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1.
V. I. Pet’kov A. V. Markin N. N. Smirnova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(8):1266-1271
The temperature dependence of the heat capacity of LiZr2(PO4)3 crystal phosphate is studied in an adiabatic vacuum calorimeter in the temperature range of 6 to 358 K. A phase transition caused by the transition of a low-temperature (triclinic) modification to a high-temperature (rhombohedral) modification is observed in the temperature range of 290–338 K and its standard thermodynamic characteristics are estimated and analyzed. Standard thermodynamic functions are calculated from experimental data: heat capacity, enthalpy, entropy, and Gibbs function in the range of T → 0 to 358 K. Fractal dimensionality D is calculated from the data on low-temperature (20 K ≤ T ≤ 50 K) heat capacity and the topology of the phosphate’s structure is estimated. 相似文献
2.
The heat capacity of a purified sample of hexacosane, n-C26H54, has been measured from 13 to 358 K. The enthalpies of transition near 325.5 K and fusion at 329.25 K, and the purity of the sample have been determined; the accuracy of the results is influenced by the closeness in temperature, and overlap, of the crystal-to-crystal and crystal-to-liquid phase transitions. Thermodynamic properties have been calculated from the heat capacities and enthalpies. 相似文献
3.
We present in this paper a thermodynamic analysis of benzene properties under shock conditions as given by molecular dynamics (MD) simulations. Reactive MD simulations of benzene predict a decomposition threshold corresponding to the flection point on the experimental Hugoniot curve. A polymerlike carbonated structure is observed for pressures above this threshold, but the calculated Hugoniot curve is in disagreement with the experimental one at high pressure. On the contrary, a system consisting of a diamond cluster in hydrogen gas leads to a correct prediction of the pressure on the Hugoniot curves. The central question is then linked to the kinetics of the transition between the polymerlike structure and the diamond cluster. 相似文献
4.
采用平面波赝势密度泛函理论,利用第一性原理的方法研究了EuS的晶体结构、高压相变以及弹性性质.计算结果和实验值以及前人利用不同计算模型得到的理论值相吻合.研究了EuS的弹性常数、弹性模量和弹性的各向异性等力学性质随压力变化的趋势.同时研究了泊松比、德拜温度及纵波和横波的弹性波速随压力的变化趋势.基于德拜模型,进而研究了EuS在0-800K和0-60GPa下相变前后的热膨胀系数、热熔、Gruneisen参数等热力学性质. 相似文献
5.
用精密自动绝热量热计测定了4-羟甲基吡啶在79~380 K温区的摩尔热容. 实验结果表明, 该化合物在79~301 K温区无相变和热异常现象发生, 在301~331 K, 发生固-液相变, 其熔化温度、摩尔熔化焓及摩尔熔化熵分别确定为:325.12 K, 11.78 kJ•mol-1 和36.23 J•K-1•mol-1. 根据热力学函数关系式, 从热容值计算了4-羟甲基吡啶在80~380 K温区以标准状态(298.15 K)为基准的热力学函数值. 用热重法(TG)对该化合物的热稳定性作进一步考察, 从TG曲线上观察到该化合物在490 K有最大的蒸发失重速率. 相似文献
6.
Densities, heat capacities, enthalpies of dilution, osmotic coefficients and conductivities are reported for dodecylamine hydrochloride, dodecyldimethylammonium and dodecyltrimethylammonium chloride in water over a wide range of concentration. The last two properties were also measured for dodecyltrimethylammonium bromide. From the thermodynamic data partial molar volumes, heat capacities and relative enthalpies and nonideal free energies and entropies were derived as a function of the surfactant concentration. The cmc's and degree of counterion dissociation were also calculated from the transport properties. It is shown that the trends of volumes, enthalpies, free energies and entropies are quite regular whereas heat capacities present maxima and minima at concentrations which depend on the nature of surfactants. Corresponding changes were observed in the osmotic coefficients and specific conductivities. The thermodynamic functions of micellization were evaluated on the basis of the pseudo-phase transition model. Finally, the effects of the introduction of methyl groups in the hydrophilic moiety of the surfactant and of the nature of the counterion on the thermodynamic properties of monomers and micelles are examined. 相似文献
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8.
