Enthalpies and entropies of sublimation for N-acetylglycine amide (NAGA), N-acetyl-L-alanine amide (L-NAAA), and N-acetyl-D-leucine amide (D-NALA) were determined from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method.
Authors:I. Bravo-Osuna, A. Muńoz-Ruiz, M. Jiménez-Castellanos, J. Ford, and M. Whelan
The use of modulated temperature differential scanning calorimetry (TMDSC) and differential scanning calorimetry (DSC) in the measurement of the glass transition temperature (Tg) in polymer-water systems presents several important problems. These include the presence of water evaporation endotherms, partial water evaporation during scanning, changes in pan integrity due to vapour pressure developing in the pan headspace during analysis, and possible interaction between water and polymer at high temperatures. As a result, in most of the cases, only apparent Tg values can be obtained. In this study, TMDSC and DSC were used to determinate the thermal behaviour of methylmethacrylate copolymer-water systems. The samples were previously equilibrated at different relative humidities (RH) from 0 to 97% RH. Three different pan arrangements were used. In addition, thermogravimetric analysis (TG) was carried out to determine the initial amount of water in the sample. None of the pan arrangements was entirely suitable for the study of these systems. When sealed pans were used, the plastification effect of water was observed. Some evidence of degradation was also observed in which water and methylmethacrylate appeared to play roles.
Authors:G. K. Bratspies, J. F. Smith, J. O. Hill, and P. J. Derrick
A new tin dithiocarbamate containing sulphur bridges, di-μ-sulphidobis [bis(N,N-diethyldithiocarbamato)tin(IV)], has been isolated from the thermal decomposition of tetrakis(N,N-diethyldithiocarbamato)tin(IV). A dimeric structure is proposed on the basis of results from mass spectrometry, infrared spectroscopy, thermal analysis and vapour pressure osmometry.
A miniaturized effusion cell adapted to a Sorption LKB microcalorimeter has been designed, built and tested. Vaporization is performed isothermally into a vacuum through a small orifice permitting a vapour pressure very close to the equilibrium values. The cell has been tested by measuring the enthalpies of vaporization at 298.15 K of reference liquid compounds (water, benzene, propanol-1, propanol-2) with a reproducibility better than 1%. Enthalpies of vaporization of butanol-1 and deuterated water have also been determined.
Authors:L. Zelenina, T. Chusova, Yu. Stenin, and V. Bakovets
The enthalpies and temperatures of melting of RSi(CH3)3, R4Si, R3P, R3As, R3Sb, R3Bi, R2Te and R2Hg (R=C6F5) were obtained by scanning calorimetry measurements. The pressure of the saturated and unsaturated vapors of RSi(CH3)3, R2Si(CH3)2, R4Si, R3Ga, R3P, R3As, R3Sb, R3Bi, R2Te and R2Hg has been measured by the static method with a membrane-gauge manometer. It was established that all investigated substances
proceeded to vapor as monomers. Equations approximating the dependences of saturated vapor pressures on temperature and the
enthalpies and entropies of vaporization were obtained. Grafite films with silicon intercalated up to 25 at.% were grown by
CVD using R4Si as a precursor. These films showed semiconductor properties in the temperature interval 80–300 K.
The results of this study indicate that in terms of efficiency, the Packard 2250Ca liquid scintillation spectrometer is sensitive to the scintillation cocktail employed for241Pu analysis, particularly when the burst counting circuit is enabled. Cocktails exhibiting low t-SIE values should be avoided since quenching has a critical influence on such a low energy
– emitter. This effect would be independent of burst circuitry use. Cocktails which include naphthalene type derivatives such as the alkylnaphthalene solvent employed in Optiphase HiSafe 3 and Ultima Gold should be avoided since the broad pulse shapes produced are incompatible with the burst counting circuit which distinguishes background events from true
– events by means of pulse shape/duration analysis. Efficiency is also sensitive to the concentration of bis-MSB employed in conjunction with the primary fluor. Enhancements in efficiency are observed with appropriate concentrations. These results are in line with previous work with14C and are postulated as being a consequence of sharpening prompt pulse widths or suppression of afterpulsing. It is recommended that Instafluor should be used to maximize response, or a cocktail such as butyl-PBD/bis-MSB in pseudocumene at rates of 6 and 1.5 mg ml–1, respectively, where a lower vapor pressure solvent is particularly required.
