Excess molar enthalpies of the ternary system mtbe+ethanol+hexane

Excess molar enthalpies of the ternary mixture {x₁ tert-butyl methyl ether (MTBE)+x₂ ethanol+(1–x₁–x₂) hexane} and, the involved binary mixtures {x tert-butyl methyl ether (MTBE)+(1–x) ethanol}, {x tert-butyl methyl ether (MTBE)+(1–x) hexane} and {x ethanol+( 1–x) hexane} have been measured at 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials.     

Determination of excess molar enthalpies for the ternary system <Emphasis Type="Italic">p</Emphasis>-xylene+octane+diethyl carbonate

Excess molar enthalpies, H ^E, for the binary mixtures {p-xylene+(1–x) octane}, {x p-xylene+(1–x) diethyl carbonate}, {x octane+(1–x) diethyl carbonate} and the corresponding ternary system {x ₁ p-xylene+x ₂ octane+(1–x ₁–x ₂) diethyl carbonate} have been measured by using a Calvet microcalorimeter at 298.15 K under atmospheric pressure. The experimental H ^E values are all positive for the binary and ternary mixtures over the entire composition range.     

Excess molar enthalpies of the ternary system <Emphasis Type="Italic">p</Emphasis>-xylene+decane+diethyl carbonate

Excess molar enthalpies of the ternary system {x ₁ p-xylene+x ₂decane+(1–x ₁–x ₂)diethyl carbonate} and the involved binary mixtures {p-xylene+(1–x)decane}, {xp-xylene+(1–x)diethyl carbonate} and {xdecane+(1–x)diethyl carbonate} have been determined at the temperature of 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The experimental excess molar enthalpies H _m ^E are positive for all the binary systems studied over the whole composition range. Excess molar enthalpy for the ternary system is positive as well, showing maximum values at x ₁=0, x ₂=0.4920, x ₃=0.5080, H _m,123 ^E=1524 J mol^–1.     

Excess molar enthalpies of binary mixtures for (tributyl phosphate+methanol/ethanol) at 298.15 K

Excess molar enthalpies of binary mixtures for tributyl phosphate (TBP)+methanol/ethanol were measured with a TAM air Isothermal calorimeter at 298.15 K and ambient. The results for xTBP+(1–x)CH₃OH are negative in the whole range of composition, while the values for xTBP+(1–x)C₂H₅OH change from positive values at low x to small negative values at high x. The experimental results have been correlated with the Redlich–Kister polynomial. IR spectra of the mixtures were measured to investigate the effect of hydrogen bonding in the mixture.     

Experimental excess molar volumes of the ternary mixture and comparisonwith several empirical methods

Experimental excess molar volumes for the ternary system {x₁MTBE+x₂1-propanol+(1–x₁–x₂)nonane} and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+nonane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.     

Excess thermodynamic parameters of binary mixtures of methanol,ethanol, 1-propanol,and 2-butanol + chloroform at (288.15–323.15 K) and comparison with the Flory theory

In this work we used the experimental result for calculating the thermal expansion coefficients α, and their excess values α ^E , and isothermal coefficient of pressure excess molar enthalpy and comparison the obtain results with Flory theory of liquid mixtures for the binary mixtures {methanol, ethanol, 1-propanol and 2-butanol-chloroform} at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 K. The excess thermal expansion coefficients α ^E and the isothermal coefficient of pressure excess molar enthalpy ((∂H _m^E/∂P) _T,x for binary mixtures of {methanol and ethanol + chloroform} are S-shaped and for binary mixtures of {1-propanol and 2-butanol + chloroform} are positive over the mole fraction. The isothermal coefficient of pressure excess molar enthalpy (∂H _m^E/∂P) _T,x , are negative over the mole fraction range for binary mixture of {1-propanol and 2-butanol + chloroform}. The calculated values by using the Flory theory of liquid mixtures show a good agreement between the theory and experimental.     

