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1.
I. E. Paukov Yu. A. Kovalevskaya V. I. Ovcharenko G. V. Romanenko Ya. Z. Voloshin 《Journal of Structural Chemistry》2012,53(2):388-392
The temperature dependence of heat capacity of the polycrystalline sample of cobalt(II) clathrochelate in a range of 6–300 K is studied. Based on the smoothed dependence C p(T), the entropy and enthalpy values in a temperature range of 8–300 K and their standard values at 298.15 K are calculated. In the C p(T) curve in a range of 50–70 K, a process is recorded whose entropy and enthalpy are 1.2 J·(K·mol−1) and 68 J·mol−1 respectively. A comparison of the results with the data of a multitemperature X-ray diffraction study makes it possible to attribute this process to the structural phase transition. 相似文献
2.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2008,93(2):423-428
Heat capacity C
p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these measurements. At 298.15 K the values of heat capacity, C
p; entropy, S
m0(T)-S
m0(0); difference in the enthalpy, H
m0(T)-H
m0(0), are equal, respectively, to 144.6±0.3 J K−1 mol−1, 169.0±0.4 J K−1 mol−1 and 24960±50 J mol−1. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial
increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample. 相似文献
3.
B. V. Lebedev T. A. Bykova K. V. Kir'yanov I. I. Vointseva L. M. Gil'man 《Russian Chemical Bulletin》1996,45(10):2345-2349
Thermodynamic parameters of the interpolymer reaction between poly-1,1,2-trichlorobuta1,3-diene and poly(ethylene imine) giving a polymer-polymer compound (incorporating the starting components in a molar ratio of 1 : 2) have been determined by calorimetry. The enthalpy (H°m), entropy (S°m), and Gibbs function (G°m) for this reaction are negative over the whole temperature range studied. The enthalpy of the reaction in chloroform at 298.15 K is about two times smaller, due to the difference in the enthalpies of dissolution of the starting polymers and the enthalpy of swelling of the interpolymer in the same solvent. The glass transition temperature of the interpolymer lies between those of the starting polymers and coincides with the value calculated from the Fox equation. The heat capacity of the interpolymer is smaller than additive values calculated fromC
p
°
of the starting polymers. From the experimentally determinedC
p
°
for the polymers, the thermodynamic functionsC
p
°
(T),H°(T) – H°(O), andS°(T) were calculated for the 0–330 K temperature range, and their configurational entropiesS
c
°
were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2474–2478, October, 1996. 相似文献
4.
采用差示扫描量热法(DSC)测定山梨醇样品经历不同时间(ta)等温退火后, 以10 K·min-1速率进行升温时玻璃化转变温度(Tg)前后的比热容(Cp(T)). 将Gómez Ribelles (GR)提出的一种基于构型熵的现象学模型用于描述山梨醇玻璃的焓松弛行为, 考察GR模型能否适用于小分子玻璃体系. 结果表明, 单组GR模型参数拟合的曲线均能较好重现对应热历史条件下的山梨醇体系的实验所得Cp(T)曲线, 尽管并未找到不随热历史而变的一组参数作为材料常数, 但与其它现象学模型应用于小分子玻璃时, 其模型参数都随热历史变化而变化的特点相比, GR模型的某些参数基本保持不变. 且在较长退火时间下拟合得到的模型参数普适性较好. 同经历连续降温的山梨醇相比, 等温退火过程得到的松弛极限态参数(δ)的平均值与Tg处比热容增量(ΔCp(Tg))的比值明显增大, 但仍小于聚合物的值, 表明GR模型提出的亚稳极限态对小分子玻璃的影响值得商榷. 相似文献
5.
I. E. Paukov Yulia A. Kovalevskaya Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2010,100(1):295-301
Heat capacity C
p(T) of the crystalline dl-cysteine was measured on heating the system from 6 to 309 K by adiabatic calorimetry; thermodynamic functions were calculated
based on these data smoothed in the temperature range 6–273.15 K. The values of heat capacity, entropy, and enthalpy at 273.15 K
were equal to 142.4, 153.3, and 213.80 J K−1 mol−1, respectively. At about 300 K, a heat capacity peak was observed, which was interpreted as an evidence of a first-order phase
transition. The enthalpy and the entropy of the transition are equal, respectively, to 2300 ± 50 and 7.6 ± 0.1 J K−1 mol−1. 相似文献
6.
Suk Fai Lau Hidematsu Suzuki Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》1984,22(3):379-405
Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10?3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds. 相似文献
7.
