Entropy Of Fusion Research Articles

Thermophysical Properties of AlxCoCrCuFeNi High Entropy Alloys

The AlxCoCrCuFeNi (x=0.25, 0.5, 1, 2) high entropy alloys (HEAs) were prepared by arc melting and spray casting techniques. Their microstructures, hardness, and thermophysical properties such as fusion enthalpy, entropy, thermal diffusion coefficients, thermal expansion coefficients, were investigated. XRD results indicated that AlxCoCrCuFeNi (x=0.25 and 0.5) alloys were composed of a high-entropy FCC phase and Cu-rich nanophase. As the Al content increased to 1 and 2, the phase structures included the AlNi-rich B2 phase, FeCr-rich A2 phase and Cu-rich nanophase. With the increased Al content, the microstructures of AlxCoCrCuFeNi HEAs transitioned from coarse dendrites to petal-like dendrites, and the grains were continuously refined. Moreover, the Al additions reduced the density whereas increased the Vickers hardness of the alloys. The maximum hardness observed in Al2CoCrCuFeNi HEA was approximately 2.4 times greater than that of the Al0.25CoCrCuFeNi HEA. The thermal diffusion coefficients of alloys initially increased and subsequently decreased as the temperature elevated. The phase transformation induced by Al content was an effective method for rapidly homogenizing the internal temperature of alloys. Furthermore, the crystal structure, elemental segregation, lattice distortion, enthalpy and entropy of fusion, and lattice vibration frequency all mutually affected the thermal diffusion and expansion coefficients of AlxCoCrCuFeNi HEAs.

Estimation of Rheological Coefficients of Acacia nilotica Gum: A Versatile Biopolymer for Biomedical and Food Industries

Introduction: Polysaccharides are widely used in the biomedical and food industries as thickening, gelling, emulsifying, hydrating, and suspending agents. Polysaccharides have adequate viscoelastic properties and flow characteristics. The purpose of this study was to determine various rheological parameters of Acacia nilotica (Babool) gum. Methods: Understanding the influence of temperature on rheological properties is quite important for polymeric materials to be considered as pharmaceutical excipients. Thus, a polymeric solution of purified Babool gum was prepared, and the influence of temperature on its rheological behaviour (viscosity and surface tension) was investigated to develop a better understanding of the structural organization of the gum. Furthermore, viscosity, surface tension, temperature coefficient, activation energy, Gibbs free energy, Reynolds number, and entropy of fusion were calculated using the Arrhenius, Gibbs–Helmholtz, Frenkel–Eyring, and Eotvos equations, respectively. Results: The activation energy of the gum was 3.81 ± 0.18 kJ/mol. Changes in entropy and enthalpy were 0.56 ± 0.23 and 4.27 ± 0.81 kJ/mol, respectively. The calculated amount of entropy of fusion was found to be 0.014 ± 0.01 kJ mol−1 K−1. Conclusion: The study outcomes showed that the viscosity and surface tension increased as the temperature decreased. The good rheological properties of Babool gum make it a suitable excipient for its applications in the food and pharmaceutical industries.

Entropy-Driven Reversible Melting and Recrystallization of Layered Hybrid Perovskites.

Typical layered 2D A2PbX4 (A: organic ammonium cation, X: Br, I) perovskites undergo irreversible decomposition at high temperatures. Can they be designed to melt at lower temperatures without decomposition? Which thermodynamic parameter drive the melting of layered perovskites? These questions are addressed by considering the melt of A2PbX4 as a mixture of ions (like ionic liquids), and hypothesized that the increase in the structural entropy of fusion (ΔSfus) will be the driving force to decrease their melting temperature. Then to increase structural ΔSfus, A-site cations are designed that are rigid in the solid crystal, and become flexible in the molten state. Different tail groups in the A-site cations form hydrogen-, halogen- and even covalent bonding-interactions, making the cation-layer rigid in the solid form. Additionally, the rotation of ─NH3 + head group is suppressed by replacing ─H with ─CH3, further enhancing the rigidity. Six A2PbX4 crystals with high ΔSfus and low melting temperatures are prepared using this approach. For example, [I-(CH2)3-NH2(CH3)]2PbI4 reversibly melts at 388 K (decomposition temperature 500 K), and then recrystallizes back upon cooling. Consequently, melt-pressed films are grown demonstrating the solvent- and vacuum-free perovskite films for future optoelectronic devices.

