In this research, non-isothermal pyrolysis behavior and kinetics of three oil shales were studied by thermal analysis methods.
All the thermal effects were endothermic and no exothermic region was observed in DSC curves. When oil shales are heated in
nitrogen atmosphere in TG/DTG, two different mechanisms causing loss of mass were observed. The region between ambient temperature
and 500 K was distillation. The second mechanism was visbreaking and cracking and it was observed between the region 500 and
800 K. Kinetic parameters of all the samples are determined by Coats and Redfern method and the results are discussed with
regard to their accuracy and the ease of interpretation.
Authors:W. de Klerk, C. Popescu, and A. van der Heijden
At TNO Prins Maurits Laboratory the characterisation and application of energetic materials is one of the main research topics.
In this respect, the activities are focussed on using thermal analysis techniques such as TG/DTA and DSC. Standard DSC and
TG/DTA techniques usually apply a linear temperature increase. During this gradual temperature change, the sample may pass
certain phase changes related to different crystal structures, followed by a melting/decomposition of the material. In this
way physicochemical properties like phase change temperatures, melting point, enthalpy of melting, decomposition temperature,
etc. can be determined. By applying different heating rates, an analysis of the decomposition kinetics can be performed as
well, which gives additional information on the decomposition process of the material. In this way the activation energy of
the decomposition process and the 'shelf-life' of the material, when stored at a certain temperature, can be assessed. In
a co-operation with the Technical University of Aachen, two relatively new and promising energetic materials were investigated:
FOX-7 and HNF. FOX-7, or 1,1-diamino-2,2-dinitroethylene, is a less sensitive explosive, which could find application as a
substitute of RDX (less sensitive but with preservation of performance). Hydrazinium nitroformate (HNF) is an oxidiser with
potential use as a high-performance, chlorine-free ingredient in rocket propellants. The results of the TG/DTA and DSC tests,
as well as the results of the analysis of the decomposition kinetics of these two materials, will be reported and discussed
in this paper.
Authors:G. Zagorowsky, G. Prikhod'ko, V. Ogenko, and G. Koval'chuk
The kinetics of the interaction between lithium carbonate and silica with various degrees of dispersion was investigated by
TG and DTA methods. It was found that the utilization of pyrogenic silica with a specific surface area of about 300 m2g-1 instead of aerosil with one of 175 m2g-1 leads to an increase of the reaction rate between lithium carbonate and silica, which depends on the formation and growth
of lithium orthosilicate crystals in the first stage, and is conditioned by the diffusion of lithium and oxygen ions through
the lithium orthosilicate layer formed at temperatures above 800 K. This supposition is supported by the kinetic analysis
results obtained with the use of the different models. The optimal regime of heating is recommended.
The kinetics of reduction at relatively low temperatures with hydrogen of pure and doped metastable non-stoichiometric magnetite
with 1 at% Mn, Co, Ni and Cu and also with 5 at % Ni and Cu have been investigated by using isothermal thermogravimetry in
the temperature range 300–400°C. With increase in the concentration of the dopant (5 at% Ni and Cu), the reactivity increases.
The activation energies for pure magnetite varies from 7 to 9 kcal/mole with the preparation temperature of precursorf Fe2O3 (250–400°C), being the lowest for those prepared at the lowest temperatures. The corresponding activation energies for the
reduction of doped samples (Fe, M)3−zO4, it depends, apart from their porosity and surface areas, on the nature of the solute atom, amount of disorder, whether it
occupies the tetrahedral (A) or octahedral (B) sites in the non-stoichiometric spinel and possibly on hydrogen ‘Spill over’
Thermogravimetric techniques have been used to study the kinetics of thermal deamination of tris(ethylenediamine)nickel(II)
sulphate. The complex was synthesized and characterized by various chemical and spectral techniques. Thermal decomposition
studies were carried at different heating rates (5, 10, 15 and 20°C min−1) in dynamic air. The complex undergoes a four-stage decomposition pattern. The stages are not well resolved. Decomposition
path can be interpreted as a two-stage deamination, and a two-stage decomposition. Reaction products at each stage were separated
and identified by means of IR and XRD. The morphology of the complex and the residue were studied by means of SEM. Final residue
of the decomposition was found to be crystalline NiO.
