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Abstract  

The effect of some alkali metal bromides, iodides and sulphates on the diffusion of bromide, iodide and thallium ions, respectively, is studied at various temperatures. The activation energy required for the process of diffusion of these three ions in different supporting electrolytes have been calculated. It is found that activation energy for a given ion decreases in the reverse order of the charge density of alkali metal ions of the supporting electrolyte. This observed trend in activation energy is explained qualitatively by considering the distortion in the water structure caused by these ions and agar molecules.

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Abstract  

A new approach for determining the activation energy of amorphous alloys is developed. Setting the second order differential coefficient of heterogeneous reaction rate equation of non-isothermal heating as zero at extreme points of DSC curve, we obtain the new correlation taking form:

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\gamma_{1} = Lambertw\left( {\gamma_{3} e^{{ - \gamma_{2} }} } \right) + \gamma_{2}$$ \end{document}
where γ 1, γ 2 and γ 3 are symbols comprising parameters, and Lambertw(…) is the Lambert W function symbol. Through this function, the activation energy can be calculated with DSC test at single heating rate without the isoconversion assumption. To evaluate the feasibility of calculating the activation energy with the new method, the glass transition activation energy of as-cast Pd40Ni40P20 amorphous alloy is measured. The value is 1.6 eV, which agrees well with the result of viscosity measurements. Thus, it is a good possibility that the new approach can be used to determine the activation energy of amorphous phase.

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Abstract  

The activation energy of the tracer diffusion of Mn2+ ions in alkali chlorid solutions (0.1M) has been determined in agar gel medium (1–2.5%) over the temperature range of 25–45 °C. The decrease in the value of the Arrhenius parameters, E and D 0, with gel percentage is explained on the basis of the transition state theory. Further, the activation energy as a function of electrolyte concentration is also investigated using 1% agar gel in the temperature range of 25–45 °C. In both the cases, the activation energies are determined by the least square fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots.

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Abstract  

The activation energy for the tracer diffusion of Co2+ ions in multielectrolyte systems containing alkali bromides has been determined in agar gel medium over the temperature range of 25–45°C. The decrease in the value of the Arrhenius parameters, E and Do, with gel percentage is explained on the basis of the transition state theory. Further, studies of the influence of electrolyte concentration on activation energy and obstruction effect reveal that both parameters decrease with the former. The decrease in activation energy is explained by considering the changes in physical properties of the solution with concentration at microscopic level, while the decrease in the extent of obstruction effect is attributed to competitive hydration between ions and agar molecules in a diffusion system.

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Abstract  

The paper studies metastable phases of 4,4'-di-n-heptyloxyazoxybenzene (liquid crystal substance) using adiabatic calorimetry. The process of transformation between metastable and stable phases is described quantitatively. The conclusion concerns activation energies for metastable phase to stable phase transition.

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Abstract  

Activation energies for the recombination of point defects generated by the /n,/ reaction in Ba (CoEDTA)2·4H2O, t-(Co(en)2(NO2)2)Cl and (Co(en)2(NO2)2) (CoEDTA)·1H2O, have been evaluated using isothermal step annealing. The reselts were interpreted in terms of compound structures. It is possible to relate the recoil atom behaviour between single complexes and the double one.

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Abstract  

Theoretical activation energy of self-diffusion of zinc, chloride and chromate ions has been computed on the basis of the Onsager and Arrhenius equations. These values are compared with the experimentally determined ones for the self-diffusion of Zn2+ ions in the present work as well as previously reported values for self-diffusion of Cl and CrO 4 2– ions. A reasonably good agreement is observed between the two values.

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Abstract  

Traditionally, the kinetic treatment of adiabatic calorimetry data has been based on the results of one or more experiments, but always with the assumption of the kinetic model that the reaction follows to calculate the kinetic parameters. In this paper a method for the determination of the activation energy that uses a set of adiabatic calorimetry data is developed. To check the method, the thermal decompositions of two peroxides were studied.

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Abstract  

Several dynamic methods for estimating activation energies have been developed. This development has arisen largely as a matter of convenience and the desire to minimize analysis time. While these methods generally afford values which are somewhat similar, the agreement among values from various methods is never outstanding. Further, the values obtained are often, at best, only approximations of the values obtained by the traditional isothermal approach. To better ascertain the utility of dynamic methods for the determination of activation energies, the activation energy for the thermal degradation of a standard vinylidene chloride/methyl acrylate (five-mole percent) copolymer has been generated by a variety of methods. The degradation of this polymer is an ideal reaction for evaluation of the various methods. At modest temperatures (<200C), the only reaction that contributes to mass loss is the first order evolution of hydrogen chloride, i.e., there is only one significant reaction occurring and it is not impacted by competing processes. The best values (most reproducible; best correspondence to values obtained by titrimetry and other methods) are those obtained by plotting the natural logarithm of rate constants obtained at various temperatures vs. the reciprocal of the Kelvin temperature. Various dynamic methods yield values which are less reproducible and which approximate these values to a greater or lesser degree. In no case is the agreement good.

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Abstract  

Biomass tar pyrolysis behavior was investigated in absence and presence of catalyst-dolomite (10% mass) with different heating rates of 10, 20, 30 K min−1 under nitrogen atmosphere. Different kinetic methods such as distributed activation energy model (DAEM), Coats–Redfern method were used to analyze the TG/DTA data to identify reaction parameters. For Coats–Redfern method, first reaction order (n = 1) and two stages (volatilization and pyrolysis) reaction model was selected to calculate the kinetics parameters; for DAEM model, three different heating rates (10, 20, 30 K min−1) were selected to obtain the activation energy distribution (E a). The peak values of E a curves for biomass tar volatilization process are nearly 250 and 200 kJ mol−1 in absence and presence of dolomite, whereas, the value of E a for pyrolysis stage gradually increase and varied from 70 to 200 and 40 to 100 kJ mol−1 with the mass loss, respectively, in absence and presence of dolomite. The application of the new DAEM model can show the variation trend of activation energy for the whole pyrolysis process.

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