Experimental and the Theoretical Studies of the Dielectric Properties of DMSO–H<Subscript>2</Subscript>O Mixtures

This paper focuses on the measurement of the permittivity of dimethyl sulfoxide (DMSO)–water (H₂O) mixture solutions, at 2.45 GHz by using a resonant cavity perturbation method. A specific phenomenon was found, in that the imaginary part of the permittivity for the mixture solution was larger than the imaginary part for each component. Theoretical calculation indicated that the reason for that phenomenon was that the high frequency friction of the mixture was larger than that of each component. When comparing the theoretical results with the experimental data, it was found that the classical Debye equation must be modified in order to calculate the complex permittivity.     

Theoretical investigation on the kinetics and thermochemisty of H-atom abstraction reactions of 2-chloroethyl methyl ether (CH<Subscript>3</Subscript>OCH<Subscript>2</Subscript>CH<Subscript>2</Subscript>Cl) with OH radical at 298 K

Kinetics and thermochemistry of the H-atom abstraction reaction of CH₃OCH₂CH₂Cl with OH radical have been carried out using dual level of methods. Initially, geometry optimization and frequency calculations are performed at M06-2X/6-31+G(d, p) level of theory, and energetic calculations are further refined using CCSD(T)/6-311++G(d, p) level of theory in order to characterized all stationary points on potential energy surface (PES). The result shows that H-atom abstraction from –OCH₂ site of CH₃OCH₂CH₂Cl is dominant path. The rate constants are calculated using canonical transition state theory at 298 K, which are found to be in good agreement with the experimental data. We have presented the standard enthalpies of formation for CH₃OCH₂CH₂Cl and the radicals generated during the H-atom abstraction using group-balanced isodesmic reactions scheme. The atmospheric lifetime of title molecule is also calculated.     

Solubility and Ionic Interaction of the CaF<Subscript>2</Subscript>–CaSO<Subscript>4</Subscript>–H<Subscript>2</Subscript>O System at 298.1 K

Solubility isotherms of the sparingly soluble salts CaF_2(s) and CaSO₄·2H₂O_(s) in their mixed aqueous solutions have been measured at 298.1 K. It was found that the CaF_2(s) solubility decreases with increasing CaSO₄ concentration in the solution and reaches about 1/3 of the CaF_2(s) solubility in pure water in the CaSO₄·2H₂O_(S) saturated solution. A thermodynamic model was developed to predict the CaF_2(s) solubility isotherm in this system, in which the short range interactions of the species in the aqueous solution are represented by ion-association constants reported in literature, and the long range interaction, i.e., the electrostatic term, is represented by the well known Davies equation. The predicted solubility isotherm reasonably agrees with the experimental results. The contributions of the long-range term and the short-range term to the calculated solubility isotherm were investigated. It was concluded that the ionic association combining with the Davies equation is sufficient to represent the excess interaction of the CaF₂ + CaSO₄ aqueous solution at 298.15 K. This model approach could be applicable for other dilute mixed electrolyte systems in which component activity coefficients are lacking and model parameters are difficult to determine.     

Isopiestic Determination of the Osmotic Coefficients and Pitzer Model Representation for the Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript>+LiCl + H<Subscript>2</Subscript>O System at <Emphasis Type="Italic">T</Emphasis>=298.15 K

Isopiestic molalities and water activities have been measured for the Li₂B₄O₇+LiCl + H₂O system at T=298.15 K using an improved isopiestic apparatus. Two types of osmotic coefficients, φ _S and φ _E, were determined, where φ _S is based on the stoichiometric molalities of the solute Li₂B₄O₇(aq) and φ _E is based on equilibrium molalities calculated by consideration of the equilibrium speciation of Li₂B₄O₇ to partially form H₃BO₃, B(OH)₄⁻ and B₃O₃(OH)₄⁻. The stoichiometric equilibrium constant K _m for the aqueous speciation reaction was estimated. Two representations of the osmotic coefficients of Li₂B₄O₇ + LiCl + H₂O were made with Pitzer’s ion-interaction model. Model (1) involved representing the φ _S values with six parameters based on considering the ionic interactions between Li⁺, Cl⁻, and B₄O₇²⁻; and model (2) involved representing the φ _E values based on the calculated equilibrium speciation. Reasonable agreements were obtained between the experimental osmotic coefficient data and those calculated using the above models, with standard deviations of 0.075 and 0.0229, respectively, for these two models. The thermodynamic osmotic coefficients for the complex system containing polymeric boron anions and lithium cation was modelled and explained by use of Pitzer’s ion-interaction model, with minor modifications in combination with speciation reaction equilibria.     