Transport numbers and ionic conduction of eutectic methacomposites {(1 ? x )MeWO4 · x WO3}) (Me = Sr, Ba; x = 0?0.55)

Transport numbers of oxygen ions, , in methacomposites (1 − x)MeWO₄ · xWO₃, where Me = Sr and Ba and x = 0−0.55, are determined in the temperature interval 600 to 900°C by a method of the emf of an oxygen-air galvanic cell. It is demonstrated that the region of small contents of the additive (x ≤ 0.2) is predominantly characterized by oxygen-ion conduction ( = 1), which gives way to electronic conduction (t _e = 1) at x > 0.35. It is confirmed once again that subeutectic compositions (1 − x)MeWO₄ · xWO₃ where Me = Sr and Ba and x = 0−0.2 belong in the class of ion-conducting methacomposites. The threshold of percolation of electronic conduction (t _e ≥ 0.5, < 0.5) occurs at x _t ≥ 0.3. Dependences of the transport numbers of the oxygen ions on the volume ratio between components in both composites resemble one another; specifically, the threshold composition contains nearly 20 vol % of WO₃. The dramatic amplification (by 1–1.5 orders of magnitude) of the ionic conductivity in the methacomposites occurs at small contents of tungstic oxide (x ≤ 0.01). A chemical transport removal of excess tungstic oxide, which is segregated in the form of the surface compound MeW-s, from the surface of the MeWO₄ grains destroys MeW-s, leading to a 10–15-fold drop of the ionic conductance. At x ≥ 0.05, the oxygen-ion conductance in the methacomposites is practically independent of their composition. A model for the formation and architecture of the methacomposites is qualitatively modified. The modified model takes into account doubled surface activity and mobility of the MeW-s phase with respect to MeWO₄ and WO₃. Original Russian Text ? N.N. Pestereva, A.Yu. Zhukova, A. Ya. Neiman, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 11, pp. 1379–1386.     

Determination of experimental excess molar properties for MTBE+1-propanol+octane

Summary Experimental excess molar enthalpies and densities have been measured for the ternary mixture x₁MTBE+x₂1-propanol+(1-x₁-x₂)octane and the involved binary mixtures at 298.15 K and atmospheric pressure. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. A standard Calvet microcalorimeter was employed to determine the excess molar enthalpies. Densities were measured using a DMA 4500 Anton Paar densimeter. The UNIFAC group contribution model (in the versions of Larsen et al., and Gmehling et al.) has been used to estimate excess enthalpies values. Experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results.     

Solid electrolytes based on CeO<Subscript>2</Subscript> for medium-temperature electrochemical devices

CeO₂-based solid solutions with a fluorite structure are promising materials as electrolytes of medium-temperature electrochemical devices: electrolytic cells, oxygen sensors, and solid oxide fuel cells. In this work, studies are presented of the effect of the dopant cation radius and its concentration on the physico-chemical properties of the Ce_{1 − x} Ln _x O_{2 − δ} solid solutions (x = 0–0.20; Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) and also of multicomponent solid solutions of Ce_{1 − x} Ln _x/2Ln′ _x/2O_{2 − δ} (x = 0–0.20; Ln = Sm, La, Gd and Ln′ = Dy, Nd, Y) and Ce_{1 − x − y} Sm _x M _y O_{2 − δ} (M = Ca, Sr, Ba) obtained using the solid-phase synthesis technique. Electric properties of the samples were studied in the temperature range of 623–1173 K and in the oxygen partial pressure range of 0.01–10⁻²² MPa. The values of oxygen critical pressure ( p_O2 ^* )\left( {p_{O_2 }^* } \right) are presented, at which the ionic and electron conductivity values are equal. The values were calculated on the basis of experimental dependences at 1023 K at the assumption that the ionic conductivity value is determined only by the dopant concentration and its effective ionic radius and is independent of the oxygen partial pressure.     

