Dependence of carbon dioxide sorption on the petrographic composition of bituminous coals from the Czech part of the Upper Silesian Basin, Czech Republic

The effect of the rank and of the maceral composition of bituminous coal on carbon dioxide sorption capacity was studied on the basis of samples from two coal mines (Darkov, ?SM) from the Czech part of the Upper Silesian Basin. The samples from the two mines cover a small but very significant section of coalification within the transition zone between high-volatile bituminous A coal and medium-volatile bituminous coal, where porosity and sorption properties pass through their minima. The coal porous system was characterized by the micropore volume evaluated using the sorption isotherm of carbon dioxide and the volumes of meso-, macro- and coarse pores were determined by high-pressure mercury porosimetry. The micropore fraction in the coal porous system ranged between 53% and 75%. It was particularly high in coals with high vitrinite content, namely collotelinite, and also in coals with high inertinite content. The carbon dioxide sorption capacity was determined from the carbon dioxide sorption isotherms measured using a gravimetric sorption analyzer at 298 K until a relative pressure of 0.015 p/p_s, and was interpreted by characteristic parameters of the Dubinin and Langmuir equations. It was found that the adsorbed amount of CO₂ in the ?SM coal increases with the content of vitrinite and collotelinite, whereas no increase or only a slight increase was observed for the Darkov coal. The tendency of adsorption capacity to depend on maceral composition, and also to some extent on coalification, observed for the ?SM coal, may be related to higher microporosity due to the coalification process or oxidative processes leading to the formation of pseudovitrinite.     

Structural,magnetic and dielectric properties of the novel magnetic spinel compounds ZnCoSnO4 and ZnCoTiO4

The transparent semiconductor Zn₂SnO₄ with cubic spinel structure and the isostructural Zn₂TiO₄ have been magnetically doped with Co²⁺. ZnCoSnO₄ and ZnCoTiO₄ exhibit ferrimagnetism below T_N ≈ 13?K and T_N ≈ 17?K. Ferrimagnetic moments are evident in M vs H curves below T_N by small hysteresis. Fits to strictly linear Curie-Weiss plots above T_N give μ_eff ≈ 4.86 μ_B and ≈4.91 μ_B for ZnCoSnO₄ and ZnCoTiO₄, above theoretical predictions. Impedance spectroscopy data from sintered ceramic can be fitted with a standard equivalent circuit model based on two RC elements for bulk and GB areas. The relative dielectric permittivity of the bulk is ≈20 and ≈30 for Zn₂SnO₄ and Zn₂TiO₄. The semiconducting ZnCoSnO₄ and ZnCoTiO₄ceramics exhibit bulk resistivity of ≈1 10⁶?Ω?cm and ≈1 10⁵?Ω?cm at 560?K (287?°C), and bulk activation energies of E_A ≈ 1.2?eV and 1.1?eV.     

An effect of hydration entropy on adsorption of various alkylammonium ions at the mercury/water interface

The adsorption of various alkylammonium cations was investigated by measurement of the interfacial tension. Tetraethanolammonium ions (HOC₂H₄)₄N⁺ showed weaker adsorbability than that expected from its ionic radius. The adsorbabilities (relative surface excess of cation FΓ₊ and charge of specifically adsorbed cation q¹₊) of the ethyl series (C₂H₅)_nH_4?nN⁺(n = 0 ≈ 4), and of the methyl series (CH₃)_nH_4?nN⁺n = 0 ≈ 3) were directly proportional to the hydration enthalpies of these cations - ΔH⁰_h, but the proportionalities were different between the methyl and the ethyl series. A linear relation was, however, found between FΓ₊ and the hydration entropies - ΔS⁰_h without regard to the kinds of cations. A similar relation was also found between q¹₊? - ΔS⁰_h. In conclusion, the adsorbabilities of these cations were governed by the hydration entropy, not by the hydration enthalpy.     

Bond formation in electrosorbates—I correlation between the electrosorption valency and pauling's electronegativity for aqueous solutions

the electrosorption valency, γ, which can be determined experimentally, is discussed in dependence on system-specific parameters. For correlation purposes, values at the potential of zero charge, ?N, and small coverages, θ ≈ 0·1, only are used, and mixed adsorption and phase formation must be excluded. Experimental data for 50 ionic systems in aqueous solutions are summarized. For homonucleus ions, a simple correlation between the ratio, γ/z, and the electronegativity difference, |χ_M?χS|, is established. This relationship can be described using a reasonable assumption on the geometric factor, g, and Pauling's formula for the charge transfer in diatomic molecules. It follows from this simple model as well as from the experimental data that covalent adsorption (γ/z ≈ 1, ? λ/z ≈ 1), takes place in the range, |Δχ| < 0·5, but ionic adsorption (γ/z < 0·2, λ ≈ 0) occurs at |Δχ| > 1·0. For 0·5 < |Δχ| < 1·0 the partial charge transfer (0 < ?λ/z < 1) with the formation of polarized bonds is important.Heteronucleus ions are discussed qualitatively. The influence of the geometric factor seems to be dominant for these ions.     

