Heterogeneous chemical kinetics by gas effluent analysis - the unzipping of a paraform / T.R. Ingraham and D. Fraser, Extraction Metallurgy Research Section, Extraction Metallurgy Division. : M38-8/90E-PDF

"Heterogeneous chemical reactions […] are involved in many of the major chemical and metallurgical processes which support the economy of Canada. It is well established that this type of reaction occurs at a sharply defined interface between the solid reactant and the product. The observed rate of reaction varies with the area of the interface. Usual methods of relating the observed rate of reaction to the area of the interface, or to the weight of sample, are based on the unreacted-core shrinking model. The rate of reaction may be controlled by processes occurring in the interface, or by heat or mass transfer through a product layer. It has been suggested that a model combining both heat and mass transfer is often required. Many of the arguments for and against certain models are predicated on the assumption that the shrinking core model is valid and predictable from relationships such as: f = 1 – (1 – α)1/3 where f is the fractional movement of an interface or the equivalent, (weight)2/3 in a spherical particle that has decomposed to a fraction α. The experimental evidence is heavily weighted to acceptance of relationships such as that shown in [the] Equation, because they seem to be reasonably effective in resolving many of the observed experimental results. To test the validity of the shrinking core model, a series of experiments were initiated in which there was no residue that might interfere with the transfer either of heat or mass to or from the interface. It was hoped that the exact change in the geometry of the interface might be observed and related precisely to the measured reaction rate"--Introd., p. 101-102.

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