Study on volumetric measurement and correlations for MTBE+1-propanol+decane at 298.15 K and atmospheric pressure

Summary Experimental densities for the ternary mixture x₁MTBE+x₂1-propanol+(1-x₁-x₂)decane and the binary mixtures xMTBE +(1-x)1-propanol and x1-propanol+(1-x)decane have been measured at 298.15 K and atmospheric pressure, using a DMA 4500 Anton Paar densimeter. Excess molar volumes were determined from the densities of the pure liquids and mixtures. Attending to the symmetry of the studied mixtures, suitable fitting equations have been used in order to correlate adequately the experimental data. For the ternary mixture, experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results.     

Structure and electrical properties of oxygen-deficient strontium copper niobate

The transport properties of Sr_5.66 Cu_0.14Nb_2.20 O_11.30 double perovskite, which enters the homogeneity region of (Sr_1-y Cu _y )₆–_2x Nb_2+2x O_11+3x solid solution, are concerned. The total conductivity is differentiated into terms over wide ranges of temperatures and oxygen partial pressures $ p_{O_2 } $ p_{O_2 } in dry and humid atmospheres. When $ p_{O_2 } $ p_{O_2 } is low or high, a test sample has dominant electron transport of n- or p-type, respectively. In air ($ p_{O_2 } $ p_{O_2 } = 0.21 atm), the p-type electron conductivity term increases with temperature elevation. In a humid atmosphere ($ p_{H_2 O} $ p_{H_2 O} = 0.02 atm), a sample is capable of a reversible incorporation of water occlusion from the gas phase; as a result, some proton conductivity term appears and ion transference numbers increase over a wide range of $ p_{O_2 } $ p_{O_2 } values.     

Volumetric Properties and Refractive Indices for Binary Mixtures of 1-Propyronitrile-3-hexylimidazolium Bromide + Ethanol at Temperatures from 293.15 to 323.15 K

Densities and refractive indices have been measured for binary mixtures of 1-propyronitrile-3-hexylimidazolium bromide + ethanol in the temperature range 293.15–323.15 K. From the experimental data the excess molar volume V ^E, refractive index deviation Δn _D, and the coefficient of thermal expansion α were calculated and fitted to fifth- and third-order Redlich–Kister type equations, respectively. Using the measured densities, the apparent molar volumes (V _ϕ ), limiting apparent molar volumes (V_f⁰V_{\phi}^{0}) and limiting apparent molar expansivities (E_f ⁰E_{\phi} ^{0}) were also determined and the details are discussed.     

Relationship between the ionic and electronic partial conductivities of co-doped LSGM ceramics from oxygen partial pressure dependence of the total conductivity

La_0.8Sr_0.2Ga_0.85-x Mg_0.15Co _x O_3±δ-materials (further cobalt-doped LSGM), where x varied from 0 to 0.20, were synthesized by means of the conventional powder route. The total conductivity of the La_0.8Sr_0.2Ga_0.85-x Mg_0.15Co _x O_3±δ samples was measured as a function of temperature (400–900 °C) and oxygen partial pressure by means of the impedance technique. The values of the oxygen ionic and the hole conductivities were determined from non-linear regression of the oxygen partial pressure dependence of the total conductivity. It was shown that the substitution of gallium by cobalt in the LSGM results in increasing either the oxygen ionic or the hole conductivity, although the increase of the hole conductivity due to the doping by cobalt is more significant than the increase of the oxygen ionic conductivity. The hole conductivity of the selected compositions was studied by oxygen permeation- and Hebb–Wagner-polarization measurements.     

