Synthesis and characterization of LiCo3/5Mn2/5VO4 ceramics

Dielectric and a.c. conductivity properties of LiCo_3/5Mn_2/5VO₄ ceramic are investigated. This compound is prepared by solution-based chemical method and the formation is checked by X-ray diffraction (XRD) study. XRD analysis at room temperature shows an orthorhombic phase. Frequency dependence of dielectric constant (?_r) at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ?_r at different frequencies indicates the transition temperature (T_c) = 235 °C, 245 °C, 257 °C and 265 °C with (?_r)_max. ～3689, 1373, 750 and 386 for 10, 50, 100 and 200 kHz respectively. A.c. conductivity analysis indicates that electrical conduction in the material is a thermally activated process.     

Synthesis and properties of the compound: LiNi3/5Cu2/5VO4

The LiNi_3/5Cu_2/5VO₄ is synthesized by solution-based chemical method and its formation has been checked by X-ray diffraction (XRD) study. XRD study shows a tetragonal unit cell structure with lattice parameters of a = 11.6475 (18) Å, c = 2.4855 (18) Å and c/a = 0.2134 Å. Electrical properties are verified using complex impedance spectroscopy (CIS) technique. Complex impedance analysis reveals following points: (i) the bulk contribution to electrical properties up to 200 °C, (ii) the bulk and grain boundary contribution at T ≥ 225 °C, (iii) the presence of temperature dependent electrical relaxation phenomena in the material. D.c. conductivity study indicates that electrical conduction in the material is a thermally activated process.     

Salt effects on the partition coefficients of phenol in two-phase mixtures of water and carbon dioxide at pressures from (8 to 30) MPa at a temperature of 313 K

Partition coefficients K_c of phenol between an aqueous solution containing different salts and a compressed CO₂ phase have been determined at T=313 K. For NaCl and (CH₃)₄NBr a pressure range from 8 MPa to around 30 MPa was investigated, for KCl and NaBr measurements were performed at a pressure of 22 MPa. The salt concentration has been varied between (0.25 and 3.0) mol·dm⁻³. With increasing pressure a rise in K_c is observed which typically is also found in systems free of salt. Salting-out was observed for the alkali salts, salting-in has been found for the ammonium salt, both effects increased with increasing salt concentration. From the concentration dependence of the K_c values Setschenow coefficients k_S have been derived. At p>10 MPa values are obtained as found in two phase mixtures of water with other organic solvents at ambient pressure. This conclusion was confirmed with both literature and own experimental data in the case of salting-out by NaCl as well as for the salting-in by (CH₃)₄NBr from measurements with phenol in (water + cyclohexane) at T=313 K.     

Kinetics of hematite chlorination with Cl2 and Cl2 + O2: Part I. Chlorination with Cl2

Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl₂ have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (E_a) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl₂ was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms.     

Critical parameters for propane determined by the image analysis

The (p, ρ, T) measurements and visual observations of the meniscus for propane were carried out carefully in the critical region over the range of temperatures: ?60 mK ? (T ? T_c) ?  40 mK and of densities: ?4 kg · m^?3 ? (ρ ? ρ_c) ? 6 kg · m^?3 by a metal-bellows volumometer with an optical cell. Vapour pressures were also measured at T = (320.000, 343.132, 369.000, and 369.625) K. The critical point of T_c, ρ_c, and p_c was determined by the image analysis of the critical opalescence. Comparisons of the critical parameters with values given in the literature are presented.     

Critical properties of some aliphatic symmetrical ethers

The critical temperatures T_c and the critical pressures p_c of dihexyl, dioctyl, and didecyl ethers have been measured. According to the measurements, the coordinates of the critical points are T_c = (665 ± 7) K, p_c = (1.44 ± 0.04) MPa for dihexyl ether, T_c = (723 ± 7) K, p_c = (1.19 ± 0.04) MPa for dioctyl ether, and T_c = (768 ± 8) K, p_c = (1.03 ± 0.03) MPa for didecyl ether. All the ethers studied degrade chemically at near-critical temperatures. A pulse-heating method applicable to measuring the critical properties of thermally unstable compounds has been used. The times from the beginning of a heating pulse to the moment of reaching the critical temperature were from 0.06 to 0.46 ms. The short residence times provide little decomposition of the substances in the course of the experiments. The critical properties of the ethers investigated in this work have been discussed together with those of methyl to butyl ethers. The experimental critical constants of the ethers have been compared with those estimated by the group-contribution methods of Wilson and Jasperson and Marrero and Gani. The Wilson/Jasperson method provides a better estimation of the critical temperatures and pressures of simple aliphatic ethers in comparison with the Marrero/Gani method if reliable normal boiling temperatures are used in the method of Wilson and Jasperson.     

