Calculated Melting Points Research Articles

R32-Al5W: A new stable high-temperature alloy

Due to the high melting point, exceptional mechanical properties, and remarkable corrosion resistance exhibited by Al5W, researchers have conducted extensive research on the structural characteristics of Al5W. To identify the lowest energy structures and find new structures, a combination of particle swarm optimization and first-principles calculations was employed to identify energy-favorable Al5W structures under ambient pressure. The experimental P63 phase and the previously predicted R3¯c phase were identified. Notably, a new R32-Al5W phase was proposed. A comparative analysis on the structural stability, elastic, thermodynamic, and electronic properties of these three Al5W phases were conducted. The results indicate that R32-Al5W exhibits favorable thermodynamic stability, with a predicted bulk modulus close to that of R3¯c-Al5W. All the three Al5W phases demonstrate brittle behavior. The P63-Al5W phase displays larger shear anisotropy in the (010) and (001) planes, while the R32-Al5W phase shows greater shear anisotropy on the (100) plane compared to other two phases. Furthermore, employing Clarke’s and Cahill’s models, the minimum thermal conductivity of Al5W phases was predicted, revealing a magnitude order of P63 >R3¯c > R32. Our calculated melting points also conform to this trend.

Ionic liquid derived novel deep eutectic solvents as low viscous electrolytes for energy storage

This work investigates a newly emerging class of solvents to be used as alternatives to or complementarily with ionic liquid (IL) electrolytes. Three novel deep eutectic solvents (DESs) comprised of the hydrogen bond donors (HBDs), namely N-Methylacetamide (NMAc) and formamide, were formulated with three variants of the methyl imidazolium-based ionic liquids (ILs) as hydrogen bond acceptors (HBAs). ILs consisting of 1-butyl-3-methyl imidazolium ([BMIM]) cation with anions namely methanesulphonate ([MeSO3]), bis(trifluoromethylsulfonyl)imide ([Tf2N]), and hexafluorophosphate ([PF6]) were used as hydrogen bond acceptors. Initially, the eutectic points of the DESs were estimated using a quantum chemical-based thermodynamic model, namely Conductor like Screening Model-Segment Activity Coefficient (COSMO-SAC). The calculated melting points of the DESs were determined to be markedly lower than those of both the constituent components. Further, physical and chemical characterization was done on the synthesized DESs. The viscosities (<20 cp) were found to be significantly lower than those of conventionally used pure room temperature ILs, and ionic conductivities (>5 mS/cm) were found to be appreciably higher than those of the corresponding constituent ILs. Thermogravimetric analysis revealed negligible mass loss up to 80–100 °C. Linear scan voltammetry (LSV) was employed to determine the electrochemical stable potential window (ESPW) of the solvents with a glassy carbon (GC) electrode. LSV provided electrochemical stabilities in the range of 3.8–4 V for all three studied deep eutectic solvents, comparable to pure ILs and far higher than the potential windows of mixtures of ILs and organic solvents, a blend commonly used as electrolytes.

Melting curve of magnesium up to 460 GPa from ab initio molecular dynamics simulations

Based on ab initio molecular dynamics simulations, we determined the melting curve of magnesium (Mg) up to ∼460 GPa using the solid–liquid coexistence method. Between ∼30 and 100 GPa, our melting curve is noticeably lower than those from static experiments but is in good agreement with recent shock experiments. Up to ∼450 GPa, our melting curve is generally consistent with the melting points from first-principles calculations using the small-cell coexistence method. We found that, at high pressures of a few hundred GPa, due to the strong softening of interatomic interactions in the liquid phase, solid–liquid coexistence simulations of Mg show some characteristics distinctively different from other metal systems, such as aluminum. For example, at a given volume, the pressure and temperature range for maintaining a stable solid–liquid coexistence state can be very small. The strong softening in the liquid phase also causes the unusual behavior of reentrant melting to occur at very high pressures. The onset of reentrant melting is predicted at ∼305 GPa, close to that at ∼300 GPa from the small-cell coexistence method. We show that the calculated melting points, considering reentrant melting, can be excellently fitted to a low-order Kechin equation, thereby making it possible for us to obtain a first-principles melting curve of Mg at pressures above 50 GPa for the first time. Similar characteristics in solid–liquid coexistence simulations, as well as reentrant melting, are also expected for other systems with strong softening in the liquid phase at high pressures.

