Thermophysical Study Research Articles

Thermophysical Study of 2-Thiobarbituric Acids by Differential Scanning Calorimetry

The present study reports a differential scanning calorimetry (DSC) study of 2-thiobarbituric acid [CAS Registry No. 504-17-6] and its derivative 1,3-diethyl-2-thiobarbituric acid [CAS Registry No. 5217-47-0] in the temperature interval from T = 268 K to their respective melting temperatures. Temperatures, enthalpies, and entropies of fusion of both compounds are reported. 2-Thiobarbituric acid exhibits solid–solid phase transitions in the temperature interval studied. The polymorphic form of commercially available 2-thiobarbituric acid was identified by powder X-ray diffraction comparisons with the literature, and the heat capacity was measured from T = (268 to 430) K, temperatures below the first observable phase transition. The heat capacity of 1,3-diethyl-2-thiobarbituric acid was measured from T = (268 to 365) K. Commercially available 1,3-diethyl-2-thiobarbituric acid was likewise characterized by its X-ray powder diffraction pattern. Total phase change entropies and heat capacities of the two mater...

Thermophysical Study of Several α- and β-Amino Acid Derivatives by Differential Scanning Calorimetry (DSC)

The present study reports a differential scanning calorimetry (DSC) study of the amino acids sarcosine [CAS Registry No. 107-97-1], α-alanine (dl) [CAS Registry No. 302-72-7], β-alanine [CAS Registry No. 107-95-9], N-benzyl-α-alanine (dl) [CAS Registry No. 40297-69-6], and N-benzyl-β-alanine [CAS Registry No. 5426-62-0] in the temperature interval from T = 268 K to their respective melting/decomposition temperatures. Temperatures and heat capacities as a function of temperature of all solids and the enthalpies and entropies of fusion of two of the amino acids, sarcosine and N-benzyl-β-alanine, are reported.

Thermophysical study of the n-hexane or n-heptane with 1-chloropropane systems

Densities, speeds of sound and refractive indices at atmospheric pressure and at a temperature range of 283.15–313.15K, and isothermal vapour liquid equilibrium at 298.15K for the binary mixtures of n-hexane or n-heptane with 1-chloropropane have been determined. Excess volumes, excess isentropic compressibilities, refractive index deviations and excess Gibbs functions were calculated from the experimental data. All these properties provide an insight into the nature of interactions operating on the present systems.

Thermal behavior and polymorphism in medium–high temperature range of the sulfur containing amino acids l-cysteine and l-cystine

A thermophysical study of the sulfur containing amino acids l-cysteine and l-cystine has been carried out by differential scanning calorimetry (DSC). Heat capacities of both compounds were measured in the temperature interval from T = 268 K to near their respective melting temperatures. DSC and variable temperature powder X-ray diffraction analysis (PXRD) gave evidence for a solid–solid phase transition close to the melting point only in the l-cysteine sample. DSC experiments show that this solid–solid transition is not reversible in the temperature interval T = 235–485 K and presents a behavior depending on heating temperature, time, and rate. This behavior is also supported by variable-temperature PXRD. The patterns for the commercial samples, at room temperature, are consistent with those simulated for the orthorhombic and hexagonal polymorphic forms from the single-crystal X-ray analysis.

Thermophysical study of sandstone reservoir rocks

Thermal conductivity of both dry and fully water (brine solution, 5 g/l NaCl concentration) saturated rocks have been measured for 35 sandstone core samples obtained from both Hungary and Egypt. Measurements are executed in order to look for thermal anisotropy. The rock porosity, permeability and density were measured beside thermal conductivity, while some correlations were performed in order to differentiate among clayey laminated, flaser bedding and clean sandstone reservoirs. There is a very close correlation among thermal conductivity, rock porosity, bulk density, gas permeability and ultrasonic wave velocities for non laminated clean sandstones, while in banded sandstone reservoirs these relations show more than one trend giving a strong impression indicating the presence of more than one grain–fabric system and/or complex diagenesis. The relationship among the measured thermal conductivity for the core axis, the top and bottom are close and homogeneous for isotropic clean non laminated Szolnok sandstones, while they are vary in a wide range for banded and laminated Bahariya sandstone samples. The measured specific heat capacity indicates that some banded sandstone samples of the Bahariya Formation have bound water appears at 100 °C and giving low specific heat capacity value. This bound water can acted on all petrophysical parameters especially electrical properties. The prediction of specific heat capacity and heat flow from the reservoir temperature is possible using the calculated multi-regression and linear regression models.