Ni–Al hydrotalcite-like material as the catalyst precursors for the dry reforming of methane at low temperature

Nickel–aluminium and magnesium–aluminium hydrotalcites were prepared by co-precipitation and subsequently submitted to calcination. The mixed oxides obtained from the thermal decomposition of the synthesized materials were characterized by XRD, H₂-TPR, N₂ sorption and elemental analysis and subsequently tested in the reaction of methane dry reforming (DRM) in the presence of excess of methane (CH₄/CO₂/Ar = 2/1/7). DMR in the presence of the nickel-containing hydrotalcite-derived material showed CH₄ and CO₂ conversions of ca. 50% at 550 °C. The high values of the H₂/CO molar ratio indicate that at 550 °C methane decomposition was strongly influencing the DRM process. The sample reduced at 900 °C showed better catalytic performance than the sample activated at 550 °C. The catalytic performance in isothermal conditions from 550 °C to 750 °C was also determined.     

Salt effect on (liquid + liquid) equilibrium of (water + tert-butanol + 1-butanol) system: Experimental data and correlation

(Liquid + liquid) equilibrium data for the quaternary systems (water + tert-butanol + 1-butanol + KBr) and (water + tert-butanol + 1-butanol + MgCl₂) were experimentally determined at T = 293.15 K and T = 313.15 K. For mixtures with KBr, the overall salt concentrations were 5 and 10 mass percent; for mixtures with MgCl₂, the overall salt concentrations were 2 and 5 mass percent. The experimental results were used to estimate molecular interaction parameters for the NRTL activity coefficient model, using the Simplex minimization method and a concentration-based objective function. The correlation results are extremely satisfactory, with deviations in phase compositions below 1.7%.     

Novel BaCo0.7Fe0.3−yNbyO3−δ (y = 0–0.12) as a cathode for intermediate temperature solid oxide fuel cell

The BaCo_0.7Fe_0.3?yNb_yO_3?δ oxides (BCFNy, y = 0.00–0.12) were synthesized by the conventional solid state reaction process and investigated as a novel cathode for intermediate temperature solid oxide fuel cells(IT-SOFCs). Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y ? 0.04. The unit cell volumes increased with y, reached a maximum at y = 0.10, and then decreased. The niobium doping concentration also had a significant effect on the electrochemical performance of BCFNy materials. Among the various BCFNy oxides tested, BCFN0.10 possessed the smallest interfacial polarization resistance (R_p). The R_p was as low as 0.9406, 0.1300, 0.0211, and 0.0082 Ω cm² at 500, 600, 700, and 800 °C, respectively. With a 220 μm-thick Sm_0.2Ce_0.1O_1.9 (SDC) as electrolyte and BCFN0.10 as the cathode, a fuel cell provides maximum power densities of 202, 350, 569, 820, and 1006 mW cm^?2 at 600, 650, 700, 750, and 800 °C, respectively. The encouraging results suggested that BCFN0.10 was a very promising cathode material for IT-SOFCs.     

Enhancement of electrochemical performance and thermal compatibility of GdBaCo2/3Fe2/3Cu2/3O5+δ cathode on Ce1.9Gd0.1O1.95 electrolyte for IT-SOFCs

Transition-metal doped double-perovskite structure oxides GdBaCo_2/3Fe_2/3Ni_2/3O_5+δ (FN-GBCO), GdBaCo_2/3Fe_2/3Cu_2/3O_5+δ (FC-GBCO), GdBaCoCuO_5+δ (C-GBCO) and pristine GdBaCo₂O_5+δ (GBCO) were synthesized via a citrate combustion method. The thermal-expansion coefficient (TEC) and electrochemical performance of the oxides were investigated as potential cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The TEC exhibited by the FC-GBCO cathode up to 900 °C is 14.6 × 10^?6 °C^?1, which is lower than the value of GBCO (19.9 × 10^?6 °C^?1). Area specific resistances (ASR) of 0.165 Ω cm² at 700 °C and 0.048 Ω cm² at 750 °C were achieved for the FC-GBCO cathode on a Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte. An electrolyte supported (300 μm thick) single-cell configuration of FC-GBCO/CGO/Ni-CGO attained a maximum power density of 435 mW cm^?2 at 700 °C. The unique composition of GBCO co-doped with Fe and Cu ions in the Co sites exhibited reduced TEC and enhancement of electrochemical performance and good chemical compatibility with CGO, and this composition is proving to be a potential cathode for IT-SOFCs.     

