It has been known from the very beginning of the thermal analysis that the transport processes can significantly influence the thermoanalytical results. In this paper, three characteristic examples are given to show that this problem is more complex and arises more frequently than it is generally believed. The studied reactions are the carbon monoxide evolution from calcium oxalate, the thermal degradation of polytetrafluoroethylene, and the thermal decomposition of azodicarbonamide. TG and DSC experiments were carried out with sample masses varying between 0.05 and 8 mg. The necessity of the development of new kinetic models is concluded.
Zusammenfassung Seit den Anfängen der Thermoanalyse ist bekannt, dass Transportprozesse die thermoanalytischen Ergebnisse weitgehend beeinflussen können. Es werden hier drei Beispiele beschrieben, die zeigen, dass dieses Problem weitauf komplizierter ist und häufiger auftritt als allgemein angenommen wird. Die untersuchten Reaktionen sind die Kohlenmonoxidabspaltung aus Calziumoxalat, die thermische Zersetzung von Polytetrafluoräthylen und der thermische Zerfall von Azodicarbonamid. Die TG- und DSC- Untersuchungen wurden mit Probenmassen zwischen 0.05 und 8 mg durchgeführt. Es wird auf die Notwendigkeit der Entwicklung neuer kinetischer Modelle geschlossen.
An implicit heating programme is suggested for minimization of the effect of the difference between the sample temperature and the programmed temperature in a thermoanalytical set-up.
Zusammenfassung Es wird ein implizites Aufheizprogramm beschrieben, das den Einfluss des Unterschiedes zwischen Probentemperatur und programmierter Temperatur für die Probe minimalisiert.
It is suggested that besides its traditional application to describe random nucleation, the first-order equation F1 can be used for the diffusion kinetics of gas-solid small particles reactions.
A new set of spectroscopic constants of the 16O3 molecule (ωi, xij, yijk, γDD, iX, βijX,…), which determine vibrational dependence of band centres and rotational parameters, is derived from recent accurate analysis of high-resolution experimental ro-vibrational spectra through the theoretical approach based on second-order perturbation expansions in normal coordinates accounting for Darling–Dennison resonance interactions. These values are used to update empirical values of anharmonic coefficients (kijl, kijlm) of the potential function expansion in normal coordinates. Quadratic frr, fr, frr′, f as well as cubic frst and quartic frstl force constants in internal (bond lengths, bond angle) coordinates are also derived. A detailed discussion is devoted to the accuracy of parameter determination for each of four steps of calculations. It is emphasised that the conventional method based on the inversion of formulae of the perturbation theory gives the largest uncertainties at the last step of calculations: the determination of the anharmonic force field in internal coordinates. 相似文献
A study was made of the change in the properties of tin-antimony and bismuthmolybdenum oxide catalysts during the partial reduction of their surfaces with propylene and a propylene-ammonia mixture. Different characteristics of the interaction of ammonia with the surface of the catalysts studied were established.
The molecular structures and electron affinities of the C6HCl5 and C6Cl6 molecules have been determined using seven pure Density Functional Theory (DFT) or hybrid Hartree–Fock/DFT methods. The EAs of ten kinds of monochlorobenzene, dichlorobenzene, trichlorobenzene and tetrachlorobenzene are also predicted. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. These methods have been carefully calibrated (Chem. Rev. 2002, 102, 231). The geometries are fully optimized with each DFT method independently. The equilibrium configuration of hexachlorobenzene is found to be planar with D6h symmetry. The pentachlorobenzene is planar with C2υ symmetry. Three different types of the neutral-anion energy separations reported in this work are the adiabatic Electron Affinity (EAad), the vertical Electron Affinity (EAvert), and the Vertical Detachment Energy (VDE). The most reliable adiabatic electron affinities of the chlorinated benzenes obtained at the BHLYP level of theory are −0.18 eV (C6H5Cl), 0.07 eV (1,2-C6H4Cl2), 0.07 eV (1,3-C6H4Cl2), 0.04 eV (1,4-C6H4Cl2), 0.29 eV (1,2,3-C6H3Cl3), 0.31 eV (1,2, 4-C6H3Cl3), 0.31 eV (1,3,5-C6H3Cl3), 0.51 eV (1,2,3,4-C6H2Cl4), 0.48 eV (1,2,4,5-C6H2Cl4), 0.50 eV (1,2,3,5-C6H2Cl4), 0.74 eV (C6HCl5) and 0.79 eV (C6Cl6), respectively. 相似文献
The IUPAC recommended factor 2 preceding rate coefficients in the radical termination kinetic equations is claimed to be incorrect and confusing. This recommendation can lead to incorrect analysis of experimental data, especially while applying kinetic Monte Carlo simulations. The statement is based on the derivation of the corresponding relationships.