Crystal structure of KAsUO<Subscript>6</Subscript>·<Subscript>3</Subscript>H<Subscript>2</Subscript>O at 100 and 293 K

The crystal structure of KAsUO₆·3H₂O was solved at 100 K and 293 K. KAsUO₆·3H₂O at T = 100 K: tetragonal, P4/ncc, a = 7.2037(6) Å, c = 17.811(2) Å; Z = 4, R1 = 0.0263, wR2 = 0.0546, for 618 independent reflections; at T = 293 K: tetragonal, P4/ncc, a = 7.1600(4) Å, c = 17.746(1) Å; Z = 4, R1 = 0.0263, wR2 = 0.0433 for 427 independent reflections. The results of X-ray analysis are compared with our previous data on heat capacity of this compound, and changes that take place in the structure at elevated temperature are considered.     

Study of kinetics and thermodynamics of the dehydration reaction of AlPO<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

The kinetics and thermodynamics of the thermal dehydration of aluminum phosphate monohydrate, AlPO₄ · H₂O were studied using thermogravimetry (TG-DTG-DTA) at four heating rates in dry air atmosphere. The activation energies of the dehydration step of AlPO₄ · H₂O were calculated through the methods of Friedman (FR) and Flynn–Wall–Ozawa (FWO) and the possible conversion function has been estimated through the Achar and Li–Tang equations. The independent activation energies on extent of conversions and the better kinetic model of the dehydration reaction for AlPO₄ · H₂O indicate single kinetic mechanism and the F _2.05 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”, respectively. The positive values of ΔH^# and ΔG^# for the dehydration reaction show that it is endothermic and non-spontaneous process and it is connected with the introduction of heat. The kinetic and thermodynamic functions calculated for the dehydration reaction by different techniques and methods were found to be consistent.     

Experimental Determination of the Isotherm at 15°C of the System Mg<Superscript>2+</Superscript>/Cl<Superscript>−</Superscript>, SO<Subscript>4</Subscript><Superscript>2</Superscript>–H<Subscript>2</Subscript>O

Summary.  The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.  Corresponding author. E-mail: ariguib@planet.tn Received October 16, 2002; accepted (revised) December 3, 2002 Published online April 24, 2003 RID="a" ID="a" Dedicated to Prof. Dr. Heinz Gamsj?ger on the occasion of his 70^th birthday     

Isopiestic Determination of the Osmotic and Activity Coefficients of K<Subscript>2</Subscript>HPO<Subscript>4</Subscript>(aq), Including Saturated and Supersaturated Solutions,at <Emphasis Type="Italic">T</Emphasis>=298.15 K

The osmotic coefficients of K₂HPO₄(aq) have been measured at T=298.15 K by the isopiestic vapor pressure method over the range of molalities from 1.3846 mol⋅kg⁻¹ to 13.939 mol⋅kg⁻¹ (oversaturation) with CaCl₂(aq) as the reference solution. The molalities and osmotic coefficients of saturated solutions in equilibrium with K₂HPO₄⋅xH₂O(cr) were measured simultaneously by the same method. Available literature osmotic coefficients of K₂HPO₄(aq) at T=298.15 K, and our new experimental data, were combined and modeled using an extended form of Pitzer’s equation and the Clegg-Pitzer-Brimblecombe equation based on the mole-fraction-composition scale. These equations were used to calculate the activity coefficients of K₂HPO₄(aq) at T=298.15 K.     

Impedance Study of the Conductivity of Solid Oxide Electrolyte Films SrZr<Subscript>0.95</Subscript>Y<Subscript>0.05</Subscript>O<Subscript>3–δ</Subscript> and CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3–δ</Subscript>

Information on the across-plane conductivity of films of solid-oxide electrolytes SrZr_0.95Y_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ deposited on ion-conducting supports is acquired by the impedance method. It is shown that the support/film interface and the intergrain boundaries considerably affect the across-plane charge transfer in the film. The effect of the crystallographic orientation of the YSZ support on the microstructure and conductivity of the CaZr_0.9Y_0.1O_3–δ electrolyte film is demonstrated.     

