Gas phase PVT properties and second virial coefficients of dimethyl ether

Dimethyl ether (DME) is an important chemical material and gets more and more attention as a clean alternative fuel and refrigerant nowadays. The gas phase PVT properties of dimethyl ether were measured using the Burentt-isochoric coupling method in the temperature range of 328–403 K with two Burnett expansions at 383 and 403 K. A total of 126 experimental points have been obtained. The experimental measurement uncertainties were estimated to be within ±10 mK for temperature and ±0.7 kPa for pressure. The second virial coefficients along 16 isotherms were derived using the present data.     

Path-integral calculation of the third virial coefficient of quantum gases at low temperatures

We derive path-integral expressions for the second and third virial coefficients of monatomic quantum gases. Unlike previous work that considered only Boltzmann statistics, we include exchange effects (Bose-Einstein or Fermi-Dirac statistics). We use state-of-the-art pair and three-body potentials to calculate the third virial coefficient of (3)He and (4)He in the temperature range 2.6-24.5561 K. We obtain uncertainties smaller than those of the limited experimental data. Inclusion of exchange effects is necessary to obtain accurate results below about 7 K.     

The viscosity of triethylamine vapor at low densities and in the saturated vapor phase

For the first time, results of high-precision measurements of the viscosity coefficient of triethylamine vapor at low densities are reported. The relative measurements with an all-quartz oscillating-disk viscometer were carried out along seven isochores at densities from 0.002 to 0.009 mol m⁻³ in the temperature range between 298 and 498 K. The uncertainty is estimated to be ±$\pm$0.2% at ambient temperature, increasing up to ±$\pm$0.3% at higher temperatures. First isothermal values were recalculated from the original experimental data and then evaluated with a first-order expansion for the viscosity, in terms of density. In addition, viscosity values of the saturated vapor were determined at low temperatures. The results are utilized to model the viscosity coefficient of triethylamine vapor at moderately low densities. A so-called individual correlation on the basis of the extended theorem of corresponding states was employed to describe the zero-density viscosity coefficient, whereas the Rainwater–Friend theory was used to represent the initial density dependence expressed as second viscosity virial coefficient.     

Evaluation of the parameters of the Bender equation of state for low acentric factor fluids and carbon dioxide

Volumetric properties of several low acentric factor fluids (Ar, CH₄, C₂H₆, Kr, N₂, Ne, O₂, Xe) as well as CO₂ are modeled using the Bender equation of state. This equation is a linear function of 19 adjustable parameters, which are evaluated from properties data, using a linear numerical procedure. The validity of the EOS is tested by calculating the Joule-Thomson inversion curve. A simple model is in particular used to correlate the inversion properties predicted by the Bender equation, expressed in term of reduced pressure as a function of reduced temperatures ranging from 0.8 to 6. The simple correlation reproduces accurately the used data. We employ data on state behaviour ρ(P,T) of homogeneous fluid phases, vapour-liquid equilibrium, second virial coefficient and the coordinates of the critical point.     

Estimation of activity coefficients at different temperatures by using the mean spherical approximation

A method of estimating activity coefficients for a variety of electrolytes at different temperatures is presented. The MSA approximation is used to calculate the activity coefficients from experimental data available in the literature. This strategy provides suitable results within a wide range of temperatures, electrolyte stoichiometries and concentrations of investigated solutions.     

Estimation of activity and osmotic coefficients of strong electrolytes in water at elevated temperatures

It was found over a wide concentration and temperature range that differences between osmotic coefficients of a given electrolyte and a standard electrolyte, - ^st , can be approximated by a linear relation. Sodium chloride, calcium chloride and sodium sulfate were chosen as standard electrolytes for 1:1, 2:1 and 1:2 electrolytes, respectively. Special numerical procedures were developed for the prediction and estimation of activity and osmotic coefficients at elevated temperatures based on data at two temperatures or on data at room temperature only. Reasonable agreement was found between activity coefficients estimated by the present procedure and those correlated by Pitzer's and Meissner's equations.     

