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1Author    C. Margheritis, A. Marini, C. SinistriRequires cookie*
 Title    Thermodynamics of /J-cyclodextrine/water Interactions  
 Abstract    From a purely enthalpic standpoint, the ß-CD hydration, as studied by semiempirical calcula-tions, appears improbable, in contrast to experiment. For the spontaneous hydration process, a compensation mechanism, connected with substrate stabilization and/or entropy increase, is sug-gested on the basis of simple thermodynamic considerations. The analysis is done on the basis of a single parameter £ w (> 0), which represents the energy needed to transfer a mole of water from the liquid to the ß-CD absorbed phase. The model, although simple, allows predictions largely consistent with the experimental results, while suggesting possible interpretations. 
  Reference    Z. Naturforsch. 52a, 348—350 (1997); received January 3 1996 
  Published    1997 
  Keywords    ß-cyclodextrine, Water interactions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0348.pdf 
 Identifier    ZNA-1997-52a-0348 
 Volume    52 
2Author    Heinz Gamsjäger1, Harald Marhold1, Erich Königsberger1, YiJung Tsai1, Hans Kolmer2Requires cookie*
 Title    S o lid - 3) 4 * **H20  
 Abstract    S o lu te P h a s e E q u ilib ria in A q u e o u s S o lu tio n s IX . T h e rm o d y n a m ic A n a ly s is o f S o lu b ility M e a s u r e m e n ts : L a (0 H) M(C 0 Dedicated to Prof. Hitoshi Ohtaki on the occasion of his 60th birthday The aqueous solubilities of La(OH)p^(COaJjA 0.1 H20, basic lanthanum carbonate of ancylite type, have been investigated as a function of ionic strength at 25.0 °C. The stoichiometric solubility constants defined by log* K1 0 = log [La3 + ] + 1.1 log pco — 3 log [H+1 have the values 11.10, 11.32, 11.42, 11.63, and 11.70 for / = 0.1, 0.25, 1.0, 2.0, and 4.0 mol kg (Na)C104 respectively. The extrapolation to infinite dilution using the Pitzer equations resulted in a "thermodynamic" solubility constant, log* K° 0 = 10.48 ± 0.08. This in turn led to the Gibbs energy of ancylite formation: Af G f98 {La(OH)08(CO3)11 0.1 H20} = -1.531.5 kJ mol-1. 
  Reference    Z. Naturforsch. 50a, 59—64 (1995); received October 1 1994 
  Published    1995 
  Keywords    Solubility, Carbonates, Lanthanum, Thermodynamics, Pitzer model 
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 TEI-XML for    default:Reihe_A/50/ZNA-1995-50a-0059.pdf 
 Identifier    ZNA-1995-50a-0059 
 Volume    50 
3Author    M. Sandmann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4'-w-Hexyl-Biphenyl-4-Carbonitrile (6CB) and 4 -w-Heptyl-Biphenyl-4-Carbonitrile (7CB) up to 300 MPa  
 Abstract    P, V m , 7" data were established for 4'-n-hexyl-biphenyl-4-carbonitrile (6CB) and 4'-n-heptyl-biphen-yl-4-carbonitrile (7CB) between 300 and 370 K up to 300 MPa, and specific volumes were determined for the liquid crystalline, isotropic, and also partly for the crystal phases. Volume and enthalpy chang-es at the phase transitions are also presented. In the case of 6CB, a new crystal phase has been detect-ed, corresponding to a triple point at 338 K and 196 MPa. The p, V m , T data enabled us to separate the entropy change into a volume-dependent part and configurational part. From the molar volumes along the nematic-isotropic phase transition T Nl (p), the molecular field parameter y= 3lnT NI /3ln V NI was deter-mined. 
