The speed of sound and derived thermodynamic properties of pure water at temperatures between (253 and 473) K and at pressures up to 400 MPa

The speed of sound in high-purity water has been measured in the temperature range (253 to 473) K at pressures up to 400 MPa. The experimental technique used was based on a double-path pulse-echo method with a single 5-MHz ultrasound transducer placed between two unequally spaced reflectors. The cell was calibrated in water at T = 298.15 K and p = 1 MPa against the speed of sound given by the 1995 equation-of-state formulation of the International Association for the Properties of Water and Steam (IAPWS-95) which, for that state point, has an uncertainty of 0.005%. Corrections for the effects of temperature and pressure on the path length difference are considered in detail. The estimated expanded relative uncertainty of the speed of sound determined in this work is shown to be between 0.03% and 0.04% at a confidence level of 95%. The density and isobaric specific heat capacity of water have been obtained in the temperature range (253.15 to 473.15) K at pressure up to 400 MPa by thermodynamic integration of the sound-speed data subject to initial values computed from IAPWS-95 on the isobar at p = 0.1 MPa. The speed of sound, density, and isobaric specific heat capacity were compared with IAPWS-95 with corresponding absolute relative deviations within 0.3%, 0.03%, and 1%, respectively at T ≥ 273.15 K and p ≤ 400 MPa; larger deviations, especially for heat capacity, were found at lower temperatures. The results imply that the uncertainties of properties computed from IAPWS-95 may be significantly reduced over the major part of the region investigated in this work.     

A new method to calculate the thermodynamical properties of liquids from accurate speed-of-sound measurements

In this work, a new method for the determination of the thermodynamical properties of fluids, based on experimental speed-of-sound measurements, is described. This method consists in the solution of recursive equations (REM, Recursive Equations Method) for the determination of the density ρ(p,T) and specific heat capacity at constant pressure c_p(p,T), using the initial values of density ρ(p₀,T) and isobaric specific heat capacity c_p(p₀,T) known at a reference pressure p₀, as a function of the temperature, if the speed-of-sound function, u(p,T), is known, at least over a certain temperature and pressure range. A complete uncertainty analysis has also been developed. As an example of the good performances of this analysis method, firstly density and isobaric specific heat capacity have been calculated for water and the results have been compared with those predicted by the International Association for the Properties of Water and Steam 95 Formulation (IAPWS-95), as delivered by Wagner and Pruss. One more application has been made starting from experimental speed-of-sound values in pure acetone. These results have been compared with those calculated by the most advanced numerical integration methods and with the prevision of the dedicated NIST equation of state (EoS) by Lemmon and Span.     

The heat capacity of lead from 300 to 850°k: conversion of cp to cv for liquid lead

Abstract

Recent measurements of the heat capacity at constant pressure C_p for lead from 300 to 850°K have shown that C_p for liquid lead decreases continuously from the melting point to 850°K. Using data in the literature of density and velocity of sound, the dilation correction has been applied to C_p to obtain the heat capacity at constant volume C_v for liquid lead. Application of the dilation correction to solid lead gives a C_v curve which uncreases only about one joule/gm-atom-°K from 300 to 600°K, whereas the C_v curve for liquid lead decreases almost 5 joules/gm-atom-°K from 600 to 850°K. A careful assessment of the uncertainty in the quantities used in the dilation correction leads to an uncertainty in C_v of ± 2.5% (about one joule/gm-atom-°K), and thus the decrease in C_v for liquid lead is quite real.     