Coexistence curves of ionic liquid in oil microemulsions of {[bmim][BF4] + T-X100 + cyclohexane} with various molar ratio of [bmim][BF4] to T-X100 in the critical region

The coexistence curves (T, n), (T, Φ), and (T, Ψ) (n, Φ, and Ψ are the refractive index, volume fraction, and effective volume fraction, respectively) for the ionic liquid microemulsion systems of {polyoxyethylene tert-octylphenyl ether (T-X100) + 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]) + cyclohexane} with various molar ratio (ω) of [bmim][BF₄] to T-X100 have been determined by measuring refractive indices at a constant pressure in the critical region. The critical temperatures (T_c) and critical volume fraction (Φ_c) were obtained for the ionic liquid microemulsions. The critical exponents were deduced precisely from the coexistence curves within about 1 K below T_c and the values were consistent with the 3D Ising value.     

Crystal growth and magnetic properties of the new iridates Ln1−xNa1+xIrO4 (Ln = Gd–Er,Y; x = 0.04–0.25)

We report the single crystal structures and magnetic properties of a series of lanthanide-containing iridates, Ln_1−xNa_1+xIrO₄ (Ln = Gd–Er, Y; x = 0.04–0.26) grown from a mixed sodium and cesium hydroxide flux. The compounds crystallize in the hexagonal space group P-62m (#189) with lattice parameters ranging from a = 9.3872(2)–9.4596(3) Å and c = 3.1512(1)–3.2030(2) Å and are structurally related to other iridium oxides. The oxidation state of iridium ranges from +4.08 (Gd) to +4.50 (Er). Magnetic susceptibility measurements reveal the existence of antiferromagnetic correlations below 15 K.     

Structure and properties of Gd4Pd10In21

Gd₄Pd₁₀In₂₁ was synthesized from the elements in a glassy carbon crucible in an induction furnace and investigated by X-ray powder and single crystal diffraction: C2/m, a = 2293.3(2), b = 444.49(3), c = 1934.3(1) pm, β = 133.00(1)°, wR2 = 0.0496, 1564 F² values, and 106 variable parameters. The five crystallographically independent palladium atoms have all a trigonal prismatic coordination. Together, the palladium and indium atoms build up a three-dimensional [Pd₁₀In₂₁] network in which the gadolinium atoms fill distorted pentagonal channels. Magnetic susceptibility measurements show that Gd₄Pd₁₀In₂₁ orders antiferromagnetically at T_N = 14.2(1) K. Two further magnetic transitions were found at temperatures 11.8 and 6.4 K, respectively. Below T_irr = 10 K, strong irreversibility between ZFC and FC magnetic susceptibilities are observed. The zero-field specific heat measurements show a clear peak around the magnetic transition temperatures T_N. Measured quadrupole interaction constants by ¹⁵⁵Gd Mössbauer spectroscopy give estimations for the V_zz component of the electric field gradient tensor at both gadolinium sites in Gd₄Pd₁₀In₂₁.     

Vapour pressures of n-hexane determined by comparative ebulliometry

The vapour pressures of n-hexane have been measured using comparative ebulliometry with water as the reference fluid. The measurements cover the temperature and pressure range (315.7 K, 41.1 kPa) to (504.0 K, 2876.8 kPa) and join smoothly with results selected from the literature to provide consistent results down to (289.7 K, 13.8 kPa). The combined data set have been described by a Wagner style equation with a fractional standard deviation of 4.2 · 10⁻⁵ in the vapour pressure. The critical pressure p_c was treated as an adjustable parameter and the value of p_c = 3027 kPa was calculated from the smoothing equation using a selected critical temperature of T_c = 507.49 K. The calculated normal boiling temperature is T_b = 341.866 K and an extrapolation to the triple-point temperature T_tp = 177.87 K predicts a triple-point pressure of p_tp = 1.23 Pa.     

Synthesis,crystal structure and luminescent properties of pyrovanadates A2CaV2O7 (A = Rb,Cs)

The novel vanadium oxides Rb₂CaV₂O₇ and Cs₂CaV₂O₇ have been prepared by solid-state reaction and their crystal structures determined and refined using X-ray, neutron powder and electron diffraction data. Rb₂CaV₂O₇ and Cs₂CaV₂O₇ are isostructural, crystallizing in space group P2₁/n with unit cell parameters: a = 13.8780(1), b = 5.96394(5), c = 10.3376(1) Å, β = 104.960(1)° and a = 14.0713(2), b = 6.0934(1), c = 10.5944(1) Å, β = 104.608(1)°, respectively. Their crystal structures can be described as a framework of CaO₆ octahedra and V₂O₇ pyrogroups with alkaline metals found in the tunnels formed. Photoluminescence (PL) and PL excitation spectra of the considered pyrovanadates have been studied in the vacuum ultraviolet (VUV) to visible light (Vis) range as well as their pulse cathode luminescence (PCL) spectra and the kinetic parameters of PCL. In the PL and the PCL spectra of both pyrovanadates recorded at T = 300 K a broad band with maxima at 2.2, 2.4 eV and two shoulders (bands) at 2.0 and 2.58 eV have been observed. At T = 10 K the band at 2.0 eV becomes the main band in the spectra. Two types of luminescence centers for each pyrovanadate, with very similar excitation bands at 3.75, 4.84, 6.2, 7.3 and 9.1 eV, have been found. The nature of the luminescence centers connected with the bands at 2.0, 2.2, 2.4 and 2.58 eV is discussed.     

