Showing papers on "Enthalpy published in 2015"

Thermodynamic and Transport Properties of Silicate Melts and Magma

Abstract: Petrogenetic problems including the generation, segregation, ascent, storage, differentiation, contamination, eruption, and solidification of magma to form volcanic and plutonic rocks can only be quantified by artful consideration of the fundamental thermodynamic and transport properties of melts and multiphase magmas. Critically important thermodynamic properties include density, heat capacity, volatile solubility, enthalpy, entropy, and volume of fusion, liquidus temperatures and the variations of all properties with temperature, pressure, and composition. Magma transport is governed by conservation of energy, momentum, and mass that depends on thermal conductivity, shear viscosity, and diffusivity (tracer, chemical and isotopic), and varies with temperature, pressure, composition, phase proportions, and shear rates in complex and interwoven ways. In this chapter magma properties are reviewed in the context of petrogenesis and transport phenomena together with underlying theory. Results are presented both graphically and in tabular form providing a survey across the dominant compositions and conditions relevant to igneous petrology.

Accurate Adsorption Thermodynamics of Small Alkanes in Zeolites. Ab initio Theory and Experiment for H-Chabazite

Abstract: Heats of adsorption of methane, ethane, and propane in H-chabazite (Si/Al = 14.4) have been measured and entropies have been derived from adsorption isotherms. For these systems quantum chemical ab initio calculations of Gibbs free energies have been performed. The deviations from the experimental values for methane, ethane, and propane are below 3 kJ/mol for the enthalpy, and the Gibbs free energy. A hybrid high-level (MP2/CBS): low-level (DFT+dispersion) method is used to determine adsorption structures and energies. Vibrational entropies and thermal enthalpy contributions are obtained from vibrational partition functions for the DFT+dispersion potential energy surface. Anharmonic corrections have been evaluated for each normal mode separately. One-dimensional Schrodinger equations are solved for potentials obtained by (curvilinear) distortions of the normal modes using a representation in internal coordinates.

Raman Spectroscopy of Water-Ethanol Solutions: The Estimation of Hydrogen Bonding Energy and the Appearance of Clathrate-like Structures in Solutions.

Abstract: The structure of aqueous alcohol solutions at the molecular level for many decades has remained an intriguing topic in numerous theoretical and practical investigations. The aberrant thermodynamic properties of water-alcohol mixtures are believed to be caused by the differences in energy of hydrogen bonding between water-water, alcohol-alcohol, and alcohol-water molecules. We present the Raman scattering spectra of water, ethanol, and water-ethanol solutions with 20 and 70 vol % of ethanol thoroughly measured and analyzed at temperatures varying from -10 to +70 °C. Application of the MCR-ALS method allowed for each spectrum to extract contributions of molecules with different strengths of hydrogen bonding. The energy (enthalpy) of formation/weakening of hydrogen bonds was calculated using the slope of Van't Hoff plot. The energy of hydrogen bonding in 20 vol % of ethanol was found the highest among all the samples. This finding further supports appearance of clathrate-like structures in water-ethanol solutions with concentrations around 20 vol % of ethanol.

Designing of anion-functionalized ionic liquids for efficient capture of SO2 from flue gas

Abstract: Five kinds of anion-functionalized ionic liquids (ILs) with different basicity and substituent were selected, prepared and applied in the capture of SO2 from flue gas, where the concentration of SO2 is only 2000 ppm. The effect of the anion on SO2 absorption capacity, desorption residue, and available absorption capacity under 2000 ppm was investigated. The relationship between available absorption capacity and absorption enthalpy was also studied. Through a combination of thermodynamic analysis and quantum calculation, the results indicated that the effect of the cation in the IL on absorption enthalpy was significant. However, the effect of chain length in the cation was weak. Hence, a new IL with low molecular weight, [P4442][Tetz], was further designed and applied for the capture of SO2, which shows the high absorption capacity of 0.18 g SO2 per g IL and excellent reversibility for 2000 ppm SO2. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2028–2034, 2015

Recrystallization Behavior of CoCrCuFeNi High-Entropy Alloy

Abstract: We investigated the recrystallization behavior of a cold-rolled CoCrCuFeNi high-entropy alloy (HEA). Two different face-centered cubic phases having different chemical compositions and lattice constants in the as-cast specimen have different chemical compositions: One phase was the Cu-lean matrix and the other was the Cu-rich second phase. The second phase remained even after a heat treatment at 1373 K (1100 °C) and Cu enriched more in the Cu-rich second phase. The calculated mixing enthalpies of both Cu-lean and Cu-rich phases in the as-cast and heat-treated specimens explained that Cu partitioning during the heat treatment decreased the mixing enthalpy in both phases. In the specimens 90 pct cold rolled and annealed at 923 K, 973 K, and 1073 K (650 °C, 700 °C, and 800 °C), recrystallization proceeded with increasing the annealing temperature, and ultrafine recrystallized grains with grain sizes around 1 μm could be obtained. The microhardness tended to decrease with increasing the fraction recrystallized, but it was found that the microhardness values of partially recrystallized specimens were much higher than those expected by a simple rule of mixture between the initial and cold-rolled specimens. The reason for the higher hardness was discussed based on the ultrafine grain size, sluggish diffusion expected in HEAs, and two-phase structure in the CoCrCuFeNi alloy.

