show the highest activity, the process of α-Fe2O3 reduction in these samples proceeds through the stage of reduction to magnetite, followed by complete reduction to metal through the combination of reduction stages of oxides. The calcination of α-Fe2O3 samples at 1000–1100 °C leads to a significant decrease in the oxidizing ability, the α-Fe2O3 reduction initiates at temperatures 50–100 °C higher, proceeds without separating individual reduction stages of oxide, there is no complete reduction of α-Fe2O3 under the studied conditions. It has been established that with an increase in the calcination temperature of the hematite samples, the X‑ray density of α-Fe2O3 increases, which indicates a decrease in the degree of crystal lattice disorder and an increase in the binding energy of lattice oxygen and manifests itself in a significant decrease in the reactivity of α-Fe2O3 in the oxidation of hydroge

Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass‐loss rate and stabilization

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large‐scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass‐loss rates and stabilization factors of plant‐derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy‐to‐degrade components accumulate during early‐stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass‐loss rates and stabilization, notably in colder locations. Using TBI improved mass‐loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early‐stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Effect of Acid Leaching on Helium and Neon Permeability of Microspherical Membranes Based on Cenospheres

На основе узкой фракции ценосфер, выделенной из концентрата ценосфер от сжигания экибастузского угля, получены микросферические мембраны, характеризующиеся высоким уровнем гелиевой проницаемости в сочетании с высокой селективностью He/Ne. Кислотное травление полученных микросферических мембран в 8,6 M HNO3 способствовало развитию микропористости их оболочки (объемная доля микропор с преобладающими размерами 5, 6.4 и 13 Å увеличилась с 6.7 до 34.0 %). Это привело к увеличению коэффициента гелиевой проницаемости при Т=298 K примерно в 2 раза до значения 2.27·10-18 (моль·м)/(м2·с·Па).Полученные микросферические мембраны характеризуются высокой селективностью α(He/Ne)=170 при 553 K и превосходят синтетические стеклянные микросферы 3М К37 Glass Bubbles (3МТМ, США) по уровню гелиевой проницаемости в 34-57 раз, а полимерный мембранный материал (полисульфон) – по селективности в отношении He/Ne в 34-52 разаThe microspherical membranes based on narrow fraction of cenospheres with high permeability to helium and high selectivity for He/Ne were recovered from cenosphere concentrate from Ekibastuz coal combustion. Acid leaching of the obtained microspherical membranes by 8.6M HNO3 contribute to microporosity development in their shell (volume percentage of the micropore with predominant sizes of 5, 6.4 and 13 Å was increased from 6.7 to 34.0 vol. %).This led to increase in helium permeation at T=298 K about to 2 times, i.e. up to a value of 2.27·10-18 (mol·m)/(m2·sec·Pa). The obtained microspherical membranes are characterized by high selectivity α(He/Ne)=170 at 553K, and exceed the synthetic glass hollow microspheres 3M K37 Glass Bubbles (3MTM, USA) in helium permeation to 37-57 times, and the polymeric membrane material –(poly)sulphone in selectivity for He/Ne to 34-52 time

Scanning Electron Microscopy–Energy-Dispersive X-ray Spectrometry (SEM–EDS) Analysis of PM1–2 Microspheres Located in Coal Char Particles with Different Morphologies.

Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to analyze individual microspheres, 1–2 μm in size, located in coal char particles of Inertoid and Fusinoid/Solid morphological types. It was shown that PM1-2 is formed in the porous structure of the carbon matrix, which control microspheres size, from authigenic minerals that determine their composition. Depending on the contents of SiO2, Al2O3, and FeO, the studied microspheres fall into various groups differing in mineral precursors. The precursor of Group 1 microspheres with specific composition of SiO2 + Al2O3 > 95 wt. % and FeO ≤ 1.5 wt. % is NH4-illite. Microspheres containing SiO2 + Al2O3 < 95 wt. % and FeO in increasing contents up to 4, 6 and 10 wt. %, included in Group 2, Group 3, and Group 4, respectively, are formed from mixed-layer K-illite-montmorillonite minerals subjected to cationic substitution with iron, 2 followed by the entry of Fe3+ in interlayer sites. Calcite, dolomite, gypsum, magnesite, rutile, and siderite are involved in the formation of Group 5 microspheres with a high content of Ca, Mg, Ti, or Fe. The significant part of PM1-2 is represented by microspheres of Groups 2, 3 and 4 regardless of the type of coal char particles (62% for Inertoid and 75% for Fusinoid/Solid ones). About 1/3 of microspheres for both char morphotypes refer to Group 5. Microspheres of Group 1 (8%) are located only in the Inertoid char particles, which results from the characteristic effect of the maceral-mineral composition of original coal. It has been suggested that Inertoid and Fusinoid/Solid char particles are formed from various macerals: semifusinite and fusinite, respectively. Due to the closed-cell structure, semifusinite contains non-cation-exchanged NH4- illite, the mineral precursor of microspheres with low contents of Fe, K, Na, and Mg. The fusinite structure allows cationic substitution in NH4-illite with the formation of mixed-layer Killite and montmorillonite, the mineral precursors of significant part of PM1-2

