Entropy Of Formation Research Articles

Operational Limits of Redox Metal Oxides Performing Thermochemical Water Splitting

Solar thermochemical hydrogen production is an attractive technology that stores intermittent solar energy in the form of chemical bonds. Efficient operation requires the identification of a redox‐active metal oxide (MOx) material that can achieve high conversion of water to hydrogen at minimal energy input. Water splitting occurs by consecutive reduction and reoxidation reactions of MOx. MOx is reduced to MOx−δ and, in the second step, is reoxidized by water recovering the initial MOx and generate H2. The material must reduce at temperatures achievable in concentrated solar receiver/reactors, while maintaining a thermodynamic driving force to split water. At equilibrium, extent of reduction depends on temperature and oxygen partial pressure, and in this analysis, a set of thermodynamic properties, namely, enthalpy and entropy of oxygen vacancy formation, is sufficient to represent MOx. Herein, a method to easily classify materials based on these thermodynamic properties under any condition of oxygen partial pressure and temperature is presented. This method is based on fundamental thermodynamic principles and is applicable for any redox material with known thermodynamic properties. Despite the simplicity of the method, it is believed that this analysis will support future research in targeting thermodynamic properties of redox‐active metal oxides.

(H,H)-Isomerism of cis- and trans-di[benzo]porphyrazines: Quantum chemical modeling within the framework of the DFT method

Quantum-chemical calculation of the molecular structures of potential isomeric (NNNN)- donoratomic macrocyclic tetradentate ligands, cis- and trans-di[benzo]porphyrazines, was carried out using the density functional theory (DFT) B3PW91/TZVP. It is noted that the first of these compounds can exist in four forms [so-called ([Formula: see text]-isomers], differing from each other by the mutual orientation of hydrogen atoms bonded to the nitrogen atoms, while the second compounds take the form of two similar isomers. The values of the most important bond lengths, bond and non-bond angles in each of these ([Formula: see text] -isomeric compounds, as well as the values of their relative energy, standard enthalpy, entropy, and Gibbs energy of formation are presented. It was found that the most stable among both cis- and trans-di[benzo]porphyrazines is the ([Formula: see text]-isomer with the trans-orientation of hydrogen atoms bonded to nitrogen atoms, while the ([Formula: see text] -isomers with cis-oriented hydrogen atoms for both of these compounds had significantly higher relative energies.

Thermodynamic study of manganese tellurides by the electromotive force method

The thermodynamic properties of manganese tellurides were determined using an electromotive force (EMF) method with a liquid electrolyte in a temperature range from 300 to 450 K. EMF measurements were performed using equilibrium samples taken from the two-phase regions, namely MnTe2 + Te and MnTe + MnTe2, of the Mn–Te system. The phase compositions of all samples were controlled with the X-ray diffraction (XRD) method. The partial molar functions of manganese in alloys, as well as the standard thermodynamic functions of the formation and standard entropies of MnTe and MnTe2, were calculated. A comparative analysis of obtained results with literature data is performed

Thermodynamic Assessment of Chemical Equilibrium for the Synthesis of Solketal in the Liquid Phase

AbstractThe synthesis of solketal is one of the innovative routes of glycerol valorization to value‐added products, and the simulation of the process requires the knowledge of thermodynamic properties that are not still available in the literature. In this work, the specific heat capacity as a function of temperature and the enthalpy and entropy of formation of all compounds involved in the reaction were calculated by employing a second‐order group‐additivity method. Expressions for the enthalpy of reaction and equilibrium constant as a function of temperature were also obtained. The glycerol conversion at equilibrium was calculated at different temperatures, pressures, acetone/glycerol molar ratios, and initial water contents, considering the nonideality of the liquid phase.

Entropy formation of an electrical double layer with divalent off-centre charge cations: Monte Carlo studies

Grand canonical Monte Carlo simulations are employed to study the entropy of formation of a planar electric double layer containing equi-sized valency ions. The cation charge is displaced from the ion-sphere centre towards its surface with the displacement being temperature dependent in general, while the monovalent anion charge is held fixed at the centre of the anion sphere. The results for the electrode-ion distributions, the charge density distributions, the differential capacitance, the temperature derivative of the electrode potential, and the entropy of formation of the double layer have been obtained as functions of the electrode charge. For zero cation charge displacement, or for temperature-independent cation charge displacements, a negative temperature dependence of the differential capacitance is observed, while for the temperature-dependent cation charge displacement at negative electrode charges, this temperature dependence can be positive. In the former case, the entropy of formation is negative decreasing on either side of the zero surface charge, while in the latter case the decrease slows down at negative charges reaching positive values at high negative charges. The positive temperature dependence of the differential capacitance is associated with an increase in entropy.