Correlation of gasification rates of various coals measured by a rapid heating method in a steam atmosphere at relatively low temperatures

Twenty-five kinds of coals (carbon content on dry ash-free basis, C[%], ranges from 65.0 to 92.8%) were pyrolysed and gasified simultaneously by use of a rapid heating method (heating rate ≈ 1600 K min⁻¹) in steam at temperatures between 750 and 850 °C to clarify the factors which control the gasification rates of various coals. The relationships were examined in detail between the reactivity of each coal, represented by the initial gasification rate − r_cm0, and various properties such as pore surface area of char, ultimate and proximate analyses of coal, reflectance of coal, contents of metals in char, and the amount of oxygen trapped by char. For gasification at 800 °C, the relation between − r_cm0 and the carbon content C[%] changed abruptly at C ≈ 75–80%. For higher rank coals (C > 75–80%), − r_cm0 was rather small and was well correlated by C[%]. On the other hand, the plot of − r_cm0versus C % scattered largely for the lower rank coals (C < 75–80%). For these coals, the rate of CO₂ formation was much greater than that of CO formation, and was almost proportional to − r_cm0. The CO₂ formation reaction is known to be catalysed by alkali or alkaline earth metals such as Na, K and Ca. Then the reactivities of lower rank coals were supposed to be controlled mainly by the catalytic effect of the minerals in the coal.     

Microstructure and dielectric properties of Ag-BaTiO3 composite ceramics

Di-phase composite ceramics based on BaTiO₃ with 5?vol% of Ag filler have been prepared by sintering the mixture of powders at temperatures above the silver melting point (1000?°C–1300?°C/2?h). As predicted by finite element calculations, the addition of metallic particles should produce a field concentration in some regions of the BaTiO₃ matrix and therefore, an enhanced dielectric response with respect to pure BaTiO₃. The role of oxygen vacancies on the dielectric relaxation mechanisms of Ag-BaTiO₃ composites has been investigated. The sintering temperature of 1200?°C provided optimized ceramics with excellent dielectric properties, i.e. with low losses (tanδ?<?3%) and room temperature permittivity measured at 50?kHz exceeding 6500 (and above 13,000 at the Curie temperature), as result of a good densification (94% relative density) and a synergy effect of the metallic particles inclusions and ceramic grain size in the range of ≈1?μm, where BaTiO₃ has a well-known maximum of its permittivity.     

Image analysis of the porous yttria-stabilized zirconia (YSZ) structure for a lanthanum ferrite-impregnated solid oxide fuel cell (SOFC) electrode

Image analysis and quantification were performed on porous scaffolds for building SOFC cathodes using the two types of YSZ powders. The two powders (U1 and U2) showed different particle size distribution and sinterability at 1300?°C. AC impedance on symmetrical cells was used to evaluate the performance of the electrode impregnated with 35-wt.% La_0.8Sr_0.2FeO₃. For example, at 700?°C, the electrode from U2 powder shows a polarization resistance (R_p) of 0.21?Ω?cm², and series resistance (R_s) of 8.5?Ω?cm² for an YSZ electrolyte of 2-mm thickness, lower than the electrode from U1 powder (0.25?Ω?cm² for R_p and 10?Ω?cm² for R_s) does. The quantitative study on image of the sintered scaffold indicates that U2 powder is better at producing architecture of high porosity or long triple phase boundary (TPB), which is attributed as the reason for the higher performance of the LSF-impregnated electrode.     

Substitution of Na,Fe and Si in tricalcium aluminate and the polymorphism of solid solutions

The roles of (Na + Fe³⁺) and (Na + Si) substituted in Ca₃Al₂O₆ have been determined by making approximately 200 experiments on 50 compositions. Pure oxide powders were heated at subliquidus temperatures until reaction was complete.High Na + Fe contents stabilize the pseudotetragonal phase to ambient temperatures. The extent of Si substitution at equilibrium is small; ca 0.5 to 2.0 wt %. While Na alone causes the unit cell to shrink from 15.2687 Å for pure Ca₃Al₂O₆ to ≈ 15.24 Å at 2.0 – 2.5% Na₂O, Na + Si substitution results in a further marked contraction to 15.19 Å at ≈ 2.5% Na₂O and ≈ 0.4% SiO₂.     

