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
Authors:L. Barral, J. Cano, A. López, P. Nogueira, and C. Ramírez
Using dynamic mechanical analysis (DMA) we have studied the variation with the frequency of the dynamic mechanical properties
(storages modulus,E'; loss modulus,E'' and loss tangent or tan σ) for a system containg a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcyclohexane
(1,3-BAC). These properties were measured both in the glass transition and β transition regions. An increase in frequency
caused a shift of tan σ peak positions in both regions toward higher temperature. Finally, we report the activation energies
of a DGEBA/1,3-BAC expoxy system for α and β transitions.
Authors:T. M. Carvalho, A. T. Adorno, A. G. Magdalena, and R. A. G. Silva
mass%Ag; ( c ) Cu–11 mass%Al– X mass%Ag
The methods of Kissinger and Ozawa were used to study the influence of additions of 4, 6, 8, and 10 mass%Ag on the activationenergy of the (α + γ 1 ) → β reverse eutectoid
Authors:D. Patidar, Sonalika Agrawal, and N. S. Saxena
]. This model (Kissinger) is also employed to study the thermal stability of current CdS/PMMA system in terms of activationenergy which is given by the following relation:
where α is the heating rate, C is constant, and E t is the glass
The validity of the Friedman method is assessed for systems of overlapping reactions. By means of mathematical analysis and numerical examples it is shown that, in the case of competitive reactions, the method gives the true value of the instantaneous mean activation energy. However, some error may be incurred if this method is applied to systems of independent reactions. The relative accuracy of the Friedman and Ozawa-Flynn-Wall methods is discussed in respect of complex systems of reactions.
Authors:M. Reading, D. Dollimore, J. Rouquerol, and F. Rouquerol
The uncertainty surrounding the significance of the measured kinetic parameters of solid state decomposition reactions is discussed briefly. Some suggestions are made about what precautions should be taken in order to favour the measurement of undistorted results. Some criteria are proposed for deciding whether a measuredE value can be considered to have its usual meaning. The results of a series of experiments aimed at measuring the activation energy of the decomposition of calcium carbonate using a variety of methods, sample sizes and experimental conditions are presented. These results are compared with results found in the literature and it is concluded that it is possible to measure a reproducible value forE and it is tentatively proposed that this value is meaningful in terms of the energy barrier model of chemical reaction kinetics.
Authors:Mohan T. Hosamani, Narasimha H. Ayachit, and D. K. Deshpande
to calculate thermodynamic parameters such as change in activationenergy for dipole orientation Δ G* , enthalpy Δ H* , entropy of activation Δ S* , and the other temperature dependent parameters such as relaxation time τ , the distribution parameter
The activation energies of the same process are often reported to have different values, which are usually explained by the
differences in experimental conditions and sample characteristics. In addition to this type of uncertainty, which is associated
with the process (ΔEprocess) there is an uncertainty related to the method of computation of the activation energy (ΔEmethod). For a method that uses fitting single heating rate data to various reaction models, the value of ΔEmethod) method is large enough to explain significant differences in the reported values of the activation energy. This uncertainty
is significantly reduced by using multiple heating rate isoconversional methods, which may be recommended for obtaining reference
values for the activation energy.
Activation energy was experimentally determined using the curve-fitting, initial-rise and the peak-shape methods involving
pulse annealing experiments in NaCl samples irradiated at 10, 20, 30 and 40 Gy beta-doses and infrared stimulated luminescence
(IRSL) signal at a temperature range of 100-300 °C. It was observed that the activation energy for NaCl decreases as the dose
increased. The results were compared to other studies and discussed.