Factors for increasing strength of composite materials based on fine high-calcium fly ash

Industrial high-calcium fly ashes obtained by burning Kansk-Achinsk coal at a thermal power plant and selected from different fields of electrostatic precipitators of an ash collecting plant were studied as the basis for composite binders (CB). The main factors influencing the properties of such CBs are the particle size, the concentration of superplasticizer at a water:binder (w/b) ratio of 0.25, and the proportion of HCFA in the mixture with cement. In particular, for cementless CBs at w/b 0.4, it was found that a change in the particle size d90 from 30 μm to 10 μm leads to an increase in compressive strength by more than 2 times – from 5.5–14 MPa to 11–36 MPa, accordingly, with a curing age of 3–300 days. The 0.12% additive of Melflux 5581F superplasticizer at w/b 0.25 increases the compressive strength – up to 14–32 MPa and up to 24–78 MPa, accordingly. The HCFA-cement blends were investigated in the range of 60–90% HCFA and the maximum compressive strength 77 MPa at 28 days of hardening was found at 80% HCFA. On the basis of 80% HCFA blend with the 0.3% addition of Melflux 5581F and 5% silica fume, the specimens of ultra-high strength (108 MPa at 28 days of hardening) were obtained

Hydrothermal synthesis and sorption performance to Cs(I) and Sr(II) of zirconia-analcime composites derived from coal fly ash cenospheres

The paper is concerned with (i) the hydrothermal synthesis of hydrous zirconium dioxide (HZD) bearing analcime (HZD-ANA, zirconia-analcime) and (ii) its sorption properties with respect to Cs+ and Sr2+. The HZD-ANA particles were synthesized from coal fly ash cenospheres composed of aluminosilicate glass with (SiO2/Al2O3)wt.=3.1 and characterized by PXRD, SEM-EDS, STA, and low-temperature N2 adsorption. The non-radioactive simulant solutions of different acidity (pH=2–10) and Cs+/Sr2+ content (0.5–50.0 mg/L) were used in the work. The effect of synthesis conditions on the HZD-ANA particle size, zirconia content and localization as well as the sorption behavior with respect to Cs+ and Sr2+ (capacity, KD) were clarified. It was found that the small-sized HZD-ANA composites surpasses the Zr free analcime and large-sized HZD-ANA material in the Cs+ and Sr2+ sorption parameters (KD ~104–106 mL/g). The conditions to synthesize the zirconia-analcime composite of the highly enhanced sorption ability with respect to Sr2+ (KD ~106 mL/g) were determined. The high-temperature solid-phase re-crystallization of Cs+/Sr2+-exchanged HZD-ANA composites was shown to occur at 1000 °C resulting in a polyphase system based on nepheline, tetragonal ZrO2, and glass phase

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

Composition−Structure Relationship of Skeletal−Dendritic Ferrospheres Formed during Industrial Combustion of Lignite and Coal

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The structure−composition relationship of skeletal−dendritic ferrospheres (FSs) isolated from fly ash from the coal and lignite combustion has been studied systematically by scanning electron microscopy (SEM) and energy-dispersive Xray spectroscopy. It is shown that illite is the aluminosilicate precursor determining the structure of globules in both cases. The formation of skeletal−dendritic globules occurs due to the “seed” of Al, Mg-ferrospinel that is formed in the thermochemical conversion of illite from initial coals. The dependence CaO = f(SiO2) that reflects the influence of glass-forming components reveals six groups of FSs, the composition of which is represented by linear regression equations. An analysis of SEM images of polished sections from six globule groups reveals that an increase in the concentration of glass-forming components in all groups is accompanied by gradual changes in the structure of globules, from the coarse-grained crystalline skeletal type to the finecrystalline dendritic type with a high content of the glass phase. The observed change in the structure is explained by expansion of the liquation region in the FeO−Fe2O3−SiO2 system, a rise in the oxidation potential, an increase in the proportion of ferrite complexes [Fe3+O2]− and [Fe23+O5]4− in high-calcium melts, and a decrease in the concentration of ferrospinel-forming Fe2+ and Fe3+ ions

Composition–Structure Relationship of Skeletal–Dendritic Ferrospheres Formed during Industrial Combustion of Lignite and Coal

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The structure−composition relationship of skeletal−dendritic ferrospheres (FSs) isolated from fly ash from the coal and lignite combustion has been studied systematically by scanning electron microscopy (SEM) and energy-dispersive Xray spectroscopy. It is shown that illite is the aluminosilicate precursor determining the structure of globules in both cases. The formation of skeletal−dendritic globules occurs due to the “seed” of Al, Mg-ferrospinel that is formed in the thermochemical conversion of illite from initial coals. The dependence CaO = f(SiO2) that reflects the influence of glass-forming components reveals six groups of FSs, the composition of which is represented by linear regression equations. An analysis of SEM images of polished sections from six globule groups reveals that an increase in the concentration of glass-forming components in all groups is accompanied by gradual changes in the structure of globules, from the coarse-grained crystalline skeletal type to the finecrystalline dendritic type with a high content of the glass phase. The observed change in the structure is explained by expansion of the liquation region in the FeO−Fe2O3−SiO2 system, a rise in the oxidation potential, an increase in the proportion of ferrite complexes [Fe3+O2]− and [Fe23+O5]4− in high-calcium melts, and a decrease in the concentration of ferrospinel-forming Fe2+ and Fe3+ ions

