Showing papers on "Enthalpy published in 1988"
01 Jun 1988-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the Gibbs and Langmuir adsorption isotherms were used to calculate the entropy and enthalpy of surface active components such as oxygen, sulfur, selenium, and tellurium.
Abstract: Since the fluid flow, heat transfer, and the resulting weld properties are significantly affected by interfacial tension driven flow, the variation of interfacial tension in dilute binary solutions is studied as a function of both composition and temperature. Entropy and enthalpy of adsorption of surface active components such as oxygen, sulfur, selenium, and tellurium in Fe-O, Fe-S, Fe-Se, Cu-O, Cu-S, Cu-Se, Cu-Te, Ag-O, and Sn-Te systems were calculated from the analysis of the published data on interfacial tension of these systems. For these calculations, a formalism based on the combination of Gibbs and Langmuir adsorption isotherms was used. Interfacial tensions in Cr-O, Co-S, and Ni-S systems, where the data are scarce, were predicted by using certain approximations. The computed values were found to be in reasonable agreement with the data available in the literature. Temperature coefficients of interfacial tensions were calculated for several binary systems. It was demonstrated that in dilute solutions, the temperature coefficient of interfacial tension is strongly influenced by the heat of adsorption which, in turn, is influenced by the difference in electronegativity between the solute and solvent ions.
470 citations
TL;DR: In this article, the thermodynamics of thermoelastic martensitic transformations are reformulated from the point of view of calorimetric experiments, and it is shown that the heat released or absorbed by the specimen is due to a triple contribution: the latent heat of transformation, the reversibly stored elastic enthalpy and the irreversible work mainly spent in moving the interfaces.
295 citations
TL;DR: In this paper, the ionization constants of water, NH3, HCl, NaCl, and NH3 have been fitted in terms of a model with dependence on density and temperature.
Abstract: Electrochemical and electrical conductance cells have been widely used at ORNL over the years to quantitatively determine equilibrium constants and their salt effects to 300°C (EMF) and 800°C (conductance) at the saturation pressure of water (EMF) and to 4000 bars (conductance). The most precise results to 300°C for a large number of weak acids and bases show very similar thermodynamic behavior, which will be discussed. Results for the ionization constants of water, NH3(aq), HCl(aq), and NaCl(aq), which extend well into the supercritical region, have been fitted in terms of a model with dependence on density and temperature. The entropy change is found to be the driving force for ion-association reactions and this tendency increases (as it must) with increasing temperature at a given pressure. Also, the variation of all thermodynamic properties is greatly reduced at high fixed densities. Considerable variation occurs at low densities. From this analysis, the dependence of the reaction thermodynamics on the P-V-T properties of the solvent is shown, and the implication of large changes in hydration for solutes in the vicinity of the critical temperature will be discussed. Finally, the change in the molar compressibility coefficient for all reactions in water is shown to be the same and dependent only on the compressibility of the solvent.
227 citations
TL;DR: Determination of the change in free energy of unfolding and extrapolation into the nontransition region revealed that beta-Lg increases its stability by increasing the magnitude of thechange in freeEnergy of unfolding at the temperature of maximum stability, as well as by increasingThe temperature ofmaximum stability.
Abstract: The thermodynamic stability of beta-lactoglobulin (beta-Lg) was studied at acidic and near-neutral pH values using equilibrium thermal-unfolding measurements. Transition temperature increased with a decrease in pH from 7.5 to 6.5 and 3.0 to 1.5, suggesting an increase in the net protein stability. Determination of the change in free energy of unfolding and extrapolation into the nontransition region revealed that beta-Lg increases its stability by increasing the magnitude of the change in free energy of unfolding at the temperature of maximum stability, as well as by increasing the temperature of maximum stability. The relative difference in the change in free energy of unfolding at 70 degrees C (with a reference pH of 7.5) was positive and its magnitude increased with a decrease in pH from 7.0 to 1.5 van't Hoff plots of thermal unfolding of beta-Lg at all pH values studied were non-linear and the measured changes in the enthalpy and entropy of unfolding for beta-Lg were high and positive. The relative magnitude of change of both enthalpy and entropy at 70 degrees C (compared with pH 7.5) increased with a decrease in pH up to 1.5. A possible mechanism for the increased stability of beta-Lg at low pH is discussed.
166 citations
TL;DR: In this article, annealing of polymers below the glass transition temperature results in a decrease in enthalpy that is recovered during heating, which is visible as an endothermic peak in a differential scanning calorimetry scan.
