Calcium carbonate thermal decomposition in white-body wall tile during firing. I. Kinetic study

Abstract

This study examines the thermal decomposition of calcium carbonate, contained in disk-shaped test pieces formed from a mixture of raw materials of a similar composition and characteristics to those of the mixtures customarily used for the manufacture of white-body wall tile.The experiments were conducted under isothermal conditions at different temperatures in the range 825-950°C in an air stream free of carbon dioxide.The experimental results have been interpreted using the Shrinking Unreacted Core kinetic model, assuming that, at low conversion degrees, the process is only controlled by the chemical reaction step of CaCO₃ decomposition, while at high conversion degrees the diffusion of the resulting CO₂ through the porous structure of the reacted ceramic layer also affects the process. The derived equations, which relate the conversion degree of calcium carbonate in the ceramic body to residence time, temperature, and initial porosity of the test pieces, allow the experimental results to be satisfactorily reproduced. © 2010 Elsevier Ltd.