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191.
Kristina I. Lilova Alexandra Navrotsky Brent C. Melot Ram Seshadri 《Journal of solid state chemistry》2010,183(6):1266-1271
CoAl2O4, CoGa2O4, and their solid solution Co(GazAl1−z)2O4 have been studied using high temperature oxide melt solution calorimetry in molten 2PbO·B2O3 at 973 K. There is an approximately linear correlation between lattice parameters, enthalpy of formation from oxides, and the Ga content. The experimental enthalpy of mixing is zero within experimental error. The cation distribution parameters are calculated using the O’Neill and Navrotsky thermodynamic model. The enthalpies of mixing calculated from these parameters are small and consistent with the calorimetric data. The entropies of mixing are calculated from site occupancies and compared to those for a random mixture of Ga and Al ions on octahedral site with all Co tetrahedral and for a completely random mixture of all cations on both sites. Despite a zero heat of mixing, the solid solution is not ideal in that activities do not obey Raoult's Law because of the more complex entropy of mixing. 相似文献
192.
提出了“有机同秩列”、“有机同秩物”、“有机同秩异构体”等概念体系,并以单取代烷烃同秩物Xi-(CH2)/-H(Xi=F、CI、Br、I、NO2、CN、NC、OH、NH2、SH、COOH、CHO)为例,对其气相标准摩尔生成焓(△rHm)、电离能(IP)的结构-性能关系进行了研究,分别对j=2~8的七组同秩物的生成焓及j=2~4的三组同秩物的电离能建立了数学模型:△rHm(j)=a+b△iHm(1)+cPEI(R)和IP(j):a+bIP(1)+bPEI(R),得到了有意义的结果.研究表明,从有机同秩物的角度可以建立一种新的分子结构.性能相关方法,它与有机同系物方法相互独立又互为补充.本文提出的概念体系不仅增加了新的有机化学理论和概念,还为有机物结构-性能变化规律的研究开辟了新视角. 相似文献
193.
The room temperature Mössbauer spectra of 57Fe were measured for iron-based solid solutions Fe1−xCrx with x in the range 0.01≤x≤0.05. The obtained data were analysed in terms of the binding energy Eb between two chromium atoms in the studied materials using the extended Hrynkiewicz–Królas idea. It was found that the energy is positive or Cr atoms interact repulsively. The extrapolated value of Eb for x=0 was used for computation of an enthalpy of solution of Cr in Fe. The result was compared with corresponding data derived from calorimetric measurements and resulting from the cellular atomic model of alloys by Miedema as well as with the proper values given in the literature which were calculated on the basis of density functional theory (DFT). The comparison shows that our findings are in good agreement with the recent DFT computations for ferromagnetic Fe–Cr alloys. 相似文献
194.
Al-Cu-Ag eutectic alloy was directionally solidified upwards with different growth rates (1.83-498.25 μm/s) at a constant temperature gradient (8.79 K/mm) and with different temperature gradients (3.99-8.79 K/mm) at a constant growth rate (8.30 μm/s) by using a Bridgman type directional solidification apparatus. The dependence of microhardness (HV) on the growth rate (V), temperature gradient (G) and microstructure parameter (λ) were found to be HV = k1 V0.10, HV = k2 G0.13 and HV = k3 λ−0.22, respectively. The electrical resistivity of the Al-Cu-Ag eutectic cast alloy increases linearly with the temperature in the range of 300-780 K. The enthalpy of fusion and specific heat change during melting for same alloy were also determined to be 223.8 J/g, and 0.433 J/g K, respectively by a differential scanning calorimeter from heating curve during the transformation from eutectic solid to eutectic liquid. 相似文献
195.