Abstract: Annealing of polymers below the glass transition temperature results in a decrease in enthalpy that is recovered during heating. The enthalpy recovery is visible as an endothermic peak in a differential scanning calorimetry (DSC) scan. The position of this peak depends on the thermal treatment given and on the structure of the material itself. Because different polymers behave differently, the phenomenon can be utilized to investigate polymel-polymer miscibility of polymers with similar Tg values. Therefore, by annealing the blends at the temperature of interest and subsequent sub-T, annealing, one can monitor phase behavior resulting from the initial treatment by inspection of the enthalpy recovery. Two systems were investigated to illustrate this: an immiscible blend of poly(viny1 chloride) and poly(isopropy1 methacrylate) and a miscible blend of poly(viny1 chloride) and poly(methy1 methacrylate).
129 citations
TL;DR: N,N′-Dialkyl-1,4-benzenedicarboxamides melt with anomalously small enthalpy changes The 1,3-analogs behave similarly but at lower temperatures.
Abstract: N,N′-Dialkyl-1,4-benzenedicarboxamides melt with anomalously small enthalpy changes The 1,3-analogs behave similarly but at lower temperatures These observations provide a clue to design novel me
125 citations
TL;DR: In this article, the second order approach was applied to the condensed phase of the gas phase and a total of 1311 comparisons were made between experimentally determined values and those calculated using additive group values.
Abstract: An estimation method developed by S. W. Benson and coworkers, for calculating the thermodynamic properties of organic compounds in the gas phase, has been extended to the liquid and solid phases for hydrocarbon compounds at 298.15 K. The second order approach which includes nearest neighbor interactions has been applied to the condensed phase. A total of 1311 comparisons are made between experimentally determined values and those calculated using additive group values. Of the 559 comparisons given for the enthalpy of formation (Δf H°) in the gas, liquid, and solid phases, the average difference (residual), without regard to sign, is 2.6 kJ/mol. The average differences for 390 comparisons for the heat capacity (C○p) and 352 comparisons for the entropy (S°) in the three phases are 1.9 and 2.3 J.mol⋅K, respectively. The good agreement between experimental and calculated values shows that the Benson group additivity approach to the estimation of thermodynamic properties of organic compounds is applicable to t...
121 citations
TL;DR: Stoltze and Norskov as mentioned in this paper showed that the largest contribution to the activation enthalpy for the catalytic synthesis of NH3 at high pressures is the energetic cost of creating two free sites on the surface of the working catalyst.
115 citations
TL;DR: In this paper, the ideal-gas thermodynamic properties of quinoline and isoquinoline were determined by adiabatic heat-capacity calorimetry, comparative ebulliometry, densitometry, and combustion and vibrational spectral frequencies.
108 citations
TL;DR: In this article, the authors measured the temperature dependence of the surface potential at the γ-Al2O3/electrolyte interface by applying the surface site dissociation model, which can be interpreted in terms of the enthalpy changes of the ionization reactions of surface sites.
103 citations
TL;DR: In this paper, a detailed thermodynamic study of water (W)-ethylene glycol (EG) mixtures has been carried out as function of temperature (5, 25 and 45°C) and over the entire composition range.
Abstract: A detailed thermodynamic study of water (W)-ethylene glycol (EG) mixtures has been carried out as function of temperature (5, 25 and 45°C) and over the entire composition range. The data comprise heats of mixing, densities, heat capacities and compression coefficients. Using excess free energy data from earlier work, molar excess functions were calculated for free energies GE, enthalpies HE and entropies TSE, volumes VE, isobaric and isochoric heat capacities C
P
E
, C
V
E
, adiabatic and isothermal compression KE, K
T
E
and thermal expansion EE, as well as the temperature derivatives of K, C and E functions. The corresponding partial molar quantities were also calculated except for G, H and S and are reported for both EG and W. Also calculated were cohesive energy density, internal pressure and Kirkwood-Buff integrals. The data reported here for EG-W mixtures are compared with similar data for other mixtures as available in order to gain insight into: 1) the relative discriminating ability of various thermodynamic coefficients towards weak cooperative intermolecular interactions in liquids; 2) the quantitative similarities and differences between liquid water and ethylene glycol; 3) the intermolecular phenomena which dominate the properties of EG-W mixtures of varying composition; 4) the usefulness of a qualtitative description of liquid water proposed by Lumry et al. which involves hydrogen-bonding interactions, hydrogen-bonding connectivity and small cooperative fluctuation units.