Dielectric,ferroelectric, and energy storage properties in dysprosium doped sodium bismuth titanate ceramics

In this work, Na_0.5(Bi_1-xDy_x)_0.5TiO₃ (0?≤?x?≤?15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy³⁺ into Sodium Bismuth Titanate (Na_0.5Bi_0.5TiO₃) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (??/?_(150?°C) ≤?±?15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2?J/cm³ obtained for 2%Dy composition at 200?°C. The obtained results are very promising for energy storage capacitors operating at high temperatures.     

Influence of strontium co-doping on the structural,optical, and electrical properties of erbium-doped ceria electrolyte for intermediate temperature solid oxide fuel cells

This study mainly aimed to elucidate the effects of strontium co-doping on the structural, optical, and electrical properties of erbium-doped ceria (Ce_0.8Er_0.2O_2-δ). Ce_1-x-yEr_xSr_yO_2-δ co-doped electrolytes were synthesized through sol–gel-assisted citric acid–nitrate combustion technique and sintered at 1500?°C for 6?h. X-ray diffraction results confirmed that the sintered electrolytes possessed a cubic fluorite crystal structure. However, a perovskite secondary phase (SrCeO₃) was observed in Ce_0.8Er_0.125Sr_0.075O_2-δ co-doped composition due to the low solubility limit of strontium (~5?mol%) in ceria. UV–Vis spectroscopy showed that the co-doping of strontium from 0?mol% to 7.5?mol% increased the direct band gap from 3.41?eV to 3.43?eV. The relative densities and the grain size were in the range of 96.02–97.68% and 1.5–3.28?µm, respectively, with increasing the strontium content from 0?mol% to 7.5?mol%. Electrochemical impedance spectroscopy showed that the total resistance of Ce_0.8Er_0.2O_2-δ increased as the strontium content increased. Singly doped Ce_0.8Er_0.2O_2-δ electrolyte exhibited the highest ionic conductivity of 18.22 mS/cm at 700?°C and the lowest activation energy of 0.55?eV within 600–800?°C among all other studied electrolytes.     

Structural changes in humic acids during the coalification process

Humic acids from four coals, varying in rank from peat to subbituminous coal, have been characterized by elemental analysis, acidic groups, molecular weight, electrophoresis and visible, FT-i.r. and CP/MAS ¹³C n.m.r. spectroscopy. The humic acids increase in carbon content, molecular weight, condensation degree and aromaticity (f_a) with increasing maturation of the parent coals, while the oxygen content decreases with a loss of oxygen functional groups. The presence of lignin-like polymers, poly-saccharides and peptidic materials in humic acids from peat was established using i.r. and ¹³C n.m.r. spectroscopy. The structural changes observed in humic acids are in agreement with the recognized coalification theory and tend to support the hypothesis of condensation of humic acids into insoluble humin of coal.     

Characterization of whole coals by 13C CP/MAS spectroscopy at high field

Solid-state 50-MHz ¹³C spectra essentially free of spinning sidebands have been constructed for three bituminous coals by the addition of echo spectra having phase-altered spinning sidebands (PASS). The echo spectra are produced by a modified version of the Dixon pulse sequence. Quantitative analysis of the aromatic carbon content (f_a) from PASS spectra for the three coals compares favourably with results obtained by other methods. Values of f_a are found in the range 0.69–0.73. Removal of the unwanted spinning bands allows absorptions for specific structural units present in the coals to be distinguished and assigned. Spectra show an upfield shoulder at 13–15 ppm, and moderately intense absorptions at 20–24 ppm and ≈30 ppm which are characteristic of several aliphatic structures in different steric environments. In addition to the main aromatic band at ≈120 ppm, absorptions for substituted aromatic carbons appear at ≈140 and ≈155 ppm. Less intense signals from several carbonyl functional groups (160–190 ppm) and oxygen- and nitrogen-substituted aliphatic groups (50–90 ppm) are also present.     

