Fundamental Concepts of Kinetics
The solid state reaction kinetics has been extensively studied time and again in the past century. The parameters involving in the kinetics of solid state processes are often misconstrued as intrinsic constants that characterize a particular solid state r
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Fundamental Concepts of Kinetics
The solid state reaction kinetics has been extensively studied time and again in the past century. The parameters involving in the kinetics of solid state processes are often misconstrued as intrinsic constants that characterize a particular solid state reaction. But this is a delusion as solid state processes involve rigorous and complex kinetics. The study of the kinetics in the solid state explicates the mechanism of the process as well as the related kinetic parameters. Kinetic studies have traditionally been extremely useful in characterizing several physical and chemical phenomena in organic, inorganic and metallic systems, which involve thermal effects. It provides valuable qualitative, quantitative information on the thermal properties and, more importantly, kinetic information on phase transformations [1], crystallization of metallic glasses [2], solid state precipitation [3, 4], decomposition [5], quasicrystalline structure of amorphous metals and alloys [6] and structural changes associated with nanomaterials [7]. However, it is to be noted that the physical properties of the materials/particles do not solely depend on the composition, but are also functions of shape and size. It has been reported that deviation in shape and size of the nanoparticles impart a great deal of inconsistency in the results of physical properties [8]. Therefore, it is strongly felt that unless the physical properties are tailored to remain uniform through precise control of shape and size, the acceptance and applicability of the materials/ particles appears to be eclipsed. Fundamentally, realization of such control requires in-depth knowledge about the reaction mechanism and the related kinetic parameters, e.g. temperature, heating rate, etc. Kinetics and thermodynamics are two important aspects for understanding the solid state processes. Thermodynamics is concerned about the initial and final states of a process, whereas kinetics additionally deals with mechanism, reaction path and the time required. Thermodynamics always deals with equilibrium condition. Hence, kinetic study in addition to thermodynamics is required for characterizing solid state process. All the particles in a system do not undergo transformation at one and the same time. Only a fraction of the active particles can participate in the transformation process because they only have the free energy of the excess of the mean and hence are energetically suitable for transformation. The free energy of an atom or P. Deb, Kinetics of Heterogeneous Solid State Processes, SpringerBriefs in Materials, DOI: 10.1007/978-81-322-1756-5_1, The Author(s) 2014
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1 Fundamental Concepts of Kinetics
Fig. 1.1 Energy of the reacting atoms in an exothermic reaction
group of atoms during transformations first increases to a maximum and then decreases to a final value. The process is called activation and the state associated with the maximum energy is called the activation state. The activation energy is defined as the difference between
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