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 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 capacity of alkali metal borate glass

Journal of Thermal Analysis and Calorimetry - As a universal feature of glass, its low-energy inelastic scattering spectra show a broad response known as the boson peak (BP). Since the BP is the...     

Low-temperature heat capacity of some alkali metal tungstates

Heat capacity measurements have been made on the two triclinic tungstates, Li_0.2WO₃ and Na_0.33WO₃ from 1 to 60 K. In addition to the normal Debye term the data show a large contribution which can be fit to a single Einstein mode associated with the oscillation of the alkali ions in the holes formed by the corner bonding of six WO₆ octahedra. The Einstein characteristic temperatures obtained are 71 ± 2 and 78 ± 2 K for Li_0.2WO₃ and Na_0.33WO₃, respectively. The results are compared with those reported earlier for the hexagonal tungsten bronzes.     

Low-temperature heat capacity of α and γ polymorphs of glycine

Low-temperature heat capacity of two polymorphs of glycine (α and γ) was measured from 5.5 to 304 K and thermodynamic functions were calculated. Difference in heat capacity between polymorphs ranges from +26% at 10 K to -3% at 300 K. The difference indicates the contribution into the heat capacity of piezoelectric γ polymorph, probably connected with phase transition and ferroelectricity. Thermodynamic evaluations show that at ambient conditions γ polymorph is stable and α polymorph is metastable. This revised version was published online in August 2006 with corrections to the Cover Date.     

Low-temperature heat capacity and thermodynamic properties of crystalline lead formate

As one 3-D coordination polymer, lead formate was synthesized; calorimetric study and thermal analysis for this compound were performed. The low-temperature heat capacity of lead formate was measured by a precise automated adiabatic calorimeter over the temperature range from 80 to 380 K. No thermal anomaly or phase transition was observed in this temperature range. A four-step sequential thermal decomposition mechanism for the lead formate was found through the DSC and TG-DTG techniques at the temperature range from 500 to 635 K.     

Low-temperature heat capacity and standard entropy of PdO(cr.)

The temperature dependence of the heat capacity C _p ^o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86 K. Standard thermodynamic functions C _p ^o(T), H ^o(T) — H ^o(0), S ^o(T), and G ^o(T) — H ^o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium oxide are recommended: S ^o(298.15) = 39.58 ± 0.15 J/(K mol), Δ_f H ^o(298.15) = −112.69 ± 0.32 kJ/mol, Δ_f G ^o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)₂ (amorph.) with respect to PdO(cr.) was estimated.     

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 of magnesioferrite, MgFe2O4

Heat capacity of stoichiometric homogeneous spinel MgFe₂O₄ was measured from 5 to 305 K and thermodynamic functions were derived for temperatures up to 725 K using our previous high-temperature experimental data for the same sample. Anomaly in C _p was found at very low temperatures. Experimental data below 20 K contain large (up to 25% near 5 K) error arising from the difference in the thermal history between the experimental series. Magnetic contribution to the low-temperature heat capacity was tested, and the linear function was found to fit experimental data better than the three-halves power derived from the spin-wave theory.     

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 of TMS monolayers adsorbed on graphite and MgO+

The heat capacity obtained below 30 K for the tetramethylsilane monolayers, which are adsorbed either on graphite or on the (100) surface of MgO, is analyzed to investigate the vibrational properties. The 2-D Debye temperatures are approximately 60% of the Debye temperature of the bulk solid (γ -phase), reflecting the dimensionality of lattice vibrations. The contributions from the vibrations perpendicular to the surface as well as the librational motions are determined by fitting the experimental heat capacities. All the results are consistent with those obtained from the incoherent inelastic neutron scattering and the molecular dynamics simulation. This revised version was published online in August 2006 with corrections to the Cover Date.     

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 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.     

Low-temperature heat capacity of sodium borosilicate glasses at temperatures from 13 K to 300 K

Thermodynamic properties of sodium borosilicate glasses {56.7 SiO₂, (43.7  − x)B₂O₃,xNa₂O} wherex =  14.4, 22.9, and 32.5, have been studied. The heat capacity was measured using an adiabatic calorimeter at temperatures between 13 K and 300 K. The thermodynamic functions were calculated from the smoothed values ofC_{p, m} . The results differ from an additive model with pure glassy SiO₂, B₂O₃, and crystalline Na₂O as components. A model based on the assumption that the contribution of structural units of glasses to the heat capacity is equal to those of glasses with the same molecular formula is proposed.     

Low-temperature heat capacity studies on DyFe3, DyCo3, DyNi3, and LaNi3

Low-temperature heat capacity measurements were made on DyFe₃, DyCo₃, DyNi₃, and LaNi₃ over the temperature range 1.4–15°K. Two anomalies, observed at 1.8 and 9.3°K, are ascribed to the presence of an oxide and a hydride. Another anomaly exists at 3.2°K, which may be due to hydroxide. The observed electronic specific heat coefficients are interpreted in terms of the band structure of these materials.     

Low-temperature heat capacity of room-temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Heat capacities of liquid, stable crystal, and liquid-quenched glass of a room-temperature ionic liquid (RTIL), 1-hexyl-3-methylimidazolium bis(trifluromethylsulfonyl)imide were measured between 5 and 310 K by adiabatic calorimetry. Heat capacity of the liquid at 298.15 K was determined for an IUPAC project as (631.6 +/- 0.5) J K(-1) mol(-1). Fusion was observed at T(fus) = 272.10 K for the stable crystalline phase, with enthalpy and entropy of fusion of 28.34 kJ mol(-1) and 104.2 J K(-1) mol(-1), respectively. The purity of the sample was estimated as 99.83 mol % by the fractional melting method. The liquid could be supercooled easily and the glass transition was observed around T(g) approximately 183 K, which was in agreement with the empirical relation, T(g) approximately ((2)/(3)) T(fus). The heat capacity of the liquid-quenched glass was larger than that of the crystal as a whole. In the lowest temperature region, however, the difference between the two showed a maximum around 6 K and a minimum around 15 K, at which the heat capacity of the glass was a little smaller than that of crystal.