Isobaric Heat Capacity Research Articles

Deducing solute differential heat capacity from experimental solubilities. An exemplified treatment of ascorbic acid to improve solubility prediction

ContextSolubility prediction based on the general solubility equation (GSE) rests on reliable values for the isobaric heat capacity difference ΔCp,1 of the solid solute. Usually, this value is estimated with either zero or the melting entropy ΔS1(Tm,1) or, in few cases, is extrapolated from data of thermally stable melts of the solute. This causes uncertainties in the prediction. ObjectiveTo improve prediction accuracy a simple regression method is proposed that determines ΔCp,1 from measured solubilities. Materials and methodsPublished experimental solubilities in neat organic solvents at 298 K of a model compound (L-(+)-ascorbic acid (LAA)) have been regressed using the GSE together with the Hansen parameter model for the activity coefficient. Results and discussionRegression yielded ΔCp,1 = 238 J∙mol−1∙K−1 which agrees well with cross-validation results and is consistent with estimates from various group contribution methods. It was found that prediction accuracy improved in the order of increasing ΔCp,1, that is, from 0, via 91 (=ΔS1(Tm,1)) to 238 J∙mol−1∙K−1. It could be shown that mole fraction solubility of LAA can be forecast this way with an accuracy within current inter-laboratory variation. ConclusionThe proposed method shows a general way to improve prediction accuracy of activity coefficient based solubility models by determining ΔCp,1 without resorting to common assumptions. The method is universally applicable and easy to implement.

Complex phase diagram and supercritical matter.

The supercritical region is often described as uniform with no definite transitions. The distinct behaviors of the matter therein, e.g., as liquidlike and gaslike, however, suggest "supercritical boundaries." Here we provide a mathematical description of these phenomena by revisiting the Yang-Lee theory and introducing a complex phase diagram, specifically a four-dimensional (4D) one with complex T and p. While the traditional 2D phase diagram with real temperature T and pressure p values (the physical plane) lacks Lee-Yang (LY) zeros beyond the critical point, preventing the occurrence of criticality, the off-plane zeros in this 4D scenario still induce critical anomalies in various physical properties. This relationship is evidenced by the correlation between the Widom line and LY edges in van der Waals, 2D Ising model, and water. The diverged supercritical boundaries manifest the high-dimensional feature of the phase diagram: e.g., when LY zeros of complex T or p are projected onto the physical plane, boundaries defined by isobaric heat capacity C_{p} or isothermal compression coefficient K_{T} emanates. These results demonstrate the incipient phase transition nature of the supercritical matter.

Ab initio thermodynamic properties of iridium: A high-pressure and high-temperature study

The high-pressure and high-temperature thermodynamic properties of iridium are studied using density functional theory in combination with the quasi-harmonic approximation, where both the contributions to the free energy of phonons and of electronic excitations are considered. The reliability of different exchange and correlational functionals [Perdew-Burke-Ernzerhof generalized gradient approximation (PBE) (Perdew et al. Phys. Rev. Lett. 77, 3865 (1996)), PBE modified for dense solids (PBEsol) (Perdew et al. Phys. Rev. B 100, 136,406 (2008)) and local density approximation (LDA) (Perdew et al. Phys. Rev. B 23, 5048 (1981))], for studying the equation of state (EOS), the phonon dispersions, the mode-Grüneisen parameter, and different thermodynamic properties like thermal pressure, volume thermal expansivity, isobaric heat capacity, bulk modulus, and the average Grüneisen parameter are tested. Elastic constants are studied at T = 0 K as a function of pressure. The predicted results are compared with the available experiments and previous theoretical data. We find generally a good agreement with experiments with at least one functional, but none of the three outperforms the others in all the investigated thermodynamic properties. The electronic excitations contribution is minimal in bulk modulus, but it is significant for other thermodynamic properties.

Thermophysical and Electrical Properties of Ethylene Glycol-Based Nanofluids Containing CaCO3

The thermophysical properties of various types of nanofluids are often studied to find more effective working fluids for heat transfer applications. In this paper, the mass density, isobaric heat capacity, thermal conductivity, dynamic viscosity surface tension, and electrical properties of calcium carbonate-ethylene glycol (CaCO3-EG) nanofluids were investigated. The samples with mass fractions of 0.01, 0.02, and 0.03 were prepared with a two-step method and studied as well as pure base fluid (ethylene glycol). The measurements were conducted at temperatures between 283.15 and 313.15 K and the obtained results show the impact of CaCO3 nanoparticles on the thermophysical and electrical properties of ethylene glycol.