The reaction of K[H6ReL2] with [RuHCl(CO)(PPh3)3−x {P(OPri}3)x](L2 = (PMePh2)2, dppe, (AsPh3)2, or (PPh3)2; x = 0, 1 or 2) leads to [L2(CO)HRe(μ-H)3RuH(PPh3)2−y{P(OPri)3}y] (x = 0 or 1, Y = 0; X = 2, Y = 1(L2 = PPh3)) in a first step. Under the reaction conditions most of these complexes react rapidly with the liberated phosphine giving [L2(CO)Re(μ-H)3Ru(PPh3)3−y- {P(OPri)3}y] (L2 = (PMePh2)2 or dppe, Y = 0; L2 = (PPh3)2, Y = 1) as the only iso complexes. The structure of [(PMePh2)2(CO)Re(μ-H)3Ru(PPh3)3] has been establishedby X-ray structure analysis. The complex [(PPh3)2(CO)Re(μ-H)3Ru(PPh3)2(P(OPri)3)] reacts with molecular hydrogen under pressure to generate [L2(CO)HRe(μ-H)3RuH(PPh3)(P(OPri)3) as the sole product. 相似文献
Specific rate of methane conversion into C2-hydrocarbons and deep oxidation products in its interaction with O2 or N2O decreases with growing surface area of catalysts that are metal-like compounds of transition elements. This regularity is interpreted in terms of a heterogeneous-homogeneous mechanism.
This article studies the applicability of a new technique in determining the interfacial shear rheology properties of surface active compounds relevant to the petroleum industry. It presents the theory behind the determination of the rheological parameters and the results of tests performed on a set of petroleum related compounds (asphaltenes, tetra-acid model compound, fatty acid, and surfactant). It is concluded that this technique is not mature enough to determine the properties of the studied compounds. 相似文献
The experiments have been performed by a microreactor pulse method at 623 K. The activity and selectivity of the catalysts, alumina/metal chloride and silica gel/metal chloride or oxide, have been found to depend on the donor-acceptor properties of their surfaces.
Due to the increasing importance of quantified results of dynamic calorimetric measurements, the influence of single experimental parameters has been studied by some authors. We found that these results can be represented correctly only in a complex form. According to this experience, the experimental parameters were changed on the basis of statistically planned experiments. The numerous measurements were carried out with samples of indium, 1,3-dinitrobenze and polyethylene prepared in different ways. The results were evaluated in a complex form. The evaluation of the experimental data revealed a significant influence of the substance properties and the experimental parameters.
Zusammenfassung Die zunehmende Bedeutung quantifizierbarer Ergebnisse von dynamischen kalorimetrischen Messungen veranlasste die Autoren [1–9] zur Untersuchung des Einflusses einzelner experimenteller Parameter. Nach unseren Erfahrungen können diese Ergebnisse nur in komplexer Form dargestellt werden. Entsprechend wurden die Versuchsbedingungen nach einem statistischen Plan variiert. Zahlreiche Messungen wurden mit unterschiedlich präparierten Indium-, 1,3-Dinitrobenzen- und Polyethylen-Proben durchgeführt und die Ergebnisse in komplexer Form ausgewertet. Dabei zeigte sich ein signifikanter Einfluss der Probeneigenschaften und der Versuchsbedingungen.
Some characteristics of the kinetic equation of dissolution are discussed, bearing in mind that in the course of the process, along with the concentration of the solution, the surface of the soluble substance is also changed. The opportunity for the appication of an exponential kinetic equation is pointed out. Methods are proposed for calculating the solubility and also for using the integral forms of the exponential equation. The meaning of the coefficient of proportionality is explained.
Sterically hindered electron-deficient anilines are coupled to the 6-position of the purine core only when activated as their corresponding TFA-amide. The free anilines did not react under all conditions tested. After aqueous work-up, the TFA-group is lost. This procedure provides a new tool in the construction of purines functionalized with a sterically hindered electron-deficient aniline in the 6-position. 相似文献
The least distance of the closest approach, b*, of the Laidler-Landskroener equation has been evaluated by application of the Singh-Jha equation in case of acid catalyzed hydrolysis of benzyl formate in water-DMSO solvent system. The values obtained are quite reasonable.
The reasons why the starting temperature of thermal decomposition cannot be utilized for the estimation of the thermal stabilities of co-ordination compounds are discussed. To establish the sequences of kinetic or thermodynamic stabilities of co-ordination compounds in thermal dissociation processes, it is indispensable to calculate the kinetic and thermodynamic parameters of the processes.
Zusammenfassung Der Grund, weshalb die Ausgangstemperatur der Thermolyse nicht zur Schätzung der Thermostabilität von Koordinationsverbindungen eingesetzt werden kann, wird erörtert. Um die Reihenfolge der kinetischen oder thermodynamischen Stabilität von Koordinationsverbindungen in thermischen Dissoziationsvorgängen zu ermitteln ist es unumgänglich die kinetischen und thermodynamischen Parameter der Vorgänge zu errechnen.
Résumé On discute les raisons pour lesquelles on ne peut pas se servir de la température du début de la décomposition thermique pour estimer la stabilité thermique des composés de coordination. Pour établir l'ordre de succession des stabilités des composés de coordination dans les processus de dissociation thermique, il est indispensable de calculer les paramètres cinétiques et thermodynamiques des phénomènes.
