Experimental tests to validate the rate-limiting step assumption used in the kinetic analysis of solid-state reactions

The kinetic analysis of experimental data obtained in the case of solid-state reactions (thermal decompositions, reactions of gases with solids) relies on various assumptions among which two are of very high importance: the steady-state approximation and the rate-limiting step. Both assumptions may be verified using simple experimental tests. The first one needs the coupling of measurements of the kinetic rate by two methods (in general thermogravimetry and calorimetry). The second one is based on sudden changes (jumps), during an experiment, of the temperature, or of the partial pressure of gases which have an influence on the kinetic rate. The basic principles of these tests are first explained, then various examples are given in order to illustrate their application to solid-state reactions.