J. M. Meseguer Dueas A. Vidaurre Garayo F. Romero Colomer J. Ms Estells J. L. Gmez Ribelles M. Monlen Pradas 《Journal of Polymer Science.Polymer Physics》1997,35(14):2201-2217
The structural relaxation process in styrene-acrylonitrile copolymer has been characterized by means of differential scanning calorimetry (DSC) experiments. The results in the form of heat capacity, cp(T), curves are analyzed using a model for the evolution of the configurational entropy during the process recently proposed by the authors.11,12 The model simulation allows one to determine the enthalpy (or entropy) structural relaxation times and the β parameter of the Kohlrausch-Williams-Watts equation characterizing the width of the distribution of relaxation times. This material parameters are compared with their analogues determined from the dielectric and dynamic-mechanical relaxation processes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2201–2217, 1997 相似文献
8.
Igor E. Paukov Yulia A. Kovalevskaya Alexei E. Arzamastcev Natalia A. Pankrushina Elena V. Boldyreva 《Journal of Thermal Analysis and Calorimetry》2012,108(1):243-247
Heat capacity of methacetin (N-(4-methoxyphenyl)-acetamide) has been measured in the temperature range 5.8–300 K. No anomalies in the C
p(T) dependence were observed. Thermodynamic functions were calculated. At 298.15 K, the values of entropy and enthalpy are equal
to 243.1 J K−1 mol−1 and 36360 J mol−1, respectively. The heat capacity of methacetin in the temperature range 6–10 K is well fitted by Debye equation C
p = AT
3. The thermodynamic data obtained for methacetin are compared with those for the monoclinic and orthorhombic polymorphs of
paracetamol. 相似文献
9.
M. Pyda K. Van Durme B. Wunderlich B. Van Mele 《Journal of Polymer Science.Polymer Physics》2005,43(16):2141-2153
The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ1 = 647 K, Θ2 = Θ3 = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by Cp(liquid) = 72.36 + 0.136 T in J K?1 mol?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing Cp of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005 相似文献
10.
V. G. Bessergenev Yu. A. Kovalevskaya L. G. Lavrenova I. E. Paukov 《Journal of Thermal Analysis and Calorimetry》2004,75(1):331-336
Low-temperature heat capacity of the coordination compound of nickel(II) nitrate with 4-amine-1,2,4-triazole was measured in the temperature range from 11 to 317 K using a computerized vacuum adiabatic calorimeter. The thermodynamic functions have been derived from the smoothed experimental data over the whole temperature interval covered and at standard conditions. At 298.15 K, the heat capacity is 574.7±1.2 J K-1 mol-1, the entropy is 599.2±1.2 J K-1 mol-1, the enthalpy is 91070±200 J mol-1, and the reduced Gibbs energy is 293.7±1.2 J K-1 mol-1. The results on Cp(T) were compared with those for Cu(NH2trz)3(NO3)2·0.5H2O. It was revealed that the slope of the curve dCp/dT (T) changes essentially for both compounds at 110-120 K. It implies that additional degrees of freedom appear in the heat capacity at these temperatures.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
11.
J. Leitner M. Hampl K. Růžička M. Straka D. Sedmidubský P. Svoboda 《Journal of Thermal Analysis and Calorimetry》2008,91(3):985-990
The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature
dependence of the molar heat capacity in the form C
pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T
2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy
at 298.15 K S
m0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δf
H
0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional
theory. 相似文献
12.
B. Tong Z. C. Tan J. N. Zhang S. X. Wang 《Journal of Thermal Analysis and Calorimetry》2009,95(2):469-475
The low-temperature heat capacity C
p,m of erythritol (C4H10O4, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic
calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C
p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol−1 and 97.17±0.49 J K−1 mol−1, respectively. 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 standard
molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δc
H
m0(C4H10O4, cr)= −2102.90±1.56 kJ mol−1 and Δf
H
m0(C4H10O4, cr)= − 900.29±0.84 kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement
with those obtained from heat capacity measurements. 相似文献
13.
I. E. Paukov Yulia A. Kovalevskaya Irina A. Kiseleva Tatiana N. Shuriga 《Journal of Thermal Analysis and Calorimetry》2010,99(2):709-712
Low-temperature heat capacity of natural zinnwaldite was measured at temperatures from 6 to 303 K in a vacuum adiabatic calorimeter.
An anomalous behavior of heat capacity function C
p(T) has been revealed at very low temperatures, where this function does not tend to zero. Thermodynamic functions of zinnwaldite
have been calculated from the experimental data. At 298.15 K, heat capacity C
p(T) = 339.8 J K−1mol−1, calorimetric entropy S
o(Т) – S
o(6.08) = 329.1 J K−1 mol−1, and enthalpy Н
o(Т) − Н
o(6.08) = 54,000 J mol−1. Heat capacity and thermodynamic functions at 298.15 K for zinnwaldite having theoretical composition were estimated using
additive method of calculation. 相似文献
14.