Polymorphism in 5-methylsalicylic acid: Insights into relative thermal behavior, luminescent properties, crystal structure, and Hirshfeld surface analysis

Polymorphs play an important role in mediating the physical and chemical properties of compounds. Three polymorphs were obtained from different solvents used in crystallization. A new polymorph of 5-methylsalicylic acid (γ-MSA) were obtained from acetic acid. The polymorphs α-MSA and β-MSA crystallized from water, and the mixed solvent containing methanol and water, respectively. The novel morphology of γ-MSA has been characterized by single–crystal X–ray diffraction, IR spectroscopy data, and powder X-ray diffraction. Single-crystal X-ray diffraction analysis shows that γ-MSA belongs to the monoclinic system with the P21/c space group. The parameters are listed as the following: a = 7.2795(5) Å, b = 15.2560(7) Å, c = 6.7170(4) Å, β=100.834(7)°, V = 762.83(8) Å3. In the novel polymorphic structure, classical hydrogen bonds of O–H···O can be obviously observed, through which a supramolecular architecture will be generated. Apart from the classical hydrogen bonds, the weak hydrogen bonds of C–H⋯O can be only found in form γ-MSA. The luminescent maximal are 394, 398 and 406 nm for α-MSA,β-MSA and γ-MSA, respectively. The order of the luminescent maximal peaks is listed as the following: α<β<γ. Single-crystal X-ray diffraction analysis results reveal that the order of the stacking interactions and the dihedral angles occurred between the carboxylic group and phenyl ring presents the following: α<β<γ. The Hirshfeld analysis further confirms that there exists the same sequence of the C···H intercontacts in α-, β- and γ-polymorphs. The contribution of the H···O/O···H close contacts in γ-MSA is the largest among these polymorphs, being confirmed by differential scanning calorimeter (DSC) data, which is in a good agreement with that of melting point. On the basis of analysis of DSC data and the fusion rules, the enthalpies (ΔH) and entropies (ΔS) can be estimated to be 29.5 kJ mol-1 and 69.4 J K-1 mol-1 for α; 31.1 kJ mol-1 and 72.8 J K-1 mol-1 for β, and 35.4 kJ mol-1 and 74.5 J K-1 mol-1 for γ), and these polymorphs are monotropically related. The sequences of melting point, enthalpies and entropies can be proposed: α<β<γ.

Study of phase equilibria in a two-component system diphenyloxide &lt;i&gt;- n -&lt;/i&gt; nonadecane

Using the Schroeder, UNIFAC and UNIFAC Dortmund methods, the fusibility diagram of the diphenyloxide – n –nonadecane system was calculated and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. On the DTA heating curve of the eutectic alloy, two endo-effects are noted, corresponding to the polymorphic transition of n–nonadecane and the melting of the eutectic. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. For a eutectic alloy, the specific enthalpy of fusion, molar values of entropy and enthalpy of fusion, volumetric specific enthalpy of fusion and density for standard conditions are calculated. The eutectic mixture can be recommended for use as a coolant, as well as the working fluid of a heat accumulator.

Study of phase equilibria in the two-component organic system biphenyl – n-docosane

The fusibility diagram of the diphenyl – n-docosane system was calculated by Schroeder, UNIFAC and UNIFAC Dortmund methods, and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. The endo-effect corresponding to the melting of the eutectic was noted on the DTA heating curve of the eutectic alloy. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. Specific fusion enthalpy, molar values of entropy and enthalpy of fusion, volumetric specific fusion enthalpy and density for standard conditions were calculated for an eutectic alloy. The eutectic mixture can be used as a heat carrier, as well as a working fluid of a heat accumulator.

