首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The temperature dependence of heat capacity of C70 fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic characteristics were determined. From the experimental data obtained, the thermodynamic functionsH o (T)-H o(0),S o(T),G o(T)-H o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δf S o, Δf G o, and logK f o for the formation of C70 from graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998.  相似文献   

2.
The heat capacity of paramagnetic (2,2′-dipyridyl)bis(4-chloro-3,6-di-tert-butyl-o-benzosemi-quinone)cobalt was studied over the temperature range 8–390 K by precision adiabatic vacuum and high-accuracy dynamic calorimetry. The physical transformation observed at 309–388 K was caused by the transition of the semiquinone-catecholate to bis-semiquinone form of the complex. Above 388 K, thermal destruction was superimposed on the physical transition. The experimental data were used to calculate the standard thermodynamic functions C p o (T), H o(T)−H o(0), S o(T), and G o(T)−H o(0) at temperatures from T → 0 to 300 K. An analysis of the low-temperature heat capacity of the complex in terms of the Debye theory of the heat capacity of solids and its multifractal generalization led us to conclude that the complex had a predominantly chain structure.  相似文献   

3.
The temperature dependence of the heat capacity C p o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C p o(T), H o(T)-H o(0), S o(T)-S o(0), and G o(T)-H o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δc H o, and the thermodynamic characteristics of formation Δf H o, Δf S o, and Δf G o at 298.15 K and p = 0.1 MPa.  相似文献   

4.
The temperature dependence of heat capacity C p o = f(T) of fullerene derivative (t-Bu)12C60 has been measured by a adiabatic vacuum calorimeter over the temperature range T = 6–350 K and by a differential scanning calorimeter over the temperature range T = 330–420 K for the first time. The low-temperature (T ≤ 50 K) dependence of the heat capacity was analyzed based on Debye’s the heat capacity theory of solids and its fractal variant. As a consequence, the conclusion about structure heterodynamicity is given. The experimental results have been used to calculate the standard thermodynamic functions C p o (T), H o(T)−H o(0), S o(T) and G o(T) − H o(0) over the range from T → 0 to 420 K. The standard entropy of formation at 298.15 K of fullerene derivative under study was calculated. The temperature of decomposition onset of derivative was determined by differential scanning calorimetery and thermogravimetric analysis. The standard thermodynamic characteristics of (t-Bu)12C60 and C60 fullerite were compared.  相似文献   

5.
The temperature dependence of the heat capacity C p o = f(T) of crystalline calcium-zirconium phosphate was studied over the temperature range 7–650 K by precision adiabatic vacuum and dynamic scanning calorimetry. The experimental data were used to calculate the standard thermodynamic functions C p o (T), H o(T) ? H o(0), S o(T), and G o(T) ? H o(0) at temperatures from T → 0 to 650 K and the standard entropy of formation of Ca0.5Zr2(PO4)3 at T = 298.15 K. The data on low-temperature (30 K ≤ T ≤ 50 K) heat capacity were used to calculate fractal dimension D. Conclusions about the character of the topology of the structure of the phosphate were drawn.  相似文献   

6.
Temperature dependences of the heat capacities of disordered graphite-like nanostructures prepared by the thermobaric treatment of fullerite C60 (p = 2 and 8 GPa, T = 1373 K) were measured in the temperature ranges from 7 to 360 K in an adiabatic vacuum calorimeter and from 330 to 650 K in a differential scanning calorimeter. At T < 50 K, the dependences obtained were analyzed using the Debye theory of the heat capacity of solids and its multifractal version. The fractal dimensions D were determined and some conclusions on the heterodynamic character of the structures studied were made. The thermodynamic functions C p o T), H o(T) − H o(0), S o(T) − S o(0), and G o(T) − H o(0) were calculated in the temperature range from T → 0 to 610 (650) K. The thermodynamic properties of the graphite-like nanostructures studied and some carbon allotropes were compared. The standard entropies of formation Δf S o of the graphite nanostructures studied and diamond were calculated along with the standard entropies of the reactions of their synthesis from the face-centered cubic phase of fullerite C60 and their interconversions at T = 298.15 K. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1940–1945, September, 2008.  相似文献   

7.
The temperature dependence of the molar heat capacity (C0 p) of hydrofullerene C60H36 between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. The experimental data were used for the calculation of the thermodynamic functions of the compound in the range 0 to340 K. It was found that at T=298.15 K and p=101.325 kPa C0 p (298.15)=690.0 J K−1 mol−1,Ho(298.15)−Ho(0)= 84.94 kJ mol−1,So(298.15)=506.8 J K−1 mol−1, Go(298.15)−Ho(0)= −66.17 kJ mol−1. The standard entropy of formation of hydrofullerene C60H36 and the entropy of reaction of its formation by hydrogenation of fullerene C60 with hydrogen were estimated and at T=298.15 K they were ΔfSo= −2188.4 J K−1 mol−1 and ΔrSo= −2270.5 J K−1mol−1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