  Reference    Z. Naturforsch. 53a, 233—238 (1998); received March 11 1998 
  Published    1998 
  Keywords    6CB, 7CB, High Pressure, pVT, Phase transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0233.pdf 
 Identifier    ZNA-1998-53a-0233 
 Volume    53 
4Author    M. Sandmann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4'-/i-Octyl-Biphenyl-4-Carbonitrile (8CB) up to 300 MPa  
 Abstract    P, V m , Tdata have been measured for the smectic, nematic and isotropic phases of 4'-n-octyl-biphen-yl-4-carbonitrile (8CB) in the temperature range 300-370 K and pressures up to 300 MPa. At atmos-pheric pressure all phase transitions appear to be of first order due to a discontinuity in the density. The volume change at the smectic A -nematic transition is only a tenth of the volume change at the clear-ing temperature. At moderate pressures below 80 MPa the S A -N transition could be detected as a dis-continuity in the period of oscillation in measurements with a high-pressure vibrating tube densimeter. At higher pressures the discontinuity seems to die away, possibly indicating a change from first order to second order transition. From the volume changes and the slopes of the transition lines we calculate the enthalpy changes at the phase transition. The p, V m , T data enable us to calculate the volume part of the entropy and the molecular field parameter y=9ln 7 N i/3ln V NI . 
  Reference    Z. Naturforsch. 53a, 787—792 (1998); received July 10 1998 
  Published    1998 
  Keywords    8CB, High Pressure, pVT, Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0787.pdf 
 Identifier    ZNA-1998-53a-0787 
 Volume    53 
5Author    M. Sandmann, F. Hamann, A. WürflingerRequires cookie*
 Title    PVT and DTA Measurements on trans-4-w-Hexyl- (4'-CyanophenyI)-Cyclohexane (6PCH) up to 300 MPa  
 Abstract    The phase diagram of trans-4-n-hexyl-(4'-cyanophenyl)-cyclohexane, (6PCH) has been estab-lished by high-pressure differential thermal analysis. Specific volumes are presented for temper-atures between 300 and 370 K up to 300 MPa. The p,V m ,T data have been determined for the nematic, isotropic, and (partly, in the neighbourhood to the melting curve) solid phases. Volume and enthalpy changes along the phase transitions have also been calculated. As previously, the p,Vm,T data were used to calculate the volume entropy for the nematic-isotropic transition. The molar volumes along the clearing line T NI (p) enabled us to calculate the molecular field parameter 7 = ain T NI /3ln V NI , being 4.1. 
  Reference    Z. Naturforsch. 54a, 281—286 (1999); received March 13 1999 
  Published    1999 
  Keywords    6PCH, High Pressure, pVT, Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0281.pdf 
 Identifier    ZNA-1999-54a-0281 
 Volume    54 
6Author    H. Schmalfuss, W. Weissflog, A. Würflinger3, S. Masberg3, G. M. Schneider3Requires cookie*
 Title    Thermodynamic Measurements on Selected Liquid Crystals at Normal and Elevated Pressures  
 Abstract    Densities have been determined for two 5-n-alkyl-2-(4-isothiocyanatophenyl)-l,3-dioxanes (6DBT, 10DBT), 4-n-tetradecyl-4'-cyanobiphenyl (14CB), 4-n-octyl-4'-thiocyanatobiphenyl (8BT) and two laterally aryl-branched mesogens 4-cyanobenzyl 5-(4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB), 3-cyanobenzyl 2,5-bis(4-n-octyloxybenzoyloxy)benzoate (3CN-BOB). The densities have been measured in the isotropic, nematic (only 3CNBOB) and smectic phases with a vibrating tube densimeter. The densities decrease with increasing alkyl chain length within a homologous series. Furthermore the enthalpy changes accompanying the phase transitions have been determined by DSC. 
