Structures and phase transitions in (K<Subscript>1-x</Subscript>Rb<Subscript>x</Subscript>)<Subscript>2</Subscript>SeO<Subscript>4</Subscript>

Summary The phase diagram of the mixed crystal (K_1-xRb_x)₂SeO₄ was determined by means of thermal analysis and neutron scattering experiments. The hexagonal to orthorhombic phase transition line exists for any x. The normal-incommensurate phase transition temperature decreases continuously with increasing Rb content. However, the incommensurate-commensurate phase transition was not observed except for K₂SeO₄. According to the clear softening of the Σ₂- Σ ₃ phonon branches and the finite frequency at 0 K for x>0.34, an existence of the hypothetical phase transition was confirmed.     

Thermal analytical study of steels at high temperature including the range of melting

Measurements with a plate transducer, up to 1600°C, are investigated in the current paper. The calibration of the transducer, comparative measurements concerning the accuracy of specific heat capacity determination, the modelling for the high-temperature range and results for three steels are presented. The results are used to develop the database dbs for thermal simulation computations.     

Buffers for the physiological pH range: Thermodynamic constants of substituted aminopropanesulfonic acids from 5 to 55°C

ThepK ₂ values for 3-[(l,l-Dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO), and 3-[N,N-Bis(-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) have been determined at 12 temperatures over the range 5 to 55‡C by measurements of the emf of cells without liquid junction containing hydrogen and silver-silver chloride electrodes. The values of pK ₂ for AMPSO and DIPSO were found to be 9.138 and 7.576, respectively, at 25‡C. The thermodynamic quantities, δG‡, δH‡, δS‡, and δC _p ^‡ were calculated from the change of the equilibrium constants with temperature. These buffer substances are useful as secondary pH standards in the physiological region of pH 7 to 9. Camille and Henry Dreyfus Fellow, 1994–1996.     

硫酸钡微晶改性玻璃毛细管柱

为了更全面地了解硫酸钡微晶改性玻璃毛细管柱的特性，本文重点探讨了这种柱的柱容量，热稳定性以及液膜厚度与柱效能之间的关系，并给出了一些分析实例。     

Magnesium oxide as an effective catalyst in catalytic wet oxidation of H2S to sulfur

Four different magnesium oxides were studied in the wet oxidation of H₂S to sulfur. The H₂S removal capacity of MgO in the catalytic wet oxidation strongly depends on the pore size distribution. The MgO with relatively large pores (>100 ?) showed a high removal capacity of H₂S. It is suggested that the large pore size favors H₂S removal in the catalytic wet oxidation due to the limitation of diffusion. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal expansivity,volume and the effect of pressure on the isobaric heat capacity of 1-hexanamine from 0.1 to 400 MPa at 303, 353, 403 and 453 K

The thermal expansivity of 1-hexanamine has been determined as a function of pressure up to 400 MPa over the temperature range from 303 to 453 K. Measurements were performed in a pressure-scanning calorimeter by the stepwise technique. The compressibility as a function of pressure at 303 K was determined using the technique described before. The molar volume under atmospheric pressure was determined from the density measurements with a Paar instrument. From both the molar volume as a function of pressure at 303 K and the thermal expansivities the effects of pressure on the isobaric heat capacity were determined over the whole pressure and temperature range under study.

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Zusammenfassung Im Temperaturbereich 303–453 K wurde bis zu einem Druck von 400 MPa die Wärmeausdehnung von 1-Hexanamin als eine Funktion des Druckes ermittelt. Die Messungen wurden in einem Druck-Scanning Kalorimeter durch schrittweises Vorgehen ausgeführt. Unter Anwendung derselben Technik wurde bei 303 K die Kompressibilität als eine Funktion des Druckes ermittelt. Das molare Volumen bei atmosphärischem Druck wurde aus Dichtemessungen mit einem Paar-Instrument bestimmt. Aus dem molaren Volumen als eine Funktion des Druckes bei 303 K und den Wärmeausdehnungen wurde der Einfluß des Druckes auf die isobare Wärmekapazität über den gesamten untersuchten Druck- und Temperaturbereich bestimmt.

     

Modulated Differential Scanning Calorimetry

The reproducibility and reliability of the TA Instruments Modulated Differential Scanning Calorimeter (MDSC) was tested over a range of conditions. The equipment base line was found to be fairly constant with a very small fluctuation (10 W), which means a 0.1 % fluctuation on the scale of a normal polymer MDSC curve. The excellent stability of the base line and the reasonable reproducibility of the curves (5%) suggest that frequent calibration is not required.The heat capacities calculated from the modulated response to the variable temperature depend on the frequency for a given cell constant. The heat capacity cell constant is a unique function of the modulation frequency:k _c =K _c ^o p/(p–6.3) wherep is the time of the periodicity expressed in seconds and K _c ^o is the heat capacity cell constant measured on a standard material and reduced to zero frequency. The cell constants depend on the flow rate of the helium according to:K(He)=K ^o(1.298–0.004424He+1.438·10^–5 He ²) whereHe is the flow rate of helium in ml min^–1 andK ^o represents a constant at 100 cm³ min^–1. There is a strong dependence of cell constant on the flow rate ranges from 10 to 80 cm³ min^–1, while above this rate (up to 135 ml min^–1) the cell constant approaches a plateau.     

Characterization of buffers for electrokinetic separations

Buffers used in electrophoresis and electrochromatography must have a relatively low ionic strength in order to minimize ohmic heating in the presence of an applied potential. Calculation of pH, ionic strength, and the van Slyke buffer capacity, β, is therefore important. This paper describes thea priori calculation of these parameters for tris buffer made up with either glycine (a zwitterion) or HCl. A quadratic expression for pH, valid over wide ranges, is obtained for both buffer systems. The calculated values of pH, ionic strength, and buffer capacity are shown to agree with experimental results as a function of tris, HCl, and glycine concentrations ranging from 1 to 50 mM. A new parameter, the electrokinetic buffer effectiveness factor, is introduced to characterize buffers being considered for use in electrokinetic systems such as electrochromatography, and is used to determine the appropriate composition ranges for the buffer components.     

判断聚对苯基热解碳嵌锂容量的简单方法

The method to evaluate the reversible lithium insertion capacity (Qre) has been studied using poly (p-phenylence) (PPP) heat-treated at 550 1000 ℃ in inert gas atomsphere by H/C atomic ratio and FTIR measures. The H/C atomic ratio and Qre decreased with increasing heat-treament temperature. The absorption ratio of 1020cm-1 band to the 1440cm-1 band (Ra) is directly related to the Qre of carbon samples. The samples with R. >1-1 and without 807cm-1 peak tend to have high Qre (>372 mA.h-g-1). The reversible capacity for Li+ ion insertion decrease as Ra decreases.     

Thermodynamics of aqueous bile salt solutions: Heat capacity,enthalpy and entropy of dilution

Heat capacity data at various temperatures and enthalpies of dilution at 25°C are reported for aqueous bile salt solutions. The apparent molal heat contents _L have been combined with osmotic and activity coefficients to obtain the excess molal entropies. Measurements of some of these properties have also been carried out with the anionic detergent sodium dodecylsulfate so that the bile salt micellization process may be compared with that of a classical detergent. The observed data have been interpreted in terms of the hydrophobic association properties of bile salts in aqueous solution.