Thermophysical Study of Several Barbituric Acid Derivatives by Differential Scanning Calorimetry (DSC)

The present study reports a differential scanning calorimetry (DSC) study of the barbituric acid derivatives: 1,3-dimethylbarbituric acid [CAS 769-42-6], 5,5-dimethylbarbituric acid [CAS 24448-94-0], 1,3-diethylbarbituric acid [CAS 32479-73-5], 1,3,5-trimethylbarbituric acid [CAS 7358-61-4], 1,5,5-trimethylbarbituric acid [CAS 702-47-6], and tetramethylbarbituric acid [CAS 13566-66-0] in the temperature interval from T = 268 K to their respective melting temperatures. Temperatures, enthalpies and entropies of fusion, and the heat capacities of the solid compounds as a function of temperature are reported.

Mesomorphism in a binary mixture of non-mesogens: A thermo-physical study

A comprehensive study on a liquid crystal formed by mixing two non-mesogens, viz., cholesterol and cetyl alcohol has been carried out. Polarized microscopic observations confirmed that the mixture exhibits smectic A phase below 48.2 °C. The mechanism possible for the formation of ordered liquid crystal phase when two non-mesogens are mixed is discussed. Density measured using a precision density meter was found to drop drastically in the vicinity of isotropic to smectic A transition temperature. The density fluctuations at the transition are discussed on the basis of: (i) the long wavelength limit of the structure factor and (ii) the critical exponent evaluated using modified Landau—de Gennes theory. The ultrasound velocity, determined using the interferometer method, drops drastically near the smectic A—isotropic transition temperature. The temperature-dependent data of density and ultrasound velocity enabled the evaluation of the adiabatic compressibility and acoustic impedance. The specific heat at constant pressure measured using differential scanning calorimetry shows a large increase in the vicinity of the phase transition. A correlation of thermodynamic functions to thermo-elastic properties was established through thermodynamic route. This relationship, along with experimentally measured quantities forms the basis for the thermo-physical characterization of the mixture. This facilitated the evaluation of specific heat at constant volume, the ratio of specific heats, the isothermal compressibility and the Grüneisen parameter across the smectic A—isotropic phase transition.

Energetic studies of urea derivatives: Standard molar enthalpy of formation of 3,4,4′-trichlorocarbanilide

Thermochemical and thermophysical studies have been carried out for crystalline 3,4,4′-trichlorocarbanilide. The standard ( p° = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for the crystalline 3,4,4′-trichlorocarbanilide (TCC) was experimentally determined using rotating-bomb combustion calorimetry, as −(234.6 ± 8.3) kJ · mol −1. The standard enthalpy of sublimation, at the reference temperature of 298.15 K, was measured by the vacuum drop microcalorimetric technique, using a High Temperature Calvet Microcalorimeter as (182.1 ± 1.7) kJ · mol −1. These two thermochemical parameters yielded the standard molar enthalpy of formation of the studied compound, in the gaseous phase, at T = 298.15 K, as −(52.5 ± 8.5) kJ · mol −1. This parameter was also calculated by computational thermochemistry at M05-2X/6-311++G∗∗ and B3LYP/6-311++G(3df, 2p) levels, with a deviation less than 4.5 kJ · mol −1 from experimental value. Moreover, the thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = 263 K and its onset fusion temperature, T = (527.5 ± 0.4) K. A solid–solid phase transition was found at T = (428 ± 1) K, with the enthalpy of transition of (6.1 ± 0.1) kJ · mol −1. The X-ray crystal structure of TCC was determined and the three-centred N–H⋯O C hydrogen bonds present analyzed.

Thermophysical Study of 1-Butyl-2-Methylpyridinium Tetrafluoroborate Ionic Liquid

A thermophysical study of 1-butyl-2-methylpyridinium tetrafluoroborate in a wide range of temperatures has been performed. Thus, density, speed of sound, refractive index, kinematic viscosity, surface tension, and thermal properties have been measured, whereas coefficients of thermal expansion, molar refractions, dynamic viscosities, and entropies and enthalpies of surface formation per unit surface area at the studied temperatures have been calculated. Experimental results have been compared with those obtained for 1-butyl-3-methylpyridinium tetrafluoroborate and 1-butyl-4-methylpyridinium tetrafluoroborate to analyze the effect of the positional isomeric cationic structure on properties. A systematic characterization leads to understand the behavior of such compounds, being a fundamental step to develop their potential as new solvents.

Structural studies of cyclic ureas: 3. Enthalpy of formation of barbital

A thermochemical and thermophysical study has been carried out for crystalline barbital [5,5′-diethylbarbituric acid]. The thermochemical study was made by static bomb combustion calorimetry, from which the standard ( p ∘ = 0.1 MPa ) molar enthalpy of formation of the crystalline barbital, at T = 298.15 K, was derived as −(753.0 ± 1.8) kJ · mol −1. The thermophysical study was made by differential scanning calorimetry over the temperature interval (265 to 470) K. A solid–solid phase transition was found at T = 413.3 K. The vapour pressures of the crystalline barbital were measured at several temperatures between T = (355 and 377) K, by the Knudsen mass-loss effusion technique, from which the standard molar enthalpy of sublimation, at T = 298.15 K was derived as (117.3 ± 0.6) kJ · mol −1. The combination of the experimental results yielded the standard molar enthalpy of formation of barbital in the gaseous phase, at T = 298.15 K, as −(635.8 ± 1.9) kJ · mol −1. This value is compared and discussed with our theoretical calculations by several methods (Gaussian- n theories G2 and G3, complete basis set CBS-QB3, density functional B3P86 and B3LYP) by means of atomization and isodesmic reaction schemes.