Weighted Information Models for the Quantitative Prediction and Evaluation of the Geothermal Anomaly Area in the Plateau: A Case Study of the Sichuan–Tibet Railway

The prediction of geothermal high-temperature anomalies along the plateau railway will be helpful in the construction of the project and its later management. Taking the Sichuan–Tibet railway as the study area and based on Landsat8 thermal infrared images, map data, and measured data regarding the cause and distribution of geothermal high-temperature anomalies, through correlation analysis, we selected six impact factors including the LST, combined entropy of geological formation, fault density, buffer distance to rivers, magnetic anomaly, and earthquake peak acceleration as the input maps of the model. The index-overlay information model, the weights of the entropy information model, and the weights of the evidence information model were established to quantitatively predict the geothermal anomaly in the study area, and the prediction maps were divided into four classes. The results show that the weights of the evidence information model achieved a high prediction accuracy; the success index and the ratio of the high anomaly area reached 0.0053% and 0.872, respectively, and the spatial distribution of the geothermal points is basically consistent with the prediction results. This research can act as a reference for the design and construction of the Sichuan–Tibet railway.

Thermodynamic properties of 2-methylfuran

The heat capacity of 2-methylfuranin the temperature range of 8–350 K was determined by vacuum adiabatic calorimetry. The temperature, the enthalpy and the entropy of fusion and purity of investigated sample were determinedbyfractional melting. Thesmoothed thermodynamic functions (changes in enthalpy,entropyand Gibbs energy) in the region of 8–350 K were calculated. The entropies of formation and Gibbs energiesof formationof2-methylfuranat 298.15 K inthe liquid and ideal gas states werefound, using the literature data.

Solid-phase Relationships in the Tl2Te-Tl2Te3-TlTbTe2 System and Thermodynamic Properties of Thallium–Terbium Tellurides

This work presents new data on the solid-phase equilibria of the Tl-Tb-Te ternary system in the Tl2Te-Tl2Te3-TlTbTe2 composition region and the thermodynamic functions of the TlTbTe2, and Tl9TbTe6 ternary compounds. Studies were carried out by using the electromotive forces method (EFM) and the powder x-ray diffraction technique. From the EMF measurements of the concentration cells of the type (−) TbTe (s) | glycerol + KCl + TbCl3 | (Tb in Tl-Tb-Te alloys) (s) (+) in the 300-450 K temperature interval, the relative partial thermodynamic functions of TbTe and Tb in alloys of the Tl2Te3-TlTe-TlTbTe2, and TlTe-TlTbTe2-Tl9TbTe6 three-phase regions were determined. Based on the solid-phase equilibria diagram, the potential-forming reactions responsible for the indicated partial molar quantities were determined and the standard thermodynamic functions of formation and standard entropies of the TlTbTe2 and Tl9TbTe6 ternary compounds were calculated.

Fluoride electrolyte based galvanic cell: Stability of the hollandite BaRu6O12(s)

BaRu6O12(s), a quasi one dimensional hollandite with a tetragonal crystal structure, exhibits interesting electronic properties. The solid state reaction route was used for the synthesis of BaRu6O12(s), and was identified by X-ray diffraction analysis, its structural parameters determined and its hollandite structure illustrated. A fluoride ion conducting solid electrolyte based Galvanic cell was constructed and the standard molar Gibbs energy of formation of BaRu6O12(s) was determined. This cell was standardized using phase mixtures of {Ni(s) + NiF2(s)} and {Fe(s) + FeF2(s)} as the two electrodes and CaF2 as the solid electrolyte prior to the measurement of the cell electromotive force, given by:-Pt/O2(g),{CaO(s)+CaF2(s)}//CaF2//{BaF2(s)+RuO2(s)+Ru(s)+BaRu6O12(s)},O2(g)/Pt+.The measured electromotive cell measurements for the above cell along with known Gibbs energy values from literature were used to calculate the standard molar Gibbs energy of formation of BaRu6O12(s) from elements in their standard state and the equation of ΔfGo(T) for BaRu6O12(s) can be given by: ΔfGo(BaRu6O12(s))/kJ⋅ mol−1(±2.94) = - 2447.7 + 1.165 ⋅ (T/K).The slope and intercept of the above equation gives the standard molar entropy and enthalpy of formation respectively, at the average experimental temperature. Thermodynamic stability was determined of this important one dimensional hollandite BaRu6O12(s) from these studies for the first time.

