Special problems are encountered in modeling the temperature dependence of the kinetics of heterogeneous, condensed phase systems. In the division of the model for the reaction rate into two parts, a)f(α) which is physical (translational) and b)k(T) which is chemical (vibrational), complications arise in defining the temperature dependence of part a) which may take various mathematical forms and then in coupling it with the Arrhenius temperature dependence of part b). The role off(α) in thermal analysis systems is discussed. The concept of rate-controlling step is applied to the simplification of the temperature dependent term. The significance of the compensation effect in these systems is described and an heuristic rationalization for it is suggested. Maximum practical temperature ranges for thermal analysis experiments and the effect of temperature measurement imprecision on obtaining meaningful Arrhenius parameters are discussed. The WLF and other equations used to describe the temperature dependence off(α) are not found to couple compatibly with the Arrhenius equation.
Authors:M. Aizenberg, E. Fedoseev, S. Travnikov, A. Davydov, and B. Myasoedov
The temperature dependence of the vapour pressure of californium-249 hexafluoroacetylacetonate adducts with tributylphosphate /TBP/, tributylphosphineoxide /TBPO/ and dipropylsulphoxide /DPSO/ is determined. The enthalpy and entropy sublimation of the compounds are calculated.
scope of design and optimise the equipment for alcoholic distillate beverages
production, a sufficient knowledge of physical properties and phase equilibria
is necessary. In this paper we present the temperature dependence of excess
molar volumes of the ternary system ethanol+water+1-propanol at the range
288.15–323.15 K and atmospheric pressure, due to the importance of the
1-propanol among the flavour compounds contained into this type of beverages.
Derived properties were computed due to its importance in the study of specific
Authors:E. Mascato, L. Mosteiro, M. Pineiro, B. de Cominges, M. Mato, and J. Legido
Excess molar volumes and excess isoentropic compressibilities of methyl tert-butylether (MTBE)+1-butanol at 288.15, 293.15, 298.15, 303.15 and 308.15 K and atmospheric pressure have been studied. In
order to analyse the temperature dependence of this mixture, isobaric expansibility a, (dVme dT)P,xand (dHme dP)T,x, were computed by analytical differentiation of the density and excess molar volume fitting equations. Cubic equation of
state (Soave-Redlich-Kwong) has been applied to excess molar volume correlation obtaining binary interaction parameters using
different mixing rules.
Several samples of Nb2O5-doped Bi2O3 and Y2O3-doped Bi2O3 were carefully prepared and sintered at 700° for 3 hours. Extensive measurements were carried out on these samples, including X-ray diffraction spectra, infrared absorption spectra and the temperature-dependence of the DC-electrical conductivity in the solid state. The results obtained were discussed, correlated and interpreted. Finally, the optimum compositions were established and recommended for doped-Bi2O3 in the electronics industry.
In order to reveal the reactivity of monosubstituted thiophenols, the hydrogen-isotope exchange reaction between T-labeled poly(vinyl alcohol) and each monosubstituted thiophenol (unlabeled) was studied in a liquid-solid system. Using both the data obtained and theA-McKay plot method, the reaction was analyzed, and the rate constant (k) for the monosubstituted thiophenol has been obtained. Consequently, it has been found that (1) the higher the temperature is, the larger is the reactivity of monosubstituted thiophenols, (2) the temperature dependence of the effect of the substituent (in a monosubstituted thiophenol) on the reactivity of the monosubstituted thiophenol is weak, (3) the reactivity of monosubstituted thiophenols follows the Hammett rule, (4) the reactivity of monosubstituted thiophenols can be enhanced with one of the electron-attractive substituents.
Stoichiometrically adjusted antimony triselenide and antimony tritelluride semiconductors were carefully prepared for the first time. Numerous measurements were carried out, involving X-ray diffraction analysis, true density, thermogravimetric analysis and the temperature-dependence of the magnetic susceptibility. The results obtained indicated that antimony triselenide and antimony tritelluride polycrystals possess mass susceptibilities of −0.361×10−6 and −0.386×10−6 C.G.S., respectively. The results are discussed on the basis of electronegativity difference, partial ionicity of the bond, and bond strength.
Among the abiotic stress factors influencing the growth and productivity of wheat varieties, extremely high temperatures have the most limiting effect. In an experiment set up in the gradient chamber of the Martonvásár phytotron to test the effect of various temperatures on four winter wheat varieties and one variety of spelt, substantial differences were observed in the heat stress tolerance of the varieties. There was a considerable reduction in the number of shoots and spikes as the result of heat stress, leading to a drastic loss of grain yield. It was clear from changes in the biomass and in the grain:straw ratio that extremely high temperatures led to a substantial reduction in the ratio of grain to straw in the varieties tested. In response to high temperature the wheat plants turned yellow earlier due to the rapid decomposition of the chlorophyll content. This resulted in a considerable shortening of the vegetation period and early ripening. Reductions in the parameters tested were observed at different temperature levels for each variety, indicating considerable differences in the ability of the varieties to adapt to abiotic stress factors.
Authors:E. Kuzmann, S. Nagy, É. Csikós, A. Vértes, and I. Halász
The total area of the57Fe Mössbauer spectra of the EuBa2 (Cu0.98119Sn0.0157Fe0.01)3O7- superconductor exhibited a highly usual anomalous temperature dependence, i.e. it increased monotonously with increasing temperature between 120 and 300 K. We found also anomalous changes in the57Fe Mössbauer parameters around Tc. These latter changes could be associated with phonon softening and low temperature phase transformation.
Authors:A. A. Abd El-Rahman, K. K. Tahoon, Abd El-Salam, M. Abousehly, Abd Elwahab, and A. El-Sharkawy
The specific heat (Cp), thermal conductivity (λ), thermal diffusivity (a), and electrical conductivity (σ) were measured for polycrystalline HgS and Sb2S3 in the temperature range 300–600 K. The measurements were performed with an experimental apparatus based on a socalled flash method. The results showed that the mechanism of heat transfer is mainly due to phonons, whereas the contribution of electrons and bipolars is very small indeed. The energy gap of the samples was also calculated.