Synthesis,structure, CMC values,thermodynamics of micellization,steady-state photolysis and biological activities of hexadecylamine cobalt(III) dimethyl glyoximato complexes

Metallosurfactant complexes of the type trans- [Co(DH)₂(HA)X], where DH = Dimethyl glyoxime, HA = Hexadecyl amine and X = Cl⁻, Br⁻, I⁻, N₃ ⁻, NO₂ ⁻ or SCN⁻, were synthesized and characterized by physico-chemical and spectroscopic methods. In addition, the single crystal X-ray structure of the ionic complex trans-[Co(DH)₂(HA)₂][Co(DH)₂(I)₂)] is presented. The critical micelle concentration values of the complexes in ethanol were obtained by measuring the absorption at 290 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the thermodynamics of micellization ) \left( {\Updelta G^{0}_{{{\text{m}}}}, \Updelta H^{0}_{{{\text{m}}}}, \Updelta S^{0}_{\text{m}} } \right) . Steady-state photolysis, cyclic voltammetry and biological activities of the complexes were studied. The compounds were tested for antimicrobial activity.     

Ion-Solvation Behavior of Pyridinium Dichromate in Water–N,N-Dimethyl Formamide Solvent Mixtures

The electrical conductances of pyridinium dichromate have been measured in N,N-dimethyl formamide–water mixtures of different compositions in the temperature range 283–313 K. The limiting molar conductance, Λ₀, association constant of the ion pair, K _A, and dissociation constant K _C have been calculated using the Shedlovsky and Kraus–Bray equations. The effective ionic radii (r _i ) of C₅H₅NH⁺ and Cr₂O₇ ^-\mathrm{Cr}_{2}\mathrm{O}_{7}^{ -} have been determined from the L_i⁰\Lambda_{i}^{0} values using Gill’s modification of Stokes’ law. The influence of the mixed solvent composition on the solvation of ions is discussed with the help of the ‘R’-factor ( R = \frachL _±⁰(solvent)hL _±⁰(water)R = \frac{\eta \Lambda_{ \pm}^{0}(\mathrm{solvent})}{\eta\Lambda_{ \pm}^{0}(\mathrm{water})}). Thermodynamic parameters are evaluated and reported. The results of this study are interpreted in terms of ion–solvent interactions and solvent properties.     

Behavior of (La,Sr)CoO3- and La2NiO4-based ceramic anodes in alkaline media: compositional and microstructural factors

The behavior of dense ceramic anodes made of perovskite-type (x = 0.30–0.70; y = 0–0.05; z = 0–0.20) and K₂NiF₄-type (Me = Co, Cu; x = 0–0.20) indicates significant influence of metal hydroxide formation at the electrode surface on the oxygen evolution reaction (OER) kinetics in alkaline solutions. The overpotential of cobaltite electrodes was found to decrease with time, while cyclic voltammetry shows the appearance of redox peaks characteristic of Co(OH)₂/CoOOH. This is accompanied with increasing effective capacitance estimated from the impedance spectroscopy data, because of roughening of the ceramic surface. The steady-state polarization curves of in the OER range, including the Tafel slope, are very similar to those of model Co(OH)₂–La(OH)₃ composite films where the introduction of lanthanum hydroxide leads to decreasing electrochemical activity. La₂NiO₄-based anodes exhibit a low electrochemical performance and poor stability. The effects of oxygen nonstoichiometry of the perovskite-related phases are rather negligible at high overpotentials but become significant when the polarization decreases, a result of increasing role of oxygen intercalation processes. The maximum electrocatalytic activity to OER was observed for A-site-deficient , where the lanthanum content is relatively low and the Co⁴⁺ concentration determined by thermogravimetric analysis is highest compared to other cobaltites. Applying microporous layers made of template-synthesized nanocrystalline leads to an improved anode performance, although the effects of microstructure and thickness are modest, suggesting a narrow electrochemical reaction zone. Further enhancement of the OER kinetics can be achieved by electrodeposition of cobalt hydroxide- and nickel hydroxide-based films. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

Mixed-conducting dense ceramic membranes for air separation and natural gas conversion

