Results 1 - 10 of 2325
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[en] Thermal and kinetics behaviors of the low-rank coals from different annual periods (Kolubara (2015)/(2018) and TENT A (2015)/(2018)) during combustion process in air atmosphere, using simultaneous TGA-DTG-DTA-MS measurements were investigated. The FTIR spectroscopy was used to gain additional information on coals structures. Kolubara and TENT A coals from (2015)/(2018) annual periods show differences in reactivity, where the reason for this demeanor lies in differences in decomposition kinetics of these coals. The conclusions made on the basis of model-based analysis clearly indicate that differences in combustion reaction pathways (especially in transitions from primary to secondary combustion stages) arise from continual changes in physical structure of the coals. It was found that the mineral matter significantly influences on the reactivity of coal during combustion, where this is particularly pronounced for TENT A coal particles. © 2019 Elsevier B.V.
[en] Cold-cap reactions are multiple overlapping reactions that occur in the waste-glass melter during the vitrification process when the melter feed is being converted to molten glass. In this study, we used differential scanning calorimetry (DSC) to investigate cold-cap reactions in a high-alumina high-level waste melter feed. To separate the reaction heat from both sensible heat and experimental instability, we employed the run/rerun method, which enabled us to define the degree of conversion based on the reaction heat and to estimate the heat capacity of the reacting feed. Assuming that the reactions are nearly independent and can be approximated by the nth order kinetics, we obtained the kinetic parameters using the Kissinger method combined with least squares analysis. The resulting mathematical simulation of the cold-cap reactions provides a key element for the development of an advanced cold-cap model
[en] Dielectric relaxation spectra of three representatives of the class of hydroxyethylammonium carboxylate protic ionic liquids (PILs), namely 2-hydroxyethylammonium formate [2-HEAF], 2-hydroxyethylammonium propionate [2-HEAP] and 2-hydroxyethylammonium butanoate [2-HEAB], were recorded over a wide frequency range (0.05 ≤ ν(GHz) ≤ 50) at 25 °C. The thermal decomposition kinetics of these ionic liquids derived from organic acids was studied by thermogravimetry (TG) using nonisothermal experiments. For the purpose of kinetic analysis, the thermal behavior of the samples was studied in the temperature interval from ambient temperature up to 420 °C at different heating rates (5, 10, 15 and 20 °C min−1). Isoconversional kinetic analysis was performed using Friedman's (FR) differential method and the integral Kissinger–Akahira–Sunose (KAS) method. The dependence of the apparent activation energy (E) on the conversion fraction (α) for the investigated decomposition processes was analyzed. It was found that the molecular structure of the involved anion significantly influences the dielectric properties of the studied PILs. It was also established that a change in the anion structure drastically affects the shape of the thermo-analytical curves. Among the considered PILs [2-HEAF] has the highest thermal stability. However, considering kinetic properties, certain deviations were observed and referred to hydrogen bonding development and steric impediment effects. © 2018 Elsevier B.V.
[en] The oxidation of UO2 was investigated by TG, DSC and X-ray diffraction. UO2 samples were prepared by the reduction of UO3 at Psub(H2)+Psub(N2)=100+50 mm Hg and 50C min-1 up to 8000C. In order to obtain six UO2 samples with different preparative histories, UNH, UAH and ADU were used as starting materials and their thermal decomposition was carried out at 450-6250C for 0-9 h at an air flow rate of 100 ml min-1. α-UO3, γ-UO3, UO3.2 H2O, and their mixtures were obtained. The reduction of UO3 gave β-UOsub(2+x) with different x values from 0.030 to 0.055. The oxidation carried out at Psub(O2)=150 mm Hg was found to consist of oxygen uptake at room temperature, UO2→U3O7 (Step I) and U3O7→U3O8 (Step II). TG and DSC curves of the oxidation showed two plateaus and two exothermic peaks corresponding to Steps I and II. In the case of two of the samples, the DSC peak of Step II split into two substeps, which were assumed to be due to the different reactivities of U3O7 formed from α-UO3 and that from other types of UO3. The increase in O/U ratio due to the oxygen uptake at room temperature changed from 0.010 to 0.042 except for a sample prepared from ADU which showed an extraordinarily large value of 0.445. TG curves showed an increase in O/U from room temperature to near 2500C for Step I and the plateau at 250-3500C where O/U was about 2.42, and showed a sharp increase in O/U above 350C for Step II and the plateau above 4000C where O/U was 2.72-2.75. It is thought that the prepared UO2 had a defective structure with a large interstitial volume to accomodate the excess oxygen. (Auth.)
[en] Interpretation of all thermal effects which occur on heating zirconium phosphates is possible when simultaneous DTA, ETA, and TG are applied. A rapid transition of poorly crystalline zirconium phosphate into normal cubic modification at high temperatures is clearly shown by DTA when amorphous zirconium phosphate is used. In contrast, because of the more rigid crystal lattice, this reaction is only visible in ETA when crystalline preparations are heated. Especially after exchange of protons by cations, some amorphous zirconium phosphates exhibit a second exotherm in DTA. This reaction is believed to depend on growing up of partially crystalline structures
[en] Several hydrated lanthanide salts of heptafluorobutyric acid have been prepared and characterized. Hydration studies have shown the compounds to exist in various hydration states across the series. Powder X-ray diffraction studies support the existence of variable hydration states in that three distinct crystalline forms exist. Infrared analysis revealed two types of structures to be present. Upon dehydration of the lighter rare earth hydrates to intermediate dihydrates, all of the compounds showed similar structures. Decomposition was found to be exothermic. The volatile decomposition products were identified by infrared analysis and found to consist of CO, CO2, CF3CF2COF and CF3CF2CF2COF. The amounts of each gas were found to be dependent on the decomposition temperature. The non-volatile decomposition products were identified by powder X-ray diffraction and found to consist of LnF3, LnOF and Ln2O3
[en] The specific heat, entropy, enthalpy, and Gibbs free energy of cyclopropene-d0, cyclopropene-1-d1, cyclopropene-3-d1, cyclopropene-1,2-d2, cyclopropene-3,3-d2, cyclopropene-1,3,3-d3, and cyclopropene-d4 have been calculated for the temperature range 100-1500 K using the rigid-rotor and harmonic oscillator model. The standard enthalpy and Gibbs free energy of formation of cyclopropene-d0 have also been evaluated for the same temperature range using the experimental standard enthalpy of formation at 298.15 K. (Auth.)
[en] Lanthanide trifluoromethyl sulfonates, M(SO3CF3)3.9H2O, have been prepared and characterized by analysis, optical properties and thermal behaviour. Dehydration proceeded in two steps for the lanthanum, cerium, praseodymium and neodymium salts and in three steps for other members of the lanthanide series. Thermal decomposition to lanthanide fluoride, carbonyl fluoride and sulfur dioxide occurred at temperatures greater than 4000C. This decomposition has been shown to be a two step process. (Auth.)
[en] Vaporization behavior of Na4FeO3(s) was thermodynamically studied from 590 to 717K by means of high temperature mass spectrometry. It was found that Na4FeO3(s) decomposed into Na3FeO3(s) and released sodium vapor. The temperature dependence of partial vapor pressure of sodium over Na4FeO3(s) was measured so that the Gibbs energy of formation of Na3FeO3(s) was evaluated as ΔfG(Na3FeO3)=-1168629+338.34xT