Entropy Of Fusion Research Articles

On the macrosegregation of silicon in niobium silicide based alloys

Sixty nine Nb–Si based alloys with Al, B, Cr, Fe, Ge, Hf, Mo, Sn, Ta, Ti, V, W, Zr additions that were produced using cold hearth based solidification processing were used to study the macrosegregation of Si. The study used chemical analysis data for the compositions of the cast alloys and phases present in their microstructures to calculate various material parameters and the partitioning of solutes. The material parameters were based on the melting temperatures and enthalpies of melting of sd and sp electronic configuration alloying elements in Nb. The key material parameters controlling the macrosegregation of Si were the alloy melting temperature Tm, the melting temperature of the sd elements of the alloy Tmsd, the enthalpy of melting of the sd elements ΔHmsd, the ratio of the melting temperatures of the sd and sp elements in the alloys Tmsd/Tmsp and the “alloy entropy of fusion” ΔHm/Tm. The macrosegregation of Si was explained using the concepts of “alloy entropy of fusion”, and “alloy enthalpy of melting” ΔHm and Tm and by considering (i) the stability of S/L interfaces in terms of constitutional supercooling theory and the growth of S/L interfaces in terms of their structure and (ii) the partitioning of solutes between the Nbss and the intermetallics present in the microstructures of the alloys. High Si macrosegregation was observed in alloys that had high ΔHm/Tm and Tmsp values and low Tmsd/Tmsp and Tm.

Effect of the structure, solid state and lipophilicity on the solubility of novel bicyclic derivatives

Novel bicyclic derivatives have been synthesized. The solubility of drug-like substances in phosphate buffer рН 7.4 has been measured within the range of (9.02·10−5 to 1.05·10−4)mol/l. The relationship between the chemical nature and the structure of the aryl substituents and the solubility parameter was investigated. The fusion temperatures, enthalpies and entropies have been determined experimentally. The influence of thermophysical characteristics and lipophilicity on the solubility was studied using regression analysis. The calculations by the solubility/lipophilicity equation showed an overall improvement of the predictions equal to 0.5 log units. It was concluded that the solvation has a considerable influence on the solubility of the compounds under consideration. It was also determined that the alkyl- and halogen-derivatives solubility values correlate with HYBOT descriptors characterizing the (donor+acceptor) properties of the substances. The thermodynamic parameters of the solubility process were calculated using the temperature dependences. The study also revealed that the solubility of the bicyclic compounds is characterized by high endothermicity of the processes and negative entropies.

Molar heat capacities and standard molar enthalpy of formation of pyrimethanil butanedioic salt

A noval anilino-pyrimidine fungicide, pyrimethanil butanedioic salt (C28H32N6O4), was synthesized by a chemical reaction of pyrimethanil and butanedioic acid. The low-temperature heat capacities of the compound were measured with an adiabatic calorimeter from 80 to 380 K. The thermodynamic function data relative to 298.15 K were calculated based on the heat capacity fitted curve. The thermal stability of the compound was investigated by TG and DSC. The TG curve shows that pyrimethanil butanedioic salt starts to sublimate at 455.1 K and totally changes into vapor when the temperature reaches 542.5 K with the maximal speed of weight loss at 536.8 K. The melting point, the molar enthalpy (Δfus H m), and entropy (Δfus S m) of fusion were determined from its DSC curves. The constant-volume energy of combustion (Δc U m) of pyrimethanil butanedioic salt was measured by an isoperibol oxygen-bomb combustion calorimeter at T = (298.15 ± 0.001) K. From the Hess thermochemical cycle, the standard molar enthalpy of formation was derived and determined to be Δf H m o (pyrimethanil butanedioic salt)=−285.4 ± 5.5 kJ mol−1.