TL;DR: In this article, the authors determined the heat of formation from oxides for perovskite compounds by high-temperature solution calorimetry using an alkali borate solvent.
TL;DR: In this paper, the gel-sol transition of polyvinyl alcohol (PVA)-borate aqueous solutions was investigated as a function of polymer concentration, molecular weight, boric acid concentration and pH.
TL;DR: It is concluded that the molecular volume of lipid in bilayers can be obtained to an accuracy better than 0.002 nm3 (2A3) which is less than0.2% of typical molecular volumes of lipids.
TL;DR: In this paper, heat capacities of KCl solutions have been measured from 413 to 573 K at 200 bar over the molality range of 0.05-3.0 mol kg/sup -1/.
Abstract: Heat capacities of KCl solutions have been measured from 413 to 573 K at 200 bar over the molality range of 0.05-3.0 mol kg/sup -1/. These were combined with literature data on volumes, heat capacities, enthalpies, and osmotic coefficients up to a temperature of 599 K and a pressure of 500 bar to yield comprehensive equations for the calculation of the thermodynamic properties of KCl(aq) to high temperatures and pressures by using ion-interaction approach of Pitzer.
TL;DR: In this article, the authors modeled the physical ageing process as a diffusion process in which the positive density fluctuation defects are annihilated by the corresponding negative ones, and each diffusion molecular jump induces hierarchically correlated molecular rearrangements which conform to a stretched exponential law.
TL;DR: All three of the blue phases of the liquid-crystal cholesteryl nonanoate are thermodynamically stable and that all the phase transitions observed are first order.
Abstract: An adiabatic scanning calorimeter has been used to study the thermal behavior of the liquid-crystal cholesteryl nonanoate in a temperature range covering all phase transitions involving the three different blue phases occurring in this substance. Results for the temperature dependence of the enthalpy and the heat capacity are reported. It is found that all three of the blue phases are thermodynamically stable and that all the phase transitions observed are first order.
TL;DR: In this paper, a new determination, using high temperature drop-solution calorimetry, of the enthalpy of transformation of MgSiO3 pyroxene to ilmenite gives ΔH298 = 59.03 ± 4.26 kJ/mol.
Abstract: A new determination, using high temperature drop-solution calorimetry, of the enthalpy of transformation of MgSiO3 pyroxene to ilmenite gives ΔH298 = 59.03 ±4.26 kJ/mol. The heat capacity of the ilmenite and orthopyroxene phases has been measured by differential scanning calorimetry at 170–700 K; Cp of MgSiO3 ilmenite is 4–10 percent less than that of MgSiO3 pyroxene throughout the range studied. The heat capacity differences are consistent with lattice vibrational models proposed by McMillan and Ross (1987) and suggest an entropy change of -18 ± 3 J-K-1 ·mol-1, approximately independent of temperature, for the pyroxene-ilmenite transition. The unit cell parameters of MgSiO3 ilmenite were measured at 298–876 K and yield an average volume thermal expansion coefficient of 2.44 × 10-5 K-1. The thermochemical data are used to calculate phase relations involving pyroxene, β-Mg2SiO4 plus stishovite, Mg2SiO4 spinel plus stishovite, and ilmenite in good agreement with the results of high pressure studies.
TL;DR: The enthalpy of transformation to ice Ic of ice II, IX, V, VI, and VIII that have been recovered at 77 K and ambient pressure, and of the transformation of ice Ic to Ih, has been measured in a heat chamber as discussed by the authors.
Abstract: The enthalpy of transformation to ice Ic of ice II, IX, V, VI, and VIII that have been recovered at 77 K and ambient pressure, and of the transformation of ice Ic to Ih, has been measured in a heat...
TL;DR: In this paper, the Ramaman spectra were obtained from liquid water between 3 and 95/sup 0/C under absolute intensity conditions and a narrow v/sub 2/ component centered approx. = 30-45 cm/sup -1/ above a broad v/Sub 2/component was observed to increase with temperature rise.