Monolayers of amphiphilic melamine derivatives are good candidates for the formation of supramolecular structures by hydrogen-bonding of nonsurface active species dissolved in the aqueous subphase by molecular recognition. In the present work, the thermodynamic and structural properties of the Langmuir monolayers of a homologous series of a selected amphiphilic melamine-type are characterized. Good candidates for such studies are the decyl, undecyl, and dodecyl homologues of the 2,4-di(n-alkylamino)-6-amino-1,3,5-triazine (2CnH(2n+1)-melamine) monolayers because of their two-phase coexistence region in the accessible temperature range. The characterization of the structural and phase behavior is performed by a combination of surface pressure studies with Brewster angle microscopy (BAM) imaging and Grazing incidence X-ray diffraction (GIXD) measurements. A comprehensive thermodynamic analysis provides good agreement between the experimental surface pressure - area (Pi-A) isotherms and the theoretical curves that were calculated on the basis of equations of state for a large region of monolayer stages developed by us in J. Phys. Chem. 1999, 103, 145. Theoretical curves calculated by application of equations of state only for the fluid monolayer state proposed recently by Rusanov (J. Chem Phys. 2004, 120, 10736) are in good agreement with the experiments in a limited temperature range. A rigorous equation is derived and applied to the experimental results for the calculation of the enthalpy of two-dimensional phase transition. The combination of BAM and GIXD illustrates that the microscopic long range ordering of the condensed monolayer phases is related to the lattice structure of the condensed monolayer. 相似文献
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10.
卤代硅烯异构化为卤代甲硅烷基硅烯的热力学与动力学分析 总被引:1,自引:0,他引:1
利用密度泛函理论(DFT) 中的B3LYP方法,全参数优化了卤代硅烯HXSi=SiXH(X=F、Cl、Br、I)异构化反应的反应物、产物及过渡态的几何构型,计算出了它们的振动频率、零点振动能(ZPVE)和总能量,并对它们进行了振动分析,以确定过渡态的真实性。又计算了反应的热力学函数变化,平衡常数及速率常数,比较了不同卤素对反应的影响。热力学与动力学计算结果表明,该异构化反应过程是一个放热的、且在低温下可自发进行的反应,但对于溴代硅烯和碘代硅烯而言,当温度达到1000 K时,反应开始转化为非自发反应。 相似文献
11.
S. S. Batsanov 《Russian Chemical Bulletin》1989,38(10):2159-2160
The Mulliken method was used to evaluate the energies of bonds of zerovalent transition metal atoms with ligands, and the strengths of these bonds were found relative to the normal covalent bonds of the same elements. The corresponding atomic radii were calculated and found to be in good accord with experiment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2347–2348, October, 1989. 相似文献
12.
H. Yurtseven E. Kilit Dogan 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(6):1208-1212
Thermodynamic properties of the cholesteryl myristate (CM) and its binary mixture CM/PCPB (p-pentylphenyl-2-chloro-4(p-pentylbenzoyl)-benzoate) are studied at the concentrations of xPCPB = 0.052 and 0.219 as a function of temperature near the cholosteric/smectic A transition. By analyzing the observed molar volume from the literature, the temperature dependences of the thermal expansion, isothermal compressibility and the difference in the specific heat are calculated and, the Pippard relations are established for those compounds close to the cholesteric/smectic A transition. Predictions of the thermodynamic quantities and the Pippard relations can be examined by the experimental measurements of the CM and its binary mixture of CM/PCPB close to the cholesteric/smectic A transition. 相似文献
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14.
S. S. Sologubov A. V. Markin N. N. Smirnova N. A. Novozhilova E. A. Tatarinova A. M. Muzafarov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2018,92(2):235-243
The heat capacity of a first-generation carbosilane dendrimer with terminal phenylethyl groups as a function of temperature in the range from 6 to 520 K is studied for the first time via precision adiabatic vacuum calorimetry and differential scanning calorimetry. Physical transformations, such as low-temperature structural anomaly and glass transition are detected in the above-mentioned range of temperatures, and their standard thermodynamic characteristics are determined and analyzed. The standard thermodynamic functions of the studied dendrimer in the range of T → 0 to 520 K are calculated from the experimental data, as is the standard entropy in the devitrified state at T = 298.15 K. The standard thermodynamic characteristics of the carbosilane dendrimers studied in this work and earlier are compared. 相似文献
15.