The deamination kinetics was studied using model-free isoconversional methods viz., Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose
(KAS) methods. It is observed that the activation energy varies with the extent of conversion; indicating the complex nature
of the deamination reaction.
Summary In this work the kinetics of the high-temperature oxidation of the powder amorphous carbon and bulk single-wall carbon nanotubes is studied. The thermal degradation of the sample is measured by differential scanning calorimetry using the continuous heating regime up to 1273 K. Also, the oxidation resistance of the samples is evaluated by the mass loss in a thermogravimetric analyzer. Both flowing and static oxygen and dry-air atmospheres are used. The specific role of the external diffusivity of the reagent gas is analyzed. The kinetics of the chemical reaction is specified using the Kissinger, Coats and Redfern methods.
Fe(III) chloride hydrate (FeCl3·xH2O) undergoes simultaneous dehydration and dehydrochlorination from its molten phase in the temperature range 100–200‡C. The kinetics of these two parallel thermal processes has been studied by both isothermal and non-isothermal methods. Whereas for the dehydration reaction at temperature below 125‡C a second order rate model (F2) fits well, a three-dimensional diffusion (D3) model is found to fit better at temperature above 135‡C. For the dehydrochlorination reaction an interface growth controlled model of 1/3 order (F 1/3) appears to be the most suitable over a wide range of reaction. Dynamic thermogravimetry reveals two major steps in the temperature range 50–250‡C. The first step which corresponds to the loss of about 4 mols of H2O, invariably follows second order kinetics (F2). The second step which is predominantly a process of dehydrochlorination, generally fits mixed diffusion controlled models due to the overlapping with the dehydration process. There is an excellent agreement in results among the isothermal and non-isothermal methods of determining kinetic parameters.
The main reasons for changes in the environment surrounding us are discussed on the basis of thermodynamics of irreversible
processes. Subsequently, relations between thermodynamics of irreversible processes and chemical kinetics are shown, then
the possibilities of theoretical determination of rate constants on the framework of the modified RRKM theory are presented.
These latter considerations are supplemented by a discussion concerning the possibilities of determining the activation barriers
and structural changes (necessary to account for entropy changes upon reaction) in molecules kept on the surface of crystalline
phases by combination of quantum chemistry methods for isolated molecules with those reflecting the influence of the environment
(i.e. interaction within the lattice). Finally, the future of theoretical methods in examining the reactivity of solid state
systems is briefly discussed.
Kinetics of mechanically induced CO2 extensive sorption by silicate minerals (labradorite, diopside, okermanite, ghelenite and wollastonite) was considered. Mechanical
activation of the silicates was carried out in a planetary mill in CO2 at atmospheric pressure. Carbon dioxide was consumed by the silicates in the form of carbonate ions and its content in the
samples after 30 min of mechanical treatment reached 3–12 mass% CO2 depending on mineral composition. Equations that reasonably good represent kinetics of CO2 mechanosorption by silicates were proposed. These equations enable to calculate mechanosorption coefficients that characterize
the diffusivity of CO2 into disordered silicate matrix under intensive mechanical impact. Thermal analysis of the mechanically activated silicates
showed that there was positive correlation between temperature of complete carbonate decomposition and mechanosorption coefficient.
Authors:N. Sbirrazzuoli, L. Vincent, J. Bouillard, and L. Elégant
In the case of a complex mechanism of two parallel independent reactions, peak maximum evolution methods and model-fitting
methods give only a mean value of the kinetic parameters, while isoconversional methods are useful to describe the complexity
of the mechanism. Isothermal and non-isothermal isoconversional methods can be used to elucidate the kinetics of the process.
Nevertheless, isothermal isoconversional methods can be limited by restrictions on the temperature regions experimentally
available because of duration times or detection limits.