Composition, Structure, and Formation Routes of Blocklike Ferrospheres Separated from Coal and Lignite Fly Ashes

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The structure−composition relationship of blocklike ferrospheres (FSs) isolated from fly ash from the coal and lignite combustion has been studied systematically by scanning electron microscopy and energy dispersive X-ray spectroscopy. Groups of globules for which the gross composition of polished sections corresponds to the general equations for the relationship of the concentrations SiO2 = f(Al2O3) and CaO = f(SiO2) are highlighted from FSs of two series. It is shown that blocklike FSs are formed during the sequential transformation of dispersed products of thermal conversion of mineral precursor associates: pyrite, quartz, and Ca, Al-humates in the case of brown coal; and pyrite, siderite, quartz, and calcite in the case of coal. Anorthite is the aluminosilicate precursor of blocklike FSs of both series. The dependence CaO = f(SiO2) that reflects the influence of glass-forming components reveals six groups of FSs. An analysis of SEM images of polished globule sections demonstrates that an increase in the concentration of glass-forming components in all groups is accompanied by gradual changes in the structure of globules, from a large blocklike type to a fine crystalline type with a high glass-phase content. The size and shape of crystallites are controlled by the size of a local melt area where the total concentration of spinel-forming oxides exceeds 85 wt %. An increase in the glass-phase concentration and a decrease in the crystallite size in globules with FeO ≤ 46−50 wt % are explained by expansion of the segregation region in the FeO−Fe2O3−SiO2 system as the oxidation potential rises

Anomalous Diffusion of Helium and Neon in Low-Density Silica Glass

The diffusion properties of low-density non-porous silica glasses (expanded silica glasses) were researched with the aim of searching for the molecular structure of membrane materials intended for the effective separation of helium–neon gas mixtures. It has been shown on a large number (84) of computer models of such glasses that there are molecular structures of silica in which various helium and neon diffusion mechanisms are simultaneously implemented: superdiffusion for helium and subdiffusion for neon. This makes it possible to significantly (by 3–5 orders of magnitude) increase the helium permeability of such glasses at room temperature and maintain a high selectivity for the separation of helium and neon (at the level of 104–105) at the same time

Separation of Nonmagnetic Fine Narrow Fractions of PM10 from Coal Fly Ash and Their Characteristics and Mineral Precursors

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.Nonmagnetic fine narrow fractions of particles with mean diameters of 2, 3, 6, and 10 μm were for the first time separated from fly ash produced by pulverized combustion of Ekibastuz coal using aerodynamic classification with subsequent magnetic separation. These fractions were characterized by the size distribution, bulk density, and chemical and phase compositions. The particle size distributions correspond to d50 values of 1.9, 2.3, 5.1, and 9.2 μm. As the fraction particle size increases, the bulk density was found to rise gradually from 0.90 to 1.07 g/cm3. The main components of the chemical composition were SiO2 (65–70 wt %) and Al2O3 (23–28 wt %). The phase composition was represented by the glass phase (64–69 wt %), mullite (17–21 wt %), and quartz (10–18 wt %). The main morphological particle types were microspheres with a nonporous smooth surface and microspheres with a porous shell. With an increase in the fraction particle size, the percentage of microspheres with a porous shell increases. The largest fraction contains particles with a network structure. Single-particle scanning electron microscopy–energy dispersive X-ray spectroscopy analysis of nonporous microspheres with a diameter of 1–2 μm, approximate in composition to the internal coal minerals, indicated that, depending on the content of SiO2, Al2O3, and FeO, they form several groups differing in mineral precursors. Thus, for microspheres of group 1 (SiO2 + Al2O3 > 95 wt %), the mineral precursors are NH4-illite and montmorillonite; group 2 (SiO2 + Al2O3 = 90–95, FeO ≤ 4 wt %)—minerals of the isomorphic montmorillonite-illite series, including phases with a low level of iron cation substitution; group 3 (SiO2 + Al2O3 = 90–95, 4 < FeO ≤ 6 wt %) and group 4 (SiO2 + Al2O3 < 90, 3 < FeO ≤ 9 wt %)—minerals of the illite-montmorillonite series, with a high level of iron cation substitution and with Fe3+ in interlayer sites

Ab initio parameterization and testing of He and Ne effective potentials in silica

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The article is devoted to the development and testing of He and Ne effective potentials designed for molecular simulation of He and Ne solubility and migration in silicate matrices. The H12Si12O30 cage structure, also known as a double-six ring (D6R), was used for ab initio parameterization. Ab initio calculations of the interaction energy between guest He and Ne atoms and the host were performed using the DLPNO‒CCSD(T) method, which enables correct calculations of the dispersion forces that play an important role in the interaction between dissolved noble gas atoms and the silicate matrix. The physical meaning of effective potentials as well as convergence and uniqueness of the obtained solutions are discussed. The solubility of He and Ne in silica glass over a wide temperature range (260–1500 K) has been calculated to test the effective potentials. The calculated values are in good agreement with the experimental data reported in the literature