Low-temperature heat capacities and thermodynamic properties of crystalline isoproturon

An incremental integral isoconversional method for the determination of activation energy as a function of the extent of conversion is presented. The method is based on the treatment of experimental data without their transformation so that the resulting values of activation parameters should not be biased. The method was tested for recovering the activation energies from simulated data and employed for the treatment of experimental data of the NiS recrystallisation. This revised version was published online in July 2006 with corrections to the Cover Date.     

2-碘-3-硝基甲苯的低温热容和热力学性质

通过精密自动绝热热量计测定了2-碘-3-硝基甲苯(C~7H~6INO~2)在79～373K温区的摩尔热容。实验结果表明,这个化合物在331～340K温度区间有一个固-液熔化相变,其熔化温度、摩尔熔化焓、摩尔熔化熵以及该样品的化学纯度分别为：(339.311±0.13)J·mol^-^1·K^-^1和99.73%。用热容多项式议程进行数值积分获得了该物质在298.15～370K温区每隔5K的热力学函数值。用DSC分析对它的固-液相变过程作了进一步的研究。     

Low-temperature heat capacity and thermodynamic properties of endo-Tricyclo[5.2.1.0]decane

Endo-Tricyclo[5.2.1.0^2,6]decane (CAS 6004-38-2) is an important intermediate compound for synthesizing diamantane. The lack of data on the thermodynamic properties of the compound limits its development and application. In this study, endo-Tricyclo[5.2.1.0^2,6]decane was synthesized and the low temperature heat capacities were measured with a high-precision adiabatic calorimeter in the temperature range from (80 to 360) K. Two phase transitions were observed: the solid-solid phase transition in the temperature range from (198.79 to 210.27) K, with peak temperature 204.33 K; the solid-liquid phase transition in the temperature range from 333.76 K to 350.97 K, with peak temperature 345.28 K. The molar enthalpy increments, ΔH_m, and entropy increments, ΔS_m, of these phase transitions are ΔH_m=2.57 kJ · mol⁻¹ and ΔS_m=12.57 J · K⁻¹ · mol⁻¹ for the solid-solid phase transition at 204.33 K, and, Δ_fusH_m=3.07 kJ · mol⁻¹ and Δ_fusS_m=8.89 J · K⁻¹ · mol⁻¹ for the solid-liquid phase transition at 345.28 K. The thermal stability of the compound was investigated by thermogravimetric analysis. TG result shows that endo-Tricyclo[5.2.1.0^2,6]decane starts to sublime at 300 K and completely changes into vapor when the temperature reaches 423 K, reaching the maximal rate of weight loss at 408 K.     

Low-temperature heat capacity and thermodynamic properties of crystalline carboxin (C12H13NO2S)

Carboxin was synthesized and its heat capacities were measured with an automated adiabatic calorimeter over the temperature range from 79 to 380 K. The melting point, molar enthalpy (Δ_fusH_m) and entropy (Δ_fusS_m) of fusion of this compound were determined to be 365.29±0.06 K, 28.193±0.09 kJ mol⁻¹ and 77.180±0.02 J mol⁻¹ K⁻¹, respectively. The purity of the compound was determined to be 99.55 mol% by using the fractional melting technique. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range between 80 and 360 K. The thermal stability of the compound was further investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The DSC curve indicates that the sample starts to decompose at ca. 290 °C with the peak temperature at 292.7 °C. The TG-DTG results demonstrate the maximum mass loss rate occurs at 293 °C corresponding to the maximum decomposition rate.     

1-甲基-3,5-二苯基-吡唑的低温热容和热力学性质

通过精密自动绝热热量计测量了自己合成并提纯1-甲基-3,5-二苯基-吡唑在78～370K温区的摩尔热容。实验结果表明,这个化合物有一个固-液熔化相变,其熔化温度、摩尔熔化焓以及摩尔熔化熵分别为：(332.903±0.152)K,(17463.48±21.81)J·mol^-1和(52.55±0.06)J·mol^-1·K^-1。通过分步熔化法得到样品的纯度和绝对纯样品熔点分别为：0.9954(摩尔分数)和333.115K。在热容测量的基础上计算出了该物质每隔5K的热力学函数值。用DSC技术对该物质的固液熔化过程作了进一步研究,结果与热容实验相一致。     

Low-temperature heat capacities and thermodynamic properties of 2,2-dimethyl-1,3-propanediol