Thermodynamics of cavity formation in different solvents: Enthalpy, entropy, and the solvophobic effects

For a long time thermodynamics of cavity formation in non-aqueous solvents remained virtually unexplored. We evaluated the entropic and enthalpic contributions into the Gibbs free energy of cavity formation in 22 structurally different organic solvents and water at 298 K. The calculations were carried out using 50–100 ns long molecular dynamics trajectories of solvents and Widom test particle insertion method with up to 1011 insertions per trajectory. It is shown that protic solvents with three-dimensional hydrogen bond networks, namely water, formamide, glycerol, ethylene glycol, propylene glycol, and diethylene glycol, behave differently from other considered solvents. They are characterized with lower values of the entropy of cavity formation than other considered solvents, which also leads to the higher Gibbs free energies. Water has a particularly low entropy as well as the lowest enthalpy of cavity formation at room temperature. We point out the similar tendencies observed for the thermodynamic functions of the cavities and solvation of real molecules in the considered solvents using entropy vs enthalpy and Gibbs free energy vs enthalpy plots. The cavity term governs the difference in solvation properties of protic hydrogen-bonded and aprotic solvents giving rise to the hydrophobic and more general solvophobic effects.

Analysis of thermodynamic parameters for designing quasicrystalline Al-Ni-Fe alloys with enhanced corrosion resistance

In this work, the compositions of Al-Ni-Fe alloys were determined based on thermodynamic parameters optimization. Decagonal quasicrystalline phase D-Al70.83Fe9.83Ni19.34 was identified in the alloy with the highest Gibbs free energy of solid solution formation, i.e., Al71Ni24Fe5. According to this, the configurational entropy and enthalpy of solid solution formation must reach equilibrium to form quasicrystals in Al-Ni-Fe alloys. Differential thermal analysis and X-ray diffraction were used to describe the crystallization mechanism as a function of Fe concentration. 57Fe Mössbauer spectroscopy was used to describe the Fe local environment in crystalline alloys and quasicrystals. Moreover, the influence of quasicrystalline phases on improving the corrosion resistance was investigated. Quasicrystalline Al71Ni24Fe5 alloy had a six-times lower corrosion rate than its crystalline counterparts. Although this alloy showed the best corrosion resistance, all high-pressure cast Al-Fe-Ni alloys displayed improved corrosion resistance.

Solubilization of cationic dye in single and mixed micellar media

The effect of mixed-micellization of anionic/non-ionic surfactants on the solubilization of a cationic dye (Methylene blue) is presented in this manuscript. Interactions of dye with the single anionic surfactant sodium dodecyl sulfate (SDS), and its mixture with the non-ionic surfactant (Triton X-100), were investigated. The non-ionic surfactant was initially screened, and then its concentration was kept constant at its critical micellar concentration. The critical micellar concentration, entropy, enthalpy, and free energy of micelle formation (ΔGmic°) were determined by electrical conductivity measurements. The solubilization parameters in terms of the partition coefficient (Kx) and binding constant (Kbind) were assessed by UV–Visible spectroscopy. The role of non-ionic surfactants on the electrostatic interactions of cationic dye and surfactant was also elaborated. Mixed micellization significantly enhanced the solubility of dye molecules as shown by conductivity and absorbance analysis. The disruption of structured water in the vicinal environment of hydrophobic groups of surfactants was responsible for the increase in critical micelle concentration (CMC). The negative values of energies of binding, partitioning, and micellization indicated the spontaneity and feasibility of micellar systems. The experimental outcomes supported the superiority of anionic/non-ionic mixed micellar solubilization over a single anionic surfactant. Thus, the mixed micellar system (SDS + TX-100) assured a higher degree of solubilization than the corresponding single system (SDS).

