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Abstract  

The thermal degradation of the epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) and diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diaminecyclohexane (DCH) containing calcium carbonate filler immersed and not immersed in hydrochloric acid have been studied by thermogravimetric analysis in order to compare their decomposition processes and to determine the reaction mechanism of the degradation processes. The value of the activation energies, necessary for this study, were calculated using various integral and differential methods. Analysis of the results suggests that hydrochloric acid does not affect the decomposition of the epoxy network and that the reaction mechanisms produce sigmoidal-type curves for the systems not immersed in HCl and deceleration curves for the same systems immersed.

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Abstract  

For the enhancement of thermal stability of poly(p-dioxanone) (PPDO), the isocyanate end-capping reagent was prepared by treatment of toluene-2,4-diisocyanate with an equivalent of 1-hexyl alcohol. The end-capping reagent and the end-capping PPDO with an inherent viscosity of 0.26 dL g−1 were characterized by FTIR and 1H-NMR. Thermal stability of the end-capping PPDO with an inherent viscosity of 0.92 dL g−1 was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry. It has been shown that the addition of the prepared isocyanate can enhance significantly the thermal stability of PPDO. The activation energies for non-isothermal degradation estimated by Kissinger method and Friedman method are 91, 81 kJ mol−1 for as-prepared PPDO, and 160, 149 kJ mol−1 for the end-capping PPDO, respectively. The activation energy increases by about 70 kJ mol−1 through the end-capping.

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Abstract  

It has been found that the modified Zhuravlev equation, [(1−α)−1/3−1]2=ktn, which describes the kinetics of oxidation of V2O4 and V6O13 in the temperature range 820–900 K and in the oxygen pressure range 1.0–20 kPa, can be derived via the assumption that the changes in the observed activation energy result from the changing contributions of the two diffusion processes controlling the reaction rate. The values of the observed activation energy are in the range 160–175 kJ mol−1 for V2O4 and 188–201 kJ mol−1 for V6O13 in the scope of the experimental oxygen pressures and temperatures and conversion degrees of 0.1–0.9.

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Abstract  

Effects induced by γ -irradiation in the dose range of 0-10 Mrad on Tuffak polycarbonate track detector films have been studied by thermogravimetry (TG). The samples were irradiated with 60Co γ -rays for doses of 3, 5 and 10 Mrad. The TG studies indicate that unirradiated and the γ -irradiated samples degrade in two steps. The kinetics of the two steps of degradation was also evaluated from the TG curves. Irradiation enhances the degradation rate and the effect increases further with increasing radiation dose. The activation energy values calculated for all the steps decrease on irradiation. A linear relationship observed between the decrease in activation energy and the dose received by the sample suggests the possibility of the use of Tuffak polycarbonate detector as γ dosimeter.

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Abstract  

In this research, the relationship between particle size and combustion kinetics and combustion properties of lignite samples was examined by utilizing the thermogravimetric (TG/DTG) and differential thermal analysis (DTA) techniques. The lignite samples separated into different size fractions were subjected to non-isothermal thermogravimetric analysis between ambient and 900�C in the presence of 50 mL min−1 air flow rate. Activation energy (E) and Arrhenius constant (A r) of combustion reaction of each size was evaluated by applying Arrhenius kinetic model to the resulting data. Combustion properties of the samples were interpreted by careful examination of the curves. The apparent activation energies in major combustion region were calculated as 41.03 and 53.11 kJ mol−1 for the largest size (−2360+2000 μm) and the finest size (−38 μm), respectively.

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Abstract  

Isothermal decomposition kinetic of three lanthanide mixed complexes with the general formula of Ln(thd)3phen (where Ln=Nd3+, Sm3+ or Er3+, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this work. The powders were characterized by their melting point, elemental analysis, FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been recorded under the same conditions at 265–285, 265–285 and 250–270°C for Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen, respectively. The kinetic parameters, i.e. activation energy, reaction order and frequency factor were obtained through the technique of lineal regression using the relation g(α)=kt+g 0. The analysis was done at decomposed fractions between 0.10–0.90. The values of activation energy were: 114.10, 114.24 and 115.04 kJ mol–1 for the Nd(thd)3phen, Sm(thd)3phen and Er(thd)3phen complexes, respectively. The kinetic models that best described the isothermal decomposition reaction the complexes were R1 and R2. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen<Sm(thd)3phen<Er(thd)3phen.

