Search Results

You are looking at 1 - 10 of 1,009 items for :

  • "nonisothermal" x
  • Refine by Access: All Content x
Clear All

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

Restricted access
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

Restricted access

Steps in a minefield

Some kinetic aspects of thermal analysis

Journal of Thermal Analysis and Calorimetry
Author: M. Brown

Abstract  

This paper is a review of some of the controversial kinetic aspects of thermal analysis, starting from the ‘šesták questions’ posed in 1979 and looking at developments in some areas since that time. Aspects considered include: temperature programmes and variations, models and mechanisms, kinetic parameters, distinguishability and extent of fit of kinetic models, complementary evidence for kinetic models, the Arrhenius equation and the compensation effect. The value of the ideas of non-isothermal kinetics in chemical education is emphasized.

Restricted access
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

Restricted access

Nonisothermal thermogravimetry of polymers

V. Bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide)

Journal of Thermal Analysis and Calorimetry
Authors: J. Líška, J. Rychly, and E. Borsig

Abstract  

The model of weight loss taking place in each step of a scheme of consecutive reactions was applied to nonisothermal thermogravimetric records of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide). The release of HBr was found to be faster in air than in nitrogen. A significant reduction in the apparent activation energy of dehydrobromination as compared with decomposition of the nonbrominated polymer was ascribed not only to a reduction in the activation energy of the initiation reaction, but also to an increase in the order of the termination reaction (from 1 for the nonbrominated polymer to 2 for the highly brominated polymer).

Restricted access

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.

Restricted access

desirable and in some cases essential, in order to minimize the effect of moisture on biomass pyrolysis. Therefore, it is necessary to research the biomass characteristics, such as heat transfer, mass transfer and nonisothermal drying kinetics, during the

Restricted access

Introduction Iso-conversional methods are used for non-isothermal analysis, in which the transformation rate at a constant extent of conversion is only a function of temperature as suggested by Vyazovkin et al. [ 1 – 4 ] and

Restricted access

Conclusions The effects of mechanical activation on the thermal behavior of kaolinite – alumina ceramic system and the non-isothermal kinetics of mullite formation were investigated and the following results were obtained. In the kaolinite

Restricted access

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).

Restricted access