Thermodynamic properties of acetone calculated from accurate experimental speed of sound measurements at low temperatures and high pressures

Thermodynamic properties of fluids are both required for designing and implementing industrial processes and in different research fields; in particular they play a fundamental role in the development of equations of state (EoS). This paper describes very accurate speed of sound measurements in liquid-phase acetone along eleven isotherms in the temperature range of (248.15 and 298.15) K and over a wide range of pressure (up to 100 MPa). Since very accurate direct measurements of the fluids properties (like density and isobaric heat capacity) are relatively easy at atmospheric pressure, but difficult at elevated pressures, a combination of speed of sound measurements and numerical integration offers a well balanced approach to determine the thermodynamic properties of liquids. In this case, density and heat capacity of the liquid at high pressures are calculated by numerical integration of u^?2(p, T), using, as initial values, the same quantities (density and heat capacity) at atmospheric pressure as a function of temperature. The experimental values of speed of sound are subjected to an overall estimated uncertainty of about 0.1%.     

High-precision adiabatic calorimetry and the specific heat of cyclopentane at low temperature

We describe a fully automated adiabatic calorimeter designed for high-precision covering the temperature range 15 to 300 K. Initial measurements were performed on synthetic sapphire (20 g). The statistical error of the apparatus estimated from the scattering of theC _p data of sapphire is about 0.1% and the average absolute error of specific heat between 100 and 300 K was 0.7% compared to values given in the literature. The heat capacity and the three phase transitions of cyclopentane (C₅H₁₀) which is recommended as a standard for the temperature calibration of scanning calorimeters have also been measured. The transition temperatures were determined to be (literature values in parentheses): 122.23 K (122.39 K) 138.35 K (138.07 K) and 178.59 K (179.69 K), with an experimental error of ±40 mK.     

On the specific heat of nonstoichiometric ceria

Ceria (CeO₂) can readily be reduced to form a wide range of binary compounds CeO_y, 2 ≥y ≥ 1.5. Specific heat measurements at constanty were carried out for the composition range 2≥y > 1.714 and for the temperature range 300 K <T < 1200 K. In thisy,T region the specific heat exhibits a complex form reflecting various transformations. The results and theoretical evaluations of the specific heat are presented as the temperature is varied from low values (T ≈ 400K) where two phases coexist, through several phase transformations to a high temperature α phase. Special features of the specific heat due apparently to increased internal local pressure appearing for small deviations from stoichiometry are also discussed.     

Heat capacity, enthalpy, entropy, and gibbs energy of terbium diboride as determined from calorimetric measurements within 5–300 K

The heat capacity at constant pressure C _p (T) of terbium diboride synthesized from elements via an intermediate hydride phase was studied experimentally within 5–300 K. A ferromagnetic phase transition manifests itself in the C _p (T) dependence as a sharp maximum at 142.4 ± 0.1 K. The C _p (T) dependence was used to calculate the tempreature dependences of the enthalpy, entropy, and the Gibbs energy and to determine the parameters of the electronic, lattice, and magnetic contributions to the heat capacity of TbB₂.     

Densities,viscosities, speed of sound,and IR spectroscopic studies of binary mixtures of tert-butyl acetate with benzene,methylbenzene, and ethylbenzene at T = (298.15 and 308.15) K

Densities, viscosities, speed of sound, and IR spectroscopy of binary mixtures of tert-butyl acetate (TBA) with benzene, methylbenzene, and ethylbenzene have been measured over the entire range of composition, at (298.15 and 308.15) K and at atmospheric pressure. From the experimental values of density, viscosity, speed of sound, and IR spectroscopy; excess molar volumes V^E, deviations in viscosity Δη, deviations in isentropic compressibility Δκ_s and stretching frequency ν have been calculated. The excess molar volumes and deviations in isentropic compressibility are positive for the binaries studied over the whole composition, while deviations in viscosities are negative for the binary mixtures. The excess molar volumes, deviations in viscosity, and deviations in isentropic compressibility have been fitted to the Redlich–Kister polynomial equation. The Jouyban–Acree model is used to correlate the experimental values of density, viscosity, and speed of sound.     