The molar heat capacities C _p,m of 2,2-dimethyl-1,3-propanediol were measured in the temperature range from 78 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-solid and a solid-liquid phase transitions were found at T-314.304 and 402.402 K, respectively, from the experimental C _p-T curve. The molar enthalpies and entropies of these transitions were determined to be 14.78 kJ mol⁻¹, 47.01 J K⁻¹ mol⁻ for the solid-solid transition and 7.518 kJ mol⁻¹, 18.68 J K⁻¹ mol⁻¹ for the solid-liquid transition, respectively. The dependence of heat capacity on the temperature was fitted to the following polynomial equations with least square method. In the temperature range of 80 to 310 K, C _p,m/(J K⁻¹ mol⁻¹)=117.72+58.8022x+3.0964x ²+6.87363x ³−13.922x ⁴+9.8889x ⁵+16.195x ⁶; x=[(T/K)−195]/115. In the temperature range of 325 to 395 K, C _p,m/(J K⁻¹ mol⁻¹)=290.74+22.767x−0.6247x ²−0.8716x ³−4.0159x ⁴−0.2878x ⁵+1.7244x ⁶; x=[(T/K)−360]/35. The thermodynamic functions H _T−H _298.15 and S _T−S _298.15, were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The thermostability of the compound was further tested by DSC and TG measurements. The results were in agreement with those obtained by adiabatic calorimetry.     

Low-temperature heat capacity and standard thermodynamic functions of 1-butyl-3-methylimidazolium lactate

The heat capacities of 1-butyl-3-methylimidazolium lactate ionic liquids ([C₄mim][Lact]) were measured with a highly accurate automatic adiabatic calorimeter over the temperature range from 79 to 406 K. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The standard molar heat capacity was determined to be 1734.46?±?5.12 J K^?1 mol^?1 at 298.15 K. The molar enthalpy and molar entropy of the transition were determined to be 15.575?±?0.045 and 64.44?±?0.14 J K^?1 mol^?1. Other thermodynamic properties, such as (H_T???H_298.15) and (S_T???S_298.15), were also calculated. Furthermore, when the temperature reaches 241.87 K, the strongest peaks appeared by analysis of the heat capacity curve. This phenomenon could be explained from the interionic interaction, which is the hydrogen bond between the anions and cations.     

Zeolite 4A: heat capacity and thermodynamic properties

The heat capacity of zeolite 4A (also known as LTA, Linde Type A and sodium zeolite A), in the temperature range from 37 to 311 K, is reported. The heat capacity shows no anomalies in this temperature range. Thermodynamic parameters, H, S and G, relative to their values at T=0 K were derived. From these data, we find that zeolite 4A is stabilized by strong enthalpic interactions. Furthermore, its thermodynamic stability results from the strong Si---O and Al---O bonds in the primary building units, with bond strengths very close to those in other similar materials.     

Low-temperature heat capacity of diglycylglycine

Heat capacity of tripeptide diglycylglycine was measured in a temperature range from 6.5 to 304 K. The results were compared with those for glycine and glycylglycine. Peptide bonding was found not to change C _P(T) virtually above 70 K, where heat capacity does not obey the Debye model. Comparison with literature data allows one to expect a significant difference in the heat capacity for enantiomorph and racemic species of valine and leucine, like it was found recently for D-and DL-serine.     

Low-temperature thermodynamic properties of L- and DL-valines

Heat capacities C _p(T) of L-valine and DL-valine were measured in the temperature range 6–300 K with an adiabatic calorimeter; thermodynamic functions were calculated based on these measurements. At 298.15 K, the values of heat capacity, C _p; entropy, S _m ⁰ (T) ? S _m ⁰ (0); enthalpy, H _m ⁰ (T) ? H _m ⁰ (0) of L-valine are equal, respectively, to 167.9 ± 0.3 J K^?1 mol^?1; 178.5 ± 0.4 J K^?1 mol^?1; and 27510 ± 60 J mol^?1. For DL-valine, these values are equal, respectively, to 167.3 ± 0.3 J K^?1 mol^?1, 174.4 ± 0.3 J K^?1 mol^?1, and 27000 ± 50 J mol^?1. The difference between the heat capacities of enantiomer and racemate has been calculated and compared with the similar data for serines, cysteines, and phenylglycines.     

Low-temperature heat capacity and thermodynamic properties of layered perovskite-like oxides NaNdTiO4 and Na2Nd2Ti3O10

We report the results of the study of thermodynamic properties for layered perovskite-like oxides NaNdTiO₄ and Na₂Nd₂Ti₃O₁₀. Isobaric heat capacity of the compounds was measured in an adiabatic calorimeter in the range of 5–340 K. Low-temperature heat capacity anomaly was observed in the heat capacity curve of Na₂Nd₂Ti₃O₁₀. Standard thermodynamic properties of the oxides were evaluated from the experimental heat capacity temperature dependencies. Finally, on the basis of the experimental data obtained in this work, we tested applicability of the additivity principle for prediction of thermodynamic properties for layered compounds built of fragments of various structural types.     