NMR determination of crystallinity for poly(?-l-lysine)

Crystallinity of poly(?-l-lysine) (?-PL) was discussed by analyzing the differences in the ¹H spin-spin relaxation times (T₂^H), the ¹³C spin-lattice relaxation times (T₁^C), and the ¹³C NMR signal shapes between the crystalline and the non-crystalline phases. The observed ¹H relaxation curve (free induction decay followed by solid-echo method) showed the sum of Gaussian and exponential decays. Similarly, the observed ¹³C relaxation curves obtained from the Torchia method were double-exponential. The ¹³C NMR spectrum of ?-PL was divided into the narrow and the broad lines by utilizing the intrinsic differences in the ¹H spin-lattice relaxation times in the rotating-frame between them, which are attributed to the crystalline and the non-crystalline phases, respectively. Even though the crystallinity is obtained from the identical NMR measurements, the estimated values are different with each other. The crystallinity estimated from the T₂^H differences was 75.8 ± 0.1% at 333 K and 60.7 ± 0.4% at 353 K. From the T₁^C differences, the value was estimated to be 62 ± 11%. Furthermore, the value estimated from the NMR signal separation was 54 ± 5%. In this study we have explained these discrepancies by the difference in susceptibility among the experiments for the inter-phase, which exists in-between the crystalline and the amorphous phases. Furthermore, the estimated crystallinity was ascertained by the X-ray diffraction experiment.     

Strain-induced crystallization of natural rubber as studied by high-resolution solid-state C NMR spectroscopy

A series of high-resolution solid-state ¹³C NMR experiments were performed on both unstretched and in situ stretched natural rubber samples. From the ¹³C CP/MAS spectra, it was found that natural rubber does form small crystals at room temperature though the degree of crystallinity is very small. Furthermore, from the ¹³C DD/MAS spectra, the crystalline signals were found to increase with the increase of draw ratio. ¹³C spin-lattice relaxation time (T₁) and ¹H spin-spin relaxation time (T₂) of in situ stretched natural rubber were measured for the first time, which provided further evidences for the conclusion that there exist crystals in both stretched and unstretched natural rubber samples. Quantitative ¹³C NMR measurements indicated that strain-induced crystallization occurs when the draw ratio reaches about 2.0 and the maximum crystallinity of our natural rubber samples can be as high as 19.3% upon stretching.     

Thermosensitive nanosized micelles from cholesteryl-modified hydroxypropyl cellulose as a novel carrier of hydrophobic drugs

The thermosensitive micelles based on the two series of cholesteryl-modified hydroxypropyl cellulose (series 1 and 2, respectively) were used as a promising drug carrier. The polymers 1a and 2a with side chain substitution degrees D _Chol?=?0.7 and 2.1?mol% were selected for micelle preparation, respectively. Polymeric micelles were prepared by the co-solvent evaporation method. The aqueous self-assembly of the polymers was studied using fluorescence analysis and transmission electron microscopy (TEM). The critical micelle concentrations (CMCs) values of the various D _Chol of polymers were evaluated in the range of ca. 0.13?C0.29?g/L which decreased with the increase of D _Chol in both series. Furthermore, the CMC values displayed a downtrend profile, with increasing the temperature. The polymer 1a with less D _Chol had lower CMC than that of polymer 2a. By using the naproxen as a hydrophobic model drug, the drug-loaded micelles were prepared. The TEM image of naproxen-loaded micelles of polymer 1a with 40?% drug-loading efficiency and 8?% loading capacity showed that micelles were regularly spherical in shape with a mean diameter of 70?nm. The unmodified HPC exhibited a lower critical solution temperature (LCST) of more than 41?°C in water, while polymeric micelles in aqueous solution presented an LCST of 38.7?°C. A drug release study was performed by dialysis method in phosphate-buffered solution at 25, 37 and 40?°C, respectively. The release kinetics of naproxen from the polymeric micelles revealed a thermosensitivity, since its release rate was higher at 40?°C than at 25?°C.     

Criterion for estimating the number of phases in phase-separated glass of the Na2O-K2O-B2O3-SiO2 system by dilatometric analysis

The data of dilatometry and electron microscopy of four series of xNa₂O-(8 ? x)K₂O-32B₂O₃-60SiO₂, xNa₂O-(8 ? x)K₂O-22B₂O₃-70SiO₂, xNa₂O-(6 ? x)K₂O-34B₂O₃-60SiO₂, and xNa₂O-xK₂O-(40 ? 2x)B₂O₃-60SiO₂ phase-separated glass heat-treated at 550°C for 144 h (for glass containing 70 mol % SiO₂) and 24 h (for glass containing 60 mol % SiO₂) for separation on phases are summarized. The comparison of dilatometric data and electron microscopy allow one to conclude that glass with a difference between the onset deformation temperature and a glass transition temperature of more than 100°C is phase-separated; and glass with a difference of less than 65°C is single-phase. Curves for the glass transition temperature as a function of the K₂O content reveal a mixed alkali effect, namely, minimums for glass containing 60% SiO₂, and maximums for glass containing 70% SiO₂.     