Study of thermal properties of TiCNO by Debye-Einstein model and Debye-Grüneisen model

The thermal properties of TiCNO are studied from the Debye-Einstein model based on the first-principle in combination with the special quasi-random structural model, meanwhile the derived result is compared with those obtained by the Debye-Grüneisen model. The present results show that Debye-Einstein model is excellent in predicting the thermal properties of multicomponent random structure materials due to consideration of the 3 n − 3 optical frequencies at the Γ point to represent the contributions of optic branches, although the Debye-Grüneisen models is also effective methods for predicting the thermal properties of multicomponent materials. The two methods show that when temperature rises, the thermal expansion coefficients of TiCNO first increase rapidly and then slowly, and Debye-Einstein predicts a stronger volume sensitivity to lower temperature due to the contribution of 3 n − 3 optic frequencies at Γ point. Although both models also predict a comparable temperature dependence of bulk modulus, the high temperature softening effect of TiCNO calculated by Debye-Einstein is gentler than that from Debye-Grüneisen, which demonstrates that the influence of optical branches cannot be negligible. With temperature increasing, the thermodynamic entropy predicted by both models increases due to the greater disorder degree of the system. Moreover, the thermodynamic entropy predicted by Debye-Einstein is larger owing to considering the optical frequencies at the Γ point. Due to the strong coupling between the acoustic and optical phonons lying in low frequency regime, both isobaric and isochoric heat capacities predicted by Debye-Einstein are larger than those predicted by Debye-Grüneisen at low temperatures. This work is a useful reference for predicting the thermal properties of multicomponent materials.

Influence of crystal structure on the thermophysical properties and figures-of-merit of propylene glycol: water-based SiC nanofluids

Silicon carbide is a material with a promising thermal conductivity. However, no literature has been found on SiC nanofluids based on propylene glycol:water mixtures (widely used in renewable installations). Likewise, the contribution of α-SiC and β-SiC to the thermophysical properties of nanofluids has scarcely been explored. In this work, dispersions of α-SiC and β-SiC on propylene glycol:water 30:70 wt% at 1 and 2% wt% concentration are designed. Densities, thermal conductivities, dynamic viscosities, and isobaric heat capacities from 293.15 to 313.15 K are obtained by vibrating tube densimetry, transient-hot-wire technique, rotational rheometry and differential scanning calorimetry, respectively. Convective heat transfer performance is also assessed using figures-of-merit. Thermal conductivity and viscosity show a greater dependence on the crystal structure. The β-SiC nanofluids present the highest increases of thermal conductivity (12%) and dynamic viscosity (17%). The least complex crystal structure (β-SiC) exhibits better prospects for convection applications both for laminar and turbulent flow.

Hierarchy of hydrogen bonding among constitutional isomers of hexanol

The strength and thermal stability of the hydrogen bonding influence the bulk properties of associating liquids, such as higher alcohols. Temperature-induced decay of the hydrogen bonds translates into uncommon trends in the heat capacity of the liquid, frequently exhibiting vast plateaus or distinct maxima. Experimental isobaric heat capacities of sixteen aliphatic hexanols in their liquid phase, resulting from Tian-Calvet calorimetry in the temperature range of 260–340 K, are presented. This temperature range is extended to 380 K with a power-compensation DSC for thirteen compounds. Among the studied compounds, a maximum on the temperature dependence of the heat capacity is explicitly observed below 380 K for six species. Upon derivation of residual heat capacities, this maximum gets amplified and can be recognized for 13 species (below 400 K). Molecular dynamics simulations of pure samples of all hexanol isomers are performed to interpret the observed trends. The hydrogen-bonding hierarchy is established computationally in terms of structural and energetic descriptors of bulk liquids. The strength of the hydrogen bonds is directly related to the extent of steric hindrance imposed on the hydroxyl moieties by the side alkyl chains in the bulk liquid. The hexanol isomers predicted computationally to form the weakest hydrogen bonds in the liquid match those, for which the non-monotonous trends of the heat capacities were observed. The position of the heat capacity maximum is sensitive to a subtle variation of the hydrogen bonding strength and shifts to higher temperatures upon strengthening of the hydrogen bonding for less branched and primary hexanol isomers.