Studies on an ionic compound (3-ATz)+ (NTO)–: crystal structure, specific heat capacity, thermal behaviors and thermal safety

A new ionic compound (3-ATz)⁺ (NTO)^?C was synthesized by the reaction of 3-amino-1,2,4-triazole (3-ATz) with 3-nitro-1,2,4-triazol-5-one (NTO) in ethanol. The single crystals suitable for X-ray diffraction measurement were obtained by crystallization at room temperature. The crystal is monoclinic, space group p _2(1)/c with crystal parameters of a?=?0.6519(2)?nm, b?=?1.9075(7)?nm, c?=?0.6766(2)?nm, ???=?94.236(4)°, R ₁?=?0.0305 and wR ₂?=?0.0789. The thermal behaviors were studied, and the apparent activation energy and pre-exponential constant of the exothermic decomposition stage were obtained by Kissinger??s method and Ozawa??s method. The self-accelerating decomposition temperature is 505.40?K, and the critical temperature of the thermal explosion is obtained as 524.90?K. The specific heat capacity was determined with Micro-DSC method and the theoretical calculation method, and the standard molar specific heat capacity is 221.31?J?mol^?1?K^?1 at 298.15?K. The Gibbs free energy of activation, enthalpy of activation, and entropy of activation are 151.55?kJ?mol^?1, 214.52?kJ?mol^?1 and 122.44?J?mol^?1?K^?1. The adiabatic time-to-explosion of the compound was estimated to be a certain value between 5.0 and 5.2?s, and the detonation velocity (D) and pressure (P) were also estimated using the nitrogen equivalent equation according to the experimental density.     

Thermodynamic properties and equation of state of liquid di-isodecyl phthalate at temperature between (273 and 423) K and at pressures up to 140 MPa

We report measurements of the thermodynamic properties of liquid di-isodecyl phthalate (DIDP) and an equation of state determined therefrom. The speed of sound in DIDP was measured at temperatures between (293.15 and 413.15) K and a pressures between (0.1 and 140) MPa with a relative uncertainty of 0.1%. In addition, the isobaric specific heat capacity was measured at temperatures between (293.15 and 423.15) K at a pressure of 0.1 MPa with a relative uncertainty of 1%, and the density was measured at temperatures between (273.15 and 413.15) K at a pressure of 0.1 MPa with a relative uncertainty of 0.015%. The thermodynamic properties of DIDP were obtained from the measured speeds of sound by thermodynamic integration starting from the initial values of density and isobaric specific heat capacity obtained experimentally. The results have been represented by a new equation of state containing nine parameters with an uncertainty in density not worse than 0.025%. Comparisons with literature data are made.     

Speed of sound,ideal-gas heat capacity at constant pressure,and second virial coefficients of HFC-227ea

The speed of sound of the gaseous 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) was measured for temperatures from 273 to 333 K and pressures from 26 to 315 kPa with a cylindrical, variable-path acoustic interferometer operating at 156.252 kHz. The uncertainty of the speed of sound was less than ±0.05%. The ideal-gas heat capacity at constant pressure and the second acoustic virial coefficients were determined over the temperature range from the speed of sound measurements. The uncertainty of the ideal-gas heat capacity at constant pressure was estimated to be less than ±0.5%. The ideal-gas heat capacity at constant pressure results and second virial coefficients calculated from the present speed of sound measurements were compared with the available data.     

Heat capacity and thermodynamic functions of MnBr2 · 4D2O and MnCl2 · 4D2O

The heat capacities of MnBr₂ · 4D₂O and MnCl₂ · 4D₂O have been experimentally determined from 1.4 to 300 K. The smoothed heat capacity and thermodynamic functions (H°_TH°₀) and S°_T are reported for the two compounds over the temperature range 10 to 300 K. The error in the thermodynamic functions at 10 K is estimated to be 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. A λ-shaped heat capacity anomaly was observed for MnCl₂ · 4D₂O at 48 K. The entropy associated with the anomaly is 1.2 ± 0.2 J/mole K.     