Thermodynamics of risperidone and solubility in pure organic solvents

The solid–liquid solubility of the thermodynamically stable form I of the drug risperidone has been determined by a gravimetric method in nine pure organic solvents in the temperature range 278.15–323.15K. The melting temperature and associated enthalpy of fusion of risperidone form I has been determined by differential scanning calorimetry (DSC) to be 442.38K and 43.94kJmol−1, respectively. The heat capacity of the solid form I and the melt have been determined over a range of temperatures by temperature-modulated DSC, and extrapolated data has been used to calculate the Gibbs energy, enthalpy and entropy of fusion from ambient temperature up to the melting point. The ideal solubility within a Raoult's law framework is obtained from the Gibbs energy of fusion, and the solution activity coefficient at equilibrium in the nine solvents quantified. Solutions in all solvents exhibit positive deviation from Raoult's law, with the highest solubility (closest to ideality) in toluene, an aprotic apolar solvent. The solubility curves plotted in a van’t Hoff graph show non-linear behaviour and are well-approximated by a second order polynomial.

Thermodynamics of fenofibrate and solubility in pure organic solvents

Calorimetric data on the melting of 1-methylethyl 2-[4-(4-chlorobenzoyl)-phenoxy]-2-methylpropanoate (fenofibrate) and the heat capacity of the solid and the melt have been determined, from which the Gibbs energy, enthalpy and entropy of fusion are calculated. Solid-liquid solubility data have been collected by a gravimetric method in seven pure solvents (methanol, ethanol, 1-propanol, 2-propanol, ethyl acetate, acetonitrile, and acetone) across a range of temperatures. Fenofibrate is much more soluble in ethyl acetate, acetonitrile and acetone compared to alcohols. In the alcohols the solubility increases with aliphatic chain length. The Gibbs energy of fusion is used to estimate the activity of the solid within a Raoult's law framework. Except for ethyl acetate solutions which are almost ideal, solutions in all evaluated solvents exhibit positive deviation from Raoult's law, and in the alcohols the activity coefficient ranges up to 25. It is shown that the heat capacity component of the enthalpy of fusion is not negligible at room temperature, in spite of the proximity to the melting point, and furthermore that the temperature dependence of the activity coefficient in the saturated solution has a governing influence on the van’t Hoff enthalpy of solution in acetonitrile and the alcohols. Crystals obtained by two different methods from a range of solvents have been analysed by PXRD, FTIR and NMR spectroscopy, TGA and DSC, and have in all cases been shown to consist of the stable polymorph (form I).

Molecular dynamics study of melting curve, entropy of fusion and solid–liquid interfacial energy of cobalt under pressure

We performed molecular dynamics (MD) simulations with the two embedded atom method (EAM) potentials to calculate the melting curves of cobalt over a wide range of pressure. Zhou׳s EAM potential can produce satisfying results, in better agreement with the experiment compared with Pun׳s. Based on Zhou׳s potential, we simulated the melting of Co with two approaches, i.e., the one-phase (hysteresis) method and two-phase (solid–liquid coexistence) method. Both approaches can effectively reduce the superheating, and their results are in the close proximity at the applied pressures. With the one-phase method, during the investigation of the entropy of fusion of Co, we found that with the pressure increasing, the entropy of fusion decreases rapidly first and then oscillates with pressure; when the pressure is beyond 100GPa, the entropy of fusion shows less pressure effect. When taking account of the solid–liquid interfacial energy at different pressures, we found that it increases monotonically with pressure, and can be well described as a fifth-order polynomial relation. Moreover, the thermal equation of state (EOS) and the temperature dependence of atomic structures of Co have been obtained successfully.

Direct Measurement of Fusion Enthalpy of LaAlO3 and Comparison of Energetics of Melt, Glass, and Amorphous Thin Films

Enthalpy of fusion and melting temperature of perovskite LaAlO3 were measured using thermal analysis method as 124 ± 10 kJ/mol at 2134 ± 10°C, providing a value of 52 ± 4 J·(mol·K)−1 for entropy of fusion. Crystallization enthalpy of amorphous LaAlO3 thin films was found to change from −24 to −17 kJ/mol with decrease in film thickness from 100 to 20 nm. Differences in energetics of amorphous LaAlO3 films and glass cannot be explained exclusively by surface energy contribution but must reflect differences in structure between films and glasses in this system.

