Heat Capacity Functions Research Articles

Low-temperature heat capacity and thermodynamic functions of Ga2Te3

The heat capacity of Ga2Te3 is measured from 9 to 310 K using adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of Ga2Te3. Its thermodynamic properties under standard conditions are C p 0 (298.15 K) = 119.3 ± 0.2 J/(K mol), S 0(298.15 K) = 209.8 ± 0.4 J/(K mol), H 0(298.15 K) − H 0(0) = 27.19 ± 0.05 kJ/mol, and Φ0(298.15 K) = 118.6 ± 0.2 J/(K mol). The Debye characteristic temperature of Ga2Te3 evaluated from the heat capacity data is 280 ± 20 K.

Low-temperature heat capacity and thermodynamic functions of GaTe

The heat capacity of GaTe is measured from 6.8 to 337.95 K using adiabatic calorimetry. The results are used to calculate the heat capacity, entropy, enthalpy increment, and reduced Gibbs energy of GaTe in the temperature range 10–320 K under standard conditions. The 298.15-K thermodynamic properties of GaTe are Cp0(298.15 K) = 48.96 ± 0.10 J/(K mol), S0(298.15 K) = 81.30 ± 0.16 J/(K mol), H0(298.15 K) − H0(0 K) = 10.84 ± 0.02 kJ/mol, and Φ0(298.15 K) = 44.95 ± 0.09 J/(K mol).

Heat capacity functions of polystyrene in glassy and in liquid amorphous state and glass transition

The heat capacity or the specific heat is for any crystalline, partially amorphous or completely amorphous substance or material a significant thermodynamic property. The glass transition may be regarded as the melting point of amorphous substances and materials, a transition property of an outstanding technical importance. A crucial point is the fact that the presence of a glass transition is an unequivocal proof of an amorphous content of a material. Furthermore, the change of the specific heat at the glass transition temperature enables the quantitative determination of the amorphicity on a relative or absolute level of any substance or material. The absolute determination of the amorphicity affords a calibration with a reference corresponding to the material under investigation. The crystallinity for this reference substance must be known from the preparation and or by any independent analytical method. The literature data for the specific heat and the glass transition of polystyrene were collected and evaluated. Data were found for the specific heat in literature from 10 to 470 K. The data were unified for each of the reported temperature in a mean value and the corresponding standard deviation was determined. An excellent conformity was found in the glassy state of polystyrene with standard deviations lower than 0.7%. The standard deviations above the glass transition were considerably higher. All these literature data were transferred for each of the literature sets separately into linear specific heat functions in the vicinity of the glass transition. One set of our measurements performed with the DSC 204 and with polystyrene SRM 705a as sample material was additionally integrated in the mean of these functions for the glassy state and the liquid amorphous state respectively. The addition of our results gave practically no change of the mean coefficients and only a decrease of the standard deviations. In such a way, the data with the best statistical base for the specific heat of polystyrene are listed in this paper ( ‘Conclusions’). The glass transition as a transition in and out of a non-equilibrium state, the glassy state, is sensitive to all kind of influences such as thermal and mechanical treatments as well as to the selected experimental conditions. Therefore, certain standardized conditions procedures must be fulfilled to get reproducible data. The literature data for the glass transition temperature were also used to get a mean value. However, two values were omitted for the formation of the mean, because the authors reported values, which were too low on the base of impurities present. The mean value of the glass transition for polystyrene is according to the literature 369±2 K. A mean value of 370±2 K was extrapolated for an infinite molecular mass. The DSC and TMDSC measurements for the three thermodynamic properties reported in this paper, namely the specific heat, the glass transition temperature and the corresponding change of the specific heat gave results without significant differences compared with the literature values. Atactic polystyrene is a rather ideal polymer together with sapphire as calibration substance to elucidate and validate the DSC and TMDSC procedures for the determination of the specific heat and the glass transition.