Numerical experiments on phonon properties of isotope and vacancy-type disordered graphene

We have studied phonon properties of graphene theoretically with different concentrations of ¹³C isotope and vacancy-type defects. The forced vibrational method, which is based on the mechanical resonance to extract the pure vibrational eigenmodes by numerical simulation, has been employed to compute the phonon density of states (PDOSs) and mode pattern of isotope-disordered graphene as well as a combined isotope and vacancy-type defective graphene structure. We observe a linear reduction of the E_2g mode frequencies with an increase in ¹³C concentration due to the reduced mass variation of the isotope mixture. We find a downshift of the E_2g mode of 65 cm^− 1, which is a very good agreement with the experimental results, and the phonon frequencies described by the simple harmonic oscillator model. The vacancy-type defects break down the phonon degeneracy at the Г point of the LO and TO modes, distort and shift down the phonon density of states significantly. The PDOS peaks for the combined isotope and vacancy-type defects show the remarkable increase in the low-frequency region induced by their defect formations. Due to phonon scattering by ¹³C isotope or vacancies, some graphene phonon wave functions become localized in the real space. Our numerical experiments reveal that the lattice vibrations in the defective graphene show the remarkably different properties such as spatial localization of lattice vibrations due to their random structures from those in the perfect graphene. The calculated typical mode patterns for in-plane K point optical phonon modes indicate that the features of strongly localized state depend on the defect density, and the phonon is localized strongly within a region of several nanometers in the random percolation network structures. In particular, for in-plane K point optical phonon modes, a typical localization length is on the order of ≈ 7 nm for isotope impurities, ≈ 5 nm for vacancy-type defects and ≈ 6 nm for mixed-type defects at high defect concentrations of 30%. Our findings can be useful for the interpretation of experiments on infrared, Raman, and neutron-diffraction spectra of defective graphene, as well as in the study of a wide variety of other physical properties such as thermal conductivity, specific heat capacity, and electron–phonon interaction.     

Effects of composition and reflowing on the corrosion behavior of Sn-Zn deposits in brine media

Tin-zinc deposits with the Zn content varying from 13 to 0 weight percents (wt%) (close to the eutectic point of the Sn-Zn alloy, Sn-9Zn) were electroplated onto iron-coated copper substrates from a near-neutral (pH 5.0), non-cyanide bath. The corrosion parameters, including open-circuit potential-time curves (E_OCP-t), corrosion potentials (E_CORR), and corrosion currents (i_CORR), of this series of materials before and after reflowing in N₂ at 250 °C for 10 min were determined and systemically compared in a brine medium containing 3 wt% NaCl. For the as-prepared deposits, the Sn-5Zn deposit showed an activity very close to but more active than that of Fe in this brine medium. This deposit also exhibited the highest corrosion resistance in the study of electrochemical impedance spectroscopy (EIS). For the reflowed deposits, the anticorrosive ability of Sn-Zn deposits with the Zn content <9 wt% became relatively poorer than that of their corresponding as-prepared counterparts while the Sn-9Zn and Sn-5Zn deposits with reflowing showed the best anticorrosive properties in the 3 wt% NaCl solution. The crystalline information and the surface morphologies of the deposits before and after the reflowing treatment were compared by means of the X-ray diffraction (XRD) and scanning electron microscopic (SEM) analyses.     

Magnetocaloric properties of Gd2MoO6 prepared by a simple and fast method

The experimental study of the specific heat, magnetic susceptibility, and magnetization of Gd₂MoO₆ powder sample was performed in the temperature range between 0.4 K and 300 K in the magnetic fields up to 9 T. Powder sample was prepared via nonconventional mechanochemical/thermal process from powdered oxide precursors. Magnetic ion Gd³⁺ with spin S = 7/2 is responsible for the magnetic properties. The specific heat study in zero magnetic field revealed two anomalies; a phase transition to the ordered state at T_N1 ≈ 0.98 K and a smaller maximum at T_N2 ≈ 0.6 K. Relatively high magnetic density 6.85 g/cm³ of Gd₂MoO₆ predetermines this compound as potential magnetocaloric material with a high cooling performance at cryogenic temperatures. A large conventional magnetocaloric effect was found around 3 K with magnetic entropy change ?ΔS_max ≈ 44 J/(kg K) (300 mJ/(Kcm³)) for magnetic field change from 9 T down to zero with a refrigerant capacity of 464 J/kg. Maximal temperature change -ΔT_ad ≈ 23.8 K was found for initial temperature T_init ≈ 29.9 K for the mentioned change of magnetic field. Alternating susceptibility measurements revealed the presence of two relaxation channels in Gd₂MoO₆ existing in two different time scales ≈ 10^-3 s and ≈ 1 s.