Diffusion and reaction between two inorganic solids, zinc oxide and aluminium oxide, was undertaken in single cylindrical pellets with their end faces in contact with each other. Assuming a second-order irreversible reaction between the reactants, the second-order rate constants were determined as functions of particle size, compaction pressure and temperature. The activation energies required for reaction alone were computed. Generalized correlations for the second-order rate constant as a function of initial porosity of the compact were also established. © 1985, The Society of Chemical Engineers, Japan. All rights reserved.