Mass attenuation coefficients of B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–CaF<Subscript>2</Subscript> glass system at 0.662 and 1.25 MeV gamma energies

The total mass attenuation coefficients, partial interaction and the effective atomic numbers (Z_eff) of glass system (80−x)B₂O₃–10Al₂O₃–10SiO₂–xCaF₂ (where x = 5, 10, 20, 25, 30, 35 and 40 mol %) have been calculated at photon energies 0.662 and 1.25 MeV using the WinXCom software on the basis of mixture rule. Results indicated that the total mass attenuation coefficients showed a decrease with increasing the CaF₂ concentration, due to a decrease in Compton scattering probability, which gave a dominant contribution to the total mass attenuation coefficients for the studied glass samples at both energies. However, the photoelectric absorption and coherent scattering showed an increase with increasing the CaF₂, concentrations at same energies. For a comparison, the total mass attenuation coefficients of the glass system had lower values at the energy 1.25 MeV than that at 0.662 MeV. Z_eff was found to increase linearly with the increase of CaF₂ concentrations. It was concluded that low CaF₂ concentrations in glass system, under study, have Z_eff close to that of human tissue and have higher total absorption coefficients at energy of 0.662 MeV than that at 1.25 MeV. These results are very useful in designing gamma radiation detectors using thermoluminescence technique. Therefore, it is recommended to use low CaF₂ concentration of our glass system as good gamma detectors at energy of 1.25 MeV.     

Synchrotron X-ray structures of cellulose I<Subscript>β</Subscript> and regenerated cellulose II at ambient temperature and 100 K

Synchrotron X-ray data have been collected to 1.4 Å resolution at the NE-CAT beam-line at the Advanced Photon Source from fibers of cellulose I_β and regenerated cellulose II (Fortisan) at ambient temperature and at 100 K in order to understand the effects of low temperature on cellulose more thoroughly. Crystal structures have been determined at each temperature. The unit cell of regenerated cellulose II contracted, with decreasing temperature, by 0.25%, 0.22% and 0.1% along the a, b, and c axes, respectively, whereas that of cellulose I_β contracted only in the direction of the a axis, by 0.9%. The value of 4.6×10^?5 K^?1 for the thermal expansion coefficient of cellulose I_β in the a axis direction can be explained by simple harmonic molecular oscillations and the lack of hydrogen-bonding in this direction. The molecular conformations of each allomorph are essential unchanged by cooling to 100 K. The room temperature crystal structure of regenerated cellulose II is essentially identical to the crystal structure of mercerized cellulose II.     

Quantum Chemical Study of Niobium and Tantalum M<Subscript>4</Subscript>O<Subscript>10</Subscript> Oxide Clusters and M<Subscript>4</Subscript>O<Stack><Subscript>10</Subscript><Superscript>–</Superscript></Stack> Anions

Structural parameters and vibrational frequencies of the clusters (T_d)–Nb₄O₁₀, (C_3v)-TaNb₃O₁₀, (D_2d)-Nb₄O ₁₀ ^– , and (C_s)-TaNb₃O ₁₀ ^– were calculated. According to the (U)DFT/SDD calculations with BLYP, B3LYP, and PBE0 functionals magnetization of the anion (D_2d)-Nb₄O ₁₀ ^– is distributed equally among four niobium atoms. In the anion (C_s)-TaNb₃O ₁₀ ^– unpaired electron presumably occupies niobium atoms. The distinction in contributions from Nb atoms in the magnetization of the tantalum-containing cluster grows with the exchange component of the DFT functional in the series of functionals BLYP < B3LYP < PBE0 < UHF.     

