Contact nucleation: in situ and ex situ observations of surface damaging

To investigate the damaging done to a crystal surface potassium dihydrogen phosphate, KDP and potassium hydrogen phthalate, KAP) due to a crystal-rod contact, both ex situ and in situ experiments were performed and the impact sites studied either using an interference contrast microscope or a scanning electron microscope. An ex situ contact (performed in air) causes subsurface cracks and the breakage of small fragments (KDP) or the removal of thin plates (KAP) from the surface. In the former case the fragments have thicknesses roughly corresponding to the height of macrosteps present on the surface. Contacts during growth on KAP produced secondary nuclei; the crystal size distribution of these nuclei displays a log-normal behaviour.