Jacek Smolka Zbigniew Bulinski Adam Fic Andrzej J. Nowak Krzysztof Banasiak Armin Hafner 《Applied Mathematical Modelling》2013
A mathematical model of the compressible transonic single- and two-phase flow of a real fluid is discussed in this paper. The model was originally developed to simulate a refrigerant flow through a heat pump ejector. In the proposed approach, a temperature-based energy equation is replaced with an enthalpy-based formulation, in which the specific enthalpy, instead of the temperature, is an independent variable. A thermodynamic and mechanical equilibrium between gaseous and liquid phases is assumed for the two-phase flow. Consequently, real fluid properties, such as the density, the dynamic viscosity and the diffusion coefficient, are defined as functions of the pressure and the specific enthalpy. The energy equation formulation is implemented in commercial CFD software using subroutines that were developed in-house. The formulations was tested extensively for a single-phase flow of the R141b refrigerant, and for a two-phase flow of the R744 fluid (carbon dioxide) that occurred in a 3-D model of the ejector motive nozzle. In the model validation procedure, a satisfactory comparison between the experimental and computational results of the primary and secondary mass flow rates was obtained for both flow regimes. In addition, in the case of the R744 flow, the pressure distribution along the centre line of the ejector was accurately predicted as well. Furthermore, the results also shows that geometry modelling and measurement accuracy play an important in the final numerical results. As a result of the reasonable computational times, this method can be effectively used for the design of ejectors and also in geometric optimisation computations. 相似文献
196.
Mahmoud Jourabian Mousa Farhadi Ahmad Ali Rabienataj Darzi 《Applied Mathematical Modelling》2013,37(20-21):8813-8825
Heat transfer enhancement of water-(Ice) as a phase change material (PCM) through dispersion of Cu-nanoparticles is the centerpiece of this research study. The nanoparticle-enhanced phase change material (NEPCM) demonstrates increased thermal conductivity and decreased melting time in comparison with the conventional PCM. An enthalpy-based lattice Boltzmann method (LBM) with a double distribution function (DDF) model is implemented to trace phase change front in a cylindrical-horizontal annul. The subcooling case is neglected and Prandtl number, Stefan number and Rayleigh number are fixed to 6.2, 1 and 105, respectively. In addition, the effects of varying the position of heated cylinder and nanoparticle volume fractions on the transient isotherms and liquid fractions are discussed. 相似文献
197.
Melerin Madekufamba 《The Journal of chemical thermodynamics》2006,38(12):1563-1567
Enthalpies of solution of TiCl4(l) in aqueous perchloric acid have been measured in an isothermal calorimeter at T = 298.15 K at ionic strengths of (1.964, 3.002, and 4.062) mol · kg−1. These results were extrapolated to zero ionic strength using an extended Debye-Hückel equation, to yield the standard enthalpy of solution ; from which the standard partial molar enthalpy of formation of the titanyl ion was derived: . 相似文献
198.
Stefan Perişanu Iulia Contineanu Mircea D. Banciu Hui Zhao Nigam Rath James Chickos 《Structural chemistry》2006,17(6):639-648
Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol−1, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol−1) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol−1) adjusted from DSC measurements at the melting temperature (1, (T
fus, 357.7 K, 16.9 ± 1.3 kJ mol−1)); 2, (T
fus, 383.3 K, 10.9 ± 0.1) kJ mol−1) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol−1) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol−1) and 7-heptadecanone ((94.5 ± 1.8) kJ mol−1) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T
fus, 312.7 K, 18.4 ± 0.5) kJ mol−1) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound
1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone. 相似文献
199.
200.
Vladimir N. Emel’yanenko 《The Journal of chemical thermodynamics》2008,40(12):1661-1665
Molar enthalpies of sublimation of two crystal forms of caffeine were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. A large number of primary experimental results on the temperature dependences of vapour pressure and phase transitions have been collected from the literature and have been treated in a uniform manner in order to derive sublimation enthalpies of caffeine at T = 298.15 K. This collection together with the new experimental results reported here has helped to resolve contradictions in the available sublimation enthalpies data and to recommend a consistent and reliable set of sublimation and formation enthalpies for both crystal forms under study. Ab initio calculations of the gaseous molar enthalpy of formation of caffeine have been performed using the G3MP2 method and the results are in excellent agreement with the selected experimental data. 相似文献