Thermodynamic properties of 1-butyl-3-methylpyridinium tetrafluoroborate

Pressure, density, temperature (p, ρ, T) data of 1-butyl-3-methylpyridinium tetrafluoroborate [C4mpyr][BF₄] at T = (283.15 to 393.15) K and pressures up to p = 100 MPa are reported with an estimated experimental relative combined standard uncertainty of Δρ/ρ = ±(0.01 to 0.08)% in density. The measurements were carried out with a newly constructed Anton-Paar DMA HPM vibration-tube densimeter. The system was calibrated using double-distilled water, methanol, toluene and aqueous NaCl solutions. An empirical equation of state for fitting of the (p, ρ, T) data of [C4mpyr][BF₄] has been developed as a function of pressure and temperature to calculate the thermal properties of the ionic liquid (IL), such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient and internal pressure. Internal pressure and the temperature coefficient of internal pressure data were used to make conclusions on the molecular characteristics of the IL.     

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.     

Critical parameters for isobutane determined by the image analysis

(p, ρ, T) Measurements and visual observations of the meniscus for isobutane were carried out carefully in the critical region over the range of temperatures: −15 mK ? (T − T_c) ? 35 mK, and of densities: −7.5 kg · m⁻³ ? (ρ − ρ_c) ? 7.5 kg · m⁻³ by a metal-bellows volumometer with an optical cell. Vapor pressures were also measured at T = (310, 405, 406, 407, and 407.5) K. The critical point of T_c and ρ_c was determined by the image analysis of the critical opalescence which is proposed in this study. The critical pressure p_c was determined to be the pressure measurement at the critical point. Comparisons of the critical parameters with values given in the literature are presented.     

Thermodynamic properties of carbon dioxide derived from the speed of sound

Thermodynamic properties of CO₂ are derived from speed of sound in the temperature range 300 to 360 K (from 0 to 6 MPa), and 300 to 220 K (from 0 to 90% of the saturation pressure). The density, the specific heat capacity at constant pressure, and the specific heat capacity at constant volume are obtained by numerical integration of differential equations connecting the speed of sound with other thermodynamic properties. The set of differential equations is solved as the initial value problem, with the initial values specified along the isotherm at 300 K in terms of several accurate values of the density and the specific heat capacity at constant pressure. The density, the specific heat capacity at constant pressure and the specific heat capacity at constant volume are derived with the absolute average deviations of 0.018%, 0.19%, and 0.18%, respectively. The results of numerical integration are extrapolated to the saturation line for ρ, c _p , and c _v with the absolute average deviations of 0.056%, 2.31%, and 1.32%, respectively.     

Thermophysical properties of 1-butyl-4-methylpyridinium tetrafluoroborate

Thermophysical properties, {(p, ρ, T) at T = (283.15 to 393.15) K, pressures up to p = 100 MPa, and viscosity at T = (283.15 to 373.15) K and p = 0.101 MPa}, of 1-butyl-4-methylpyridinium tetrafluoroborate [b4mpy][BF₄] are reported. The measurements were carried out with a recently constructed Anton-Paar DMA HPM vibration-tube densimeter and a fully automated SVM 3000 Anton-Paar rotational Stabinger viscometer. The vibration-tube densimeter was calibrated using double-distilled water, methanol, toluene, and aqueous NaCl solutions.An empirical equation of state for fitting of the (p, ρ, T) data of [b4mpy][BF₄] has been developed as a function of pressure and temperature to calculate the thermal properties of the ionic liquid (IL), such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient, and internal pressure. Internal pressure and the temperature coefficient of internal pressure data were used to make conclusions on the molecular characteristics of the IL.     

(p, ρ, T) properties, and apparent molar volumes V? of ZnBr2 in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa

The (p, ρ, T) properties of pure methanol, the (p, ρ, T) properties and apparent molar volumes V_? of ZnBr₂ in methanol at T = (298.15 to 398.15) K and pressures up to p = 40 MPa are reported, and apparent molar volumes have been evaluated. The experimental (p, ρ, T, m) values were described by an equation of state. For the solutions the experiments were carried out at molalities m = (0.05772, 0.37852, 0.71585 and 1.95061) mol · kg⁻¹ of zinc bromide.     

Crosslinking, thermal properties and relaxation behaviour of polyisoprene under high-pressure

The transient hot-wire method has been used to measure the thermal conductivity κ and heat capacity per unit volume ρc_p of untreated (virgin) and crosslinked cis-1,4-poly(isoprene) (PI) in the temperature range 160-513 K for pressures p up to 0.75 GPa. The results show that the crosslinking rate of the polymer chains becomes significant at ∼513 K on isobaric heating at 0.5 GPa changing PI into an elastomeric state within 4 h without the use of crosslinking agents. The crosslinked PI and untreated PI have about the same κ = 0.145 Wm⁻¹ K⁻¹ and c_p = 1.81 kJ kg⁻¹ K⁻¹ at 295 K and 20 MPa, but different relaxation behaviours. Two relaxation processes, corresponding to the segmental and normal modes, could be observed in both PI and crosslinked PI but these have a larger distribution of relaxation times and become arrested at higher temperatures (∼10 K) in the latter case. The arrest temperature for the segmental relaxation of untreated and crosslinked PI, for a relaxation time of ∼1 s, are described well by the empirical relations: T(p) = 209.4 (1 + 4.02 p)^0.31 and T(p) = 221.3 (1 + 2.33 p)^0.40 (p in GPa and T in K), respectively, which thus also reflects the pressure variations of the glass transition temperatures.     