Thermal properties of some small peptides (N-acetyl-amino acid-N′-methylamides) with non-polar side groups

Temperatures and molar enthalpies of fusion of a series of uncharged small peptides, namely the methylamides of N-acetyl substituted glycine, α-amino-butyric acid, alanine, valine, norvaline, leucine, isoleucine, norleucine, and proline, were measured by differential scanning calorimetry (d.s.c.), and molar entropies of fusion were derived. Both l- and dl-compunds were taken into account for the chiral molecules. No solid-to-solid transitions were detected from room temperature to fusion except for N-acetyl-N′-methyl alaninamide. Comparisons were made with the values for the N-acetyl amides of the corresponding amino acids previously reported. Both l enantiomers and dl racemates of α-aminobutyric acid, alanine, valine and isoleucine methylamides displayed temperatures of fusion sharply increasing as a function of molar mass, whereas much lower values, in countertendency with their molar mass increase, were found for proline and leucine methylamides. The racemic dl crystals showed temperatures of fusion of about 40°C lower than those of the corresponding pure l enantiomers, except for proline and leucine derivatives. The enthalpies and entropies of fusion also varied as a function of molar mass following a similar trend with that of temperatures of fusion, except for alanine derivatives which showed lower values than expected. The values of ideal solubility of solids at T=298.15K were estimated based on their temperatures and molar entropies of fusion. Results were discussed with reference to the packing patterns based on hydrogen bonding and hydrophobic interactions.

ChemInform Abstract: Developments and Future Directions of Phase Diagram, Physicochemical and Optical Studies of Binary Organic Complexes

AbstractReview: 117 refs.

Interpretation of fusion and vaporisation entropies for various classes of substances, with a focus on salts

Entropies of fusion and vaporisation of a variety of elements and compounds have been derived from literature data. Fusion entropies range from low values for metals and certain cyclic hydrocarbons (e.g., cyclopentane) through modest values for salts to high values for materials undergoing drastic rearrangement or disentanglement such as aluminium chloride and n-alkanes. Entropies of vaporisation for most substances are close to the Trouton’s Law value of ∼100J·deg.−1·mol−1, with low values for species which associate on boiling (e.g., acetic acid) and higher values signifying simple dissociation (e.g., nitrogen tetroxide) or total decomposition (e.g., some ionic liquids). The nature of inorganic and semi-organic salts in all 3 phases is discussed.

Faceting of a rough solid–liquid interface of a metal induced by forced convection

The solid–liquid interface of metallic systems of small entropy of fusion is characterized by a rough interface and dendritic morphology. In contrast, systems of high entropy of fusion like semimetals and semiconductors show smooth interfaces and facetted interfaces. The present work demonstrates that, in an undercooled melt of a metal–metalloid alloy Ni2B of intermediate entropy of fusion, a transition from a rough to a smooth interface is induced by forced convection of the melt. Electrostatic levitation is used to container-less undercool droplets in a quiescent state with no convection while electromagnetic levitation (EML) is used to undercool droplets with forced convection. The growth velocity of the solid phase is monitored as a function of undercooling by a high-speed video camera. The data are analysed within dendrite growth theory. In the case of EML, a transition from a rough to a smooth interface is indicated during dendrite growth in the undercooled melt. This is confirmed by facetted microstructures of samples solidified upon undercooling by EML. Hopper-like crystals are formed like in non-metals as bismuth, halite and ice.

Dimensionless Entropy of Fusion as a Simple Criterion To Predict Agglomeration in the Supercritical Antisolvent Process

The aim of this work was to understand the agglomeration phenomenon and to predict the agglomeration behavior of materials in the supercritical antisolvent (SAS) process. Carbon dioxide-induced melting point depression is believed to be one of the major causes of the formation of agglomerates during the SAS process. Here, we attempted to observe the CO2-induced melting behaviors of nine target materials and to recrystallize them in the SAS process. On the basis of the multicomponent Clapeyron equation, which describes the interaction between solute and carbon dioxide, the thermodynamic properties of 32 materials were investigated to correlate melting point depression with the agglomeration phenomenon. In this analysis, the dimensionless entropy of fusion was utilized as a simple criterion to predict agglomeration behavior. The extent of melting point depression was assumed to be inversely proportional to the entropy of fusion of the solute. This assumption enables us to predict the agglomeration behavior of recrystallized pharmaceuticals with dimensionless entropy of fusion during the SAS process. Furthermore, a correlation between the tendency of agglomeration and whether the recrystallized particles have either faceted or nonfaceted form was observed.

