Heat capacity and thermodynamic functions of nano-TiO2 rutile in relation to bulk-TiO2 rutile

Several conflicting reports have suggested that the thermodynamic properties of materials change with respect to particle size. To investigate this, we have measured the constant pressure heat capacities of three 7 nm TiO₂ rutile samples containing varying amounts of surface-adsorbed water using a combination of adiabatic and semi-adiabatic calorimetric methods. These samples have a high degree of chemical, phase, and size purity determined by rigorous characterization. Molar heat capacities were measured from T = (0.5 to 320) K, and data were fitted to a sum of theoretical functions in the low temperature (T < 15 K) range, orthogonal polynomials in the mid temperature range (10 > T/K > 75), and a combination of Debye and Einstein functions in the high temperature range (T > 35 K). These fits were used to generate $\mathit{Cp}\text{,}{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{H}_{\text{m}}^{\circ }$, and ${\phi }_{\text{m}}^{\circ }$ values at selected temperatures between (0.5 and 300) K for all samples. Standard molar entropies at T = 298.15 K were calculated to be (62.066, 59.422, and 58.035) J · K⁻¹ · mol⁻¹ all with a standard uncertainty of 0.002·${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$ for samples TiO₂·0.361H₂O, TiO₂·0.296H₂O, and TiO₂·0.244H₂O, respectively. These and other thermodynamic values were then corrected for water content to yield bare nano-TiO₂ thermodynamic properties at T = 298.15 K, and we show that the resultant thermodynamic properties of anhydrous TiO₂ rutile nanoparticles equal those of bulk TiO₂ rutile within experimental uncertainty. Thus we show quantitatively that the difference in thermodynamic properties between bulk and nano-TiO₂ must be attributed to surface adsorbed water.     

Heat capacity and thermodynamic properties of 1-hexadecanol

Three different nitrocellulose (NC) samples produced from linters were investigated. DSC studies on the NC+sym-diethyldiphenylurea (C1) mixtures were carried out. The influence of storage time on their pore structures was examined using thermoporometry. The results led to conclusion that large pores are multiples of small ones. The parameter n was used to characterize the number of C1 molecules equivalent to NC ring. Its value for short storage time was about 9 but for longer time reached the value of 3. The influence of thermal history on the phase transition and porosity of the different nitrocellulose samples was different.     

Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ 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: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

Cesium chromate,Cs2CrO4: heat capacity and thermodynamic properties from 5 to 350 K

The heat capacity of a sample of Cs₂CrO₄ was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure C_p^o(298.15 K), the entropy S^o(298.15 K), the enthalpy {H^o(298.15 K) - H^o(0)} and the function $\text{? {G}{}^{\mathrm{o}}\text{(298.15}\text{K}\text{) - H}{}^{\mathrm{o}}\text{(0)}}\text{298.15}\text{K}$ were found to be (146.06 ± 0.15) J K^?1 mol^?1, (228.59 ± 0.23) J K^?1 mol^?1, (30161 ± 30) J mol^?1, and (127.43 ± 0.13) J K^?1 mol^?1, respectively. The heat capacity C_p^o(298.15 K) and entropy S^o(298.15 K) and entropy S^o(298.15 K) of Rb₂CrO₄ are estimated to be (146.0 ± 1.0) J K^?1 mol^?1 and (217.6 ± 3.0) J K^?1 mol^?1, respectively.     

Heat capacity (Cp) and entropy of olivine-type LiFePO4 in the temperature range (2 to 773) K

The heat capacity of olivine-type lithium iron phosphate (LiFePO₄ – LFP) has been measured covering a temperature range from (2 to 773) K. Three different calorimeters were used. The Physical Property Measurement System (PPMS) from Quantum Design was applied in the range between T = (2 and 300) K, a Micro-DSC II from Setaram within the range between T = (283 and 353) K and data between T = (278 and 773) K were measured by means of a Sensys DSC (Setaram) using the Cp-by-step method. Experimental data are given with an error of (1 to 2)% above T = 20 K and up to 8% below 20 K. The data were subdivided into appropriate temperature intervals and fitted using common heat capacity functions. The low temperature results permit the calculation of standard entropies and temperature coefficients of electronic, lattice, as well as magnetic (antiferromagnetic transition at T = 49.2 K) contributions to the heat capacity. The obtained experimental values were compared to results of a recently published first principles phonon study (DFT) and to few available experimental data from the literature.     

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。     

Heat capacity of hafnium mononitride from temperatures of 5 to 350 K: An estimation procedure

Measurements of the heat capacity by quasi-adiabatic, intermittent energy increments from 5 to 350 K show small high heat-capacity anomalies near 7 and 10 K which are attributed to superconducting transitions seen by magnetic measurements on the same carefully synthesized and well-characterized sample of (Hf_0.934Zr_0.057)(N_0.97). Although no previous heat capacity measurements over the cryogenic region are known, the estimated 298.15 K standard entropy values (S/R) vary in the literature from about 200 per cent higher to 5 per cent lower than our measured value of (5.28±0.01)R^–1 when the formula is represented as above. A simple scheme to represent and predict values based on both molar volumes and atomic masses for related materials is presented which seems more reliable on a limited sample than do others despite the intrusion of lanthanide contraction.This revised version was published online in November 2005 with corrections to the Cover Date.     