8.
The heat capacity and the enthalpy increments of strontium niobate Sr2Nb2O7 and calcium niobate Ca2Nb2O7 were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (720–1370 K). Temperature dependencies of the molar heat capacity in the form Cpm = 248.0 + 0.04350T − 3.948 × 106/T2 J K−1 mol−1 for Sr2Nb2O7 and Cpm = 257.2 + 0.03621T − 4.434 × 106/T2 J K−1 mol−1 for Ca2Nb2O7 were derived by the least-square method from the experimental data. The molar entropies at 298.15 K, Sm°(298.15 K) = 238.5 ± 1.3 J K−1 mol−1 for Sr2Nb2O7 and Sm°(298.15 K) = 212.4 ± 1.2 J K−1 mol−1 for Ca2Nb2O7, were evaluated from the low-temperature heat capacity measurements.  相似文献   

9.
10.
The temperature dependence of the heat capacity of star-shaped fullerene-containing poly-N-vinylpyrrolidone was studied over the temperature range 6–390 K by precision adiabatic vacuum and dynamic scanning calorimetry. The temperature intervals and thermodynamic characteristics of phase transitions were determined. The low-temperature dependence of the heat capacity of the substance was analyzed according to the Debye theory of the heat capacity of solids and its multifractal generalization. The data obtained were used to calculate the standard thermodynamic functions C p o (T),H o(T)-H o(0), S o(T), and G o(T)-H o(0) of fullerene-containing poly-N-vinylpyrrolidone from T → 0 to 390 K. The standard entropy of formation of the polymer from simple substances and the entropy of its synthesis from poly-N-vinylpyrrolidone and fullerite C60 at 298.15 K were calculated. The thermodynamic characteristics of fullerene-containing poly-N-vinylpyrrolidone are compared with those of the polymer-analogue without C60.  相似文献   

11.
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), Δf H o(298.15) = −112.69 ± 0.32 kJ/mol, Δf G o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)2 (amorph.) with respect to PdO(cr.) was estimated.  相似文献   

12.
The heat capacity of MnAs0.88P0.12 has been measured by adiabatic shield calorimetry from 10 to 500 K. It is shown that very small energy changes are connected with two magnetic order-order transitions, indicating that these can be regarded as mainly “noncoupled” magnetic transitions. At higher temperatures contributions to the excess heat capacity arises from a magnetic order-disorder transition, a conversion from low- to high-spin state for manganese, and a MnP- to NiAs-type structural transition. The observed heat capacity is resolved into contributions from the different physical phenomena, and the character of the transitions is discussed. In particular it is substantiated that the dilational contribution, which includes magnetoelastic and magnetovolume terms as well as normal anharmonicity terms, plays a major role in MnAs0.88P0.12. The entropy of the magnetic order-disorder transition is smaller than should be expected from a complete randomization of the spins, assuming a purely magnetic transition. Thermodynamic functions have been evaluated and the respective values of Cp, {SOm(T) - SOm(0)}, and -{GOm(T) - HOm(0)}/T at 298.15 K are 68.74, 72.09, and 32.30 J K−1 mole−1, and at 500 K 56.05, 108.12, and 56.64 J K−1 mole−1.  相似文献   

13.
The temperature dependence of the heat capacity of carbosilane dendrimer of the seventh generation of series 3 × 3 with phenylic substituent on the initial branching center and terminal butyl groups was studied by the methods of precision adiabatic vacuum calorimetry and differential scanning calorimetry over the temperature range T = 7–580 K for the first time. Physical transformations in the above temperature range were detected and their standard thermodynamic characteristics estimated and analyzed. The experimental results were used to calculate standard thermodynamic functions C p (T), H (T)-H (0), S (T)-S (0), and G (T)-H (0) (0) over the range T → 0–580 K and standard entropy of formation of dendrimer at T = 298.15 K. The thermodynamic properties of carbosilane dendrimers of the seventh generation of series 4 × 3 with terminal butyl groups and the samples studied in this work were compared.  相似文献   

