Effect of glycine,dl-alanine and dl-2-aminobutyric acid on the temperature of maximum density of water

The effect of glycine, dl-alanine and dl-2-aminobutyric acid on the temperature of maximum density of water was determined from density measurements using a magnetic float densimeter.Densities of aqueous solutions were measured within the temperature range from T = (275.65 to 278.65) K at intervals of T = 0.50 K over the concentration range between (0.0300 and 0.1000) mol · kg⁻¹. A linear relationship between density and concentration was obtained for all the systems in the temperature range considered.The temperature of maximum density was determined from the experimental results. The effect of the three amino acids is to decrease the temperature of maximum density of water and the decrease is proportional to molality according to Despretz equation. The effect of the amino acids on the temperature of maximum density decreases as the number of methylene groups of the alkyl chain becomes larger. The results are discussed in terms of (solute + water) interactions and the effect of amino acids on water structure.     

Electrically rechargeable zinc-oxygen flow battery with high power density

The development of a powerful, cyclically stable and electrically rechargeable zinc-oxygen battery with a three-electrode configuration is reported. A copper foam was used as stable substrate for zinc deposition in flowing potassium hydroxide electrolyte, while oxygen reduction and evolution were accomplished by a commercial silver electrode and a nickel foam, respectively. The cell could be charged and discharged with up to 600 mA cm^− 2, delivered a peak power density of 270 mW cm^− 2, and performed for more than 600 cycles, although short circuits by dendrite formation could not yet be completely avoided. At a current density of 50 mA cm^− 2 and a temperature of 30 °C, a promising energy efficiency of 54% was achieved.     

Hydrogen production by catalytic steam reforming of acetic acid,a model compound of biomass pyrolysis liquids

An environmentally friendly and cost-competitive way of producing hydrogen is the catalytic steam reforming of biomass pyrolysis liquids, known as bio-oil, which can be separated into two fractions: ligninic and aqueous. Acetic acid has been identified as one of the major organic acids present in the latter, and catalytic steam reforming has been studied for this model compound. Three different Ni coprecipitated catalysts have been prepared with varying nickel content (23, 28 and 33% expressed as a Ni/(Ni + Al) relative at.% of nickel). Several parameters have been analysed using a microscale fixed-bed facility: the effect of the catalyst reduction time, the reaction temperature, the catalyst weight/acetic acid flow rate (W/m_HAc) ratio, and the effect of the nickel content. The catalyst with 33% Ni content at 650 °C showed no significant enhancement of the hydrogen yield after 2 h of reduction compared to 1 h under the same experimental conditions. Its performance was poorer when reduced for just 0.5 h. For W/m_HAc ratios greater than 2.29 g catalyst min/g acetic acid (650 °C, 33% Ni content) no improvement was observed, whereas for values lower than 2.18 g catalyst min/g acetic acid a decrease in product gas yields occurred rapidly. The temperatures studied were 550, 650 and 750 °C. No decrease in product gas yields was observed at 750 °C under the established experimental conditions. Below this temperature, the aforementioned decrease became more important with decreasing temperatures. The catalyst with 28% Ni content performed better than the other two.     

Chemical modification of cellulose extracted from sugarcane bagasse: Preparation of hydroxyethyl cellulose

Cellulose was extracted from sugarcane bagasse by alkaline extraction with sodium hydroxide followed by delignification/bleaching using sodium chlorite/hexamethylenetetramine system. Factors affecting extraction process, including sodium hydroxide concentration, hexamethylenetetramine concentration and temperature were studied and optimum conditions for alkaline extraction were found to be boiling finely ground bagasse under reflux in 1 N sodium hydroxide solution and then carrying out the delignification/bleaching treatment at 95 °C using 5 g/l sodium chlorite together with 0.02 g/l hexamethylenetetramine. The extracted cellulose was used in the preparation of hydroxyethyl cellulose through reaction with ethylene oxide in alkaline medium. Factors affecting the hydroxyethylation reaction, like sodium hydroxide concentration during the alkali formation step, ethylene oxide concentration, reaction temperature and reaction duration were studied. Optimum conditions for hydroxyethylation reaction were using 20% NaOH solution and 200% ethylene oxide (based on weight of cellulose), carrying out the reaction at 100 °C for 60 min.     