Thermodynamic Study of Alkylsilane and Alkylsiloxane-Based Ionic Liquids.

The thermodynamic properties of ionic liquids (ILs) bearing alkylsilane and alkylsiloxane chains, as well as their carbon-based analogs, were investigated. Effects such as the replacement of carbon atoms by silicon atoms, the introduction of a siloxane linkage, and the length of the alkylsilane chain were explored. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to study the thermal and phase behavior (glass transition temperature, melting point, enthalpy and entropy of fusion, and thermal stability). Heat capacity was obtained by high-precision drop calorimetry and differential scanning microcalorimetry. The volatility and cohesive energy of these ILs were investigated via the Knudsen effusion method coupled with a quartz crystal microbalance (KEQCM). Gas phase energetics and structure were also studied to obtain the gas phase heat capacity as well as the energy profile associated with the rotation of the IL side chain. The computational study suggested the existence of an intramolecular interaction in the alkylsiloxane-based IL. The obtained glass transition temperatures seem to follow the trend of chain flexibility. An increase of the alkylsilane chain leads to a seemingly linear increase in molar heat capacity. A regular increment of 30 J·K-1·mol-1 in the molar heat capacity was found for the replacement of carbon by silicon in the IL alkyl chain. The alkylsilane series was revealed to be slightly more volatile than its carbon-based analogs. A further increase in volatility was found for the alkylsiloxane-based IL, which is likely related to the decrease of the cohesive energy due to the existence of an intramolecular interaction between the siloxane linkage and the imidazolium headgroup. The use of Si in the IL structure is a suitable way to significantly reduce the IL's viscosity while preserving its large liquid range (low melting point and high thermal stability) and low volatilities.

Phase transitions of choline dihydrogen phosphate: A vibrational spectroscopy and periodic DFT study.

Choline dihydrogen phosphate, [Chol][H2PO4], is a proton-conducting ionic plastic crystal exhibiting a complicated sequence of phase transitions. Here, we address the argument in the literature around the thermal properties of [Chol][H2PO4] using Raman and infrared microspectroscopy. The known structure of the low-temperature crystal, which contains the anti-conformer of [Chol]+ and hydrogen-bonded dimers of anions, was used to do periodic density functional theory calculations of the vibrational frequencies. Raman spectra indicate that the solid-solid transition at 20 °C is linked to a conformational change to the gauche [Chol] conformer with a concurrent local rearrangement of the anions. The distinct bands of lattice modes in the low-frequency range of the Raman spectra vanish at the 20 °C transition. Given the ease with which metastable crystals can be produced, Raman mappings demonstrate that a sample of [Chol][H2PO4] at ambient temperature can contain a combination of anti- and gauche conformers. Heating to 120 °C causes continuous changes in the local environment of anions rather than melting as suggested by a recent calorimetric investigation of [Chol][H2PO4]. The monotonic change in vibrational spectra is consistent with earlier observations of a very small entropy of fusion and no abrupt jump in the temperature dependence of ionic conductivity along the phase transitions of [Chol][H2PO4].

Melt-quenched carboxylate metal–organic framework glasses

Although carboxylate-based frameworks are commonly used architectures in metal-organic frameworks (MOFs), liquid/glass MOFs have thus far mainly been obtained from azole- or weakly coordinating ligand-based frameworks. This is because strong coordination bonds of carboxylate ligands to metals block the thermal vitrification pathways of carboxylate-based MOFs. In this study, we present the example of carboxylate-based melt-quenched MOF glasses comprising Mg2+ or Mn2+ with an aliphatic carboxylate ligand, adipate. These MOFs have a low melting temperature (Tm) of 284 °C and 238 °C, respectively, compared to zeolitic-imidazolate framework (ZIF) glasses, and superior mechanical properties in terms of hardness and elastic modulus. The low Tm may be attributed to the flexibility and low symmetry of the aliphatic carboxylate ligand, which raises the entropy of fusion (ΔSfus), and the lack of crystal field stabilization energy on metal ions, reducing enthalpy of fusion (ΔHfus). This research will serve as a cornerstone for the integration of numerous carboxylate-based MOFs into MOF glasses.

