Determination of the standard molar Gibbs energy of formation of calcium zirconate by a galvanic cell involving calcium-ion conducting solid electrolyte

The standard molar Gibbs energy of formation of CaZrO₃from CaO andZrO₂ has been determined by the e.m.f. measurements of a galvanic cell with calcium-ion conducting solid-state electrolyte in the temperature range 1073 K to 1273 K. The average values of the standard enthalpy and the standard entropy in the temperature range covered by the e.m.f. measurements have also been estimated. The results have been compared with those obtained by other authors.     

The standard molar Gibbs free energy of formation of NiO from high-temperature e.m.f. measurements

The standard molar Gibbs free energy of formation of NiO was determined in the temperature range 760 to 1275 K from measurements on reversible galvanic cells of the form: $\text{Pt}\text{Ni}\text{+}\text{NiO}\text{ZrO}{}_2\text{+}\text{CaO}\text{O}{}_2\text{(air)/Pt}$. The results can be represented by the equation: Δ_fG_m^o(NiO) = {?232450+83.435(T/K)} J·mol^?1, in excellent agreement with those previously reported.     

Determination of nitrogen diffusivities in liquid cyclohexane over a wide temperature range

The diffusivity of nitrogen in liquid cyclohexane has been measured at temperatures from 21 °C to 140 °C and at pressures of 10 – 15 atm, using a high pressure wetted sphere absorber apparatus. The diffusivity increased from 4.0 × 10⁻⁵ cm² s⁻¹ to 2.8 × 10⁻⁴ cm² s⁻¹ over this temperature range.Rippling of the film at the higher flow rates restricted the flow rate range which could be utilized for the diffusivity determinations. The measured absorption rates for flows in which rippling occurred were up to 15% higher on a 20 mm sphere and up to 40% higher on a 30 mm sphere. This limited the suitability of the wetted sphere absorber for this type of work.     

Determination of the standard Gibbs free energies of formation of barium zirconates in the temperature range (1073 to 1273) K

The standard molar Gibbs free energies of formation of BaZrO₃, and Ba₂ZrO₄ have been determined by solid-state galvanic cells involving a single crystal CaF₂ as a solid-state electrolyte. The e.m.f. measurements were performed in the temperature range (1073 to 1273) K. The average values of the standard molar enthalpy and the standard molar entropy of formation in the temperature range covered by the e.m.f. measurements have been also estimated. The results have been compared with those obtained by other authors.     

The standard Gibbs free energy of formation of calcium chromium (III) oxide in the temperature range (1073 to 1273) K

The standard molar Gibbs free energy of formation of CaCr₂O₄ from CaO and Cr₂O₃ has been determined by the e.m.f. measurement of galvanic cells involving a single crystal CaF₂ and a polycrystalline CaZrO₃ solid-state electrolytes in the temperature range (1073 to 1273) K. Reproducible e.m.f. values were obtained. The average values of the standard molar enthalpy and the standard molar entropy in the temperature range covered by the e.m.f. measurements have been also estimated. The results have been compared with those obtained by other authors.     

The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C₅H₈O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900–1500 K, 110–560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663–773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉_down is a fixed 400 cm^?1. Arrhenius expressions for k_∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.     

Rate of the retro-Diels-Alder dissociation of 1,2,3,6-tetrahydropyridine over a wide temperature range

Rate constants for the retro-Diels-Alder dissociation of 1,2,3,6-tetrahydropyridine, to 1,3-butadiene and methanimine, have been measured over 650–1450 K. To cover this range, three separate techniques were used at three laboratories: laser schlieren and single pulse shock tube methods, and a comparative rate flow system technique. The derived rate constants are extrapolated to the high-pressure limit with an RRKM model parameterized to fit the falloff observed in the laser-schlieren measurements. The resulting high-pressure rate constants show a reduction in activation energy of about 10 kcal/mol, comparing the isoelectronic cyclohexene, but little change in A-factor. There is an apparent increase in activation energy of 4 kcal/mol over the temperature range of these experiments, which is just outside probable error. Such a rise in activation energy is in marked contrast to the drop usually seen in simple bond fission, and may reflect a change from a concerted to a stepwise, biradical mechanism at high temperatures.     

Dielectric constants of fluid mixtures over a wide range of temperature and density

A new expression is presented for estimating the dielectric constant of a fluid mixture as a function of temperature, density and composition. The estimated dielectric constants (and their derivatives) are required for phase-equilibrium calculations, based on an equation of state, for systems containing electrolytes and nonelectrolytes. The new expression holds for the entire range of fluid densities, from zero to liquid-like densities. Mixing of components is performed on a volume-fraction basis at constant temperature and constant reduced density. For polar components where data are not available at the temperature and/or reduced density of interest, the well-characterized behavior of water is used to extrapolate the available pure-component data. The importance of using the correct density of the mixture is shown. Using one adjustable parameter for each nonideal binary subsystem, predicted results can be significantly improved.     

NO在Er2O3/Bi2O3催化剂上的程序升温分解

NOx是造成大气污染的化学物质之一,因此,消除NOx是环境保护的一项重要任务,目前比较成熟的消除NOx工艺是用氨为还原剂和V2O5/TiO2为催化剂的选择催化还原(SCR)法[1],但其成本过高.     