Heat capacity and thermodynamic functions of theRFe2 compounds (R =Gd,Tb, Dy,Ho, Er,Tm, Lu) over the temperature region 8 to 300 K

Experimental heat capacity data for the Laves phaseRFe₂ intermetallic compounds (R =Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been determined over the temperature range 8 to 300 K. The error in these data is thought to be less than 1%. Smoothed heat capacity values and the thermodynamic functions, (H°_T ? H°₀) and S°_T, are reported throughout the temperature range for theRFe₂ series. In addition, (G°₂₉₈ ? H°₀) at 298 K is reported for all theRFe₂ compounds. These data were analyzed and it was shown that the maxima in the thermodynamic functions near HoFe₂ are due to the magnetic contribution of the lanthanide element. The lattice contribution to the entropy at 300 K was estimated, and from this quantity the Debye temperature was calculated to be about 300 K, which is in good agreement with the low-temperature heat capacity. Furthermore, this analysis indicates that the apparent electronic specific heat constants, γ′, for TbFe₂, DyFe₂, and HoFe₂, reported earlier, are in error.     

Heat capacity and thermodynamic functions of MnCl2·2H2O and MnCl2·2D2O

The heat capacities of MnCl₂·2H₂O and MnCl₂·2D₂O have been experimentally determined from 1.4 to 300 K. The smooth heat capacity and the thermodynamic functions (H°_T − H°₀) and S°_T are reported for the two compounds over the 10 and 300 K temperature range. The error in the thermodynamic functions at 10 K is estimated at 3%. Additional error in the tabulated values arising from the heat capacity data above 10 K is thought to be less than 1%. Lambda-shaped heat capacity features associated with antiferromagnetic ordering were observed at 6.67 ± 0.08 and 6.61 ± 0.08 K for the dihydrate and dideuterate, respectively. In addition, compound heat capacity anomalies consisting of a small lambda-shaped feature at 57.7 ± 0.5 K with a comparably large high-temperature shoulder extending to approximately 70 K were observed in both the dihydrate and dideuterate. The entropies associated with these anomalies are 0.42 ± 0.04 and 1.04 ± 0.04 J/mole-K, respectively.     

Concentration,temperature, and isotopy effects on the heat capacity of aqueous urea

Relations for the apparent molar heat capacity ?_c of urea in an aqueous solution depending on the molality m and temperature were obtained. A transition to the relations ?_c(m,T) for D₂O-(ND₂)₂CO and T₂O-(NT₂)₂CO systems was effected by temperature scaling. At low temperatures, the isotherms of the molar heat capacity C _p(m) of the protium and deuterium systems have minima shifted to more dilute solutions at elevated temperatures. At m = 1, C _p of a solution does not depend on temperature in both systems. The dependences C _p(T) also have minima at constant concentrations. The temperature of the minimum heat capacity is most effectively lowered by small additions of urea. For m = 0.25, T _min is 7.5 K lower than T _min of pure water, and its heat capacity is 0.08 J/(mol K) higher. A transition from m = 1.5 to m = 2 lowers the temperature of the minimum heat capacity by 3.6 K; thus, the heat capacity of solutions differs by 0.02 J/(mol K) only.     

Thermodynamic properties of mixtures of N-methyl-2-pyrrolidinone and methanol at temperatures between 298.15 K and 343.15 K and pressures up to 60 MPa

We report measurements of the speed of sound in mixtures of N-methyl-2-pyrrolidinone and methanol at temperatures between 298.15 K and 343.15 K and at pressures up to 60 MPa. The measurements were made using a dual path pulse-echo apparatus operating at a frequency of 5 MHz. We have also measured the isobaric specific heat capacity of each mixture as a function of temperature at ambient pressure, by means of a Setaram DSC III microcalorimeter. The experimental results have been combined with literature data for the density of the same mixtures as a functions of temperature at ambient pressure to obtain the density, isobaric specific heat capacity, and other thermodynamic properties at temperatures between 298.15 K and 343.15 K and at pressures up to 60 MPa. Detailed comparisons with the literature data are presented.     