Thermodynamic properties of chalcogenide and pnictide ternary tetrahedral semiconductors

In this paper, we present thermodynamic properties such as heat of formation, heat of fusion and entropy of fusion for chalcopyrite structured solids with the product of ionic charges and nearest neighbour distance d (Å). The heat of formation (∆Hf) of these compounds exhibit a linear relationship when plotted on a log-log scale against the nearest neighbour distance d (Å), but fall on different straight lines according to the ionic charge product of the compounds. On the basis of this result two simple heat of formation (∆Hf)heat of fusion (∆HF), and heat of formation (∆Hf)entropy of fusion (∆SF), relationship are proposed and used to estimate the heat of fusion (∆HF) and entropy of fusion (∆SF) of these semiconductors. We have applied the proposed relation to AIIBIVC2 V and AI BIIIC2 VI chalcopyrite semiconductor and found a better agreement with the experimental data than the values found by earlier researchers. The results for heat of formation differ from experimental values by the following amounts: 0.3% (CuGaSe2), 6.7% (CuInSe2), 5% (AgInSe2), 5% (ZnGeP2), 6% (ZnGeP2), 0.4% (ZnSnP2), 0.7% (ZnSiAs2), 2.6% (ZnGeAs2), 1.2% (ZnSnAs2), 3.8% (CdGeP2), 6.4% (CdGeAs2), the results for heat of fusion differ from experimental values by the following amounts: 2.6% (CuGaS2), 0.6% (CuInTe2), 6% (ZnGeAs2), 8.8% (ZnSiAs2) and the results for entropy of fusion differ from experimental values by the following amounts: 6% (CuInSe2), 8% (CdSiP2).

Critical assessment of the data for Pure Cu from 0 K, using two-state model for the description of the liquid phase

Critical assessment of the thermodynamic data for pure copper was carried using careful analysis of the existing experimental data. An extended Einstein model was used for the crystalline phase and the two state model was applied for the liquid phase. Special attention is paid in this work to the precise description of the following thermodynamic functions: So298, Ho298–Ho0, the melting temperature, and the entropy and enthalpy of fusion. In order to fullfill the need for a precise evaluation of So298 we needed to use an additional technique, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0K up to the melting point. Relative stabilities of the BCC_A2 and HCP_A3 phases were derived.

QSPR models for enthalpy and entropy of organic compounds based on a set of norm indices

In this study, quantitative structure–property relationship (QSPR) models are developed to predict the standard vapourisation enthalpy (ΔvapH°), enthalpy of fusion (ΔfusH), entropy of fusion (ΔfusS), and standard sublimation enthalpy (ΔsubH°) of organic compounds. Molecular size and shape parameters describing the structural information are introduced to improve the accuracy and robustness of the predictive effect. The correlation coefficients (R2) for ΔvapH°, ΔfusH, ΔfusS, and ΔsubH° are 0.981, 0.851, 0.888, and 0.844, respectively, and these results indicate the high accuracy of models. Because some experimental values of the ΔfusH and ΔfusS are less than average absolute error (AAE) of QSPR models, which leads to negative values by linear models, nonlinear models are proposed to mitigate this problem. Additionally, a comparison with previously published results further demonstrates that these QSPR models can achieve high precision for data set comprising numerous chemical substances. From a holistic perspective, the novel QSPR models can be widely used in multiple domains, such as chemical reaction and predesign prediction.