Measurements of the isochoric heat capacity,the critical point (TC, ρC) and vapor–liquid coexistence curve (TS, ρS) of high-purity toluene near the critical point

Isochoric heat capacities (C_V, V, T), phase boundary properties (T_S, ρ_S) and the critical (T_C, ρ_C) parameters for high-purity (0.9999+ mole fraction) toluene have been measured with a high temperature, high pressure, nearly constant volume adiabatic calorimeter and quasi-static thermogram technique. Measurements were made at three selected liquid and vapor isochores 777.8, 555.25, and 214.64 kg m⁻³ in the temperature range from 379 to 591 K. For five near-critical isochores 268.68, 281.68, 296.62, 301.52, and 318.28 kg m⁻³, the measurements were made in the immediate vicinity of the coexistence curve in order to accurately determine the phase transition temperatures (T_S, ρ_S) (shape of the coexistence curve near the critical point) and the critical parameters (T_C, ρ_C). The total combined uncertainty of heat capacity, density, and temperature measurements were estimated to be less than 2%, 0.06%, and 15 mK, respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The uncertainty of the phase transition and the critical temperature value was 0.02 K. The Krichevskii parameter for some toluene-containing binary mixtures was calculated. The derived values of the Krichevskii parameter were used to estimate the effect of dilute impurities on the critical parameters of toluene. The measured values of saturated density near the critical point were interpreted in terms of the “complete scaling” theory in order to study singularity behavior of the coexistence curve diameter. The measured isochoric heat capacities and saturated densities were compared with the data reported by other authors and values calculated from an equation of state and other correlations.     

The investigation of the (p,ρ,T) and (ps,ρs,Ts) properties of {(1−x)CH3OH + xLiBr} for the application in absorption refrigeration machines and heat pumps

The (p,ρ,T) and (p_s,ρ_s,T_s) properties of {(1−x)CH₃OH + xLiBr} over a wide range of state parameters are reported for the first time. The experiments were carried out in a constant volume piezometer over a temperature range from 298.15 K to 398.15 K, at 0.08421, 0.13617, 0.19692, 0.23133 and 0.26891 mole fractions and from atmospheric pressure up to 60 MPa. The experimental uncertainties are ΔT=±3 mK for temperature, Δp=±5·10⁻² MPa for high pressure and Δp=±5·10⁻⁴ MPa for atmospheric pressure, Δρ=±3·10⁻² kg · m⁻³ for density. An equation of state was derived for correlation of the experimental data of the solutions.     

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.     

Thermodynamics of 2D polymerized tetragonal phase of fullerene C60 in the range from T→0 to 650 K at standard pressure

By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C₆₀ has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C₆₀, namely, the heat capacity C°_p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C₆₀.     

Magnetic,transport and thermodynamic properties of Ce5Ni2Si3 compound

The magnetization M(T,H), specific heat C_p(T,H), electrical resistivity ρ(T), magnetoresistance MR(T,H), thermal conductivity κ(T) and thermopower S(T) measurements were performed on the antiferromagnetic compound Ce₅Ni₂Si₃ with the Néel temperature T_N = 5.7 K. The estimated effective moment μ_eff is close to the free ion value of Ce in its trivalent state. The negative sign of the paramagnetic Curie temperature θ_p indicate the antiferromagnetic nature of the magnetic ordering. The variation of magnetic resistivity ρ_mag with temperature in Ce₅Ni₂Si₃ can be explained by a competition of the crystal electric field (CEF) splitting, the Kondo effect and the magnetic order. Based on the thermopower and employing a simple single-ion Kondo model the Kondo temperature have been estimated. Magnetocaloric effect is small but shows a sign change, which may be caused by a metamagnetic behavior.     

A nonparametric scaling equation of state for liquids

A new nonparametric scaling equation of state is suggested. The equation correctly describes the p-ρ-T data and heat capacities of liquids close to the critical vaporization points. It was obtained with the use of the S spinodal and the mixing of scaling fields as a first approximation (asymmetric and nonasymptotic terms were ignored). The new equation was used to approximate the data on ⁴He, C₂H₄, and H₂O in the critical region. The results showed that it correctly described the critical behavior of thermodynamic functions, including isochoric heat capacity, not only in the asymptotic but also over a fairly wide density region at the critical point. The suggested equation of state describes the p-ρ-T data with the same error as the Schofield parametric equation of state. The new equation, however, better reproduces the behavior of heat capacities and is much simpler to use. As distinct from the Schofield equation, the new equation, like classic equations of state, allows the spinodal to be determined from the (?p/?v) _T = 0 condition at T < T _c .     