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Abstract  

The aim of this work is to highlight the importance of controlling the residual water vapour pressure above the sample as well as the rate of the thermal decomposition during the thermal dehydration of cerium cyclotriphosphate trihydrate CeP3O9·3H2O. For this reason, the dehydration of the titled compound was followed by both techniques: the constant rate thermal analysis at P H2O = 5 hPa and the conventional TG-DTA in air. It has been shown that the pathway of the thermal dehydration depends strongly on the nature of atmosphere above the sample. However, in air atmosphere CeP3O9·3H2O decomposes in two well defined steps to give first an amorphous, phase in the temperature range 440–632 K, then the cerium polyphosphate Ce(PO3)3 crystallizing in orthorhombic system (C2221) at T>632 K. Whereas decomposition carried out at 5 hPa water vapour pressure, also occurring in two steps, leads first to a crystallized intermediate monohydrate at 259<T<343 K and second to a crystallized anhydrous cerium polyphosphate, at 343<T<791 K, with a structure different from those of all lanthanide polyphosphate known actually and particularly from that of Ce(PO3)3 obtained in air. The activation energy corresponding to the dehydration of the initial phosphate was also measured experimentally by means of two CRTA curves and was found equal to 81±5 kJ mol−1.

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Abstract  

Spontaneous structural changes of a polymer that is its ageing due to thermal energy, radiation energy, chemical compounds and micro-organisms lasting at least several season cycles change the characteristics of polymer products. Changes of polymer characteristics found during ageing can be reversible or irreversible. The most substantial changes occur as the result of UV radiation. Tests of selected aliphatic diamides of terephthalic acid as stabilisers of low density polyethylene (LD-PE) used for the production of gardening films were performed. Accelerated ageing of films for a period of one year was done in the Xenotest Alpha type apparatus. Studies were made for 0.1 mm thick commercial films. Studies of selected mechanical properties of LD-PE films without stabilisers and of LD-PE sheeting containing an addition of one of the synthesised diamides of terephthalic acid or the standard Tinuvin 783 stabiliser were performed before and after the ageing process. To determine the effect of stabilisers on the ageing process of LD-PE films, thermogravimetric analysis was applied. This allowed us to determine the decomposition activation energy of the investigated films before and after the ageing process and the influence of stabilisers on the observed changes.

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Abstract  

In this research, pyrolysis and combustion behavior of three different oil shale samples from Turkey were characterized using thermal analysis techniques (TG/DTG). In pyrolysis experiments, two different mechanisms causing mass loss were observed as distillation and cracking. In combustion experiments, two distinct exothermic peaks were identified known low and high temperature oxidation. On the other hand, determination of activation energies are required for the estimation of oil extraction conditions from the oil shales. Differential methods are used to determine the activation energies of the samples where various f(α) models are applied from the literature. It was observed that the activation energies of the all oil shale samples are varied between 13.1–215.4 kJ mol−1 in pyrolysis and 13.1–408.4 kJ mol−1 in combustion experiments which are consistent with other kinetic results.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Daviti, K. Chrissafis, K. Paraskevopoulos, E. Polychroniadis, and T. Spassov

Abstract  

The kinetics of the α-β phase transition of HgI2 were investigated by isothermal and non-isothermal differential scanning calorimetry. The effective activation energy of the transition, 41540 kJ mol-1, was determined applying the methods of Kissinger and Ozawa. The transition kinetics were described by the Johnson-Mehl-Avrami model and the value of the Avrami exponent n was found to range from high values (n>3) at the early stages to lower values at later stages of the transformation, with an average value of 2.

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