Phase transitions properties of N,N-dimethyl-4-nitroaniline

The present work reports an experimental study aiming to determine several thermodynamic properties of fusion and sublimation of the chromophore N,N-dimethyl-4-nitroaniline. This compound is commonly used as a reference in studies focused on the non-linear optical (NLO) characteristics of chromophores. Using the Knudsen mass-loss effusion method, the vapor pressures of the crystalline phase of N,N-dimethyl-4-nitroaniline were measured over the temperature range between 341.1 K and 363.5 K. The standard molar enthalpy, entropy, and Gibbs energy of sublimation were calculated from the experimental results, at 298.15 K, and compared with those given in the literature. Differential scanning calorimetry was used to determine the temperature and enthalpy of fusion, as well as the isobaric heat capacities of the crystalline compound under study. Additionally, the enthalpic and entropic contributions to N,N-dimethyl-4-nitroaniline’s volatility were assessed, and it was determined that is greatly conditioned by enthalpic factors.

Revealing the effects of thermal properties of supercritical CO2 on proppant migration in supercritical CO2 fracturing

In supercritical CO2 (Sc-CO2) fracturing, the temperature variation along the fracture significantly impacts Sc-CO2's density and viscosity. Furthermore, alterations in Sc-CO2's density induce volumetric changes, affecting the flow velocity in fractures. In pursuit of a comprehensive investigation, this study integrates the heat transfer and fluid leak-off models within the Eulerian-Eulerian two-fluid framework. This integration facilitates a systematic exploration of the combined effects of Sc-CO2's thermal properties, including density, viscosity, and density-induced volumetric changes, on proppant migration under different injection temperatures, formation temperatures, and formation pressures. To accurately capture Sc-CO2's thermal properties, its density, viscosity, isobaric heat capacity, and thermal conductivity are all temperature and pressure-dependent. The results showed that the temperature field in the fracture could be classified into four distinct zones, with Zones A and B recognized as primary flow regions, largely impacting the proppant migration process. Furthermore, the outcomes underscored the intricate interplay between Sc-CO2's volumetric expansion or shrinkage and its concurrent density and viscosity alterations. The dominance of either of these effects and the directions of their influence were contingent upon the injection and formation conditions. In aggregate, a longer proppant bed was achieved through elevated formation pressure, increased formation temperature, and reduced injection temperature. These findings enhance the temperature field's comprehension and provide valuable insights for designing and optimizing Sc-CO2 fracturing processes.

Bound-state energy spectrum and thermochemical functions of the deformed Schiöberg oscillator

In this study, a diatomic molecule interacting potential such as the deformed Schiöberg oscillator (DSO) have been applied to diatomic systems. By solving the Schrödinger equation with the DSO, analytical equations for energy eigenvalues, molar entropy, molar enthalpy, molar Gibbs free energy and constant pressure molar heat capacity are obtained. The obtained equations were used to analyze the physical properties of diatomic molecules. With the aid of the DSO, the percentage average absolute deviation (PAAD) of computed data from the experimental data of the 7Li2 (2 3Πg), NaBr (X 1Σ+), KBr (X 1Σ+) and KRb (B 1Π) molecules are 1.3319%, 0.2108%, 0.2359% and 0.8841%, respectively. The PAAD values obtained by employing the equations of molar entropy, scaled molar enthalpy, scaled molar Gibbs free energy and isobaric molar heat capacity are 1.2919%, 1.5639%, 1.5957% and 2.4041%, respectively, from the experimental data of the KBr (X 1Σ+) molecule. The results for the potential energies, bound-state energy spectra, and thermodynamic functions are in good agreement with the literature on diatomic molecules.

Highly Accurate Densities and Isobaric and Isochoric Heat Capacities of Compressed Liquid Water Derived from New Speed of Sound Measurements

Comprehensive and accurate measurements of the speed of sound in liquid water are reported. The measurements were carried out by a double-path-length pulse-echo technique and cover the temperature range from 273.65 K to 368.15 K with pressures up to 100 MPa. The relative expanded (k=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${ k}=2$$\\end{document}) uncertainties are 2.1 mK in temperature, 45 parts-per-million (ppm) in pressure, and between 40 ppm and 70 ppm in speed of sound. Furthermore, values for the density and specific isobaric and isochoric heat capacities were derived from the speed of sound data in the measured temperature range up to 100 MPa by the method of thermodynamic integration. Very accurate values for the derived properties were obtained by using density data of Takenaka and Masui (Metrologia 27:165–171, 1990) and isobaric heat capacity data of Osborne et al. (J Res Natl Bur Stand 23:197, 1939) at ambient pressure as initial values in combination with an accurate correlation of our speed of sound. The relative expanded (k=2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${ k}=2$$\\end{document}) uncertainties of the derived properties are 2 ppm in density, 0.11% in isobaric heat capacity, and 0.12% in isochoric heat capacity. The experimental speeds of sound and derived properties are compared with experimental data of other authors from the literature, the IAPWS-95 (International Association of the Properties of Water and Steam) formulation for the thermodynamic properties of water, and a recent equation of state for supercooled water.