  Reference    Z. Naturforsch. 56a, 262—266 (2001); received December 5 2000 
  Published    2001 
  Keywords    Specific Volumes, Density, DSC, Liquid Crystals, Thermodynamics 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0262.pdf 
 Identifier    ZNA-2001-56a-0262 
 Volume    56 
7Author    O. Akinlade, Z. Badirkhan3, G. PastorebRequires cookie*
 Title    Thermodynamics and Structure of Liquid Metals from a New Consistent Optimized Random Phase Approximation  
 Abstract    We study thermodynamics and structural properties of several liquid metals to assess the validity of the generalized non-local model potential (GNMP) of Li et al. [J. Phys. F16, 309 (1986)]. By using a new thermodynamically consistent version of the optimized random phase approx­ imation (ORPA), especially adapted to continuous reference potentials, we improve our previous results obtained within the variational approach based on the Gibbs -Bogoliubov inequality. Hinging on the unified and very accurate evaluation of structure factors and thermodynamic quantities provided by the ORPA, we find that the GNMP yields satisfactory results for the alkali metals. Those for the polyvalent metals, however, point to a substantial inadequacy of the GNMP for high valence systems. 
  Reference    Z. Naturforsch. 56a, 605—612 (2001); received March 1 2001 
  Published    2001 
  Keywords    Liquid Metals, Liquid Structure, ORPA, Pseudopotentials, Thermodynamics 
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 TEI-XML for    default:Reihe_A/56/ZNA-2001-56a-0605.pdf 
 Identifier    ZNA-2001-56a-0605 
 Volume    56 
8Author    C. J. Soeder, E. Hegewald, E. Fiolitakis, J.U G RobbelaarRequires cookie*
 Title    Temperature Dependence of Population Growth in a Green Microalga: Thermodynamic Characteristics of Growth Intensity and the Influence of Cell Concentration  
 Abstract    Growth intensity o f the green alga, Scenedesmus obliquus, was measured in autotrophic cultures, diluted once daily, between 20 and 30 °C in a light-dark cycle o f 16 : 8 h at initial optical densities between 0.02 and 1.2. Arrhenius analyses o f the results showed linear relationships be­ tween growth intensity and temperature below the temperature optimum. The temperature effects on growth, activation energy, deactivation energy and normalized Q i0 values were signifi­ cantly influenced by the amount o f available light energy per unit biomass. The temperature dependence o f nutrient-lim ited growth was not considered. 
  Reference    Z. Naturforsch. 40c, 227—233 (1985); received Decem ber 5 1984 
  Published    1985 
  Keywords    M icroalgae, Growth, Temperature, Light, Thermodynamics 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0227.pdf 
 Identifier    ZNC-1985-40c-0227 
 Volume    40 
9Author    M. Sandmann, F. Hamann, A. WürflingerRequires cookie*
 Title    PVT Measurements on 4-/i-Pentyl-4'-Cyano-Biphenyl (5CB) and trans-4-(4'-Octyl-Cyclohexyl)-Benzonitrile (8PCH) up to 300 MPa  
 Abstract    Specific volumes are presented for 4-n-pentyl-4'-cyanobiphenyl (5CB) and trans-4-(4'-octyl-cyclo-hexyl)-benzonitrile (8PCH) for temperatures between 300 and 370 K up to 300 MPa. The p,V m ,T data were determined for the liquid crystalline and isotropic phases, and partly also for the solid phase adjacent to the melting curve. Stable and metastable crystal phases can be distinguished. The density and melting temperature of the metastable form are lower than for the stable one. Volume and enthalpy changes accompanying the phase transitions are reported as well. The p,V m ,T data allow to calculate the entropy change for a hypothetical transition at constant volume. The molar volumes along the nematic-isotropic phase transition T NI (p) allow to determine the molecular field parameter y = S In T NI /0 In F N ,. 