14.
The temperature dependences of the heat capacity (C p°) of carbynoid structures prepared by alkaline dehydrochlorination of poly(vinylidene chloride) and 1,1,2- and 1,2,3-polytrichlorobutadienes were studied by adiabatic vacuum calorimetry between 5 and 340 K with an accuracy of 0.2%. The low-temperature relaxation transitions and abnormal patterns of the C p° vs. T dependences were identified and characterized. The experimental results were used to calculate the thermodynamic functions C p°(T), H°(T) – H°(0), S°(T) – S°(0), and G°(T) – H°(0) for 0—340 K. These data were compared with the corresponding data for carbyne produced by oxidative dehydropolycondensation of acetylene, which is a mixture of amorphous - and -forms with a minor impurity of crystals of both forms.  相似文献   

15.
The thermodynamic properties of carbosilane dendrimer of second generation with terminal methoxyundecylene groups were studied between 6 and 340 K by adiabatic vacuum calorimetry: the temperature dependence of the molar heat capacity Cp 0 was measured, the physical transformations were established and their thermodynamic characteristics were obtained. The experimental data were used to calculate the thermodynamic functions Cp 0 (T), H 0(T)-H 0(0), S0(T), G 0(T)-H 0(0) of the compound in the range 0 to 340 K. from the relation Cp 0 (T) the fractal dimension of the dendrimer was experimentally determined. The heat capacity of the dendrimer was compared with the corresponding additive values calculated from the properties of its constituents - a dendritic matrix (carbosilane dendrimer of second generation) and the corresponding amount of moles of methyl ester of 11-(tetramethyldisiloxy)undecanoic acid serving as terminal groups. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
The heat capacities Cpo of undercanolactone, tridecanolactone, and pentadecanolactone have been measured between 10 and 370 K in a vacuum adiabatic calorimetric cryostat within about 0.2 per cent. The temperatures and enthalpies of physical transitions have been also estimated. The enthalpies of combustion of the compounds have been measured in an isothermal calorimeter with an accuracy of 0.05 per cent. From the results the functions {H (T) ? H (0)}, So(T), and {Go(T) ? Ho(0)} have been calculated over the range 0 to 340 K, and the values of ΔHfo, ΔGfo and ΔSfo have been evaluated at T = 298.15 K.  相似文献   

17.
By adiabatic vacuum and dynamic calorimetry, heat capacity for poly[bis(trifluoroethoxy)phosphazene] has been determined over the 6–620 K range. Physical transformations of the polymer on its heating and cooling have been detected and characterized. Smoothed heat capacity C p0(T) and standard thermodynamic functions (H 0(T)-H 0(0), S 0(T) and G 0(T)-H 0(0)) of poly[bis(trifluoroethoxy)phosphazene] have been evaluated for the temperature range from T→0 to 560 K. The standard entropy of formation Δf S 0 at T=298.15 K has been also determined. Fractal dimensions D in the heat capacity function of the multifractal variant of Debye’s theory of heat capacity of solids characterizing the heterodynamics of the tested polymer have been determined.  相似文献   

18.
In the present research for the first time, the heat capacity C\textp ° C_{\text{p}}^{ \circ } of crystalline tetraphenylantimony acetophenoneoxymate Ph4SbONCPhMe has been measured using the methods of precision adiabatic vacuum calorimetry over the range from 6 to 350 K, the standard thermodynamic functions: heat capacity C\textp ° (T ) C_{\text{p}}^{ \circ } (T ) , enthalpy H°(T) − H°(0), entropy S°(T), and Gibbs function G°(T) − H°(0) have been calculated over the range from T → 0 K to 350 K. Low-temperature (20 K ≤ T ≤ 50 K) heat capacity data have shown a chain-layered structure topology of the compound under study. The energy of combustion of the compound has been determined in the isothermal combustion calorimeter with a stationary bomb. The standard thermodynamic functions of formation of crystalline Ph4SbONCPhMe at 298.15 K have been calculated. The differential scanning calorimetry and thermogravimetric analysis studies have shown the compound melts with decomposition and its melting temperature has been estimated. Thermodynamic properties of Ph4SbONCPhMe, Ph5Sb and Ph4SbONCPh2 have been compared.  相似文献   

19.
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   

20.
In the present work temperature dependence of heat capacity of rubidium niobium tungsten oxide has been measured first in the range from 7 to 395 K and then between 390 and 650 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity ^ (T), C_{\text{p}}^{\text{o}} (T), enthalpy H\texto (T) - H\texto (0) H^{\text{o}} ({\rm T}) - H^{\text{o}} (0) , entropy S\texto (T) - S\texto ( 0 ) S^{\text{o}} (T) - S^{\text{o}} \left( 0 \right) , and Gibbs function G\texto (T) - H\texto (0) G^{{^{\text{o}} }} ({\rm T}) - H^{{^{\text{o}} }} (0) , for the range from T→0 to 650 K. The high-temperature X-ray diffraction and the differential scanning calorimetry were used for the determination of temperature and decomposition products of RbNbWO6.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号