Additivity and isokinetic behaviour in relation to particle dissolution

Additivity and isokinetic behaviour in relation to particle dissolution have been examined. As a starting point, the analytical time dependent solutions for dissolution of plate-like and spherical precipitates in an infinite matrix have been manipulated and rewritten in a state variable form. The validity of these solutions during continuous heating and cooling is then checked against more exact numerical calculations based on the control volume approach. It is concluded that the state variable formulation, which represents an extension of the isokinetic concept, provides an adequate description of the dissolution process under conditions where these solutions are valid, except in cases where back diffusion leads to transient particle growth. This phenomenon is mainly associated with plate-like precipitates, and has its origin in the development of a negative concentration gradient at the particle/matrix interface during cooling because of a sluggish transport of solute away from the interface and into the adjacent matrix. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.