As we learn more about the physics, chemistry and engineering of materials at the nanoscale, we find that the development of a complete understanding is not (in general) possible using one technique alone. Computer simulations provide a very valuable addition to our scientific repertoire, but it is not immediately intuitive which of the many methods available are right for a given problem. In this paper, various computational approaches are described as they apply to the study of the structure and formation of discrete inorganic nanoparticles. To illustrate how these methods are best used, results of studies from many research groups are reviewed, and informal case studies are constructed on carbon, titania and gold nanoparticles.

http://iopscience.iop.org/article/10.1088/0034-4885/73/8/086502/pdf

Modelling of nanoparticles: approaches to morphology and evolution

In the present study, isothermal methods of kinetic analysis are used to investigate the kinetics of the thermal decomposition of calcium carbonate Thermogravimetric analyzer experiments were carried out in standard temperature values In order to determine the decomposition mechanism and the conversion function form that governs it, four different methods of isothermal kinetic analysis were used The kinetic model that was found to better fit the experimental results was that of phase boundary controlled reaction The activation energy was evaluated from the Arrhenius plots, as well as by applying an alternative method, and the results confirmed the predominance of the chemical mechanism © 2001 SDU All rights reserved

Kinetic study of the thermal decomposition of calcium carbonate by isothermal methods of analysis

Calcium carbonate decomposes under well-defined conditions giving CaO (solid) and CO2 (gas). The process kinetics are known to be strongly influenced by the CO2 partial pressure and temperature. In dynamic conditions, as in thermogravimetric analysis (TG) and differential thermal analysis (DTA), kinetics influence the observed heat effect and mass losses, as was shown in semi-static studies by Hyatt et al. (J Am Ceram Soc 41:70–74, 1). However, differing DTA and TG curve shapes are reported in the literature even under supposedly comparable conditions. The differences are attributed in part to the design of the equipment and in part to differing crystalline states of the precursor calcium carbonate. To resolve these uncertainties, the TG has been performed at different heating rates and at different but controlled partial pressures of CO2. The results are reported and critically evaluated in the light of the data obtained, and the kinetic parameters as reported by Hyatt et al. (J Am Ceram Soc 41:70–74, 1) are re-evaluated.

Calcium carbonate decomposition

Various manifestations of the kinetic compensation effect are considered in reactions involving the participation of solid substances under isothermal and nonisothermal conditions, as well as manifestations of other isoparametric correlations. It is shown that isoparametric correlations can be used for the analysis of solid-phase reactions and the exclusion of artefacts in nonisothermal kinetics.

Isoparametric kinetic relations for chemical transformations in condensed substances (Analytical survey). II. Reactions involving the participation of solid substances

Thermogravimetric studies on two varieties of calcium carbonate, namely, analytical reagent-grade and in situ product from thermal degradation of calcium oxalate monohydrate, were carried out at four rates of linear increase of the temperature. The kinetics and mechanism of their solid-state thermal decomposition reaction were evaluated from the TG data using four calculation procedures and isoconversion method, as well as 27 mechanism functions. The comparison of the results obtained with these calculation procedures showed that they strongly depend on the selection of proper mechanism function for the process. Therefore, it is very important to determine the most probable mechanism function. In this respect the isoconversion calculation procedure turned out to be more appropriate. In the present work, the values of apparent activation energy E, preexponential factor A in Arrhenius equation, as well as the changes of entropy , enthalpy , and free Gibbs energy for the formation of the activated complex from the reagent are calculated. All calculations were performed using programs compiled by ourselves.

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Non-Isothermal Degradation Kinetics of CaCO3 from Different Origin

Some specific factors which may cause the kinetic compensation effect (k.c.e.) during the decomposition of CaCO3 are identified. The role of the CO2 equilibrium pressure is examined in relation to the k.c.e. The article also shows why non-isothermal experiments must sometimes necessarily yield a value of activation energy different from the value obtained from isothermal experiments.

The kinetic compensation effect in the decomposition of calcium carbonate

Johnson-Mehl equation is written as dα/dt=k
n
t
n−1 (1−α) whereα is the degree of reaction,t time andn a constant. Use of this equation in kinetic analysis present problems because of the presence of a ‘t’ term on the right hand side. The equation is not a true kinetic equation andk is not a true rate constant. This paper presents a brief discussion on the use of this equation as such or in a modified form and also indicates the proper procedure for evaluating kinetic parameters correctly. Some experimental data on the reduction of Fe2O3 to Fe3O4 have been used to test the mathematical procedure proposed. This reaction is known to follow the typical trend described by Johnson-Mehl equation.

Analysis of kinetic data by johnson-mehl equation

Kinetic data on the reduction of iron ore-coal pellets are compared with similar data for lump ore. It is shown that, when ore and coal are mixed intimately, the reduction reactions are accelerated considerably. Ore-coal pellets offer some additional advantages, as discussed in the text. It is shown that the kinetics of ore-coal reduction can be studied by using a pseudo kinetic parameter,f (fraction of reaction), defined as the instantaneous weight loss divided by the maximum possible weight loss. Plots off versust have been analysed to establish the kinetic equations and evaluate the kinetic parameters.

Kinetics of reduction of iron ore—coal pellets

Differential thermal analysis technique has been applied to determine the heat of reduction of iron oxide by aluminium. It has been observed that the DTA curve can be used for quantitative determination of heats of reactions at high temperature ranges where differential scanning calorimetry is not applicable. The experimental results obtained agree closely with the theoretical value of the heat of reaction.

H. S. Ray

Papers

The kinetic compensation effect in the decomposition of calcium carbonate

Analysis of kinetic data by johnson-mehl equation

Kinetics of reduction of iron ore—coal pellets

Thermoanalytical investigation of the aluminothermic reduction of iron(III) oxide

On the determination of heats and activation energies of decomposition of carbonate materials