Thermodynamic Protonation Parameters of some Sulfur-Containing Anions in NaCl<Subscript>aq</Subscript> and (CH<Subscript>3</Subscript>)<Subscript>4</Subscript>NCl<Subscript>aq</Subscript> at <Emphasis Type="Italic">t</Emphasis>=25 °C

Protonation constants of one thiocarboxylate (thioacetate) and four sulfur-containing carboxylates (2-methylthioacetate, thiolactate, thiomalate, 3-mercaptopropionate) were determined by potentiometric measurements in a wide ionic strength range [0≤I≤5 mol⋅L⁻¹ in NaCl and 0 ≤I≤3 mol⋅L⁻¹ in (CH₃)₄NCl] at t=25 °C. For two of these ligands (2-methylthioacetate and thiolactate), the protonation enthalpies were also determined by calorimetric measurements in NaCl ionic medium [0 ≤I≤5 mol⋅L⁻¹] at t=25 °C. Individual UV spectra of the protonated and unprotonated 3-mercaptopropionate species, together with values of the protonation constants, were obtained by spectrophotometric titrations. Results were analyzed in terms of their dependence on the ionic medium by using different thermodynamic models [Debye-Hückel type, SIT (Specific ion Interaction Theory) and Pitzer’s equations]. Differences among protonation constants obtained in different media were also interpreted in terms of weak complex formation.     

Synthesis and crystal structures of [K(H<Subscript>2</Subscript>O)(Piv)]<Subscript>∞</Subscript> and [K<Subscript>2</Subscript>(Phen)(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>(Piv)<Subscript>2</Subscript>]<Subscript>∞</Subscript>

A method for the synthesis of potassium pivalates (trimethylacetates) from potassium tert-butoxide and pivalic acid was proposed. The complexes of the formulas [K(H₂O)(Piv)]_∞(I) and [K₂(Phen)(H₂O)₂(Piv)₂]_∞ (II) (Piv denotes the pivalate anion and Phen denotes 1,10-phenanthroline) were obtained and characterized by elemental analysis and IR and ¹H NMR spectroscopy. The crystal structures of complexes I and II were determined using X-ray diffraction. Crystal structure I has a layered motif with two nonequivalent K atoms (C.N.s 5 + 2 and 6). The coordination of phenanthroline in II gives rise to a ribbon motif, the structure containing three nonequivalent K atoms (C.N.s 6, 6 + 1, and 8).     

Molar heat capacity and thermodynamic properties of crystalline [Nd(Glu)(H<Subscript>2</Subscript>O)<Subscript>5</Subscript>(Im)<Subscript>3</Subscript>](ClO<Subscript>4</Subscript>)<Subscript>6</Subscript>·2H<Subscript>2</Subscript>O

A complex of neodymium perchloric acid coordinated with L-glutamic acid and imidazole, [Nd(Glu)(H₂O)₅(Im)₃](ClO₄)₆·2H₂O was synthesized and characterized by IR and elements analysis for the first time. The thermodynamic properties of the complex were studied with an automatic adiabatic calorimeter and differential scanning calorimetry (DSC). Glass transition and phase transition were discovered at 221.83 and 245.45 K, respectively. The glass transition was interpreted as a freezing-in phenomenon of the reorientational motion of ClO₄⁻ ions and the phase transition was attributed to the orientational order/disorder process of ClO₄⁻ ions. The heat capacities of the complex were measured with the automatic adiabatic calorimeter and the thermodynamic functions [H _T-H _298.15] and [S _T-S _298.15] were derived in the temperature range from 80 to 390 K with temperature interval of 5 K. Thermal decomposition behavior of the complex in nitrogen atmosphere was studied by thermogravimetric (TG) analysis and differential scanning calorimetry (DSC).     

Rapid synthesis,kinetics and thermodynamics of binary Mn<Subscript>0.5</Subscript>Ca<Subscript>0.5</Subscript>(H<Subscript>2</Subscript>PO<Subscript>4</Subscript>)<Subscript>2</Subscript> · H<Subscript>2</Subscript>O

The non-isothermal kinetics of dehydration of AlPO₄·2H₂O was studied in dynamic air atmosphere by TG–DTG–DTA at different heating rates. The result implies an important theoretical support for preparing AlPO₄. The AlPO₄·2H₂O decomposes in two step reactions occurring in the range of 80–150 °C. The activation energy of the second dehydration reaction of AlPO₄·2H₂O as calculated by Kissinger method was found to be 69.68 kJ mol⁻¹, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction of heat and is non-spontaneous process.