The thermodynamic characteristics of reactions resulting in the conversion of the antiaromatic three-membered aza heterocycle 1H-azirine into isomeric 2H-azirine have been calculated by the SCF-MO-LCAO method and perturbation theory. The proton affinity has been investigated, and it has been shown that protonation occurs at a carbon atom with the subsequent transition to 2H-azirine protonated at the nitrogen atom.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 481–486, Jnly–August, 1989. 相似文献
16.
The molar heat capacities of the binary mixture
composed of water and n-butanol were measured with an adiabatic calorimeter
in the temperature range 78–320 K. The functions of the heat capacity
with respect to thermodynamic temperature were established. A glass transition,
solid–solid phase transition and solid–liquid phase transition
were observed. The corresponding enthalpy and entropy of the solid–liquid
phase transition were calculated, respectively. The thermodynamic functions
relative to a temperature of 298.15 K were derived based on the relationships
of the thermodynamic functions and the function of the measured heat capacity
with respect to temperature. 相似文献
17.
Theoretical Study on the Structures,Spectra and Thermodynamic Property of Herbicidal Monosulfuron 总被引:2,自引:0,他引:2
The structure optimization and frequency calculation have been carried out at the B3LYP/6-31G* level towards herbicidal monosulfuron using density functional theory.The computed results showed that the intramolecular hydrogen bond N-H…N can stabilize the molecule.IR spectra,Raman spectra and thermodynamic properties under different temperatures were also obtained.The first vertical excited state electronic transition energy was calculated by time-dependent density function theory,and absorption wavelength of the lowest energy excitation was obtained at 339.59 nm,belonging to the near UV.These results provided the basis for studies on compound's structure-activity relationship. 相似文献
18.
M. S. Kozlova A. V. Markin V. N. Larina I. A. Letyanina 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(2):207-212
The temperature dependence of the heat capacity of crystal ferrocene dicarboxylic acid is studied in a precision adiabatic vacuum calorimeter in the range of 8 to 350 K. Its standard thermodynamic functions are calculated in the range of T → 0 to 350 K. The thermal and physical heat properties of ferrocene dicarboxylic acid are studied on a differential scanning calorimeter in the range of 260 to 573 K. The enthalpy of combustion for the investigated compound is measured in an isoperibol calorimeter. The standard thermodynamic functions of the formation of ferrocene dicarboxylic acid in the crystal state at 298.15 K are calculated. 相似文献
19.
Alexander Ya. Potemkin Vladimir B. Koltsov Maria G. Vahrameeva 《Monatshefte für Chemie / Chemical Monthly》2005,31(9):1877-1883
The main reason of the degradation of silicon monocrystals at heating is a structural transformation connected with a partial
transition of the diamond-like structure into the structure of white tin. The reason for this transformation being observed
under high pressures is the appearance of stress zones at the boundaries of variously oriented crystal microvolumes due to
heat expansion anisotropy. The high stress concentration in the microvolumes provides sufficient pressure for the indicated
phase transformation which results in the observed degradation of the electrophysical properties of silicon. The prevention
of the structural transformation is considered to be possible by doping of Si by transition or rare-earth metals which increases
the interatomic energy and decreases the thermal expansion coefficient. The choice of the doping additions is based on the
bonding energy and the charge density calculated for a system of non-polarised ionic radii. The technology to increase the
thermal stability of silicon has been patented#. 相似文献
20.
《Physics and Chemistry of Liquids》2012,50(1):1-16
Abstract We have investigated a number of structural, thermodynamic and atomic transport properties of various liquid noble and transition metals. The underlying theory combines a simple form of the N-body potential and the thermodynamically self-consistent variational modified hypernetted chain (VMHNC) theory of liquid. The static structure factors calculated by using the VMHNC resemble, as expected, the hard sphere (HS) values. Consequently the HS model is used to calculate thermodynamic properties, viz. the specific heat, entropy, isothermal compressibility and the shear viscosity of liquid Ni, Cu, Ag, and Au. The results are in reasonable accord with the experimental values. 相似文献