The Effect of Chitin Alkaline Deacetylation at Different Condition on Particle Properties

The abundant biopolymer chitin, found mainly in crustaceous exoskeleton, such as crab, shrimp and lobster, can be deacetylated to yield chitosan. This slightly different biopolymer is more reactive than chitin, being more effective for many applications in fields as environmental remediation, biomedical sciences, catalysis and so on. The main process for chitin deacetylation used sodium hydroxide solutions at high temperatures for long times to obtain chitosan with high deacetylation degree (DD). The present study has evaluated the effect from room temperature (RT), 363 and 393 K, hydroxide concentration (2.0 or 10.0 mol dm³) and time (3 and 24 h) on shrimp chitin deacetylation. Similar amounts of chitin and sodium hydroxide solutions were stirred jointly and the resultant solids were filtered and washed until pH 7, than dried at environmental conditions. The obtained samples were characterized by several techniques, such as elemental analysis, X-rays diffraction (XRD), laser scattering and absorption spectroscopy at infrared region with Fourier transform (FTIR), which was used for DD calculation. The results showed that all chitin-chitosan samples did not reach DD > 90%, as observed for some good commercial chitosans. The highest DD was obtained by the sample prepared at more drastic conditions, as expected, however the higher sodium hydroxide concentration leads to decrease of molecular mass when associated with high temperatures. The crystallinity was influenced mostly by reaction time, which change the positions and intensities as indicated by XRD main peaks, located at 9.3 and 19.4° 2Θ. Particle sizes were strongly diminished by treatment at 393 K, what imply also some increase at the pressure, favoring chain dissociation reactions. This work mapped several properties for chitin-chitosan samples achieved by the described conditions.     

Vapour pressures of n-pentane determined by comparative ebulliometry

The vapour pressures of n-pentane have been measured using comparative ebulliometry with water as the reference substance. The measurements cover the temperature and pressure ranges 309 K and 102 kPa to 456 K and 2728 kPa. When combined with selected literature results, the range was extended downwards to a temperature and pressure of 268.8 K and 19.9 kPa and the combined data sets were correlated by a Wagner-type equation with a standard deviation of 18 Pa in the vapour pressure. The critical pressure was treated as an adjustable parameter and the value p_c = 3367.4 kPa was obtained using a selected critical temperature, T_c = 469.7 K. The calculated normal boiling temperature was T_b = 309.207 K and an extrapolation to the triple point temperature T_tp = 143.48 K predicted a pressure of p_tp = 0.078 Pa.     

Diffusion coefficients of nickel chloride in aqueous solutions of lactose at T = 298.15 K and T = 310.15 K

Binary mutual diffusion coefficients (interdiffusion coefficients) of nickel chloride in water at T = 298.15 K and T = 310.15 K, and at concentrations between (0.000 and 0.100) mol · dm^?3, using a Taylor dispersion method have been measured. These data are discussed on the basis of the Onsager–Fuoss and Pikal models. The equivalent conductance at infinitesimal concentration of the nickel ion in these solutions at T = 310.15 K has been estimated using these results. Through the same technique, ternary mutual diffusion coefficients (D₁₁, D₂₂, D₁₂, and D₂₁) for aqueous solutions containing NiCl₂ and lactose, at T = 298.15 K and T = 310.15 K, and at different carrier concentrations were also measured. These data permit us to have a better understanding of the structure of these systems and the thermodynamic behaviour of NiCl₂ in different media.     

Enhanced oxygen evolution at hydrous nickel oxide electrodes via electrochemical ageing in alkaline solution

The effect of electrochemically ageing hydrous nickel oxide films via slow repetitive potential multi-cycling across the main nickel (II/III) redox peak was investigated in an aqueous base environment using cyclic voltammetry and steady state polarisation curves in the oxygen evolution reaction (OER) region. Similarities between hydrous nickel oxide films and electroprecipitated ‘battery type’ nickel oxide were shown due to their similar change in redox and oxygen evolving properties as a result of film ageing. This ageing method was found to significantly enhance the OER performance of the hydrous nickel oxide electrode with the OER overpotential decreasing by 60 ± 2 mV and experiencing a 10 fold increase in OER rate for a fixed overpotential over that of an un-aged electrode. The OER turnover frequency for an aged electrode was found to be 1.16 ± 0.07 s^− 1 in comparison to 0.05 ± 0.003 s^− 1 for a hydrous nickel oxide electrode not subjected to ageing.     

Thermodynamic characterization of NiAl

Thermodynamic properties of the high-stability intermetallic compound nickel aluminide, NiAl, have been determined from mass-spectrometric, weight-loss effusion, and calorimetric measurements, using samples from a single preparation with a composition determined to be Ni_0.986Al_1.014. Per mole of NiAl molecules, the specific heat capacity at room temperature of 298 K is 48.54 J · K^?1 · mol^?1, with a linear temperature dependence of +0.0104 J · K^?2 · mol^?1. At the same temperature, the enthalpy of formation is ?133.7 kJ · mol^?1, the entropy is about 53.8 J · K^?1 · mol^?1 and the enthalpy difference between room temperature and absolute zero is 7.97 kJ · mol^?1. The Gibbs free-energy is ?130.2 kJ · mol^?1 at T = 298 K, with a linear temperature dependence of +5.04 J · K^?1 · mol^?1. The Debye temperature is 452 K, while the electronic density-of-states at the Fermi-level is about 0.29 states per eV-atom. The NiAl⁺ ions were observed in the high-temperature mass spectra. Pressures for the gas at these temperatures were estimated and used with the results of quantum-mechanical calculations of total energy, specific heat, and entropy to calculate free-energy functions for the gas. These and additional results are compared with other measurements and discussed in terms of current theories of the electronic and structural properties of the compound.     