Oxygen nonstoichiometry and thermodynamic characterization of Zr doped ceria in the 1573–1773 K temperature range

Abstract: This work encompasses the thermodynamic characterization and critical evaluation of Zr4+ doped ceria, a promising redox material for the two-step solar thermochemical splitting of H2O and CO2 to H2 and CO. As a case study, we experimentally examine 5 mol% Zr4+ doped ceria and present oxygen nonstoichiometry measurements at elevated temperatures ranging from 1573 K to 1773 K and oxygen partial pressures ranging from 4.50 × 10−3 atm to 2.3 × 10−4 atm, yielding higher reduction extents compared to those of pure ceria under all conditions investigated, especially at the lower temperature range and at higher pO2. In contrast to pure ceria, a simple ideal solution model accounting for the formation of isolated oxygen vacancies and localized electrons accurately describes the defect chemistry. Thermodynamic properties are determined, namely: partial molar enthalpy, entropy, and Gibbs free energy. In general, partial molar enthalpy and entropy values of Zr4+ doped ceria are lower. The equilibrium hydrogen yields are subsequently extracted as a function of the redox conditions for dopant concentrations as high as 20%. Although reduction extents increase greatly with dopant concentration, the oxidation of Zr4+ doped ceria is thermodynamically less favorable compared to pure ceria. This leads to substantially larger temperature swings between reduction and oxidation steps, ultimately resulting in lower theoretical solar energy conversion efficiencies compared to ceria under most conditions. In effect, these results point to the importance of considering oxidation thermodynamics in addition to reduction when screening potential redox materials.

Computational Calorimetry: High-Precision Calculation of Host–Guest Binding Thermodynamics

Abstract: We present a strategy for carrying out high-precision calculations of binding free energy and binding enthalpy values from molecular dynamics simulations with explicit solvent. The approach is used to calculate the thermodynamic profiles for binding of nine small molecule guests to either the cucurbit[7]uril (CB7) or β-cyclodextrin (βCD) host. For these systems, calculations using commodity hardware can yield binding free energy and binding enthalpy values with a precision of ∼0.5 kcal/mol (95% CI) in a matter of days. Crucially, the self-consistency of the approach is established by calculating the binding enthalpy directly, via end point potential energy calculations, and indirectly, via the temperature dependence of the binding free energy, i.e., by the van’t Hoff equation. Excellent agreement between the direct and van’t Hoff methods is demonstrated for both host–guest systems and an ion-pair model system for which particularly well-converged results are attainable. Additionally, we find that hydrogen...

Ligand Binding Thermodynamics in Drug Discovery: Still a Hot Tip?

Abstract: The use of ligand binding thermodynamics has been proposed as a potential success factor to accelerate drug discovery. However, despite the intuitive appeal of optimizing binding enthalpy, a number of factors complicate routine use of thermodynamic data. On a macroscopic level, a range of experimental parameters including temperature and buffer choice significantly influence the observed thermodynamic signatures. On a microscopic level, solute effects, structural flexibility, and cooperativity lead to nonlinear changes in enthalpy. This multifactorial character hides essential enthalpy contributions of intermolecular contacts, making them experimentally nonobservable. In this perspective, we present three case studies, reflect on some key factors affecting thermodynamic signatures, and investigate their relation to the hydrophobic effect, enthalpy–entropy compensation, lipophilic ligand efficiency, and promiscuity. The studies highlight that enthalpy and entropy cannot be used as direct end points but can...

Kinetics, isotherm and thermodynamic investigations for the adsorption of Co(II) ion onto crystal violet modified amberlite IR-120 resin

Abstract: The adsorption characteristics of crystal violet (CY)-modified amberlite IRA-120 resin for the removal of Co(II) ion from aqueous medium at different experimental conditions were established by means of batch method. The adsorption uptake was increased with the increase in contact time and temperature. The adsorption process was controlled by pseudo-first-order kinetic model. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models. The Freundlich adsorption model fitted the experimental data reasonably well compared to the Langmuir model. A well-known thermodynamic equation was used to assess the ΔG 0 (standard free energy change), ∆H 0 (enthalpy change), and ∆S 0 (entropy change). The thermodynamic data was indicative of the spontaneous nature of the endothermic sorption process of Co(II) ion onto CY-modified amberlite IRA-120 resin.

Removal of Cadmium(II) from Wastewater Using Novel Cadmium Ion-Imprinted Polymers

Abstract: Cadmium ion-imprinted polymers (Cd-IIP) were synthesized by precipitation polymerization using a complex of dithizone and cadmium as a template. The saturation adsorption capacity of the Cd-IIP is two times that of the nonimprinted polymers (Cd-NIP). Homogeneous binding sites are confirmed by the Langmuir isotherm. The adsorption kinetics fit a pseudo-second-order model well; and the adsorption equilibrium time is only approximately 20 min. The effect of coexisting ions on the Cd(II)-IIP and NIP were investigated by competing with Pb(II), Zn(II), Co(II), and Cu(II), and the ratio of relative selectivity coefficients was greater than 1.68. Thermodynamic parameters indicated that Cd(II) adsorption over IIP and NIP was a spontaneous and exothermic process. The enthalpy changes in different temperatures and adsorption energy are lower than −20.0 and 8 kJ/mol; respectively. These indicate that the adsorption process may be dominated by physisorption. The Cd-IIP was used for five cycles with a small decrease in...