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Journal of Thermal Analysis and Calorimetry
Authors: Rogério L. Pagano, Verônica M. A. Calado, Frederico W. Tavares, and Evaristo C. Biscaia

Introduction A cure kinetic study of polymeric resin can be carried out in a calorimeter analysis, operating by two models: isothermal and non-isothermal. A way to estimate the kinetic parameters using any experimental data is

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Journal of Thermal Analysis and Calorimetry
Authors: Seied Mahdi Pourmortazavi, Mehdi Rahimi-Nasrabadi, Iraj Kohsari, and Seiedeh Somayyeh Hajimirsadeghi

parameters corresponding to the thermal decomposition of NTO are still unclear. On the other hand, there is no report on the prediction of thermal decomposition parameters of NTO via non-isothermal methods using DSC data under various heating rates. Thus, in

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2 have been carried out by thermal analysis techniques (Thermogravimetry-Derivative thermogravimetry-Differential scanning calorimetry, TG-DTG-DSC) under non-isothermal conditions. Based on the energy conservation analysis of thermal effects and the

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thermal analysis [ 2 , 3 ]. The most commonly used modes are either isothermal or heating at constant rate. The drawback of the later is that the analysis of non-isothermal experiments is generally more complicated than isothermal one [ 1 , 4 ]. However

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Non-isothermal model-free predictions

Application to the formation of yttria from yttrium trifluoroacetate

Journal of Thermal Analysis and Calorimetry
Authors: Hichem Eloussifi, Jordi Farjas, Pere Roura, and Mohamed Dammak

deposition, and thermal treatment to remove the organic species and to crystallize the material. Thermal treatment can be optimized by setting up a temperature program that involves isothermal stages to slow down the reaction at the critical steps and non-isothermal

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[ 11 , 12 ] have been applied to characterize thermal properties and molecular motions of P4MP1. Although the structure and properties of P4MP1 crystallized from the bulk have been investigated [ 13 – 16 ], non-isothermal crystallization of P4MP1 has

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Abstract  

Non-isothermal crystallization kinetics of polypropylene (PP), m-isopropenyl-α,α-dimethyl-benzyl isocyanate grafted PP (PP-g-m-TMI), and styrene(St), as comonomer, together with m-TMI grafted PP (PP-g-(St-m-TMI)) was investigated by using differential scanning calorimetry (DSC) under different cooling rates. The crystallization rates of all samples increased with increasing cooling rate. The relation of the half time of crystallization (t 1/2) of the three samples, t 1/2(PP-g-(St-m-TMI)) < t 1/2(PP-g-m-TMI) < t 1/2(PP), implying the introduction of St could effectively improve the degree of grafting of m-TMI, resulting in crystallization temperature increased, and the crystallization rate was the fastest. Three methods, namely, the Avrami, the Ozawa, and the Mo, were used to describe the crystallization process of the three samples under non-isothermal conditions. The Avrami and Ozawa neglected the secondary crystallization that follows primary crystallization. The Mo method can successfully describe the overall non-isothermal crystallization process of all the samples. It has been found that the F(T)(PP-g-(St-m-TMI)) < F(T)(PP-g-m-TMI) < F(T)(PP), also meaning that the crystallization rate of PP-g-(St-m-TMI) and PP-g-m-TMI were faster than that of PP. The activation energy (ΔE) for non-isothermal crystallization of all samples was determined by using the Kissinger method. The result showed that the lower value of ΔE for crystallization obtained for PP-g-m -TMI and PP-g-(St-m-TMI) confirmed the nucleating effect of St and m-TMI on crystallization of PP.

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Abstract  

Processing of Ultra High Molecular Weight Polyethylene (UHMWPE) parts involves non-isothermal cooling leading to crystallinity variations, which cause variations in the mechanical properties. Study of non-isothermal crystallization kinetics of UHMWPE forms the basis for process modelling. The crystallization of UHMWPE was studied at seven different cooling rates. The crystallization onset and peak temperatures were linearly related to the cooling rate. The crystallization of UHMWPE was concluded to be a nucleation dominated process with small contribution from growth of nuclei. Differences in ultimate crystallinity (≈11%) were produced due to different cooling rates. A significant portion of the change in ultimate crystallinity occurred at lower cooling rates (<6C min−1). At higher cooling rates (6–22C min−1) the change in ultimate crystallinity was insignificant.

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The most debatable and discrepant viewpoints of non-isothermal kinetics are discussed in the form of twelve questions and answers. The reputation of non-isothermal kinetics when carried out by thermoanalysts; the consequences of simplified concepts transferred from the kinetics of homogeneous reactions; the physical meaning of basic kinetic parameters in solid-state processes; the kinetic compensative effect and interdependence of kinetic parameters using the Arrhenius rate constant; the mutual usefulness of differential and integral methods of kinetic data evaluation; their accuracy and correctness; the reliability of DTA measurements; non-isothermal versus isothermal investigations; equilibrium and kinetic data and their mutual effect; the extended discussion initiated by MacCallum and Tanner; non-isothermal data publication policy; and finally the use of computers.

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Non-isothermal kinetics in solids

The precision of some integral methods for the determination of the activation energy without neglecting the temperature integral at the starting temperature

Journal of Thermal Analysis and Calorimetry
Authors: J. Cai and R. Liu

Abstract  

The integral methods, which are obtained from the various approximations for the temperature integral, have been extensively used in the non-isothermal kinetic analysis. In order to obtain the precision of the integral methods for the determination of the activation energy, several authors have calculated the relative errors of the activation energy obtained from the integral methods. However, in their calculations, the temperature integral at the starting temperature was neglected. In this work, we have performed a systematic analysis of the precision of the activation energy calculated by the integral methods without doing any simplifications. The results have shown that the relative error involved in the activation energy determined from the integral methods depends on two dimensionless quantities: the normalized temperature θ=T/T 0, and the dimensionless activation energy x 0=E/RT 0 (where E is the activation energy, T is the temperature, T 0 is the starting temperature, R is the gas constant).

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