Heat capacity (Cp) and entropy of olivine-type LiFePO4 in the temperature range (2 to 773) K

The heat capacity of olivine-type lithium iron phosphate (LiFePO₄ – LFP) has been measured covering a temperature range from (2 to 773) K. Three different calorimeters were used. The Physical Property Measurement System (PPMS) from Quantum Design was applied in the range between T = (2 and 300) K, a Micro-DSC II from Setaram within the range between T = (283 and 353) K and data between T = (278 and 773) K were measured by means of a Sensys DSC (Setaram) using the Cp-by-step method. Experimental data are given with an error of (1 to 2)% above T = 20 K and up to 8% below 20 K. The data were subdivided into appropriate temperature intervals and fitted using common heat capacity functions. The low temperature results permit the calculation of standard entropies and temperature coefficients of electronic, lattice, as well as magnetic (antiferromagnetic transition at T = 49.2 K) contributions to the heat capacity. The obtained experimental values were compared to results of a recently published first principles phonon study (DFT) and to few available experimental data from the literature.     

The Ba2LnFeNb4O15 “tetragonal tungsten bronze”: Towards RT composite multiferroics

Several Niobium oxides of formula Ba₂LnFeNb₄O₁₅ (Ln = La, Pr, Nd, Sm, Eu, Gd) with the “tetragonal tungsten bronze” (TTB) structure have been synthesised by conventional solid state methods. The neodymium, samarium and europium compounds are ferroelectric with Curie temperature ranging from 320 to 440 K. The praseodymium and gadolinium compounds behave as relaxors below 170 and 300 K respectively. The praseodymium, neodymium, samarium, europium and gadolinium compounds exhibit magnetic hysteresis loops at room temperature originating from traces of a barium ferrite secondary phase. The presence of both ferroelectric and magnetic hysteresis loops at room temperature allows considering these materials as composites multiferroic. Based on crystal-chemical analysis we propose some relationships between the introduction of Ln³⁺ ions in the TTB framework and the chemical, structural and physical properties of these materials.     

Thermal properties of [Cr(NH3)6](BF4)3 studied by adiabatic and relaxation calorimetry

Four (solid–solid) phase transitions were detected in the temperature range of (9 to 300) K in polycrystalline [Cr(NH₃)₆](BF₄)₃ at T_C1 = 240.7 K, T_C2 = 108.0 K, T_C3 = 91.9 K, and T_C4 = 61.3 K by adiabatic calorimetry. The measurements by relaxation calorimetry were followed on lowering temperature from 20 K down to 0.35 K under six different external magnetic field values (9, 7, 5, 3, 1 and 0) T. For non-zero values of applied magnetic field well-defined Schottky anomaly appears. Magnetic heat capacity was calculated assuming the zero-field splitting for the decoupled Cr(III) ions. There is no discrepancy between the observed and calculated values. Isothermal magnetization curve recorded up to 5 T was measured at temperature of 1.8 K.     

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.     

The partition coefficients of ethylene between vapor and hydrate phase for methane + ethylene + THF + water systems

The vapor-hydrate equilibria were studied experimentally in detail for CH₄ + C₂H₄ + tetrahydrofuran (THF) + water systems in the temperature range of 273.15–282.15 K, pressure range of 2.0–4.5 MPa, the initial gas–liquid volume ratio range of 45–170 standard volumes of gas per volume of liquid and THF concentration range of 4–12 mol%. The results demonstrated that, because of the presence of THF, ethylene was remarkably enriched in vapor phase instead of being enriched in hydrate phase for CH₄ + C₂H₄ + water system. This conclusion is of industrial significance; it implies that it is feasible to enrich ethylene from gas mixture, e.g., various kinds of refinery gases or cracking gases in ethylene plant, by forming hydrate.     

Molybdenum electrodes for hydrogen production by water electrolysis using ionic liquid electrolytes

The hydrogen production by water electrolysis was tested with different electrocatalysts (molybdenum, nickel, iron alloys containing chromium, manganese and nickel) using aqueous solutions of ionic liquid (IL) like 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄). The hydrogen evolution reaction (HER) was performed at room temperature in a potential of −1.7 V (PtQRE). A Hoffman cell apparatus was used to water electrolysis with current density values, j, between 14.6 mA cm⁻² (for Ni electrode) and 77.5 mA cm⁻² (for Mo electrode). The system efficiency was very high for all electrocatalysts tested, between 97.0% and 99.2%. The energy activation values of HER was determined in an aqueous solution of BMI.BF₄ 10 vol.%, using platinum (23.40 kJ mol⁻¹) and Mo (9.22 kJ mol⁻¹) as electrocatalysts. The results show that the hydrogen production in IL electrolyte can be carried out with cheap material at room temperature, which makes this method economically attractive.     