Heat capacity and thermodynamic properties of N-(2-cyanoethyl) aniline (C9H10N2)

The low temperature heat capacities of N-(2-cyanoethyl)aniline were measured with an automated adiabatic calorimeter over the temperature range from 83 to 353 K. The temperature corresponding to the maximum value of the apparent heat capacity in the fusion interval, molar enthalpy and entropy of fusion of this compound were determined to be 323.33 ± 0.13 K, 19.4 ± 0.1 kJ mol⁻¹ and 60.1 ± 0.1 J K⁻¹ mol⁻¹, respectively. Using the fractional melting technique, the purity of the sample was determined to be 99.0 mol% and the melting temperature for the tested sample and the absolutely pure compound were determined to be 323.50 and 323.99 K, respectively. A solid-to-solid phase transition occurred at 310.63 ± 0.15 K. The molar enthalpy and molar entropy of the transition were determined to be 980 ± 5 J mol⁻¹ and 3.16 ± 0.02 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions of the compound [H_T − H_298.15] and [S_T − S_298.15] were calculated based on the heat capacity measurements in the temperature range of 83–353 K with an interval of 5 K.     

Heat capacity and thermodynamic properties of germanium disulfide at temperatures from T = (2 to 1240) K

The heat capacity of polycrystalline germanium disulfide α-GeS₂ has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K^?1 · mol^?1, 87.935 J · K^?1 · mol^?1 and 12.642 kJ · mol^?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol^?1, respectively. The thermodynamic functions of α-GeS₂ were calculated over the range (0 ? T/K ? 1250).     

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.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

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.     

Heat capacity and thermodynamic properties of the alkali metal compounds in the temperature range 300–800 K. I. Cesium and rubidium molybdates

The heat capacities of cesium and rubidium molybdates, Cs₂MoO₄ and Rb₂MoO₄, have been measured by differential scanning calorimetry (DSC) in the temperature range 300–800 K. These values have been combined with published low-temperature heat capacity data for Cs₂MoO₄ to obtain thermodynamic functions to 800 K. For Rb₂MoO₄, however, these functions could not be calculated because low-temperature heat capacities are unavailable. Instead, only heat capacity data are reported.     

Synthesis, structure, solid-state thermolysis, and thermodynamic properties of new heterometallic complex Li2Co2(Piv)6(NEt3)2

The reaction of lithium pivalate, polymeric cobalt pivalate [Co(Piv)₂]_n, and triethylamine in THF at 60 °С afforded the new heterometallic antiferromagnetic complex Li₂Co₂(Piv)₆(NEt₃)₂ (2). The molecular and crystal structure of complex 2 was established and its magnetic behavior was studied. The vaporization and solid-state thermolysis of 2 were investigated. The thermodynamic characteristics of complex 2 were determined. The results of the present study show that complex 2 can be used as a potential molecular precursor for the synthesis of thin films of lithium cobaltate LiCoO₂.     

Heat capacity corrections to a standard state: a comparison of new and some literature methods for organic liquids and solids

The estimation methods commonly used to correct phase change enthalpies to the standard state are compared where possible to experimental measurements. Heat capacity corrections for liquid-gas equilibria are found to correlate with molecular structure, and we suggest an improved method for estimating these corrections using group methods. A similar improvement for estimating heat capacity corrections for solid-gas equilibria using group methods is also proposed. Heat capacity corrections for liquid-solid equilibria are examined. These corrections were found to be comparable in magnitude to the experimental error associated with heat capacity measurements, so it was not possible to obtain any meaningful correlations.     

Heat capacities and thermodynamic properties of 2-benzoylpyridine (C12H9NO)

The heat capacities of 2-benzoylpyridine were measured with an automated adiabatic calorimeter over the temperature range from 80 to 340 K. The melting point, molar enthalpy, Δ_fusH^m, and entropy, Δ_fusS^m, of fusion of this compound were determined to be 316.49±0.04 K, 20.91±0.03 kJ mol^–1 and 66.07±0.05 J mol^–1 K^–1, respectively. The purity of the compound was calculated to be 99.60 mol% by using the fractional melting technique. The thermodynamic functions (H_T–H_298.15) and (S_T–S_298.15) were calculated based on the heat capacity measurements in the temperature range of 80–340 K with an interval of 5 K. The thermal properties of the compound were further investigated by differential scanning calorimetry (DSC). From the DSC curve, the temperature corresponding to the maximum evaporation rate, the molar enthalpy and entropy of evaporation were determined to be 556.3±0.1 K, 51.3±0.2 kJ mol^–1 and 92.2±0.4 J K^–1 mol^–1, respectively, under the experimental conditions.