The investigation of crystal structure, thermodynamic properties, and fluorescence properties of three new rare earth coordination compounds

Three new rare earth coordination compounds [REL3Ph]2(RE = Pr(1), Sm(2)); [ErL3Ph]2·4C2H5OH(3); (L = 2,6-dimethylbenzoate, Ph = o-phenanthroline) were synthesized. The crystal structures of the three compounds were measured by X-ray single-crystal diffraction. From the results, we made out that compounds 1–3 were binuclear structures, and 1D chain-like structures could be formed by hydrogen bonding. The thermal degradation data of the compounds and the three-dimentional infrared cumulative spectra of the gaseous decomposed products were obtained by TG/DSC-FTIR technique, and the thermal degradation patterns were explained. The isobaric molar heat capacity of compounds 1 and 2 in the low-temperature region was obtained by the DSC technique and the thermodynamic parameters were derived. The fluorescence spectrum of compound 2 was determined, showing that it had potential application value in the orange-red luminescence region.

Unified analytical formulation regarding thermodynamic properties subject to gaseous metal hydroxides

Analytical formulations concerning the Gibbs free energy for simple substances and compounds show important applications in dealing with many issues, but acquiring such a formulation with few adjustable parameters remains a challenging goal. Here, we report a unified analytical formulation regarding the Gibbs free energy subject to gaseous metal hydroxides MOH for (M=Al, Be, Cs, K, Li, Mg, Na, Sr, and Ca). It depends only on experimental data of atomic masses and six molecular constants except for an adjustable dimensionless pure number, while the temperature-dependent Gibbs free energy polynomial correlation provided in the National Institute of Standards and Technology (NIST) Chemistry WebBook has eight adjustable coefficients, which take different values in different temperature ranges for each species. The mean relative errors between the predicted Gibbs free energy values subject to nine metal hydroxides and the NIST data are within the range of 0.012 % to 0.078 %, and the predicted results of entropy, enthalpy and isobaric heat capacity are also in good agreement with the NIST data. The proposed unified model possesses the characteristics of high prediction accuracy and strong flexibility.

Synthesis and High-Temperature Heat Capacity of LaMgAl11O19 and SmMgAl11O19 Hexaaluminates

The processes occurring during heating of a stoichiometric mixture of lanthanum, samarium, magnesium, and aluminum hydroxides synthesized by the reverse precipitation method have been studied by DTA/TG and X-ray powder diffraction methods. The conditions for the synthesis of single-phase LaMgAl11O19 and SmMgAl11O19 samples of the magnetoplumbite structure type have been determined, and the isobaric heat capacity has been measured in the temperature range 317–1817 K, showing the absence of structural transformations in this range.

Heat Capacity and Thermodynamic Functions of Ho2O3·2HfO2 Solid Solution

Isobaric heat capacity measurements in the range 2.4–1807 K have been performed by relaxation calorimetry, adiabatic calorimetry, and differential scanning calorimetry on a Ho2O3‧2HfO2 solid solution sample prepared and characterized by X-ray powder diffraction, electron microscopy, and chemical analysis, and thermodynamic functions have been calculated. The Schottky anomaly contribution has been determined in the range 2.4–300 K.

The Isochoric Heat Capacity of Ice is Equal to its Isobaric Heat Capacity

The Isochoric Heat Capacity of Ice is Equal to its Isobaric Heat Capacity

Kinetics of direct and water‐mediated tautomerization reactions of nucleobases at low temperatures ⩽200 K

AbstractDetailed chemical kinetic mechanisms for the synthesis of complex organic molecules in the interstellar medium are at an early stage of developement. That such synthesis must take place is well‐known from chemical analysis of sampled asteroids. As molecular complexity increases the number of possible structural isomers also increases with the consequence that the nascent species may adopt a different spatial arrangement, to the lowest energy one. As part of a program of investigations of the hydrogen atom transfer reaction or tautomerization of imidic acid–amide species H‐O=C‐N‐ O=C‐N‐H we have studied the kinetics for a number of nucleobases, namely cytosine, thymine and uracil where a cyclic form of tautomerism (lactim–lactam) is encountered. Together with a fourth, 5‐aza‐uracil (1,3,5‐triazine‐2,4(1H,3H)‐dione), we report on the rates of reaction at low temperatures 50–200 K for both the direct unimolecular process and the similar transformation mediated by an additional water molecule. We show that these tautomerization reactions can be categorized into three classes, and highlight the importance of quantum mechanical tunneling on the rate constants at these low temperatures. We further present some thermochemistry data, such as formation enthalpies, entropies, isobaric heat capacities and enthalpy functions.