Interaction of biological buffers with electrolytes: Densities of aqueous solutions of two substituted aminosulfonic acids and ionic salts from T = (298.15 to 328.15) K

Biological buffers are of utmost importance for research in biological and clinical chemistry and in oceanography, but they may not be inert enough, thus interfering with the system under study. The N-[Tris(hydroxymethyl)methyl]-3-aminopropanesulfonic acid (TAPS) and N-[Tris(hydroxymethyl)methyl]-3-amino-2-hydroxypropanesulfonic acid (TAPSO) are useful zwitterionic buffers for pH control as standard buffers in the physiological region of pH 7.7 to 9.1 for TAPS and 7.0 to 8.2 for TAPSO, respectively. In this work, interaction between these zwitterionic compounds and electrolytes of potassium acetate (KAc), potassium bromide (KBr), potassium chloride (KCl), and sodium chloride (NaCl) were investigated through measuring the densities of these buffers in aqueous and in aqueous electrolyte solutions by a high precision vibrating tube digital densitometer from T = (298.15 to 328.15) K under atmospheric pressure. In this series of measurements, the aqueous samples were prepared with various concentrations of the zwitterionic buffers, up to saturated conditions, and over salt concentrations from (1 to 4) mol · dm^?3. The measured densities served to evaluate the cubic expansion coefficients, α(m, T) and the apparent molar volumes, V_?(m, T). An empirical equation was used to correlate quantitatively the experimental densities over the entire concentration ranges.     

Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments – A pyrolysis–GC/MS study

Gorse species (Ulex sp.) are ubiquitous in the shrublands of NW Spain and have the potential to become key players in an integral biofuel/biochar program in NW Spain. Here we present molecular characterization (using pyrolysis–GC/MS) of a biochar “thermosequence” obtained by laboratory heating of Ulex europaeus wood in a muffle furnace between 200 and 600 °C (T_CHAR). Low temperature chars (T_CHAR ≤ 350 °C) produced significant amounts of pyrolysis products of which the precursor biopolymer could be recognized, while high-temperature chars (T_CHAR ≥ 400 °C) produced mainly phenols and monocyclic and polycyclic aromatic hydrocarbons, which are not specific for any biopolymer. Carbohydrate could hardly be recognized at T_CHAR ≥ 350 °C. The thermal rearrangement of polyphenols, mainly lignin, was reflected in more detail (1) C₃-side chain shortening and probably depolymerization (T_CHAR 200–350 °C), (2) demethoxylation of syringyl and probably also some guaiacyl lignin (T_CHAR 300–400 °C), (3) elimination of virtually all remaining methoxyl groups (T_CHAR 350–400 °C), through dehydroxylation and demethoxylation, (4) almost complete dehydroxylation of lignin and other biopolymers (T_CHAR 400–500 °C), (5) progressive condensation into polyaromatic structures (T_CHAR 300–500 °C) and (6) partial elimination of alkyl bridges between (poly)aromatic moieties (T_CHAR 450–500 °C). These results were supported by Fourier transform infrared spectroscopy (FTIR) of the same samples. We conclude that pyrolysis–GC/MS can be used as a rapid molecular screening method of gorse-derived biochar. Molecular properties elucidation is an essential part of predicting the stability and agronomical behavior of gorse-derived biochar after future implementation in soils.     

Measurement and correlation of the ( p, ρ, T) relation of sulphur hexafluoride (SF 6). II. Saturated-liquid and saturated-vapour densities and vapour pressures along the entire coexistence curve

Comprehensive and accurate measurements of the saturated-liquid and saturated-vapour densities together with the vapour pressure of pure sulphur hexafluoride were carried out from the temperature T =  224 K (triple-point temperature T_t =  223.555 K) to 0.033 K below the critical temperature ( T_c =  318.723 K). Typical values of the total uncertainties of the measurements are: ⩽ ± 0.01 percent for the vapour pressures,⩽ ± 0.015 percent for the saturated-liquid densities, and⩽ ± 0.016 percent for the saturated-vapour densities. The values for the critical density and the critical pressure ( ρ_c =  742.26 kg · m ^− 3, p_c =  3.7550 MPa) and the isothermal compressibilities in the critical region close to the phase boundary have also been determined from these measurements. Comparisons with experimental results of previous workers are presented. Using the new values of this work, new correlation equations for the vapour pressure, the saturated-liquid density, and the saturated-vapour density have been established.