A simulation of the mass-transfer effects on the kinetics of solid-gas reactions

A theoretical analysis of the influence of mass-transfer effect on the kinetic of solid-gas reactions has been carried out by assuming that the partial pressures of the gases generated in the reaction are proportional to the reaction rate. The influence of mass-transfer phenomena on the apparent activation energy, calculated by the isoconversional methods of Friedman, and on the reaction model is discussed. In the present study, simulated nonisotherm, isotherm, and controlled rate thermal analysis (CRTA) data have been used. Master plots based on the differential forms of the kinetic equations describing solid-state reactions have been employed by using the concept of the generalized time (theta), introduced by Ozawa; this permits the application of these master plots to the kinetic analysis of reactions whatever the type of temperature program used for recording the experimental data. it has been shown that when the simulated mass-transfer effect is present the variable effective activation energy E remains nearly constant while the reaction model approaches zero order. (C) 2008 Wiley Periodicals, Inc.