Pure dissolution kinetics of anhydrite and gypsum in inhibiting aqueous salt solutions

In the context of the study of the wet creep of plasterboards, we have performed digital holographic interferometry measurements of the dissolution of gypsum of various quarries in water and in aqueous solutions of salts inhibiting dissolution, and of the dissolution of anhydrite in water. This technique is carried out in still water and permits to observe directly the reacting solid-liquid interface. Therefore, contrary to standard bulk measurements, the pure dissolution rate constants, free from any mass transport contribution, have been measured. These rate constants are similar for the cleavage face of the various gypsums. Thanks to their faculty of complexing the surface calcium ions, the investigated phosphate and phosphonate salts inhibit dissolution and reduce the dissolution rate constant of up to more than one order of magnitude. This strong influence may explain their anti-creep role in plasterboards.