Low-temperature heat capacity of L- and DL-phenylglycines

Heat capacity of crystalline L- and DL-phenylglycines was measured in the temperature range from 6 to 305?K. For L-phenylglycine, no anomalies in the C _p (T) dependence were observed. For DL-phenylglycine, however, an anomaly in the temperature range 50?C75?K with a maximum at about 60?K was registered. The enthalpy and the entropy changes corresponding to this anomaly were estimated as 20?J?mol^?1 and 0.33?J?K^?1 mol^?1, respectively. In the temperature range 205?C225?K, an unusually large dispersion of the experimental points and a small change in the slope of the C _p (T) curve were noticed. Thermodynamic functions for L- and DL-phenylglycines in the temperature range 0?C305?K were calculated. At 298.15?K, the values of heat capacity, entropy, and enthalpy are equal to 179.1, 195.3?J?K^?1 mol^?1, and 28590?J?mol^?1 for L-phenylglycine and 177.7, 196.3?J?K^?1 mol^?1 and 28570?J?mol^?1 for DL-phenylglycine. For both L- and DL-phenylglycine, the C _p (T) at very low temperatures does not follow the Debye law C ?C T ³ . The heat capacity C _p (T) is slightly higher for L-phenylglycine, than for the racemic DL-crystal, with the exception of the phase transition region. The difference is smaller than was observed previously for the L-/DL-cysteines, and considerably smaller, than that for L-/DL- serines.     

Low-temperature heat capacity of d-glucose and d-fructose

Journal of Thermal Analysis and Calorimetry - The thermodynamics data of crystalline states of two representative components in blood sugar, d-glucose and d-fructose, are significant in researching...     

Low-temperature heat capacity of monoclinic enstatite

Synthetic enstatite MgSiO₃ was crystallized from a melt, quenched into water, and then annealed at 873 K. The product is the monoclinic polymorph with the unit cell parameters of a=0.9619(7), b=0.8832(3), c=0.5177(4) nm, β=108.27(5)°. Heat capacity was measured from 6 to 305 K using an adiabatic vacuum calorimeter. Thermodynamic functions for clinoenstatite differ by about 5% from those predicted after a thermodynamic model in the literature, but are very close to those measured for orthorhombic enstatite.     

Low-temperature heat capacity of dysprosium diboride

A novel microcalorimeter based on a miniature liquid-in-glass thermometer is described. Heat is transduced into an optical, rather than electrical, signal, facilitating a future array format. The instrument performs batch analysis (drop mixing) with a 2 μL sample volume. Energy changes of 4 μJ produced by a dilution of sulfuric acid are resolvable. The effect of evaporation, and measures taken to limit it, are discussed.     

Low-temperature heat capacities and derived thermodynamic functions of cyclohexane

The low-temperature heat capacities of cyclohexane were measured in the temperature range from 78 to 350 K by means of an automatic adiabatic calorimeter equipped with a new sample container adapted to measure heat capacities of liquids. The sample container was described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on water. The deviations of experimental heat capacities from the corresponding smoothed values lie within ±0.3%, while the inaccuracy is within ±0.4%, compared with the reference data in the whole experimental temperature range. Two kinds of phase transitions were found at 186.065 and 279.684 K corresponding solid-solid and solid-liquid phase transitions, respectively. The entropy and enthalpy of the phase transition, as well as the thermodynamic functions {H_(T)-H _{298.15 K}} and {S _(T)-S_{298.15 K}}, were derived from the heat capacity data. The mass fraction purity of cyclohexane sample used in the present calorimetric study was determined to be 99.9965% by fraction melting approach. This revised version was published online in July 2006 with corrections to the Cover Date.     

Specific heat capacity and thermodynamic properties of CuTeO3 and HgTeO3

Tellurites of CuTeO₃ and HgTeO₃ are synthesized and their specific molar heat capacities are experimentally determined for the first time. The tellurites discussed in the present paper are used for preparation of optical glasses with special properties for optoelectronics, nuclear and power industries. The tellurites synthesized are prepared for chemical analysis, differential thermal analysis and X-ray analysis. The use of the tellurites studied is related to knowing their thermodynamic properties like specific molar heat capacity (C _p,m), enthalpy \( \left( {\Delta_{{{\text {T}}^{\prime}}}^{\text{T}} H_{\text{m}}^{0} } \right), \) entropy \( \left( {\Delta_{{{\text {T}}^{\prime}}}^{\text{T}} S_{\text{m}}^{0} } \right) \) and Gibbs energy \( \left( { - \Delta_{{{\text {T}}^{\prime}}}^{\text{T}} G_{\text{m}}^{0} } \right) \) . The temperature dependences of their molar heat capacities are determined using the least squares method. The thermodynamic properties are calculated: entropy, enthalpy and Gibbs function.     

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.