Study of forces between microcrystals of gypsum by atomic force microscopy

This paper introduces a new approach to the study of the interactions between gypsum faces. With an Atomic Force Microscope, the direct local measurement of forces permits to evaluate the free energy between gypsum faces. In air, measurements isolate the different forces between faces, which seem to be responsible of the crystal cohesion capillary force associated with Van der Waals interaction. In electrolytic solutions of calcium sulfate, the crucial feature of the crystal coagulation comes from the effective surface charge of each face. The discussion is oriented to evaluate the part of the coagulation forces compared to the rigidification in the process of setting.