Simulation of Fe-Ti-Sb Thernary Phase Diagram at Temperatures above 900 K

Heusler alloys have been considered as one of the most promising thermoelectric materials for electrical power generation in a temperature range of 500–800 °C. Establishment of phase diagrams allows one to predict formation, equilibria, and stability of phases in of these ternary alloys. In this work we report on the simulation and investigation of phase diagram and phase equilibria in ternary Ti-Fe-Sb system which is of considerable interest for thermoelectric applications. The simulation was carried out using the CALPHAD method in Pandat software. The existence of the thermoelectric Heusler TiFe1.5Sb phase was revealed in a temperature range from 970 to 1070 K. The equilibria between TiFe1.5Sb and other phases were determined. The entropy of formation was calculated for the phases existing at 970, 1020 and 1070 K using a fitting approach. A narrow equilibrium region containing pure body centered cubic Fe and TiFe1.5Sb was found.

Thermodynamic optimization of the Cu–As–S system

A literature review, critical assessment and thermodynamic modeling of matte, metal (speiss) and solid phases in the Cu–As–S system are presented. The literature data include enthalpies and entropies of formation, activity measurements using vapor pressure, phase equilibrium and element distribution data. The model for the liquid phase was developed within the framework of the Modified Quasichemical Model (MQM) in pair approximation. Liquid metal and matte phases were described using the single solution with a miscibility gap. Previously published model parameters for the liquid phase in the Cu–S system were modified to achieve agreement with the data for the Cu–As–S system. The resulting set of model parameters was incorporated into a large multicomponent thermodynamic database intended for predictions of phase equilibria, heat balance and distribution of arsenic in the course of pyrometallurgical processing of copper- and lead-containing materials.

Prediction of thermodynamic data for radium suitable for thermodynamic database for radioactive waste management using an electrostatic model and correlation with ionic radii among alkaline earth metals

Thermodynamic data for radium for radioactive waste management have been predicted using an electrostatic model and correlation with the ionic radii of the alkaline earth metals. Estimation of the standard Gibbs free energy of formation and standard molar entropy of aqueous radium species and compounds has been based on such approaches as extrapolation of the thermodynamic properties of strontium and barium, and use of a model of ion pair formation. The predicted thermodynamic data for radium have been compared with previously reported values.

Evaluation of solvate and co-crystal screening methods for CL-20 containing energetic materials

ABSTRACT The difficulty synthesizing new co-crystals has made the development of efficient methods for screening co-formers a high priority. Co-crystals have been realized as a new generation of materials with tuneable solubility, stability, and performance. Energetic co-formers have exceptionally weak intermolecular interactions making selection of co-crystallization method and parameters critical to forming a true co-crystal. COSMO-RS calculations coupled with the COSMOtherm software suite were used to screen common solvents and co-formers for CL-20. The predicted favorable solvates and co-crystal formers were compared to experimentally confirmed solvates and co-crystals to assess the accuracy of the COSMO method for CL-20-based materials. It was found that screening solvents using excess enthalpy and solvent cavity volume were able to predict experimentally confirmed CL-20 solvates. Co-crystal formation was difficult to predict using the COSMO method, highlighting the importance of entropy and solid-state interactions. The selection of good solvents is perhaps the best method for maximizing entropy. Understanding the dependence on entropy for energetic-energetic cocrystal formation coupled with an accurate method for screening co-crystal formation allows for intelligent design of co-crystallization methods.

Vacancy diffusion in palladium hydrides.

The self-diffusion coefficients of palladium in PdHx (x = 0, 0.25, 0.5, 0.75, 1) were studied using density functional theory to obtain the required thermodynamic and kinetic parameters. The enthalpy of migration decreased from 0.95 eV for Pd to 0.78 eV for PdH. The enthalpy of vacancy formation exhibited a substantial decrease from about 1.1 eV in Pd to 0.4 eV in PdH, which was ascribed to successive filling of antibonding states weakening the Pd-Pd bonds. Concurrently, the Arrhenius pre-exponential was significantly reduced from 4.75 × 10-3 cm2 s-1 for Pd to 5.67 × 10-9 cm2 s-1 for PdH due to softening of the vibrational modes that determine the entropy of vacancy formation and initial/transition state frequencies. A linear correlation between the logarithm of the pre-exponential and the activation energy was interpreted as enthalpy-entropy compensation (Meyer-Neldel rule). The Pd self-diffusion coefficients in the hydrides were within 1 order of magnitude of that in pure palladium above 200 °C for hydrogen pressures up to at least 107 Pa.