06/01605 Heat capacity and thermodynamic functions of fullerene-containing derivatives of atactic poly(methyl methacrylate): Smirnova, N. N. et al. Thermochimica Acta, 2005, 433, (1–2), 121–127

06/01605 Heat capacity and thermodynamic functions of fullerene-containing derivatives of atactic poly(methyl methacrylate): Smirnova, N. N. et al. Thermochimica Acta, 2005, 433, (1–2), 121–127

Thermal instability of viscoelastic fluids in horizontal porous layers as initial value problem

The instability of a viscoelastic fluid saturating a horizontal porous layer heated from below is studied theoretically with a dynamical system approach. The viscoelastic character of the flow is taken into account by a modified Darcy’s law. The conservation equations of mass, momentum and energy are approximated by a reduced-order system of nonlinear, ordinary differential equations, which is similar to the well-known system derived by Lorenz to describe atmospheric convection. Equilibrium points and their stability are expressed as functions of a dimensionless heat capacity and of two relaxation parameters. Qualitative expressions of the Nusselt number when the system is out of equilibrium are also derived.

Heat capacity and thermodynamic functions of LuPO 4 in the range 0–320 K

The heat capacity of LuPO 4 was measured in the temperature range 6.51–318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: C p 0 (298.15 K) = 100.0 ± 0.1 J K −1 mol −1, S 0(298.15 K) = 99.74 ± 0.32 J K −1 mol −1, H 0(298.15 K) − H 0(0) = 16.43 ± 0.02 kJ mol −1, −[ G 0(298.15 K) − H 0(0)]/ T = 44.62 ± 0.33 J K −1 mol −1. The standard Gibbs free energy of formation of LuPO 4 from elements Δ f G 0(298.15 K) = −1835.4 ± 4.2 kJ mol −1 was calculated based on obtained and literature data.

Low-Temperature Heat Capacity and Thermodynamic Functions of Nano Fe

The size of nano Fe powders was determined to be 25 nm in diameter by SEM. The isobaric molar heat capacity C-p of the nano Fe was measured with the high precision adiabatic low-temperature calorimeter in the temperature range from 84 K to 350 K. The relationship of C-p with temperature T was established as:

The low-temperature heat capacity and ideal gas thermodynamic properties of isobutyl tert-butyl ether

The heat capacities of isobutyl tert-butyl ether in crystalline, liquid, supercooled liquid, and glassy states were measured by vacuum adiabatic calorimetry over the temperature range from (7.68 to 353.42) K. The purity of the substance, the glass-transition temperature, the triple point and fusion temperatures, and the enthalpy and entropy of fusion were determined. Based on the experimental data, the thermodynamic functions (absolute entropy and changes of the enthalpy and Gibbs free energy) were calculated for the solid and liquid states over the temperature range studied and for the ideal gas state at T = 298.15 K. The ideal gas heat capacity and other thermodynamic functions in wide temperature range were calculated by statistical thermodynamics method using molecular parameters determined from density-functional theory. Empirical correction for coupling of rotating groups was used to calculate the internal rotational contributions to thermodynamic functions. This correction was found by fitting to the calorimetric entropy values.

Heat Capacity and Thermodynamic Functions of Ga2Se3 from 14 to 320 K

The heat capacity of Ga2Se3 is measured from 14 to 320 K by adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of gallium selenide. Under standard conditions, the thermodynamic properties of Ga2Se3 are C p 0 (298.15 K) = 120.8 ± 0.2 J/(K mol), S0(298.15 K) = 180.4 ± 0.4 J/(K mol), H0(298.15 K) - H0(0) = 25.32 ± 0.05 kJ/mol, and Φ0(298.15 K) = 95.52 ± 0.19 J/(K mol). The Debye characteristic temperature of Ga2Se3 evaluated from heat capacity data is 340 ± 10 K.