Study on properties of single-phase high entropy alloys with FCC structure based on the empirical electron theory

The valence electron structures, thermal properties, hardness and magnetic moments of single-phase high entropy alloys with the face-centered cubic structure have been first investigated with the empirical electron theory of solids and molecules. The theoretical bond lengths agree with the experimental ones well. The calculated melting points of CrFeCoNi, CrMnFeCoNi and CrFeCoNiCu alloys are consistent with their differential thermal analysis (DTA) measured ones. The calculated magnetic moments of ferromagnetic FeCoNi and FeCoNiX0.25 (XAl or Si) alloys agree with the observed ones well. The physical properties of these alloys are strongly associated with their valence electron structures. It is suggested that the melting point, cohesive energy, hardness and magnetic moments of the face-centered cubic high entropy alloys are mainly modulated by bonding factor f, covalent electrons per atom nc/atom, covalence electron pair nA and 3d magnetic electron, respectively.

Generalized non-integer Lennard-Jones potential function vs. generalized Morse potential function for calculating cohesive energy and melting point of nanoparticles

A generalized non-integer Lennard-Jones (L-J) potential function with an additional parameter m is proposed to calculate the cohesive energy and melting point of nanoparticles. The model based on the new generalized non-integer L-J potential function has been successful in predicting experimental values. The calculated cohesive energies show an excellent agreement with the experimental values of the cohesive energies of molybdenum (Mo) and tungsten (W) nanoparticles (Kim et al., 2002). Moreover, the calculated melting points based on the generalized non-integer L-J potential function agree with the experimental values for large gold (Au) nanoparticles including n≥1000 atoms (Buffat and Borel, 1976) and small silica-encapsulated gold (Au) nanoparticles including n≤1500 atoms (Dick et al., 2002). The stability of nanoparticles is due to two conditions: the increase of the range of the attractive force and the high gradient attractive interaction in the potential function when rij≈r0.

Complete thermodynamic description of the Mg-Ca-O phase diagram including the Ca-O, Mg-O and CaO-MgO subsystems

A complete thermodynamic description of the Mg-Ca-O system and phase diagrams is developed. It is based on our extensive thermodynamic analysis of solid CaO and MgO data and validation of the low-temperature Mg-Ca-O phase diagram up to 1050 K. This work presents the high- temperature oxygen solubilities and revisions of calculated melting points of the oxides. An extension of the empirical schemes for predicting the activity coefficient of oxygen in liquid elements is proposed to predict data for the Mg-O system. Consistent thermodynamic descriptions of the complete binary Ca-O and Mg-O systems are developed. It is shown that this framework is crucial to understand recently measured significantly different melting points of CaO under oxidizing versus reducing conditions. The revised description of the MgO-CaO quasibinary oxide system considers all experimental data, revealing significantly different melting equilibria compared to all previous publications.

Prediction of Melting Temperature and Latent Heat for Low-melting Metal PCMs

Abstract Models are presented for predicting the melting point and the latent heat of low-melting alloys to facilitate the design of phase change materials (PCMs). Based on the characteristics of entropy and enthalpy during the transition of material phase, the prediction models of melting point and latent heat for eutectic binary system were established at first, and then the models were extended into multicomponent system. Calculated melting points and latent heats of 15 selected low-melting alloys were compared with measurement results using DSC, and it is found that there exists a good agreement between the prediction and the experimental data. A criterion for preparation of metallic PCMs was also proposed. In order to obtain a higher latent heat alloys, an element with higher latent heat should be selected as component of the alloy, and the mole fraction of the element should be increased. The advantage of the models proposed is that the melting point and the latent heat of a certain PCM can be predicted mathematically, avoiding many experiments needed in conventional ways.

Influence of solid–liquid interface on the thermal stability of Li–Fe nanoalloy with rhombohedral structure: A molecular dynamics study

The thermal stability and atomic structure of the solid–liquid interface of lithium iron nanoalloys with rhombohedral configuration are examined by embedded atom method and molecular dynamics. The thermal stability of pure Li and Fe rhombohedral nanoparticles are initially evaluated. The calculated melting points for nanoparticles have a good linear relationship with nanoparticle size, and the extrapolated bulk melting temperatures of the two metals are consistent with experimental values. For Li–Fe nanoalloys, the calculated radial distribution function and atomic configuration show that Li atoms at the interface between Li and Fe maintain an ordered arrangement when temperature is larger than melting point. The melting temperature of Li shell reduces with increased Li atoms in the Li–Fe nanoalloy. The conclusion can be attributed to the structured order at the solid–liquid interface. When the total amount of Li increases, the Fe core decreases in size and the number of Li atoms in contact with Fe at the interface is lesser, which leads the melting temperature of the Li shell decreases when the total amount of Li atoms increases in the particle.