Abstract: Raman spectra were obtained from liquid water between 3 and 95/sup 0/C under absolute intensity conditions. Depolarized v/sub 2/ peak frequencies were observed to lie above the polarized peak values by 5-8 cm/sup -1/. Gaussian analysis indicated a narrow v/sub 2/ component centered approx. = 30-45 cm/sup -1/ above a broad v/sub 2/ component. The intensity of the sharp v/sub 2/ Gaussian component increased relative to the broad v/sub 2/ Gaussian component with increasing temperature. In addition, the depolarized X(ZX)Y total v/sub 2/ contour intensity was observed to increase with temperature rise, but the corresponding polarized X(ZZ)Y v/sub 2/ intensity was observed to decrease. Isosbestic points were observed in the v/sub 2/ + v/sub L/ (L = libration) combination band at 2060 cm/sup -1/, X(ZX)Y, and 2025 cm/sup -1/, X(ZZ)Y. Gaussian contour analysis revealed three components, at (1) 2050, (2) 2150, and (3) 2300 cm/sup -1/ (weak). A plot of the integrated component intensities 1n (I/sub 2/ + I/sub 3/)/I/sub 1/) versus 1/T yielded a characteristic enthalpy value of -2.5 +/- 0.1 kcal/mol of O-H ... O. The v/sub 2/ data indicated that the bending contour contains two unresolved components from fully hydrogen-bonded (4-HB) and from partially hydrogen-bonded (3-HB) structures.more » These bends are coupled to the corresponding 4-HB and 3-HB librations. One of the 3-HB librations occurs near approx. = 450 cm/sup -1/, and it plus the 3-HB bend gives rise to the 2050-cm/sup -1/ combination component, whose temperature dependence relative to the 4-HB components yields the present enthalpy value for hydrogen bond rupture. These results are compatible with the bifurcated hydrogen bond model of Giguere.« less
TL;DR: In this paper, a linear relationship between logarithms of aqueous activity coefficients and total surface areas (TSA) or total molecular volumes (TMV) was calculated from experimental solubility data and values taken from the literature, which supported the assumption that differential heat capacity (..delta..C/sub p/) equals the entropy of fusion.
Abstract: Aqueous solubilities of polychlorinated biphenyls show a linear relationship between logarithms of aqueous activity coefficients and total surface areas (TSA) or total molecular volumes (TMV). The aqueous activity coefficients were calculated from experimental solubility data and values taken from the literature. The correlations improved substantially if a differential heat capacity between supercooled liquid and solid chemical (..delta..C/sub p/) equal to the entropy of fusion (..delta..S/sub f/), instead of ..delta..C/sub p/ = O, was assumed. In addition, it was found that dissolution of 2,2',4,4'-tetra- and 2,2',4,4'5,5'-hexachlorobiphenyl was accompanied by positive enthalpy and entropy changes, the entropy being dominant at room temperature. For the former compound, it was shown that the entropy of fusion is approximately to J K/sup -1/ mol/sup -1/, which is in agreement with the Walden rule. For 2,2',4,4',5,5'-hexachlorobiphenyl, it was shown that a Hildebrand plot provides a constant slope. This supported the assumption that differential heat capacity (..delta..C/sub p/) equals the entropy of fusion.
TL;DR: In this article, a three-component, membrane-forming system: water (H2O), N-methylpyrrolidone (NMP), polyethersulfone (PES), is described.
TL;DR: Paroxetine hydrochloride exists in two solid state forms differentiated by their degrees of hydration Form I is a non-hygroscopic hemihydrate and is thermodynamically the more stable Form II is a hygroscopically anhydrate the moisture content of which is controlled by the prevailing humidity Form II converts to Form I, if seed crystals of Form I are present, when exposed to humid conditions or if subjected to compression The rates of transformation were determined by infrared spectroscopy and techniques are described to identify the solid state form in compressed tablets as mentioned in this paper
TL;DR: The speed of sound in liquid methanol has been measured at temperatures from 273 to 333 K and at pressures up to 280 MPa, using a phase comparison pulse-echo technique operating at 2 MHz as mentioned in this paper.
Abstract: The speed of sound in liquid methanol has been measured at temperatures from 273 to 333 K and at pressures up to 280 MPa, using a phase comparison pulse-echo technique operating at 2 MHz. The density, the isobaric thermal expansivity, the isothermal compressibility, the entropy, the enthalpy, and the specific heat have been evaluated from the measured sound speed following a modified computational method. The derived density data were fitted to a 16-constant equation of state within the accuracy of the measurement. In the region of overlap, the experimental data agree well with those determined by direct measurement.
TL;DR: In this paper, the properties of polycyclic aromatic hydrocarbons have been estimated using the Benson group values of Stein and Fahr for temperatures from 298.15 to 3000 K.