Measurements of the Heat Capacity of an Azeotropic Mixture of Water and n‐Butanol from 78 to 320 K

AbstractMolar heat capacities of n‐butanol and the azeotropic mixture in the binary system [water (x=0.716) plus n‐butanol (x=0.284)] were measured with an adiabatic calorimeter in a temperature range from 78 to 320 K. The functions of the heat capacity with respect to thermodynamic temperature were established for the azeotropic mixture. A glass transition was observed at (111.9±1.2) K. The phase transitions took place at (179.26±0.77) and (269.69±0.14) K corresponding to the solid‐liquid phase transitions of n‐butanol and water, respectively. The phase‐transition enthalpy and entropy of water were calculated. A thermodynamic function of excess molar heat capacity with respect to temperature was established, which took account of physical mixing, destructions of self‐association and cross‐association for n‐butanol and water, respectively. The thermodynamic functions and the excess thermodynamic ones of the binary systems relative to 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity and the calculated excess heat capacity with respect to temperature.

The Heat Capacity and Thermodynamic Functions of Ternary Manganites DyMIMgMn2O6 (MI − Na, K, Cs) in the Temperature Range from 223 to 673 K

The solid-phase method is used to synthesize ternary manganites of composition DyMIMgMn2O6 (MI − Na, K, Cs); their X-ray investigation is performed to demonstrate that they all crystallize in orthorhombic system. Their heat capacity is determined experimentally in the range from 223 to 673 K, equations are derived which describe the dependences Cpo ∼ ƒ(T), and the thermodynamic functions Cpo, Ho(T)−Ho(298.15), So(T), and Φ**(T) are calculated. Second-order phase transitions are observed in the process of investigation of heat capacity.

Heat capacity and thermodynamic functions of the CuAlS2 semiconductor in the temperature range from 80 to 300 K

AbstractThe molar heat capacity at constant pressure CP has been measured for CuAlS2 semiconductor in the temperature range from 80 to 300 K for the first time. From the experimental results the molar heat capacity at constant volume CV and thermodynamic functions such as enthalpy H and entropy S were calculated. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Heat capacity and thermodynamic functions of fullerene-containing derivatives of atactic poly(methyl methacrylate)

In the present work by precision adiabatic vacuum and dynamic scanning calorimetry the heat capacity of covalent-bonded fullerenes C 60 and C 70 containing derivatives of atactic poly(methyl methacrylate) has been measured over the range from 6 to 350 K and from 330 to 460 K, respectively. Low-temperature heat capacity has been analyzed on the basis of Debye and Tarasov theories of the heat capacity of solids and the multifractal generalization and, as a result, some conclusions on the heterodynamics of their structures have been drawn. Temperature interval and thermodynamic characteristics of devitrification as well as their thermal stability regions have been determined. The experimental data were used to calculate standard thermodynamic functions, namely, the heat capacity C p ° ( T), enthalpy H °( T) − H °(0), entropy S °( T) and Gibbs function G °( T) − H °(0), for the range from T → 0 to 430 K. The thermodynamic characteristics of fullerene-containing derivatives of atactic poly(methyl methacrylate) and a polymer-analog not including C 60 and C 70 have been compared.

Low-temperature Heat Capacity and Thermodynamic Functions of Nano ZnO

Low-temperature Heat Capacity and Thermodynamic Functions of Nano ZnO

Heat Capacity and Thermodynamic Functions of TbBr3.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Heat Capacity and Thermodynamic Functions of TbBr3

The heat capacity of solid TbBr3 was measured by differential scanning calorimetry in the temperature range from 300 K up to the melting temperature. The polynomial heat capacity dependence on temperature was used to fit experimental data. Additionally, the temperature and enthalpy of fusion of TbBr3 were also measured. By combination of these results with the literature data on the entropy at 298.15 K, (TbBr3, s, 298.15 K), the standard molar enthalpy of formation, Δform (TbBr3, s, 298.15 K), and the heat capacity of the liquid phase, (TbBr3, l), the thermodynamic functions of terbium tribromide were calculated up to T = 1300 K.