Determining the thermodynamic melting parameters of sulfamethoxazole, trimethoprim, urea, nicodin, and their double eutectics by differential scanning calorimetry

The literature data on the thermodynamic melting characteristics of sulfamethoxazole, urea, trimethoprim, and nicodin are analyzed for individual compounds. Their enthalpies and melting points, either individually or in the composition of eutectics, are found by means of DSC. The entropies of fusion and the cryoscopic constants of individual compounds are calculated.

Thermodynamic behavior of glass-forming metallic supercooled liquids

We analyze the enthalpy of crystallization Hx and fusion Hm, and calculate the average difference of the heat capacity between supercooled liquid and equilibrium crystalline solid ΔCave in a series of glass-forming metallic supercooled liquids. It is found that ΔCave is close to a constant 13.2J/mol/K which is an important feature for glass-forming metallic supercooled liquids, and there is no obvious correlation between the parameter φ(=1−Hx/Hm) and the glass-forming ability. The ratio of ΔCave to the entropy of fusion is an important parameter in determining the glass-forming ability in metallic glasses.

Isomerization effect on the heat capacities and phase behavior of oligophenyls isomers series

In this work an analysis of the effect of ortho, meta and para isomerization and the number of phenyl rings on the heat capacity and phase behavior of oligophenyls, n(Ph), from 3 up to 5 is presented. The phase behavior from 298.15K to the melting temperature was analysed by differential scanning calorimetry (DSC) and the temperature, enthalpies and entropies of fusion along the oligophenyls series were determined. With the exception of terphenyl isomers, the meta oligophenyls series show lower melting temperatures and higher entropies of fusion. Heat capacities, at T=298.15K, were determined for the ortho and meta quaterphenyl and p-quinquephenyl oligomers by means of high precision drop calorimetry. The heat capacities of the ortho and meta isomers are systematically lower than those of the corresponding para isomers. It was found that the subtle isomerization effect on the heat capacity is partially related to the ring rotation restrictions in their supramolecular structure and increases with the increase of the number of phenyl rings.

Microstructure and field emission property of Bridgman-grown Si–TaSi2 eutectic in situ composite

Using an improved Bridgman technique with high temperature gradient (210K/cm), directionally solidified Si–TaSi2 eutectic in situ composite with uniform and aligned TaSi2 fiber is obtained. The growth mechanism and field emission property of the Si–TaSi2 eutectic are investigated. It is revealed that the co-operative growth of two phases for Si–TaSi2 eutectic is related to the ratio of ΔSsi/ΔSTaSi2 (ΔS is the entropy of fusion). The novel TaSi2 sharp tip arrays with fiber curvature radius of 21nm and fiber height of 2.79–6.45µm are fabricated by selective wet etching at optimized parameters. The Si–TaSi2 cathode arrays obtained present a reasonable field emission performance with low turn-on electric field of 3.8V/μm and threshold field of 6.5V/μm and large emission area per tip of about 1874nm2, which can be used as promising materials for field emitters.

Thermodynamic properties and microstructural characteristics of binary Ag-Sn alloys

The liquidus and solidus temperatures and enthalpy of fusion for Ag-Sn alloys are systematically measured within the whole composition range by differential scanning calorimetry (DSC). The measured enthalpy of fusion is related to Sn content by polynomial functions, which exhibit one maximum value at 52 wt%Sn and two minimum values around 21 wt%Sn and 96.5 wt%Sn, respectively. The liquidus slope, the solidification temperature interval, the solute partition coefficient and the entropy of fusion are calculated on the basis of the measured results. The undercoolability of those liquid Ag-Sn alloys solidifying with primary (Ag) solid solution phase is stronger than the other alloys with the preferential nucleation of ζ and ɛ intermetallic compounds. Morphological observations reveal that peritectic reactions can rarely be completed, and the peritectic microstructures are always composed of both primary and peritectic phases.

