Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
The equilibrium structure of trans-glyoxal from experimental rotational constants and calculated vibration–rotation interaction constants
2003
A total of six high-resolution FT-IR spectra for trans-glyoxal-d2, trans-glyoxal-d1 and trans-glyoxal-13C2 were recorded with a resolution ranging from 0.003 to 0.004 cm−1. By means of a simultaneous ground state combination difference analysis for each of these isotopologues using the Watson Hamiltonian in A-reduction and Ir-representation the ground state rotational constants are obtained. An empirical equilibrium structure is determined for trans-glyoxal using these experimental ground state rotational constants and vibration–rotation interaction constants calculated at the CCSD(T)/cc-pVTZ level of theory. The least-squares fit yields the following structural parameters for trans-glyoxal…
Modellrechnungen zur Lösungsmittel- und Polymerenabhängigkeit der thermodynamischen Eigenschaften von Polymerlösungen
1974
Umfangreiche Messungen an Polymerlosungen haben gezeigt, das eine deutliche Korrelation zwischen chemischem Potential, Entropie und Enthalpie besteht. Es wurden verschiedene Modelle (quasi-chemische Naherung, Theorie der 1-2 Kopplung, Theorem der ubereinstimmenden Zustande u. a.) durchgerechnet und mit den experimentellen Werten verglichen. Hierbei ergab sich, das das Theorem der ubereinstimmenden Zustande den breitesten Anwendungsbereich hat, wohingegen die anderen Theorien fur spezielle Probleme brauchbare Resultate liefern. A great number of measurements on polymer solutions showed that there exists a distinct correlation between chemical potential, entropy and heat of dilution. Calculat…
Study of percolation and clustering in supercritical water-CO2 mixtures
2008
The microscopic structure of supercritical water-CO(2) mixture is investigated by neutron diffraction experiments exploiting the isotopic HD substitution. The investigated water reach mixtures are in the liquidlike region of the phase diagram, according to the behavior of the radial distribution functions, yet a reduction of the average number of hydrogen bonds, compared to equivalent states of pure water, is found. As a consequence, the average dimension of water clusters is reduced and the system stays below the percolation threshold. These results, along with the shift of the main peaks of the site-site radial distribution functions, suggest that the excess volume in these supercritical …
The static dielectric constant of solutions of water inn-alcohols at 15, 25, 35, and 45°C
1979
Dielectric constants (measured at 1 MHz) are reported for solutions of water (concentration range 0 to 0.2 mole fraction) in 1-propanol at 25°C, and in 1-butanol, 1-pentanol, and 1-hexanol at 15, 25, 35, and 45°C. These results, together with literature values for solutions of water in methanol, ethanol, 1-heptanol, and 1-octanol, show that water interacts with alcohols in at least two ways: (1) it can participate in the formation of dynamic hydrogen-bonded chains, thereby raising the polarizability; (2) it can form relatively stable structures such as H2O(ROH)4 which have zero net dipole moment and consequently diminish volume polarizability. For C n H 2n+1 OH alcohols,n≥4, most of the ini…
Solvent-Independent Electrode Potentials of Solids Undergoing Insertion Electrochemical Reactions: Part I. Theory
2012
A formally solvent-independent redox system can be theoretically defined using the Lovric and Scholz modeling of the voltammetry of microparticles for ion-insertion solids. The proposed theory is based on the extra-thermodynamic assumptions that no net charge accumulates at the solid|electrolyte interface and the assumption that the structure of the solid and the ion binding remain unaffected by the solvent. Under voltammetric conditions, the corresponding redox potential can be estimated from voltammetric and chronoamperometric data assuming electrochemical reversibility and diffusive charge transport in the solution and solid phases, also taking into account ion partition (electrolyte/sol…
Evaluation of the Stability of Pure Silica MCM-41 toward Water Vapor
1999
Water vapor adsorption/desorption isotherms at 298 K and XRD measurements and nitrogen isotherms at 77 K before and after exposure to water vapor were determined on pure silica MCM-41 samples; samples had different pore widths and were prepared by different synthesis methods, including hydrothermal and room-temperature procedures. It was found that prolonged exposure to water vapor provoked structural alterations in all of the MCM-41 materials studied, the most significant effects being a loss of pore shape uniformity and a large decrease in pore size and, in consequence, pore volume. Analysis of the results suggests that these alterations are due to expansion of the pore walls as well as, …
Relations between compression and thermal contraction in 1,2,4-trichlorobenzene and melting of trichlorobenzene isomers
2015
The compression and thermal expansion of crystalline 1,2,4-trichlorobenzene, C6H3Cl3, 124TCB, investigated under isobaric and isothermal conditions, are in reverse relation, as for most of crystals, however, the isochoric strain along direction c is clearly different from those along a and b. Single crystals of 124TCB have been in situ grown under isochoric and isobaric conditions, at 270 K/0.1 MPa and 295 K/0.16 GPa, and also at 100 K/0.1 MPa and 295 K/0.64 GPa, when the unit-cell volume is similar. All crystallizations yielded the same phase, of monoclinic space group P21/n, with two symmetry-independent molecules (Z′ = 2). The structure is governed by Cl⋯Cl and Cl⋯H interactions and the …
Rate-limiting reaction of C 3 S hydration - A reply to the discussion “A new view on the kinetics of tricalcium silicate hydration” by E. Gartner
2018
Abstract In the case of coupled solids-solution reactions, any mean accelerating or decelerating one of the reaction, will also change the other reaction(s) in the same way, through the coupling mediated by the solution. The observation of any kinetic change by one of these means should not lead to too rapid conclusion on the limitation of kinetics and it must be done with great caution. Contrary to what Gartner mentioned, the acceleration of C3S hydration by the addition of calcium silicate hydrate seeds, is not a trivial evidence suggesting that hydration kinetics “has to be” limited by the C-S-H precipitation and that the C3S dissolution can be neglected. In our paper, efforts have been …
Interactions between chemical evolution (hydration) and physical evolution (setting) in the case of tricalcium silicate
1994
This paper describes recent experimental results concerning investigation of the parameters which determine, on the one hand, the kinetics of hydration of tricalcium silicate and the thermodynamic, morphological and structural characteristics of C-S-H and, on the other hand, the evolution of the particle interactions at the origin of setting. It is shown that, in both cases, lime concentration in solution is the most important parameter. As a consequence, the chemical evolution of the system, which controls the lime concentration in solution, determines the nature of particle interactions and the physical evolution of the suspension or paste. In return, the contacts, between particles, resu…
Glass Transition and Food Technology: A Critical Appraisal
2002
ABSTRACT: Most low water content or frozen food products are partly or fully amorphous. This review will discuss the extent to which it is possible to understand and predict their behavior during processing and storage, on the basis of glass transition temperature values (Tg) and phenomena related to glass transition. Two main conclusions are provisionally proposed. Firstly, glass transition cannot be considered as an absolute threshold for molecular mobility. Transport of water and other small molecules takes place even in the glassy state at a significant rate, resulting in effective exchange of water in multi-domains foods or sensitivity to oxidation of encapsulated materials. Texture pr…