Additive estimates of the thermodynamic properties of triene hydrocarbons over a wide temperature range

An increment method for calculating the thermodynamic properties of aliphatic triene hydrocarbons is suggested. The method is based on substituting procedures and additive inclusion of 1,4-and 1,5-carbon-carbon intramolecular interactions. Parameter values for estimating the enthalpies of formation of gaseous alkatrienes at 298.15 K were found. A procedure for determining the thermodynamic properties of conjugated alkatrienes at arbitrary temperatures was developed. This procedure is based on the additive determination of the coefficients of polynomials that describe the temperature dependences of properties. The parameters for determining the isobaric heat capacities, entropies, and reduced enthalpies and Gibbs energies of conjugated triene hydrocarbons in the gas phase were found. Calculations reproduce experimental data with accuracy at the level of measurement errors. A thermodynamic analysis of the rearrangements of 2,6-dimethyloctatrienes (alloocimene isomers) was performed. The compositions of equilibrium mixtures of 14 aliphatic terpenes were determined at five gas phase temperatures from 298.15 to 1000 K.     

A method to estimate the Gibbs free energy of non-equilibrium alloys by thermal analysis

A method has been developed to estimate the Gibbs free energy $ \left( {G_{\text{S}}^{\text{NE}} } \right) $ of the non-equilibrium solid alloys with multicomponents based on differential scanning calorimetry (DSC) analysis. In this method, the DSC curves of the non-equilibrium and equilibrium alloys during heating up to fully melting and those of the alloys during solidifying were measured. Then the thermal effects of the solid phase transformations from non-equilibrium to equilibrium states and the equilibrium solidification could be calculated. By evolving the traditional equal-G curve principle to equal-G point, the Gibbs free energy of the equilibrium solid alloy with multicomponents could be obtained on condition that the free energy of the liquid alloy was known. Considering the thermal effects of the solid phase transformations from non-equilibrium to equilibrium states, the Gibbs free energy value of the non-equilibrium alloys with a given composition could be achieved although the phase constitution of the equilibrium solid alloys and the Gibbs free energy of each phase were not known, and the calculation errors could be reduced by dividing the alloys into many infinitesimal virtual pure metals. The Gibbs free energy of the non-equilibrium Al?CSi?CMn alloys was calculated by using this method, confirming the validity of this method.     

Calorimetric studies of poly(ethylene terephthalate) stretching over a wide temperature range

Heat effects and structural transformations in amorphous crystallizable poly(ethylene terephthalate) (PET) during uniaxial stretching accompanied by neck formation, have been investigated by calorimetric and x-ray methods over a wide range of temperatures and deformation rates. At small deformation (not exceeding 1–2%) and at temperatures below the glass transition temperature of the polymer, PET behaves as an elastic body. Upon stretching at a constant rate, constant heat power is absorbed, heat effects during loading and unloading coincide completely, and no hysteresis is observed. At large deformations (of the order of 50%), cold drawing develops in this temperature range. The internal energy change in cold drawing is zero within experimental error. A periodic heat release during the self-oscillation regime of drawing PET corresponds to periodic changes in stress, in the rate of the neck formation, and in the appearance of the sample. The temperature limits of the region where crystallization resulting from an uniaxial drawing of the polymer is possible, have been determined, and the heat effect of this phase transition has been measured. Orientation crystallization develops only from 70 to 94°C. These limits are insensitive to changes in deformation rate within one decimal order. The structure of PET in this temperature range has been investigated. The heat of phase transition of orientation crystallization of PET has been determined from the relationship between the measured values of the internal energy change during this process and the limiting degree of crystallinity for the stretched samples. This heat proves to be 5.5 ± 0.1 cal/g.     

Optimization of equilibrium carbon dioxide methane reforming parameters by the Gibbs free energy minimization method

The thermodynamic equilibrium in the carbon dioxide conversion of methane is studied by Gibbs energy minimization. The curves that represent the dependences of the degree of coke formation, the content of methane and carbon dioxide in syngas, and the syngas module on the CO₂/CH₄ mole ratio in the initial mixture and on temperature at various pressures, are plotted. The regions in which the CO₂/CH₄ mole ratio is optimal for carbon dioxide conversion and no coke formation occurs, and which are characterized by a minimal content of methane and carbon dioxide in syngas, are revealed.     

宽广温度范围的水离子积计算公式

宽广温度范围的水离子积是在理论上和实际应用上涉及面很广的重要物理化学性质之一.傅培鑫,Quist及Marshall等在总结实验数据的基础上提出了相应的计算水离子积的经验公式;Taylor还用热力学方法进行了计算.在饱和蒸气压及0～800℃范围内,以Marshall-Franck的经验公式准确度为最高,并由国际蒸气性质协会(IAPA)于1980年公布为计算宽广温度范围的水离子积公式.但是在温度较高(200～300℃)时,此公式的计算值与实验值之间的误差随温度升高而逐渐增大,平均误差为0.033pK_w单位.     

On the temperature dependence of the order parameter of liquid crystals over a wide nematic range

Abstract

Based on the ideas of Landau-de Gennes theory applied to nematic liquid crystals, several forms for the variation of the order parameter as a function of temperature are investigated over a wide nematic range. These functional forms are used to fit the experimental order parameters, determined through the use of C-13 NMR, for 4-methoxybenzylidene-4′-butylaniline (MBBA) and 4-n-pentyl-4′-cyanobiphenyl (5CB), and the physical significance of the parameters is discussed. A comparison of the results shows that the functional form which fits the experimental data best is similar to the Haller equation, a useful relation which is usually regarded as empirical. In this case, the coefficients resulting from a semi-empirical approach based on the Landau-de Gennes treatment may be thought of as quantifying the importance of the structure and rigidity of the liquid crystal in determining the temperature dependence of the order parameter for that liquid crystal. In the process, we have also examined the pretransitional behaviour in the C-13 NMR chemical shifts of liquid crystals observed within a few tenths of a degree above the nematic to isotropic transition temperature.