M-Hydroxybenzoic Acid: Quantifying Thermodynamic Stability and Influence of Solvent on the Nucleation of a Polymorphic System

Nucleation of m-hydroxybenzoic acid crystals in different pure solvents has been investigated, and the thermodynamic interrelationship between two polymorphs was analyzed. The melting properties and specific heat capacities of both polymorphs have been determined by differential scanning calorimetry, and the solubility in several solvents at different temperatures was measured gravimetrically. Absolute values of the Gibbs free energy, enthalpy and entropy of fusion, and the activity of the polymorphs have been determined as functions of temperature. It is established that the polymorphs are monotropically related, with differences in enthalpy and Gibbs free energy of approximately 1 kJ/mol at room temperature. In a total of 539 nucleation experiments, in six solvents and with different cooling rates, the visible onset of nucleation was recorded and the nucleating polymorph was isolated. It is found that the degree of supersaturation required for nucleation and the polymorphic outcome depend strongly on the solvent. The metastable polymorph is kinetically favored under all evaluated experimental conditions, and for most of the conditions it is also statistically the most probable outcome. Nucleation of the stable polymorph is increasingly promoted in solvents of increasing solubility. It is shown how this can be rationalized by analysis of solubility and rate of supersaturation generation.

Imidazolium methanesulfonate as a high temperature proton conductor

Imidazolium methanesulfonate (1) has been studied as a model proton conductor for high temperature polymer electrolyte membrane fuel cells (PEMFCs). It is found that 1 undergoes transformation from crystalline to plastic crystalline and then molten states successively from ambient temperature to 200 °C. The solid–solid phase transition of 1 at 174 °C has been preliminarily verified by differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). At the melting point of 188 °C, 1 displays a low entropy of fusion of around 24 J mol−1 K−1. In particular, a high ionic conductivity of 1.0 × 10−2 S cm−1 is reached at 185 °C in the plastic phase. The activation energy for ionic conduction decreases as 1 is heated from the crystal phase to the melt phase. In the molten state, the contribution of protons to the ionic conductivity of 1 was corroborated electrochemically. In addition, 1 is electrochemically active for H2 oxidation and O2 reduction at a Pt electrode while it shows a high electrochemical window of 2.0 V. Furthermore, a Nafion® membrane has been successfully doped with 1, as identified by infrared spectroscopy, powder XRD, grazing incidence XRD and thermogravimetric analysis. To the best of our knowledge, this may be the first report on a protic organic ionic plastic crystal (OIPC) consisting of protonated imidazole (C3H5N2+) and an organic anion. The good thermal stability, high ionic conductivity, wide electrochemical window, favorable plastic crystal behavior and simple synthesis make 1 a highly interesting model proton conductor for high temperature PEMFCs.

Pressure Dependence of Fusion Entropy and Fusion Volume of Six Metals

Molecular dynamics simulations of the melting curves of six metals including Ag, Cu, Al, Mg, Ta, and Mo for the pressure range (0 to 15) GPa are reported. The melting curves of Ag, Cu, Al, and Mg fully confirm measurements and previous calculations. Meanwhile, the melting curves of Ta and Mo are consistent with previous calculations but diverge from laser-heated diamond-anvil cells values at high pressure. Our results suggest that the melting slope at 100 kPa is related to the electronic configuration of the element. In addition, the pressure dependence of fusion entropy and fusion volume are calculated up to 15 GPa. The overall fusion entropy is separated into topological entropy of fusion (ΔSD) due to the configuration change in melting and the volume entropy of fusion (ΔSV) due to the latent volume change in melting. Furthermore, we checked the R ln 2 rule under high pressure, according to which the value of ΔSD is a constant at ambient pressure. Result shows that the value of ΔSD is close to R ln 2 at ambient pressure and reflects a slow decrease when pressure increases.