  Reference    Z. Naturforsch. 52a, 739—747 (1997); received August 13 1997 
  Published    1997 
  Keywords    5CB, 8PCH, High pressure, pVT, Phase transitions, Thermodynamics, DTA 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0739.pdf 
 Identifier    ZNA-1997-52a-0739 
 Volume    52 
10Author    Masahisa KakiuchiRequires cookie*
 Title    Hydrogen Isotope Fractionation in Aqueous Alkali Halide Solutions  
 Abstract    The D/H ratios of hydrogen gas in equilibrium with aqueous alkali halide solutions were deter-mined at 25 °C, using a hydrophobic platinum catalyst. The hydrogen isotope effect between the solution and pure water changes linearly with the molality of the solution at low concentrations, but deviates from this linearity at higher concentration for all alkali halide solutions. The magnitude of the hydrogen isotope effect is in the order; Kl > Nal > KBr > CsCl ^ NaBr > KCl > NaCl > LiCl, at concentrations up to a molality of 4 m. The sign and trend of the hydrogen isotope effect is different from that of oxygen. In aqueous alkali halide solutions, the hydrogen isotope effect is influenced by both the cation and the anion species, while the oxygen isotope effect is mainly caused by the cation species. This suggests that the mechanism of hydrogen isotope fractionation between the water molecules in the hydration spheres and the free water molecules differs from the mechanism of the oxygen isotope fractionation. The hydrogen and oxygen isotope effects for alkali halides, except LiCl and NaCl, may be influenced by changes in energy of the hydrogen bonding in free water molecules. 
  Reference    Z. Naturforsch. 52a, 811—820 (1997); received April 15 1997 
  Published    1997 
  Keywords    Hydrogen Isotope, Alkali halide, D/H fractionation, Thermodynamics, Isotope effect 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0811.pdf 
 Identifier    ZNA-1997-52a-0811 
 Volume    52 
11Author    Phineus Markwick, Stanislaw Urban, Albert WürflingerRequires cookie*
 Title    High Pressure Dielectric Studies of 8CB in the Isotropic, Nematic, and Smectic A Phases  
 Abstract    The static and complex permittivity of 4-n-octyl-4'-cyanobiphenyl (8CB) has been measured for the isotropic, nematic and smectic A phases as functions of temperature and pressure. The ranges of 297 -361 K, 0.1 -220 MPa, and 0.1 -13 MHz, were covered. Only the parallel component of the complex permittivity, £*(/) = e'(f) — ie"(f), was measured. The relaxation times T||(p, T) as well as ris(p, T) were analysed at constant temperature, pressure and volumes yielding the activation volume, A ¥ V(T), activation enthalpy A^H(p), and activation energy lyU(V), respectively. All activation parameters calculated for the smectic A phase of 8CB are smaller than those obtained for the nematic phase. The activation energy constitutes approximately half of the activation enthalpy value in all three phases studied. The pressure study allowed to calculate the pressure dependence of the retardation factor g\\(p, T), from which the nematic potential q(p,T) can be derived. Using the relationships between g\\ and q/RT proposed by Kalmykov and Coffey, the order parameter (Piip, T)) was calculated as a function of pressure. 
  Reference    Z. Naturforsch. 54a, 275—280 (1999); received March 13 1999 
  Published    1999 
  Keywords    Liquid Crystals, 8CB, High Pressure, Dielectric, Thermodynamics, Order Parameter 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0275.pdf 
 Identifier    ZNA-1999-54a-0275 
 Volume    54 
12Author    A. Würflinger, M. Sandmann, W. WeissflogRequires cookie*
 Title    PVT Measurements on 3-Cyanobenzyl 2,5-bis(4-/i-octyloxybenzoyl- oxy)benzoate up to 250 MPa and 423 K  
 Abstract    P, V m , T data have been measured for the nematic and isotropic phases of 3-cyanobenzyl 2,5-bis (4-n-octyloxybenzoyloxy)benzoate between 273 and 423 K and up to 250 MPa. The volume changes accompanying the crystal -nematic and nematic -isotropic transitions have been determined. The cor-responding enthalpy changes have been calculated using the Clausius-Clapeyron equation. The p, V m , T data enable also to estimate the volume entropy for the nematic-isotropic transition. It is found that the configurational part of the transition entropy amounts to 80%, this portion being distinctly larger than found in previous studies for conventional rod-like liquid crystals. 