Subgroup‐chain symmetry‐adapted irreducible matrices and CG coefficients of point groups

The irreducible matrices and Clebsch–Gordan coefficients of any crystallographic point group adapted to all possible canonical subgroup chains are calculated ab initio for both single‐valued and double‐valued representations and tabulated with exact values in the form of or and with components labeled by the irrep labels of the group chain in Koster notation. The phases and ordering of the components of irreducible bases for the cubic point groups are properly chosen so that irreducible matrices for all subgroup chains of G=T_d, O, O_h obey the associated relations D(G)=D(G)D(G), i=4, 6, and the complex conjugation relation for the group T, D(T)=D(T)*. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 67–80, 1999     

Dispersion properties of TiO2 nano-powder synthesized by homogeneous precipitation process at low temperatures

The dispersion stability of rutile TiO₂ powder with a unique nano-structure synthesized by homogeneous precipitation process at low temperatures (HPPLT) has been investigated with adding the various electrolytes in both pure aqueous and organic media. Zeta potential measurements have shown that the addition of electrolytes such as CsCl, CaCl₂, FeCl₃, and ZrCl₄ to aqueous and pure organic dispersion media leads to generally a charge reversal from negative to positive on the surface of TiO₂ particle. The electrostatic repulsive force acting on between TiO₂ particles dispersed in pure organic media was found to be significantly greater than that in aqueous media, which is closely related to the physical properties of the organic solvents, such as viscosities and dielectric constant. The surface potentials of TiO₂ particles have been greatly modified by the particulate properties, pH, dispersion medium, and valence of the ionic species, which governs the colloidal behavior of TiO₂ particles virtually.     

Osmotic coefficients of dilute aqueous solutions of unsymmetrical cobalt-amine type salts at 0°C

The osmotic coefficients of dilute aqueous solutions of [Co(pn)₃]X₃ [pn=1,2-diaminopropane and X=Cl^–, Br^– and (NO₃)^–] and [Co(tn)₃]X₃ (tn=1,3-diaminopropane and X=Cl^– and Br^–) have been measured from 0.00 to 0.02 mol-kg^–1 at 0°C by the freezing point method. The results have been compared with those obtained from the numerical integration of the Poisson-Boltzmann equation.     

Thermodynamics of electrolyte solutions: Activity and osmotic coefficients of aqueous NaCl in the NaCl-MgCl2-H2O system at different temperatures by the EMF method

The activity and osmotic coefficients of aqueous NaCI in the NaCl-MgCl₂-H₂O system at 25, 35 and 45°C and total ionic strengths of 0.5, 1, 2 and 3 were obtained by an EMF method using a sodium ion-selective electrode and an Ag/AgCl electrode. The Harned coefficients and Pitzer binary and ternary interaction coefficients were also determined.     

Rate coefficients of the CF3CHFCF3 + H → CF3CFCF3 + H2 reaction at different temperatures calculated by transition state theory with ab initio and DFT reaction paths

The minimum energy path (MEP) of the reaction, CF₃CHFCF₃ + H → transition state (TS) → CF₃CFCF₃ + H₂, has been computed at different ab initio levels and with density functional theory (DFT) using different functionals. The computed B3LYP/6‐31++G**, BH&HLYP/cc‐pVDZ, BMK/6‐31++G**, M05/6‐31+G**, M05‐2X/6‐31+G**, UMP2/6‐31++G**, PUMP2/6‐31++G**//UMP2/6‐31++G**, RCCSD(T)/aug‐cc‐pVDZ//UMP2/6‐31++G**, RCCSD(T)/aug‐cc‐pVTZ(spd,sp)//UMP2//6‐31++G**, RCCSD(T)/CBS//M05/6‐31+G**, and RCCSD(T)/CBS//UMP2/6‐31++G** MEPs, and associated gradients and Hessians, were used in reaction rate coefficient calculations based on the transition state theory (TST). Reaction rate coefficients were computed between 300 and 1500 K at various levels of TST, which include conventional TST, canonical variational TST (CVT) and improved CVT (ICVT), and with different tunneling corrections, namely, Wigner, zero‐curvature, and small‐curvature (SCT). The computed rate coefficients obtained at different ab initio, DFT and TST levels are compared with experimental values available in the 1000–1200 K temperature range. Based on the rate coefficients computed at the ICVT/SCT level, the highest TST level used in this study, the BH&HLYP functional performs best among all the functionals used, while the RCCSD(T)/CBS//MP2/6‐31++G** level is the best among all the ab initio levels used. Comparing computed reaction rate coefficients obtained at different levels of theory shows that, the computed barrier height has the strongest effect on the computed reaction rate coefficients as expected. Variational effects on the computed rate coefficients are found to be negligibly small. Although tunneling effects are relatively small at high temperatures (～1500 K), SCT corrections are significant at low temperatures (～300 K), and both barrier heights and the magnitudes of the imaginary frequencies affect SCT corrections. © 2012 Wiley Periodicals, Inc.