M. R. Bissengaliyeva D. B. Gogol’ N. S. Bekturganov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(2):157-163
The heat capacity of natural mineral, pyromorphite Pb5(PO4)3Cl, was measured over the temperature range 4.2–320 K using low-temperature adiabatic calorimetry. An anomalous temperature
dependence of heat capacity with a maximum at 273.24 K was observed between 250 and 290 K. The heat capacity, entropy, enthalpy,
and reduced thermodynamic potential of pyromorphite were calculated and tabulated over the temperature range 5–320 K. The
standard thermodynamic functions of the mineral are C
p298.15o = 414.98 ± 0.44 J/(mol K), S
298.15o = 585.31 ± 0.99 J/(mol K), H
298.15o − H
0o = 80.90 ± 0.08 kJ/mol, and Φ298.15o = 313.97 ± 0.84 J/(mol K). 相似文献
15.
A. V. Markin I. A. Letyanina N. N. Smirnova V. V. Sharutin O. V. Molokova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(8):1315-1321
The temperature dependence of heat capacity C
p
° = f(T) of triphenylantimony bis(acetophenoneoximate) Ph3Sb(ONCPhMe)2 was measured for the first time in an adiabatic vacuum calorimeter in the range of 6.5–370 K and a differential scanning
calorimeter in the range of 350–463 K. The temperature, enthalpy, and entropy of fusion were determined. Treatment of low-temperature
(20 K ≤ T ≤ 50 K) heat capacity was performed on the basis of Debye’s theory of the heat capacity of solids and its multifractal model
and, as a consequence, a conclusion was drawn on the type of structure topology. Standard thermodynamic functions C
p
°(T), H°(T) — H°(0), S°(T), and G°(T) — H°(0) were calculated according to the experimental data obtained for the compound mentioned in the crystalline and liquid
states for the range of T → 0–460 K. The standard entropy of the formation of crystalline Ph3Sb(ONCPhMe)2 was determined at T = 298.15 K. 相似文献
16.
Yuri I. Aristov Yulia A. Kovalevskaya Michael M. Tokarev Igor E. Paukov 《Journal of Thermal Analysis and Calorimetry》2011,103(2):773-778
Heat capacity was measured for two composite systems based on silica gel KSK and calcium chloride confined to its pores. One
corresponds to an anhydrous state, while another contains water bound with the salt to give the composition of CaCl2·2.04H2O. The measurements were performed in the temperature range of 6–300 K with a vacuum adiabatic calorimeter. The smoothed experimental
curves C
p
(T) were used for calculating the calorimetric entropy and the enthalpy increment for both studied systems as well as the effective
heat capacity associated only with water in the hydrated composite. The heat capacities C
p
(298.15 K) of both composites were compared with those calculated as a linear addition of the heat capacities of silica gel
and bulk calcium chloride (or its dihydrate) with appropriate weight coefficients. 相似文献
17.
Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec
p
E
values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc
p
E
are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C16 isomers. The excess enthalpy and entropy vary with the C16 isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C16 isomers. 相似文献
18.
Yuhta Matsunaga Hitoshi Kawaji Tooru Atake Hiroki Takahashi Takuya Hashimoto 《Thermochimica Acta》2008,474(1-2):57-61
The heat capacity, Cp, of the La1−xSrxCrO3 system and its temperature dependence have been measured by a thermal relaxation technique. Both structural and magnetic phase transitions were detected at temperatures that can be surmised from the phase diagram proposed in previous studies. The observed variation in enthalpy after the first-order structural phase transition, ΔH, showed agreement with those measured by differential scanning calorimetry (DSC). A decrease in the variation in Cp in the second-order magnetic phase transition, ΔCp, with an increase in Sr content was detected, which can be attributed to a decrease in electronic spin configuration entropy with an increase in Sr content. In the dependence of ΔCp on Sr content, a bending point was also observed at x 0.12, at which the crystal system varies from an orthorhombic-distorted perovskite structure to a rhombohedral-distorted perovskite structure. 相似文献
19.
M. Hampl J. Leitner K. Růžička M. Straka P. Svoboda 《Journal of Thermal Analysis and Calorimetry》2007,87(2):553-556
The heat capacity and the heat content of
bismuth niobate BiNb5O14 were
measured by the relaxation time method, DSC and drop method, respectively.
The temperature dependence of heat capacity in the form C
pm=455.84+0.06016T–7.7342·106/T
2 (J K–1
mol–1) was derived by the least squares method
from the experimental data. Furthermore, the standard molar entropy at 298.15
K S
m=397.17 J K–1
mol–1 was derived from the low temperature
heat capacity measurement. 相似文献
20.
V. V. Novikov D. V. Avdashchenko A. V. Matovnikov N. V. Moiseev T. Tanaka 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(11):2054-2056
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. 相似文献