Thermodynamics of dimethylene urethane and poly(dimethylene urethane) in the range from T → 0 to 490 K at standard pressure

By high-precision dynamic calorimetry the temperature dependences of heat capacity of dimethylene urethane (DMU) between 320 and 370 K and partially crystalline poly(dimethylene urethane) (PDMU) in the range 326-490 K at standard pressure have been determined within ±1.5%. The thermodynamic characteristics of fusion of the substances, namely the temperature interval of melting, temperature, enthalpy and entropy of fusion, as well as the characteristics of devitrification and glassy state for poly(dimethylene urethane) have been estimated. The first and the second cryoscopic constants have been calculated for dimethylene urethane. The experimental data obtained in the present work and literature findings on the heat capacity of the substances were used to calculate their thermodynamic functions: the heat capacity C°_p (T), enthalpy H°(T)−H°(0), entropy S°(T) and Gibbs function G°(T)−H°(0) over the range from T→0 to (370-480) K. Based on the data, the thermodynamic characteristics of polymerization process with five-membered ring opening Δ_polH°, Δ_polS° and Δ_polG° of dimethylene urethane with the formation of linear partially crystalline poly(dimethylene urethane) have been evaluated.     

Influence of the molecular weight of polystyrene on its thermodynamic properties

The thermodynamic properties of a series of polystyrene samples with different molecular weights (M _w was varied from 2.5·10³ to 6.57·10⁴) were studied by precision adiabatic vacuum, high-accuracy dynamic, and combustion calorimetry: temperature dependences of the heat capacity in a wide temperature range, thermodynamic characteristics of glass transition and glassy state under standard pressure, and energy of combustion. The thermodynamic functions C ^○ _p (T), H ^○(T) - H ^○(0), S ^○(T) - S ^○(0), and G ^○(T) - H ^○(0) of polystyrene with different molecular weights, enthalpies of combustion Δ_c H ^○, thermodynamic parameters of formation from simple substances Δ_f H ^○, Δ_f S ^○, and Δ_f G ^○ at T = 298.15 K, and parameters of their synthesis from monomers were calculated from the experimental data. The temperature dependences of the heat capacity for a region of 0–380 K, glass transition temperatures, and thermodynamic characteristics of formation and synthesis of polystyrene depending on its molecular weight were examined.     

Critical behavior of binary mixture of {(1 − x) C6H5CN + x CH3(CH2)9CH3}: Measurements of coexistence curves,turbidity, and heat capacity

(Liquid + liquid) coexistence curve, turbidity, and isobaric heat capacity per unit volume for the critical solution of {benzonitrile + n-undecane} have been measured. The critical exponents β, ν, γ, and α have been deduced, which were found to be consistent with the theoretic predictions. Meanwhile, the experimental data have also been analyzed to obtain the system-dependent critical amplitudes B, ξ₀, χ₀, A^±, and D corresponding to the difference of the general density variable of two coexisting phases Δρ, the correlation length ξ, the osmotic compressibility χ, the isobaric heat capacity per unit volume C_pV⁻¹, and the first term of correction-to-scaling for the isobaric heat capacity per unit volume, which were used to test some universal ratios. It was found that the coexistence curve may be well described by the crossover model proposed by Gutkowski et al. The critical-fluctuation induced contribution to the background heat capacity B_cr was obtained and used to analyze the asymmetric behavior of the diameter of the coexistence curve. The result indicated that the asymmetry of the coexistence curve can be well described by the complete scaling theory proposed by Anisimov et al., and the heat capacity does make a significant contribution to this asymmetric behavior.     

Concentration dependence of NaCl in a wide range of temperatures and pressures

We use our own and literature data on density, ultrasound propagation velocity, and isobaric heat capacity to study the concentration, temperature, and pressure dependences of solvation numbers in aqueous NaCl solutions. We show that, in the parameter range: m = 0–6.0 mol·kg^?1, p = 1–1000 bar, and T = 283.15–323.15 K, the solvation numbers decrease with increasing concentration, pressure, and temperature.     

Calorimetric study of poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K

For the first time, the heat capacity $ C_{\text{p}}^{^\circ } $ of poly(2-ethylhexyl acrylate) has been studied in an adiabatic vacuum calorimeter between 7 and 350 K, the standard thermodynamic functions: heat capacity $ C_{\text{p}}^{^\circ } $ (T), enthalpy H°(T) ? H°(0), entropy S°(T) ? S°(0), Gibbs function G°(T) ? H°(0) have been calculated from T → 0 to 350 K. The energy of combustion Δ_c U of the compound under study has been measured in a calorimeter with a stationary bomb and an isothermal shell. The standard enthalpy of combustion Δ_c H° and thermodynamic parameters of formation—enthalpy Δ_f H°, entropy Δ_f S°, Gibbs function Δ_f G°—at T = 298.15 K have been calculated. The results have been used to calculate the thermodynamic characteristics of 2-ethylhexyl acrylate bulk polymerization into poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K.     

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.