  Reference    Z. Naturforsch. 55a, 823—827 (2000); received July 17 2000 
  Published    2000 
  Keywords    Aryl-branched Liquid Crystals, High Pressure, pVT\ Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0823.pdf 
 Identifier    ZNA-2000-55a-0823 
 Volume    55 
13Author    A. Wiirflinger, W. WeissflogRequires cookie*
 Title    DTA and p VT Measurements on 4-cyanobenzyI-5- (4-n-octyloxybenzoyloxy)-2-undecyloxybenzoate up to 250 MPa and 383 K  
 Abstract    The phase diagram of 4-cyanobenzyl-5-(4-«-octyloxybenzoyloxy)-2-undecyloxybenzoate (4CNOUB) has been established with differential thermal analysis (DTA). The pressure range for the smectic A phase is limited, resulting in a triple point at 165 MPa and 378.26 K. p, Vm, T data have been measured for the smectic and istotropic phases of 4CNOUB between 243 and 383 K and up to 250 MPa. The vol-ume changes accompanying the crystal -smectic and scmectic -isotropic transitions have been deter-mined. The corresponding enthalpy changes have been calculated using the Clausius-Clapeyron equa-tion. The p, Km, 7 data enable also to estimate the volume entropy for the smectic -isotropic transition and the volume dependence of the clearing temperature. 
  Reference    Z. Naturforsch. 55a, 936—940 (2000); received September 15 2000 
  Published    2000 
  Keywords    Aryl-branched Liquid Crystals, High Pressure, pVT\ Phase Transitions, Thermodynamics 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0936.pdf 
 Identifier    ZNA-2000-55a-0936 
 Volume    55 
14Author    Patrizia Lau, G. Ottfried Hüttner, Laszlo ZsolnaiRequires cookie*
 Title    Reversible Öffnung von Metall-Metall-Bindungen: Quantitative Untersuchung des RingÖffnungsgleichgewichts von [Cp'(CO)2Mn]2SeAryl+ Reversible Opening of Metal Metal Bonds: Quantitative Analysis o f the Ring Opening Equilibrium for [Cp'(CO)2Mn]2SeAryl+  
 Abstract    The com pounds [Cp'(CO)2Mn]2S eR + are isoelectronic analogues o f the well known "inide-ne"-species [L"M]ER (E = P, As, Sb, Bi). While these latter "inidene" com pounds exist in an open form with no metal-metal-interaction and the main group atom in a trigonal planar envi­ ronment allowing for a three-center-4 ^-system M—E—M, their isoelectronic selenium ana­ logues generally show equilibria between the "inidene"-type metal metal non bonded forms and their metal metal bond closed cyclic isomers. In a valence bond picture the four electrons, delocalized in the three-center-4 ^-system o f the open isomers, are localized in the closed ones: two in the metal metal bond and two as a lone pair at a pyramidally coordinated selenium center. The corresponding equilibria are quantitatively analyzed for [Cp'(CO)-,Mn]-,SeR + (R = ' C F j -Q H , (1), /'C H ,-C 6H4 ('Tol) (2), °CH3-C !,H4 (°Tol) (3)) by U V /V IS spectroscopy o f their solutions at different temperatures. The ring opening process which corresponds to the reversible opening o f a metal metal bond is found to be entropically driven with reac-tion-entropies o f around 25 [JK-lm ol-1]. Correspondingly, imposing steric hindrance on R, [Cp'(CO)2Mn]2SeM es+ (4) yields a stable bond opened "inidene"-type com pound. Reducing steric hindrance in [Cp'(CO)2Mn]2Se'Pr+ (5) gives the bond closed form as the only detectable isomer. 
  Reference    Z. Naturforsch. 46b, 719—7 (1991); eingegangen am 16. Oktober 1990 
  Published    1991 
  Keywords    Reversible Metal Metal Bond Opening, Thermodynamics, "Inidene" Com pounds, Selenylium Ligands 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-0719.pdf 
 Identifier    ZNB-1991-46b-0719 
 Volume    46