A novel non-intrusive microcell for sound-speed measurements in liquids. Speed of sound and thermodynamic properties of 2-propanone at pressures up to 160 MPa

A novel high-pressure, ultrasonic cell of extremely reduced internal dimensions (∼0.8 · 10⁻⁶ m³) and good precision for the determination of the speed of propagation of sound in liquids was conceived and built. It makes use of a non-intrusive methodology where the ultrasonic transducers are not in direct contact with the liquid sample under investigation. The new cell was used to carry out speed of sound measurements in 2-propanone (acetone) in broad ranges of temperature (265<T/K<340) and pressure (0.1<p/MPa<160). (p,ρ,T) data for acetone were also determined but in a narrower T,p range (298 to 333 K; 0.1 to 60 MPa). In this interval, several thermodynamic properties were thus calculated, such as: isentropic (κ_s) and isothermal (κ_T) compressibility, isobaric thermal expansivity (α_p), isobaric (c_p) and isochoric (c_v) specific heat capacity, and the thermal pressure coefficient (γ_v). Comparisons with values found in the literature generally show good agreement.     

Effect of the temperature on the physical properties of pure 1-propyl 3-methylimidazolium bis(trifluoromethylsulfonyl)imide and characterization of its binary mixtures with alcohols

In this paper, physical properties of a high purity sample of the ionic liquid 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [PMim][NTf₂], and its binary mixtures with methanol, ethanol, 1-propanol, and 2-propanol were measured at atmospheric pressure. The temperature dependence of density, refractive index and speed of sound (293.15 to 343.15) K and dynamic viscosity (298.15 to 343.15) K were studied at atmospheric pressure by conventional techniques for the pure ionic liquid. For its mixtures with alcohols, density, speed of sound, and refractive index were measured at T = 298.15 K over the whole composition range. The thermal expansion coefficient of the [PMim][NTf₂] was calculated from the experimental results using an empirical equation, and values of the excess molar volume, excess refractive index, and excess molar isentropic compressibility for the binary systems at the above mentioned temperature, were calculated and fitted to the Redlich–Kister equation. The heat capacity of the pure ionic liquid at T = 298.15 K was determined using DSC.     

Excess heat capacities and excess volumes of binary liquid mixtures of 1,1,1,-trichloroethane with cyclic ethers at 298.15 K

Measurements of volumetric heat capacities at constant pressure, C_p/V (V being the molar volume), at 298.15 K, of the binary liquid mixtures 1,1,1-trichloroethane + oxolane, +1,3-dioxolane, +oxane, +1,3-dioxane, and +1,4-dioxane were carried out in a Picker-type flow microcalorimeter. Molar heat capacities at constant pressure. C_p, and molar excess heat capacities, C^E_p, were calculated from these results as a function of the mole fraction. C^E_p values for these systems are positive and the magnitude depends on the size of the cycle and on the relative position of the oxygen atoms in the cyclic diethers. The precision and accuracy for C^E_p are estimated as better than 2%. Molar excess volumes, V^E, for the same systems, at 298.15 K, have been determined from density measurements with a high-precision digital flow densimeter. The experimental results of V^E and C^E_p, are interpreted in terms of molecular interactions.     

Heat capacity and characteristic thermodynamic functions of dysprosium boride DyB62 in the temperature range of 2 to 300 K

Heat capacity at constant pressure C _p (T) of a dysprosium boride DyB₆₂ single crystal obtained by zone melting was studied experimentally in the temperature range of 2 to 300 K. Abnormally high values of dysprosium boride heat capacity were revealed in the range of 2–20 K, due to the magnetic contribution and the effect of disorder in the boride lattice. Temperature changes in DyB₆₂ enthalpy, entropy, Gibbs energy, and standard values of these thermodynamic functions were calculated.