Molecular dynamical simulations of the melting properties of Aln(n=13–32) clusters

Based on the Gupta-type semi-empirical inter-atomic many body potential, the melting properties of Aln(n=13–32) clusters are systematically investigated by using the molecular dynamics method combined with the simulated annealing and quenching techniques. Our results show that, except for several sizes (Al13 and Al19), in general the heat capacity curves all are in disorder (no obvious single-peak), which are consistent with the experimental observations that small aluminum clusters have messy heat capacity curves in the melting process. Reasons for the different melting behaviors (whether they exhibit regular or irregular heat capacity curves) of these small Al clusters can be explored by analyzing the energy distributions of the simulated quenching structures of these clusters at different temperatures. For the clusters with disordered heat capacity curves one can obtain the melting points from analyzing the atomic equivalence indexes of those clusters, and the variations of the calculated melting points of the aluminum clusters with increasing cluster size are in agreement with the experimental observations.

Scores of Extended Connectivity Fingerprint as Descriptors in QSPR Study of Melting Point and Aqueous Solubility

QSPR studies, using scores of SciTegic's extended connectivity fingerprint as raw descriptors, were extended to the prediction of melting points and aqueous solubility of organic compounds. Robust partial least-squares models were developed that perform as well as the best published QSPR models for structurally diverse organic compounds. Satisfactory performance of the QSPR models indicates that the scores of extended connectivity fingerprint are high performance molecular descriptors for QSAR/QSPR studies. Performance of the fingerprint-based descriptors is further validated by the satisfactory prediction of aqueous solubility of nearly 1300 organic compounds (squared correlation coefficient of 0.83 and RMSE of 0.85 log unit) with Yalkowsky's general solubility equation using both calculated melting points and calculated octanol-water partition coefficients. It demonstrates for the first time that it is feasible to predict aqueous solubility of structurally diverse organic compounds with the general solubility equation using both the calculated melting points and the partition coefficients.

The fatty acid composition of the serum phospholipids of children with sickle cell disease in Nigeria

The purpose of this study was to determine the fatty acid composition of the serum phospholipids of children with sickle cell disease (SCD) in Nigeria and to compare the relative fluidity of the acyl chains of the serum phospholipids of controls versus the subjects with SCD. It is widely accepted that the fatty acid composition of an individual's serum phospholipids reflects that of their tissue phospholipids. An alteration in the fatty acid composition of membrane phospholipids could affect critical membrane-dependent enzymes and processes (e.g., ion and solute transport, hormone–receptor interactions, signal transduction pathways). We found a significant reduction in the content of polyunsaturated n-3 fatty acids in the phospholipids of subjects with SCD which could result in a reduction of the fluidity of their tissue membranes. Specifically, there was a 40–50% reduction in the proportion of total n-3 fatty acids in subjects with SCD. On the basis of calculated melting points and double bond indices of the acyl chains of the serum phospholipids, the phospholipids of the children with SCD are less fluid relative to those of their healthy counterparts. In addition, we determined that linoleic acid, arachidonic acid, and stearic acid were the major determinants of the fluidity of the acyl chains of the serum phospholipids of the healthy controls and children with SCD.

The RI-liquid equilibrium in the ternary system n-pentadecane + n-hexadecane + n-heptadecane. Calculation of liquidus surface and thermal windows comparison with experimental data

The liquidus surface and thermal windows of the ternary system n-pentadecane + n-hexadecane + n-heptadecane were calculated from pure component data and excess Gibbs energies of binary subsystems. Calculations were made with temperature independent as well as temperature dependent excess Gibbs energies; the results were about the same. Comparison of calculated melting points of some ternary compositions with experimental values showed that the average temperature difference was within the uncertainty of the latter.

Thermodynamic model of liquid-solid equilibria for natural fats and oils

Abstract Natural fats and oils are important raw materials in the food, detergent and paint industries. However, little attention has been paid to the thermodynamic model of the phase equilibria of triglyceride mixtures, which are the main constituents of natural fats and oils. The objective of this paper is to develop a thermodynamic method to predict the melting and solidification temperatures and the equilibrium compositions of the solid and liquid phases between these two temperatures. The cloud point temperatures calculated by the present model agree with those reported values within a few degrees, however, the calculated melting points are substantially lower than those reported.

Melting behavior of polyacrylonitrile copolymers

The melting behavior of acrylonitrile copolymers, ter- and tetrapolymers was studied in the dry state and in the presence of water. The melting point depression caused by the incorporation of a specific comonomer into the polyacrylonitrile chain was shown to be dependent on the molecular structure of the comonomer. Not all comonomers gave equivalent melting point depressions on a molar basis. The Eby theory of comonomer melting was used to model the melting behavior. This theory assumes that the non-crystallizing (non-AN) comonomers enter the crystal lattice as point defects rather than being relegated to the amorphous phase. An equation was developed for predicting the melting point of copolymers, terpolymers and higher order polymers as a function of the polymer composition and the specific melting point depression constant for each comonomer. The latter constants are derived from the copolymer melting point curves. The equation is applicable to both dry and wet polymers and excellent agreement between the observed and calculated melting points for wet terpolymers and tetrapolymers was observed.