Abstract: The polycyclic aromatic hydrocarbons can be organized into an infinite number of series in each of which successive isomer groups differ by C4H2. The first series starts with benzene, and chemical thermodynamic tables are presented here for C6H6, C10H8, C14H10, C18H12, C22H14, and C26H16 in the ideal gas phase. Since chemical thermodynamic properties are known for only several polycyclic aromatic hydrocarbons, the properties of individual species have been estimated using Benson group values of Stein and Fahr for temperatures from 298.15 to 3000 K. Values of C○P, S°, ΔfH°, and ΔfG° have been calculated in joules for a standard state pressure of 1 bar. The chemical thermodynamic properties of the isomer groups have also been calculated. This provides a basis for extrapolating to higher carbon numbers where it is not feasible to consider individual molecular species.
TL;DR: In this article, steady state polarization curves for hydrogen evolution in alkaline solution at crystalline and amorphous nickel electrodes were measured at different temperatures, showing at higher c.d. the establishment of a limiting c.iR-corrected steady-state polarization curve for increasing Had coverage.
TL;DR: In this paper, the authors investigated the ability of crown ethers to separate lithium isotopes with respect to the number of oxygen atoms composing crown rings and for the substituted groups to 15-crown-5.
Abstract: Separative abilities of crown ethers to lithium isotopes were investigated for the number of oxygen atoms composing crown rings and for the substituted groups to 15-crown-5. The separation factors at 0°C were 1.057 for 12-crown-4, 1.042 for benzo-15-crown-5, 1.041 for lauryloxymethyl-15-crown-5, 1.043 for tolyloxymethyl-15-crown-5, and 1.024 for dicyclohexano-18-crown-6. The enthalpy change of the isotopic equilibrium in the absolute value was the greatest for 12-crown-4; ΔH° = −0.78 kJ/mol. In the substituted 15-crown-5s the separation factor was greatest for tolyloxymethyl-15-crown-5, and ΔH° values decreased in the order: benzo- > tolyloxymethyl- > lauryloxymethyl-15-crown-5. For enthalpy changes, benzo-15-crown-5 has the possibility of giving a larger separation factor than the present one, α = 1.042, by choosing more suitable conditions. In spite of its large distribution coefficient, dicyclohexano-18-crown-6 is not superior for isotopic separation of lithium in regard to the small enthalpy ...
TL;DR: Dingwell and Virgo as mentioned in this paper used the double-bob Archimedean technique to determine the densities of 10 melts in the CaO-FeO, Fe2O3-SiO2 system.
TL;DR: Thermodynamic analysis of the degradation of selected compounds showed that aerobic and denitrifying processes are heat driven (large enthalpy change) and analysis of published data strongly suggests that the movement of succinate, acetate, and possibly longer chain fatty acids is carrier mediated.
Abstract: Thermodynamic analysis of the degradation of selected compounds showed that aerobic and denitrifying processes are heat driven (large enthalpy change). Owing to the smaller enthalpy changes, other anaerobic processes depend more on the entropy flow of chemical substances exchanged with the environment. This results in partial degradation of the substrate and the excretion of end products which have a high free-energy content. This creates niches for organisms to use these end products as energy sources. Mechanistically, the efflux of end products can be used to conserve energy by coupling the efflux with the translocation of protons or other ions. Analysis of published data strongly suggests that the movement of succinate, acetate, and possibly longer chain fatty acids is carrier mediated. Hypothetical calculations showed that these compounds can accumulate to high internal concentrations relative to extracellular concentrations, which suggests that the efflux of these compounds can generate a proton-moti...
TL;DR: In this paper, enthalpies of interaction of urea with the groups in both categories are negative (i.e. are thermochemically favourable) but the tertiary amide group interacts with urea more favourably than primary and secondary amide groups.
Abstract: The heterotactic interactions occurring in water at 25 °C between some simple amides [formamide (F), acetamide (A), N-methylformamide (NMF), N-methylacetamide (NMA), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N,N-diethylformamide (DEF) and N,N-diethylacetamide (DEA)] and the protein denaturant urea, have been investigated using enthalpy changes on mixing. The homotactic interactions of DEF and DMA have also been obtained from enthalpies of dilution and a redetermination of the enthalpy of dilution of A has also been performed. The results are discussed using the Savage and Wood additivity-of-groups approach and although this works quite well if all amidic groups are taken as being equivalent, much better agreement between calculated and experimental results is obtained if primary and secondary amide groups are assumed to be equivalent and in one category, and tertiary amidic groups are in another category. The enthalpies of interaction of urea with the groups in both categories are negative (i.e. are thermochemically favourable) but the tertiary amide group interacts with urea in water more favourably than primary and secondary amide groups. The somewhat surprising finding is commented on and addressed using some exact theories of solutions and is also considered with regard to urea-induced protein denaturation.