Thermodynamic study on complex of neodymium with glycine

Neodymium complex with glycine, Nd(Gly)₂Cl₃·3H₂O, was synthesized and characterized by IR spectra. The thermal stability of the complex was tested through TG and DTG and a possible mechanism of thermal decomposition was proposed. The heat capacities of the complex were measured by using an automated adiabatic calorimeter over the temperature range from T = (80 to 380) K, the thermodynamic functions, [H_T − H_298.15] and [S_T − S_298.15], were calculated based on the heat capacity measurements. Two (solid + solid) phase transitions in the ranges of T = (170 to 247) K were observed with the peak temperatures of 184.896 K and 231.217, respectively. The standard molar enthalpy of formation of [Nd(Gly)₂Cl₃·3H₂O] was determined to be (−3081.3 ± 1.1) kJ · mol⁻¹ in terms of an isoperibol solution-reaction calorimeter.     

Vapor deposited ethanol–H2O ice mixtures investigated by micro-Raman scattering

Solid deposits have been formed at 88 K and 10⁻¹ Torr from ethanol–water gas collected above aqueous solutions of ethanol (EtOH) (0.6, 2, 4.5, 9 and 17 mol%). The composition of different gas mixtures varying between 1:16 and 1:0.8 EtOH:H₂O are determined at 295 K using our experimental vapor–liquid equilibrium (VLE) data in combination with the Wilson model [28]. The Wilson constants derived at this temperature are Λ₁₂ = 0.37(4) and Λ₂₁ = 0.58(5). The concentration of EtOH in the ice mixture can be calculated using these data and a kinetic model of condensation. It is found to vary between 9 and 65 mol% EtOH. The ice mixtures are analyzed in situ in a modified cryostage by micro-Raman spectroscopy. The distinct vibrational signatures of pure EtOH, EtOH aqueous solutions and EtOH–ice mixtures are identified in the 400–3800 cm⁻¹ spectral range. Internal vibrational motions of EtOH molecules are affected by temperature and concentration. The presence of amorphous EtOH–ice phases at 88 K is demonstrated by the characteristic vibrational signatures of the ν_OH stretching modes. The crystallization of an EtOH hydrate is proposed during annealing at ∼140 K of a 65 mol% EtOH–ice mixture. According to our preliminary X-ray diffraction work, this phase has apparently a distinct structure from that of solid EtOH or from EtOH–clathtrate structures usually found in frozen aqueous solutions. For ice mixtures of lower EtOH content, a distinct hydrate phase crystallizes at ∼170 K. These results suggest that ice mixtures obtained by vapor deposition reflect the existence of EtOH clusters of a distinctive structural nature with respect to those encountered in frozen aqueous mixtures.     

New experimental heat capacity and enthalpy of formation of lithium cobalt oxide

The heat capacity of LiCoO₂ (O3-phase), constituent material in cathodes for lithium-ion batteries, was measured using two differential scanning calorimeters over the temperature range from (160 to 953) K (continuous method). As an alternative, the discontinuous method was employed over the temperature range from (493 to 693) K using a third calorimeter. Based on the results obtained, the enthalpy increment of LiCoO₂ was derived from T = 298.15 K up to 974.15 K. Very good agreement was obtained between the derived enthalpy increment and our independent measurements of enthalpy increment using transposed temperature drop calorimetry at 974.15 K. In addition, values of the enthalpy of formation of LiCoO₂ from the constituent oxides and elements were assessed based on measurements of enthalpy of dissolution using high temperature oxide melt drop solution calorimetry. The high temperature values obtained by these measurements are key input data in safety analysis and optimisation of the battery management systems which accounts for possible thermal runaway events.     

Investigation of sodium 4-nitrotoluene-2-sulfonate solubility in aqueous organic solutions

The solubility of sodium 4-nitrotoluene-2-sulfonate (NTSNa) in binary solvent mixtures (methanol + water), (ethanol + water), and (2-methoxyethanol + water) was investigated over the temperature range from (288 to 344) K. The mole fraction of water in solvent mixtures ranged from 0 to 0.8. The solubility data are described by the electrolyte non-random two-liquid (E-NRTL) model. The E-NRTL binary interaction parameters are expressed as a function of temperature, and were obtained from the experimental data. The root-mean-square deviations of solubility temperature varied from (0.20 to 1.35) K.