Additivity and isokinetic behaviour in relation to particle dissolution

In the present investigation, additivity and isokinetic behaviour in relation to particle dissolution have been examined. As a starting point, the analytical time dependent solutio ns 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 duringcontinuous 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 concentrat ion gradient at the particle/matrix interface during cooling because of a sluggish transport of solute away from the interface and into the adjacent matrix.