The relationships between enthalpy and volume changes of aromatic compounds on melting at Tm and 298.15 K

Establishing the relationship between the thermodynamic parameters of melting, on the one hand, and the structural and physicochemical parameters of molecular compounds, on the other, is a long-standing problem. The volume change on melting has been long thought to be related to the entropy of fusion. In this work, we attempted to reveal the connection between the volume change on melting and the thermodynamic parameters of fusion of non-hydrogen-bonded aromatic compounds. Comparative analysis of the fusion enthalpies of different compounds, inherently melting under different conditions, may be ambiguous. Therefore, we additionally employed our recent findings on the experimental determination of the temperature dependence of the fusion enthalpy to adjust the quantities to the same temperature, 298.15 K. Linear correlations were established both at Tm and 298.15 K. An opportunity to use the correlation established at 298.15 K for predicting the fusion and sublimation enthalpies from the crystal density at 298.15 K and the molecular structure, taking advantage of existing approaches for predicting the molar volume of liquids and vaporization enthalpies, was demonstrated. Further investigation of these relationships might help to understand the nature of the melting process.

Breaking through the Thermodynamics “Wilds” of Metal–Organic Chemical Vapor Deposition Precursors: Metal tris-Acetylacetonates

Metal acetylacetonates belong to the β-diketonate family and are considered as classics among precursors for metal–organic chemical vapor deposition (MOCVD). The success of film preparation is crucially dependent on the volatilization thermodynamics of the precursors used. Data on the volatilization thermodynamics of metal acetylacetonates are in huge disarray. We amassed and analyzed experimental data on the vapor pressures and on the enthalpies and entropies of fusion, vaporization, and sublimation of acetylacetonate tris-complexes of metals(III) (Al, Sc, Cr, Mn, Fe, Co, Ru, Rh, In, and Ir) available in the literary sources. In addition, saturated vapor pressures over crystalline Al(III), Cr(III), and In(III) acetylacetonates and corresponding thermodynamic sublimation properties were determined. New findings enabled us to arbitrate the conflict among literature data. The enthalpies and entropies of sublimation, vaporization, and fusion were adjusted to the reference temperature for a correct comparison using the empirically estimated differences in heat capacities. The heat capacity of the crystalline phase was shown to depend weakly on the metal atom. As a result, a reliable set of enthalpies and entropies of the mentioned processes of fundamental importance was derived for ten metal complexes. Relationships between volatility and structure were established depending on the central metal. The suggested algorithm can be fairly easily transferred to the acetylacetonate or other β-diketonate isoligand complexes with metals of different valence.

Crystal Growth Rates from Molecular Liquids: The Kinetics of Entropy Loss

It has been established empirically that the rate of addition of molecules to the crystal during crystal growth from the melt is proportional to exp(-|ΔSfus|/R), where ΔSfus is the entropy of fusion. Here we show that this entropic slowdown arises directly from the separation of the entropy loss and energy loss processes associated with the freezing of the liquid. We present a theoretical treatment of the kinetics based on a model flat energy landscape and derive an explicit expression for the coupling magnitude in terms of the crystal-melt interfacial free energy. The implications of our work for nucleation kinetics are also discussed.

3D morphology and growth mechanism of primary Al3Ni in directionally solidified Al-16 wt% Ni alloy

The growth pattern and three-dimensional (3D) morphology of primary Al3Ni in directionally solidified Al-16 wt% Ni at different pulling rates were quantitatively and qualitatively investigated by synchrotron tomography. With the increasing cooling rate, Al3Ni crystals developed from faceted prism to non-faceted dendrites with V-shaped faceted arm ends. Faceted Al3Ni grows along [100] bounded by {011} facets, and the growth direction of non-faceted Al3Ni dendrites changes from [011̅] to [010]. The weakening of the faceted growth characteristics in the slow cooled sample is mainly due to the decrease of entropy of fusion caused by low Ni content in the liquid. A multi-layer atom model is established to describe and reveal the formation mechanism of faceted/non-faceted mixed structure at high cooling rate.