Thermochemical and thermophysical study of 2-thiophenecarboxylic acid hydrazide and 2-furancarboxylic acid hydrazide

The standard ( p ∘ = 0.1 MPa) molar energies of combustion, Δ c U m ∘ , for the crystalline 2-thiophenecarboxylic acid hydrazide and 2-furancarboxylic acid hydrazide were determined, at the temperature of 298.15 K, by rotating bomb and static bomb combustion calorimetry, respectively. For these compounds, the standard molar enthalpies of sublimation, Δ cr g H m ∘ , at T = 298.15 K, were derived by the Clausius–Clapeyron equation, from the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen effusion mass-loss technique. The results were as follows: - Δ c U m ∘ ( cr ) / ( kJ · mol - 1 ) - Δ f H m ∘ ( cr ) / ( kJ · mol - 1 ) Δ cr g H m ∘ / ( kJ · mol - 1 ) 2-Thiophenecarboxylic acid hydrazide 3359.4 ± 1.1 63.9 ± 1.3 113.3 ± 0.5 2-Furancarboxylic acid hydrazide 2620.8 ± 0.6 205.5 ± 0.9 99.0 ± 0.7 These values were used to derive the standard molar enthalpies of formation of the title compounds in their gaseous phases and the results are discussed in terms of energetic effects of the introduction of the –CONHNH 2 group in the thiophene and furan rings. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard ( p ∘ = 0.1 MPa) molar enthalpies, entropies, and Gibbs energies of sublimation, at T = 298.15 K, were derived.

Structural studies of cyclic ureas: 2. Enthalpy of formation of parabanic acid

Thermophysical and thermochemical studies have been carried out for crystalline parabanic acid. The thermophysical study was made by differential scanning calorimetry, DSC, over the temperature interval between T = (263 and 473) K. Two phase transitions were found: at T = (392.3 ± 1.6) K with the enthalpy of transition of (2.1 ± 0.4) kJ · mol −1 and at T = (509.8 ± 1.5) K, when the compound was scanned to its fusion temperature. The standard ( p ∘ = 0.1 MPa) molar enthalpy of formation, at T = 298.15 K, for crystalline parabanic acid was determined using static-bomb combustion calorimetry as −(590.2 ± 1.0) kJ · mol −1. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the variation of their vapour pressures, measured by the Knudsen-effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, as −(470.8 ± 1.2) kJ · mol −1.

Thermophysic Comparative Study of Two Isomeric Pyridinium-Based Ionic Liquids

A comprehensive thermophysical study of isomeric room-temperature ionic liquids n-butyl-3-methyl-pyridinium tetrafluoroborate and n-butyl-4-methyl-pyridinium tetrafluoroborate has been performed. This paper reports various experimental data including density, speed of sound, refractive index, surface tension, isobaric molar heat capacity, and kinematic viscosity. From the experimental results, coefficients of thermal expansion, dynamic viscosities and molar refractions of the studied ionic liquids have been determined. Results have been analyzed paying special attention to the different features of the isomers and their structural differences. Several theories and empirical relations have been applied in order to predict physical properties of ionic liquids. A good agreement between experimental and calculated data has been found. Furthermore, a study about the versatility and application of the different relationships has been carried out finding that in general density and coefficients of thermal expansion can be estimated with relatively good accuracy.

Structural studies of cyclic ureas: 1. Enthalpies of formation of imidazolidin-2-one and N, N′-trimethyleneurea

A thermophysical and thermochemical study has been carried out for crystalline imidazolidin-2-one and N, N′-trimethyleneurea [tetrahydropyrimidin-2(1 H)-one]. The thermophysical study was made by differential scanning calorimetry, d.s.c., in the temperature intervals between T = 268 K and their respective melting temperatures. Several solid–solid transitions have been detected in imidazolidin-2-one. The standard ( p ∘ = 0.1 MPa) molar enthalpies of formation, at T = 298.15 K, for crystalline imidazolidin-2-one and N, N′-trimethyleneurea [tetrahydropyrimidin-2(1 H)-one], were determined using static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, for the two compounds were derived from the variation of their vapour pressures, measured by the Knudsen effusion method, with the temperature. These two thermochemical parameters yielded the standard molar enthalpies of formation of the two cyclic urea compounds studied in the gaseous phase at T = 298.15 K. These values are discussed in terms of molecular structural contributions and interpreted on the bases of the “benzo-condensed effect” and of the ring strain of imidazolidin-2-one.