Effect of Acid Leaching on Helium and Neon Permeability of Microspherical Membranes Based on Cenospheres

На основе узкой фракции ценосфер, выделенной из концентрата ценосфер от сжигания экибастузского угля, получены микросферические мембраны, характеризующиеся высоким уровнем гелиевой проницаемости в сочетании с высокой селективностью He/Ne. Кислотное травление полученных микросферических мембран в 8,6 M HNO3 способствовало развитию микропористости их оболочки (объемная доля микропор с преобладающими размерами 5, 6.4 и 13 Å увеличилась с 6.7 до 34.0 %). Это привело к увеличению коэффициента гелиевой проницаемости при Т=298 K примерно в 2 раза до значения 2.27·10-18 (моль·м)/(м2·с·Па).Полученные микросферические мембраны характеризуются высокой селективностью α(He/Ne)=170 при 553 K и превосходят синтетические стеклянные микросферы 3М К37 Glass Bubbles (3МТМ, США) по уровню гелиевой проницаемости в 34-57 раз, а полимерный мембранный материал (полисульфон) – по селективности в отношении He/Ne в 34-52 разаThe microspherical membranes based on narrow fraction of cenospheres with high permeability to helium and high selectivity for He/Ne were recovered from cenosphere concentrate from Ekibastuz coal combustion. Acid leaching of the obtained microspherical membranes by 8.6M HNO3 contribute to microporosity development in their shell (volume percentage of the micropore with predominant sizes of 5, 6.4 and 13 Å was increased from 6.7 to 34.0 vol. %).This led to increase in helium permeation at T=298 K about to 2 times, i.e. up to a value of 2.27·10-18 (mol·m)/(m2·sec·Pa). The obtained microspherical membranes are characterized by high selectivity α(He/Ne)=170 at 553K, and exceed the synthetic glass hollow microspheres 3M K37 Glass Bubbles (3MTM, USA) in helium permeation to 37-57 times, and the polymeric membrane material –(poly)sulphone in selectivity for He/Ne to 34-52 time

Solid-State Reaction in Cu/a-Si Nanolayers: A Comparative Study of STA and Electron Diffraction Data

The kinetics of the solid-state reaction between nanolayers of polycrystalline copper and amorphous silicon (a-Si) has been studied in a Cu/a-Si thin-film system by the methods of electron diffraction and simultaneous thermal analysis (STA), including the methods of differential scanning calorimetry (DSC) and thermogravimetry (TG). It has been established that, in the solid-state reaction, two phases are formed in a sequence: Cu + Si → η″-Cu3Si → γ-Cu5Si. It has been shown that the estimated values of the kinetic parameters of the formation processes for the phases η″-Cu3Si and γ-Cu5Si, obtained using electron diffraction, are in good agreement with those obtained by DSC. The formation enthalpy of the phases η″-Cu3Si and γ-Cu5Si has been estimated to be: ΔHη″-Cu3Si = −12.4 ± 0.2 kJ/mol; ΔHγ-Cu5Si = −8.4 ± 0.4 kJ/mol. As a result of the model description of the thermo-analytical data, it has been found that the process of solid-state transformations in the Cu/a-Si thin-film system under study is best described by a four-stage kinetic model R3 → R3 → (Cn-X) → (Cn-X). The kinetic parameters of formation of the η″-Cu3Si phase are the following: Ea = 199.9 kJ/mol, log(A, s−1) = 20.5, n = 1.7; and for the γ-Cu5Si phase: Ea = 149.7 kJ/mol, log(A, s−1) = 10.4, n = 1.3, with the kinetic parameters of formation of the γ-Cu5Si phase being determined for the first time

