Reactant mixtures and experimental methods

The retarding influence of the product barrier in many solid—solid interactions is a rate-controlling factor that is not usually apparent in the decompositions of single solids. However, even where diffusion control operates, this is often in addition to, and in conjunction with, geometric factors (i.e. changes in reaction interfacial area with a) and kinetic equations based on contributions from both sources are discussed in Chap. 3, Sect. 3.3. As in the decompositions of single solids, reaction rate coefficients (and the shapes of a—time curves) for solid + solid reactions are sensitive to sizes, shapes and, here, also on the relative dispositions of the components of the reactant mixture. Inevitably as the number of different crystalline components present initially is increased, the number of variables requiring specification to define the reactant completely rises the parameters concerned are mentioned in Table 17. 

The overall composition of any reactant mixture, i.e. the total quantity of each component present, is of little practical use in kinetic studies since such (concentration-type) terms are not meaningfully related to magnitudes of rate coefficients or shapes of a—time curves. Of greater signifi- 

Reactions between solids. Parameters requiring consideration in the description of any reaction mixture and in the measurement of interaction kinetics 

Reactant components including the identities, compositions and relative quanti- 

Particle sizes sizes, size distributions and shapes of each solid compo- 

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