Non-perovskite SrFeCo_0.5O _x (SFC2) was found to have high electronic and ionic conductivities as well as structural stability. At 800°C in air, total and ionic conductivities of 17 and 7 S·cm⁻¹ were measured, respectively; the ionic transference number was calculated to be ≈0.4. This material is unique because of its high electronic conductivity and comparable electronic and ionic transference numbers. X-ray diffraction analysis showed that air-sintered SFC2 consists of three phase components, ≈75 wt% , ≈20 wt% perovskite , and ≈5 wt% rock salt CoO. Argon-annealed SFC2 contains brownmillerite Sr₂(Fe_1−x Co _x )₂O₅ and rock salt CoO. Dense SFC2 membranes were able to withstand large pO₂ gradients and retain mechanical strength. A 2.9-mm-thick disk membrane was tested in a gas-tight electrochemical cell at 900°C; an oxygen permeation flux rate ≈2.5 cm³(STP)·cm⁻²·min⁻¹ was measured. A dense thin-wall tubular membrane of 0.75-mm thickness was tested in a methane conversion reactor for over 1,000 h. At 950°C, the oxygen permeation flux rate was ≈10 cm³(STP)·cm⁻²·min⁻¹ when the SFC2 thin-wall membrane was exposed with one side to air and the other side to 80% methane balanced with inert gas. Results from these two independent experiments agreed well. The SFC2 material is a good candidate as dense ceramic membranes for oxygen separation from air or for use in methane conversion reactors.     

Rubidium and lithium butanoates binary phase diagram

The temperature and enthalpy vs. composition diagrams of the binary system [xC₃H₇CO₂Li+(1–x)C₃H₇CO₂Rb], where x=mole fraction, were determined by differential scanning calorimetry (DSC). This binary systems displays the formation of two mixed salts with a composition 1:1 and 1:2, which melt incongruently at T _fus=590.5 K, with Δ_fus H _m=11.6 kJ mol^–1, and congruently at T _fus=614.5 K, with Δ_fus H _m=20.2 kJ mol^–1, respectively. The phase diagram also presents an ionic liquid-crystalline phase in a wide temperature range: 95 K.     

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol by bis(hydrogen periodato)argentate(III) complex anion: a kinetic study

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, [Ag(HIO₆)₂]⁵⁻ has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order kinetics, being first-order in both [Ag(III)] and [MPPD]. The effects of [OH⁻] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:

Thermodynamics of the Interaction of a Homologous Series of Amino Acids with Sorbitol

The apparent molar volumes V _2,φ , apparent molar isentropic compressibilities K _S,2,φ , and enthalpies of dilution of aqueous glycine, alanine, α-amino butyric acid, valine, and leucine have been determined in aqueous 1.0 and 2.0 mol⋅dm⁻³ sorbitol solutions at 298.15 K. These data have been used to calculate the infinite dilution standard partial molar volumes V_2,m⁰V_{2,m}^{0}, partial molar isentropic compressibilities K_S,2,m⁰K_{S,2,m}^{0}, and enthalpies of dilution Δ_dil H ⁰ of the amino acids in aqueous sorbitol, along with the standard partial molar quantities of transfer of the amino acids from water to aqueous sorbitol. The linear correlation of V_2,m⁰V_{2,m}^{0} for this homologous series of amino acids has been utilized to calculate the contribution to V₂⁰V_{2}^{0} of the charged end groups (NH₃⁺\mathrm{NH}_{3}^{+}, COO⁻), the CH₂ group, and other alkyl chains of the amino acids. The results for the standard partial molar volumes of transfer, compressibilites and enthalpies of dilution from water to aqueous sorbitol solutions have been correlated and interpreted in terms of ion–polar, ion–hydrophobic, and hydrophobic–hydrophobic group interactions. A comparison of these thermodynamic properties of transfer suggest that an enhancement of the hydrophilic/polar group interactions is operating in ternary systems of amino acid, sorbitol, and water.