High temperature enthalpy, heat capacity and other thermodynamic functions of solid InN

The heat capacity and the heat content of indium nitride were measured by Calvet calorimetry (305–390 K) and by drop calorimetry (427–774 K). The temperature dependence of the heat capacity in the form C pm=43.886+8.194×10 −3T−1.007×10 6T −2+8.353×10 7T −3(J K −1 mol −1) was derived by the least squares method from the experimental data. Furthermore, the standard molar entropy S 0 m (298 K)=42.51 J K −1 mol −1 was assessed taking into account the recently reported phonon density of states, low temperature C pm and the current data. Thermodynamic functions calculated on the basis of our results and literature data on the heat of formation of InN are given.

Extended least-squares analysis of heat capacities incorporating the effect of phase transitions and its application to the deuteration-induced phase transition in Rb 3D(SO 4) 2

A non-linear least-squares method of analysis has been developed for the heat capacities of solids undergoing phase transitions. It utilizes harmonic heat capacity functions corrected for thermal expansion. The unique feature of the method is that it incorporates the effect of a gradual phase transition in the fitting function for the low temperature phase. Compact expressions approximating the Debye function and the Ising model heat capacity function have been derived and presented in practical forms for use in the Kaleidagraph software. The method has been tested on the heat capacity of sodium chloride (which lacks a phase transition) and tri-rubidium deuterium disulfate (Rb 3D(SO 4) 2, TRDS) which undergoes a phase transition at 78.5 K in the deuterated form but not in the normal hydrogenous form. The excess entropy based on the fitting was 5.27 J K −1 mol −1, close enough to R ln 2=5.76 J K −1 mol −1 to suggest an order–disorder mechanism for the phase transition.

Recommended specific heat capacity functions of Group VA elements

The objective of this study was to investigate the possibility of representing specific heat capacities of the three metals comprising Group VA of the periodic table: vanadium, niobium and tantalum, with polynomials, from ambient temperature to close to their melting point temperatures. The analysis was based on available literature data including experimental studies of these metals at the Thermophysical Properties Laboratory of the “Vinca” Institute using millisecond resolution pulse calorimetry. This work has resulted in recommended functions obtained by analysis of existing experimental data. A critical analysis of methods used in obtaining these data, pointing to possible inherent sources of systematic errors that might influence their reliability, resulted in preferential weights of different data sets. Possible use of these three metals as candidates for specific heat capacity standard reference materials is also discussed.

Structural organization of the fibrin(ogen) alpha C-domain.

We hypothesized that the alpha C-domain of human fibrinogen (residues hA alpha 221-610) and of other species consists of a compact COOH-terminal region (hA alpha 392-610) and a flexible NH(2)-terminal connector region (hA alpha 221-391) which may contain some regular structure [Weisel and Medved (2001) Ann. N.Y. Acad. Sci. 936, 312-327]. To test this hypothesis, we expressed in E. coli recombinant fragments corresponding to the full-length human alpha C-domain and its NH(2)- and COOH-terminal regions as well as their bovine counterparts, bA alpha 224-568, bA alpha 224-373, and bA alpha 374-568(538), respectively, and tested their folding status by fluorescence spectroscopy, circular dichroism (CD), and differential scanning calorimetry (DSC). All three methods revealed heat-induced unfolding transitions in the full-length bA alpha 224-568 and its two COOH-terminal fragments, indicating that the COOH-terminal portion of the bovine alpha C-domain is folded into a compact cooperative structure. Similar results were obtained by CD and DSC with the full-length and the COOH-terminal h392-610 human fragments. The NH(2)-terminal fragments of both species, b224-373 and h221-392, did not exhibit any sign of a compact structure. However, their heat capacity functions, CD spectra, and temperature dependence of ellipticity at 222 nm were typical for peptides in the extended helical poly(L-proline) type II conformation (PPII), suggesting that they contain this type of regular structure. This is consistent with the presence of proline-rich tandem repeats in the sequence of both bovine and human connector regions. These results indicate that both bovine and human fibrinogen alpha C-domains consist of a compact globular cooperative unit attached to the bulk of the molecule by an extended NH(2)-terminal connector region with a PPII conformation.