Room temperature ionic liquids are a new class of solvents of potential interest for liquid chromatography. Ionic liquids possess a combination of physical and solvation properties that are complementary to conventional organic solvents. Applications in liquid chromatography are currently limited by their unfavorable viscosity and low-wavelength absorption in the ultraviolet (UV) region. In addition, for planar chromatography, the absence of a vapor pressure does not allow evaporation of ionic liquid solvents after development. The room temperature ionic liquids are good solvents for nonionic compounds with a different blend of intermolecular interactions compared with conventional organic solvents as indicated by solvatochromic measurements and the system constants of the solvation parameter model. Current applications in column and planar chromatography are reviewed to demonstrate the potential of room temperature ionic liquids as mobile phases or mobile phase additives in separation science. A real breakthrough in their use, however, requires the identification of new room temperature ionic liquids with viscosity closer to those of conventional organic solvents as well as addressing other minor issues described in the text.
Authors:Sung Park, Dong Cho, Moon Woo, Sung Hwang, Young Kang, Jeong Kim, and Hansoo Lee
Uranium dendrites which were deposited at a solid cathode of an electrorefiner contained a certain amount of salts. These
salts should be removed for the recovery of pure metal using a cathode processor. In the uranium deposits from the electrorefining
process, there are actinide chlorides and rare earth chlorides in addition to uranium chloride in the LiCl–KCl eutectic salt.
The evaporation behaviors of the actinides and rare earth chlorides in the salts should be investigated for the removal of
salts in the deposits. Experiments on the salt evaporation of rare earth chlorides in a LiCl–KCl eutectic salt were carried
out. Though the vapor pressures of the rare earth chlorides were lower than those of the LiCl and KCl, the rare earth chlorides
were co-evaporized with the LiCl–KCl eutectic salt. The Hertz–Langmuir relation was applied for this evaporation, and also
the evaporation rates of the salt were obtained. The co-evaporation of the rare earth chlorides and LiCl–KCl eutectic were
A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits the determination of mass changes in the sulfidized sample as functions of temperature and sulfur vapour pressure with an accuracy of 10−6 g. Besides heterogeneous kinetics measurements, it has been shown that the chemical diffusion coefficients and deviations from stoichiometry of metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration measurements.
The present work is part of a broader research program on the energetics of formation of heterocycles, aiming the study of
the enthalpic effects of the introduction of different substituents into heterocycles. In this work we present the results
of the thermochemical research on sulphur heterocycles of the type substituted thiophenes with different kind of substituents,
mainly alkyl, ester, acetyl, carboxamide, acetamide, carbonitrile and carboxaldehyde.
The standard (po=0.1 MPa) molar enthalpies of formation, in the condensed phase, at T=298.15 K, of a large number of substituted thiophenes, were derived from their standard massic energies of combustion, measured
by rotating-bomb combustion calorimetry, while the standard molar enthalpies of vaporization or sublimation of those compounds
were obtained either by high temperature Calvet Microcalorimetry, or by the temperature dependence of their vapour pressures
determined by the Knudsen effusion technique. The standard molar enthalpies of formation, of the studied sulphur heterocycles
in the gaseous phase, were then derived. The results are interpreted in terms of structural contributions to the energetics
of the substituted thiophenes, the internal consistency of the results is discussed and, whenever appropriate and possible,
empirical correlations are suggested for the estimation of standard molar enthalpies of formation, at T=298.15 K, of substituted thiophenes. A Table of enthalpic increments for different group substituents in positions 2 or 3
of the thiophene ring has been established.