Application of polyvinyl alcohol/polypropylene/zinc oxide nanocomposites as sensor: modeling approach

The blending process for polymer derivatives makes it suitable for providing superior properties to more economic materials. In addition, the importance of the blending process increased with the addition of nano scale metal oxide (MO), due to their versatile applications in gas sensors, biosensor and solar cells. As a result of blending, many important properties of the materials are changed, including electronic properties, thermal properties such as enthalpy, entropy, heat capacity and final heat of formation and surface properties. This leads to continuous experimental and theoretical monitoring of the materials used for blending. A theoretical study on the electronic and thermal properties of polyvinyl alcohol (PVA) blended with polypropylene (PP) was therefore conducted using the functional density theory DFT: B3LYP/ LANL2DZ. Results indicate PVA/PP is becoming more reactive. The addition of zinc oxide (ZnO) greatly enhances the electronic characteristics of the structures studied and confirms their applicability in the production of sensing devices. It was found that, as an adsorbed state, H2S interacted with 4PVA/4PP/4OZn blend, the TDM increased to 10.0896 Debye and HOMO/LUMO band gap energy decreased to 0.6065 eV indicating the suitability of the presented blend for H2S gas sensing.

Identification of molecular cluster evaporation rates, cluster formation enthalpies and entropies by Monte Carlo method

Abstract. We address the problem of identifying the evaporation rates for neutral molecular clusters from synthetic (computer-simulated) cluster concentrations. We applied Bayesian parameter estimation using a Markov chain Monte Carlo (MCMC) algorithm to determine cluster evaporation/fragmentation rates from synthetic cluster distributions generated by the Atmospheric Cluster Dynamics Code (ACDC) and based on gas kinetic collision rate coefficients and evaporation rates obtained using quantum chemical calculations and detailed balances. The studied system consisted of electrically neutral sulfuric acid and ammonia clusters with up to five of each type of molecules. We then treated the concentrations generated by ACDC as synthetic experimental data. With the assumption that the collision rates are known, we tested two approaches for estimating the evaporation rates from these data. First, we studied a scenario where time-dependent cluster distributions are measured at a single temperature before the system reaches a steady state. In the second scenario, only steady-state cluster distributions are measured but at several temperatures. Additionally, in the latter case, the evaporation rates were represented in terms of cluster formation enthalpies and entropies. This reparameterization reduced the number of unknown parameters, since several evaporation rates depend on the same cluster formation enthalpy and entropy values. We also estimated the evaporation rates using previously published synthetic steady-state cluster concentration data at one temperature and compared our two cases to this setting. Both the time-dependent and the two-temperature steady-state concentration data allowed us to estimate the evaporation rates with less variance than in the steady-state single-temperature case. We show that temperature-dependent steady-state data outperform single-temperature time-dependent data for parameter estimation, even if only two temperatures are used. We can thus conclude that for experimentally determining evaporation rates, cluster distribution measurements at several temperatures are recommended over time-dependent measurements at one temperature.

Theoretical study of hydrogen impact on concentration of intrinsic point defects during Czochralski Si crystal growth

Control of intrinsic point defects (vacancy V and interstitial Si I) at the atomic level is required for Si substrates to satisfy the performance demands of the latest semiconductor devices. Sugimura et al. (2014) recently reported that doping hydrogen (H) atoms during Czochralski Si crystal growth affects the point defect behavior in two ways: (i) Si crystal becomes more V rich and (ii) the formation of dislocation clusters is suppressed. The finding of (ii) suggests that H-doping is a promising technique for the mass production of Si substrates used for power devices, among other applications. However, the effect of H-doping on point defect behavior during Si crystal growth is not yet fully understood. The purpose of the present study is to clarify the finding of (i). We performed first principles calculation of the formation energy and formation (vibration) entropy of V and I in the area influenced by the H atom in supercells composed of 64 and 216 Si atoms and then obtained the concentration of point defects incorporated at the melt/solid interface on the basis of the results. Our main findings are as follows. (1) There are three structures of hydrogen-vacancy complex (H-V) where the V formation energy remarkably decreases and four structures of hydrogen-interstitial Si complex (H-I) where the I formation energy remarkably decreases. (2) The H impact on V concentration is larger than that on I concentration and becomes apparent when H concentration is higher than 1015/cm3. (3) The experimental finding of H impact on the concentration of intrinsic point defects is explained quantitatively.