Thermophysical study of 1,4-dioxane with cycloalkane mixtures

Densities, refractive indices, and surface tension for the binary mixtures 1,4-dioxane with cyclopentane or cylohexane have been determined at ambient pressure and at T = (283.15, 298.15, and 313.15) K. Excess volumes and refractive index and surface tension deviations have been calculated from the experimental data. Several relations between the thermophysical properties studied here have been tested using our experimental results.

2- and 3-furancarboxylic acids: a comparative study using calorimetry, IR spectroscopy and X-ray crystallography

A thermophysical study by DSC for the 2- and 3-isomers of furancarboxylic acid, in the temperature intervals between T=268 K and their respective melting temperatures has been carried out, and an enhancement in the heat capacity curve of the 3-isomer was observed. The IR spectroscopy did not show significant changes either in the frequency band or in the relative band intensity in the temperature range where the small heat absorption occurs. The X-ray analysis reveals that the main differences in their supramolecular structure consist of the assembly of the carboxylic dimers into sheets.

Comparative Thermophysical Study of Some

Similarities and differences in the physical chemistry behaviour among several metal alkanoate series (thallium(I), lead(II) and copper(II)) previously studied are shown here. The presence of a 'condis' phase in the first two series is studied. The thallium and lead series present a smectic A mesogenic behaviour, while the copper(II) one forms molecular aggregates which develop columnar discotic liquid crystal phases. Finally, the monovalent cation salts form acid soaps with the acid; instead, when the cation is bivalent, the acid behaves as a polar solvent similarly to the water-surfactants systems.

Thermophysical, crystalline and infrared studies of the 2- and 3-thiophenecarboxylic acids

A thermophysical study by differential scanning calorimetry (DSC) for the 2- and 3-isomers of thiophenecarboxylic acid, in the temperature intervals between T=268 K and their respective melting temperatures has been carried out, and enhancements in the heat capacity curves were observed. The supramolecular structure of both compounds was analysed by X-ray crystallography and IR spectroscopy to determine which structural modifications take place in the temperature range at which the heat absorption occurs. Changes in bands assigned mainly to δ(OH) + ν(CO), δ(CH) + ν(CS) and out of plane CH vibrations point to structural modifications taking place in the temperature range at which the heat absorption occurs. All those groups are involved in the weak CH⋯O or CH⋯S contacts that form the crystal three-dimensional network and so it can be concluded that changes in these H-bond strength, are responsible for the small heat absorptions founded in the heat capacity curves.

Heat capacities of thiane sulfones and thiane sulfoxide: Refining of C p group values for organosulfur compounds and their oxides

A thermophysical study of thiane sulfone, 1; 1,3-dithiane sulfone, 2; and 1,3-dithiane sulfoxide, 3 in the temperature intervals between T=268 K and their respective melting temperatures has been carried out. The experimental values for the mole fraction, temperature, enthalpy and entropy of fusion and the associated standard deviation as determined by differential scanning calorimetry (DSC) are x = (0.9996±0.0001), T fus=(370.8±0.1) K, Δ fus H m=(18.4±0.2) kJ mol −1, Δ fus S m=(49.6±0.5) J mol −1 K −1 for thiane sulfone, 1; x = (0.9994±0.0001), T fus=(414.0±0.2) K, Δ fus H m=(22.0±0.2) kJ mol −1, Δ fus S m=(53.1±0.4) J mol −1 K −1 for 1,3-dithiane sulfone, 2; and x = (0.9977±0.0001), T fus=(361.9±0.1) K, Δ fus H m=(22.6±0.2) kJ mol −1, Δ fus S m=(62.4±0.5) J mol −1 K −1 for 1,3-dithiane sulfoxide, 3. Heat capacities in those temperature intervals and in condensed state were measured and no additional solid–solid phase transitions were observed. The heat capacities at T=298.15 K were used to refine group values for organosulfur compounds and their oxides.

Heat capacities and enthalpies of transitions of three nitrobenzonitriles

Thermophysical study of the behaviour, as a function of temperature, of the 2-, 3- and 4-isomers of nitrobenzonitriles was carried out by differential scanning calorimetry, in the temperature intervals between 268 K and its respective melting points. The temperatures, enthalpies and entropies of the fusion processes were measured. Several phase transitions were observed for the 2- and 4-isomers and their temperatures, enthalpies and entropies are given. Heat capacities of the 2-, 3- and 4-isomers of nitrobenzonitriles were measured by differential scanning calorimetry between 268 K and their melting temperature and the results obtained were correlated as a function of temperature.