A HYPERSPECTRAL REMOTE SENSING FUSION TECHNOLOGY BASED ON SPECTRAL NORMALIZATION OF GF AND ZY SERIES SATELLITES

Abstract. Globalized surface coverage, environmental monitoring and other earth system science and high-quality global surface coverage monitoring applications urgently need basic hyperspectral remote sensing reflectance data to support. Spectral reflectance is the core data product of hyperspectral satellite remote sensing data, which is directly related to the application efficiency and quality of hyperspectral satellite. Due to the differences in spectral range, resolution width, central wavelength and other factors between multispectral and hyperspectral remote sensing images, the fusion processing of hyperspectral and multispectral remote sensing images is extremely difficult. In this study, the idea of normalization of physical parameters is adopted. Based on the remote sensing data of multi-source satellites such as GF5, GF1WFV and ZY3, the physical parameters of GF series satellites are fused to improve the spatial resolution of hyperspectral remote sensing images while the physical parameters of surface parameters are maintained. According to the fusion quality evaluation results of noise, information entropy, clarity, spectral angle cosine, correlation coefficient and root mean square error, the fusion results are consistent with the original numerical performance. The noise level, information entropy and clarity index of GF5 and ZY3 fusion are better. The spectral angle cosine, correlation coefficient and root mean square error index of GF5 and GF1 fusion are better. This study provides a new way and method for high-precision and quantitative processing of hyperspectral remote sensing data.

Forecast of Phase Diagram for the Synthesis of a Complex for the Detection of Cr6+ Ions.

A new organic complex (ANNBA) was synthesized using the solvent-free, solid-state reaction involving anthranilamide (AN)–m-nitrobenzoic acid (NBA). The established phase diagram specifies the formation of a complex in a 1:1 stoichiometric ratio which melts congruently at 142 °C. The diagram also infers the formation of two eutectics, E1 and E2, on either side of the complex with their respective melting at 118 and 106 °C. The stability and novelty of the synthesized complex was confirmed by differential scanning calorimetry, powder X-ray diffraction, and spectroscopic FTIR, 1H, and 13C NMR studies. The significant thermodynamic parameters such as the heat of mixing, the entropy of fusion, the roughness parameter, the interfacial energy, and excess thermodynamic functions have been studied. The novel complex (ANNBA) material displayed intense fluorescent emission as compared to the parent and the other well-known fluorescent organic material “pyrene.” The influence of solvent’s polarity on the absorption and emission of the complex has been studied in different solvents. Herein, we have displayed remarkable affinity of the complex toward hexavalent chromium ions in water, affecting its fluorescent property. We have deployed the synthesized complex as a turn-off fluorescent sensor to detect the most hazardous hexavalent chromium ions in water for the first time.

Positron Annihilation in Stable and Supercooled Metallic Melts

Abstract The stable and supercooled melts as well as the crystalline phases of Ga, In, Sn, Pb, and Bi have been investigated in the age –momentum correlation (AMOC) positron annihilation facility at the Stuttgart pelletron. The comparison of the lineshape parameter S, characterizing the momentum distribution of the annihilating electron –positron pairs, and of the mean positron lifetime with measurements of the positron diffusivity confirms in considerable detail the ‘polaron’ model of positrons in metallic melts developed earlier. The quantitative analysis of the data provides us with valuable information on the structure of the melts. E. g., in the investigated melts the existence of an appreciable concentration of ‘free volumes’ comparable in size with the atomic volume can be excluded. It is shown that this is in accord with earlier deductions from self-diffusivity measurements. An interesting but hitherto incompletely understood correlation between the entropy of fusion and the absence of trapping of positrons by vacancies in thermal equilibrium is pointed out.

The fluctuating standard potential of lithium in organic solvents.

The standard potential of a lithium metal electrode versus the standard hydrogen electrode was calculated by constructing the thermodynamic cycle in a hypothetical electrochemical cell with a dual-phase electrolyte. It is demonstrated that the standard potential of the lithium metal electrode can fluctuate over 0.5 V in different organic solvents, and is correlated to the modified donor number by the entropy of fusion of the solvents.