Virgílio Meira Soares

Surface tension of pure and mixed simple substances at low temperatures

Abstract A new design of cell is described for measuring the gas-liquid surface tension of both pure and mixed liquefied gases by the differential capillary-rise method in the temperature range 90–250 K at pressure up to 1000 Torr. Results for the pure methane, krypton, tetrafluoromethane, ethene, ethane, and dimethyl ether at temperatures below their normal boiling point are presented, compared with literature values, and analysed in terms of simple two- and three-parameter forms of the principle of corresponding states. Results are illustrated for the mixture methane + tetrafluoromethane in the temperature range 98 to 102 K.

THERMODYNAMIC PROPERTIES OF BINARY LIQUID MIXTURES OF ETHANE AND ETHYLENE WITH METHANE AND THE RARE GASES

Two series of binary liquid mixtures containing either ethylene or ethane have been investigated, at one or more temperatures (usually at the triple-point temperature of the component with the higher melting-point). In the ethylene series liquid-vapour equilibrium and liquid density studies were carried out for mixtures with methane, krypton and xenon; the heats of mixing were also measured for the ethylene + krypton mixtures. In the ethane series, which comprised mixtures with methane, argon, krypton and xenon, all three properties were measured except for the ethane + methane and ethane + argon systems where the enthalpies of mixing were already known. The ethylene + ethane system was also investigated at 161.39 K. The results have been used to estimate the thermodynamic excess functions GE , VE and HE . The GE values decrease, within each series, as one moves from the lighter to the heavier rare gas, the values being lower in the ethane series. For the ethane + xenon mixtures both GE and HE are negativ...

The Entrepreneurial University: A Fine Answer to a Difficult Problem?.

The recent changes in the relationship between universities and society and the change of attitudes of governments towards higher education institutions are analysed. The different possible reactions of the institutions to the more demanding attitude of society as a whole are discussed. The authors present a critical view of the concept of entrepreneurial universities based on the work of Burton Clark and on the results of the quality audits of the Association of European Universities (CRE), and offer some comments about their applicability and usefulness to European higher education systems.

Surface tension for octafluorocyclobutane, n-butane and their mixtures from 233 K to 254 K, and vapour pressure, excess Gibbs function and excess volume for the mixture at 233 K

Abstract The surface tensions of octafluorocyclobutane (234 to 267 K), n-butane (238 to 273 K) and of their mixtures (232 to 254 K) have been measured by differential capillary rise; there is a slight minimum in the isotherms near x(c-C4F8) ≈ 0.8 but no maximum. The total vapour pressure and density of the liquid mixture were measured at the triple point temperature of c-C4F8, 233 K. The mixture displays marked positive azeotropy. The excess Gibbs function and excess volume are both large and positive but the deviation from ideality is insufficient for liquid—liquid immiscibility whose absence was confirmed by visual observation at temperatures down to the solid—liquid phase boundary. All the foregoing are consistent with theoretical expectations based upon the dominant effect of an interaction energy between the unlike components which is smaller than that predicted by the Berthelot geometric mean rule. No inferences can be drawn as to the role of chain flexibility.

The thermodynamic excess functions of krypton+ethene liquid mixtures☆

Abstract Measurements are reported of the total vapour pressure of liquid mixtures of krypton + ethene at the triple-point temperature of krypton (115.77 K) as a function of composition, of the excess molar volumes of the mixtures at the same temperature, and of the excess enthalpy at 117.7 K. These results are compared with those obtained for similar systems, namely methane + ethene and xenon + ethene, and interpreted in the light of some simple theories of liquid mixtures.

Thermodynamics of binary liquid mixtures involving hydrogen bromide, hydrogen chloride and xenon

The total vapour pressure of the systems hydrogen bromide + xenon and hydrogen bromide + hydrogen chloride have been measured as a function of composition at 195.42 K. The results have been used to estimate the excess Gibbs function GE. The volume of mixing VE has been determined for each system at 195.42 K. The HBr + Xe system departs considerably from ideal behaviour, while HBr + HCl is only slightly nonideal. Neither system exhibits an azeotrope at the temperature studied. These results, together with similar data reported previously for the HCl + Xe system (J.C.S. Faraday I, 1975, 71, 1372), are compared with theoretical calculations based on perturbation theory for liquids of nonspherical molecules. Agreement is good for all three systems. The results show that both dipolar and quadrupolar forces for the HCl and HBr molecules have a large effect on the phase diagram, while other types of anisotropic intermolecular forces (overlap, dispersion, induction) appear to have a considerably smaller effect.

What factors of satisfaction and motivation are affecting the development of the academic career in Portuguese higher education institutions

de De-zembro, 399 — 4450-227, Matosinhos, Portugal. E-mail: lmachado@cipes.up.pt.*** Doutoramento em engenharia quimica (quimica termodinâmica). Professor e Investigador da Universidade de Lisboa (UL) e do Cipes. Endereco: Alameda da Universidade, 1600, Lisboa, Portugl. E-mail: vmsoares@fc.ul.pt.**** Doutoramento em ciencias da educacao. Professor e investigador do Instituto Politecnico de Leiria (IPL) e do Cipes. Endereco: Rua 1

Thermodynamics of the xenon+methyl chloride system

Abstract The total vapour pressure of the xenon + methyl chloride system has been measured as a function of composition at 175.44 and 182.32 K. The resulting data have been used to evaluate the excess Gibbs functions GE at the same temperatures. The excess enthalpy and excess molar volume have also been measured at 182.32 K. The system shows large positive deviations from Raoults law but negative volumes on mixing. These results are compared with theoretical predictions of a recent molecular theory and of standard engineering methods. The calculations show the superiority of the molecular theory over more empirical procedures such as those based on the Redlich-Kwong equation of state or the regular-solution model.

Adsorption of pure vapours of ethanol and n-heptane and their liquid mixtures on activated carbon

Physical characterization of the adsorbent has been made by means of the adsorption of nitrogen at 77 K and of pure ethanol and pure n-heptane at 298 K. Analysis of these isotherms by the B.E.T. method and the αs-plot of the nitrogen isotherm reveals the existence of narrow pores of different width including ultramicropores in which the accessibility of ethanol and n-heptane is restricted.The adsorption isotherm from the liquid mixture ethanol(1)–n-heptane(2) on activated carbon has been determined at 298 K. To analyse this isotherm the results obtained from the adsorption of the pure component vapours have been used. There is a lack of consistency with a monolayer model for the liquid/solid interface in which all segments of the chain molecules lie parallel to the surface. Assuming this orientation, an adsorbed phase of at least three layers must be considered. The monolayer model requires that the adsorbed molecules are perpendicular to the surface.

Surface tension of perfluoropropane, perfluoro-n-butane, perfluoro-n-hexane, perfluoro-octane, perfluorotributylamine and n-pentane. Application of the principle of corresponding states to the surface tension of perfluoroalkanes

The orthobaric surface tensions of C3F8, n-C4F10, n-C6F14, C8F18, (C4F9)3N and n-C5H12 have been measured by the differential capillary-rise technique over various ranges of temperatures. The results for the perfluoroalkanes have been analysed in terms of the van der Waals equation, the Brock and Bird equation incorporating Pitzers acentric factor and the phenomenological corresponding-states treatment of Patterson and Rastogi; the data are fitted with varying degrees of success. The phenomenological principle of corresponding states to which the surface tensions for the perfluoroalkanes conform is not identical to that for the n-alkanes and some other homologous series, but it is similar to it, in particular in the need for at least three reduction parameters.