Ab initio predictions of pressure-dependent structural, elastic, and thermodynamic properties of CaLiX3 (X = Cl, Br, and I) halide perovskites

In this comprehensive investigation, we undertook an ab initio exploration of the pressure-dependent structural, elastic and thermodynamic attributes of lithium-based halide perovskite compounds, namely CaLiCl3, CaLiBr3 and CaLiI3. Our analytical approach encompassed a diverse set of parameters, and the main conclusions and implications of our study are summarized as follows: (i) Calculated values of formation enthalpy and cohesion energy were determined for these perovskite compounds. Our results notably affirm the structural and thermodynamic stability of these materials in their cubic lattice configuration. (ii) Our optimized network parameters, derived from ab initio calculations, demonstrated commendable congruence with previously established theoretical predictions. This agreement strengthens the credibility of our conclusions. (iii) Using strain-constraint methodology, we successfully estimated the single-crystal elastic constants (Cij) of these compounds. This data served as the basis for further analysis. (iv) Using the obtained Cij values, we calculated a complete suite of elastic moduli for CaLiX3 (X = Cl, Br and I) in polycrystalline aggregates. This encompassed bulk modulus, Young's modulus, shear modulus, Lame coefficients, Poisson's ratio and Debye temperature, thus providing valuable information on the mechanical behavior of materials. (v) Using Debye's quasi-harmonic approach, we systematically investigated the temperature dependencies of several essential thermodynamic properties. These include the lattice parameter, thermal expansion coefficient, bulk modulus, Debye temperature, and isochoric and isobaric heat capacities. These analyzes covered a wide temperature range while maintaining fixed selected pressures. Overall, our study aims to provide the scientific community with a robust and comprehensive dataset regarding the structural, elastic, and thermodynamic attributes of CaLiX3 perovskite compounds.

Characterization of the physical properties of the thermoresponsive block-copolymer PAGB2000 and numerical assessment of its potentialities in Forward Osmosis desalination

Forward Osmosis is a promising strategy for desalination processes, however some aspects have to be better characterized to make it competitive with other affirmed technologies. One of these aspects is the selection of the draw agent, i.e., a polymeric solution that has to fulfill different requirements to guarantee both high membrane performances and good regeneration process. Previous studies have identified a thermoresponsive copolymer known as PAGB2000 as potential draw agent. However, in the open literature there is no information on the thermo-physical properties required for a fully characterization of the polymer itself, hence, different experimental campaigns have been conducted to quantify: phase behavior, osmotic pressure, density, dynamic viscosity, thermal conductivity, thermal diffusivity and isobaric specific heat capacity. These properties were then used in a computational model to simulate the whole desalination process. Recovery ratio, specific electric consumption and specific thermal consumption were compared with the ones obtained in a previous work, showing that a detailed characterization of the thermo-physical properties is required to get accurate and realistic predictions of the system performance.

Ab initio investigation of structural, elastic, and thermodynamic characteristics of tetragonal XAgO compounds (X = Li, Na, K, Rb)

The present research utilizes ab initio computations to examine the thermodynamic, structural, and elastic characteristics of XAgO ternary oxides, where X signifies Li, Na, K, and Rb.The GGA-PBE and GGA-WC functionals were used to calculate the ground-state lattice parameters and atomic position coordinates of the title materials. The calculated results were in good agreement with both experimental measurements and theoretical predictions. This suggests that the GGA-PBE and GGA-WC functionals are accurate for describing the structural properties of the material under study.This study offers computational predictions for the elastic properties of monocrystalline structures and polycrystalline aggregates of XAgO compounds. These predictions encompass various key parameters, including single-crystal elastic constants, Young’s modulus, bulk modulus, Lame coefficients, Poisson’s ratio, shear modulus, and Debye temperature. Additionally, the quasi-harmonic Debye approximation is utilized to explore the temperature-dependent behavior of bulk modulus, Debye temperature, volume thermal expansion coefficient, and isobaric and isochoric heat capacities over an extensive temperature range, while maintaining constant pressures. The results obtained from this model are found to be highly successful in accurately predicting the behavior of these properties.