Thermokinetic Study of Aluminum-Induced Crystallization of a-Si: The Effect of Al Layer Thickness

The effect of the aluminum layer on the kinetics and mechanism of aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) in (Al/a-Si)n multilayered films was studied using a complex of in situ methods (simultaneous thermal analysis, transmission electron microscopy, electron diffraction, and four-point probe resistance measurement) and ex situ methods (X-ray diffraction and optical microscopy). An increase in the thickness of the aluminum layer from 10 to 80 nm was found to result in a decrease in the value of the apparent activation energy Ea of silicon crystallization from 137 to 117 kJ/mol (as estimated by the Kissinger method) as well as an increase in the crystallization heat from 12.3 to 16.0 kJ/(mol Si). The detailed kinetic analysis showed that the change in the thickness of an individual Al layer could lead to a qualitative change in the mechanism of aluminum-induced silicon crystallization: with the thickness of Al ≤ 20 nm. The process followed two parallel routes described by the n-th order reaction equation with autocatalysis (Cn-X) and the Avrami–Erofeev equation (An): with an increase in the thickness of Al ≥ 40 nm, the process occurred in two consecutive steps. The first one can be described by the n-th order reaction equation with autocatalysis (Cn-X), and the second one can be described by the n-th order reaction equation (Fn). The change in the mechanism of amorphous silicon crystallization was assumed to be due to the influence of the degree of Al defects at the initial state on the kinetics of the crystallization process

Composition, Structure and Reduction Reactivity of Composite Materials of the α-Fe₂O₃–СaFe₂O₄ System by Hydrogen

В работе изучены композиционные материалы системы α-Fe2O3–CaFe2O4, полученные методом высокотемпературного твердофазного синтеза из оксидов Са и Fe(III) с вариацией мольного отношения СаО/Fe2O3 от 0.15 до 1.00. Материалы охарактеризованы методами рентгеновской дифракции (РФА), сканирующей электронной микроскопии с системой энергодисперсионного микроанализа (СЭМ-ЭДС) и синхронного термического анализа (СТА) в режиме термопрограммируемого восстановления водородом (H2-ТПВ). СЭМ-ЭДС – исследование образцов выявило формирование сложной микроструктуры материала по типу «ядро-оболочка» с фазой гематита в качестве «ядра». H2-ТПВ образцов позволило установить, что с увеличением содержания фазы CaFe2O4 (от 33.4 до 97.5 мас. %) наблюдается снижение вклада низкотемпературных форм решеточного кислорода в областях 350-510 °С (до 2.6 раза) и 510-650 °С (до 1.7 раза) и рост вклада высокотемпературной формы кислорода в интервале 650-900 °С (до 2 раз). На основе оценки подвижности решеточного кислорода высказано предположение о перспективности использования полученных композиционных материалов с содержанием фазы CaFe2O4 более 55.2 мас. % в качестве носителей кислорода в химических циклических процессах получения синтез-газаIn this paper, α-Fe2O3–CaFe2O4 composite materials obtained by high-temperature solid-phase synthesis from Ca and Fe (III) oxides with varying molar ratio CaO/Fe2O3 in the range 0.15-1.00 were investigated. The materials are characterized by Х-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray microanalysis (SEM-EDS) and simultaneous thermal analysis (STA) in the hydrogen temperature-programmed reduction mode (H2-TPR). SEM-EDS studies of the specimens were revealed a formation of the “core-shell” type complex microstructure of material with the hematite phase as the “core”. H2-TPR of the specimens allowed to establish a decrease of the contribution of low-temperature forms of lattice oxygen in areas of 350-510 °С (up to 2.6 times) and 510-650 °С (up to 1.7 times), and the growth of the contribution of the high-temperature oxygen form in the range of 650-900 °С (up to 2 times) with an increase in the content of the phase CaFe2O4 from 33.4 to 97.5 wt. %. Relying on the assessment of lattice oxygen mobility, it was suggested, that the samples with content of CaFe2O4 phase more than 55.4 wt. % are promising for use as oxygen carriers in chemical looping processes of syngas productio