Kinematics of apophyllite leaching—A terrace–ledge–kink process within phyllosilicate interlayers

The phyllosilicate apophyllite undergoes interlayer ion leaching and swelling in acidic aqueous solutions. These processes propagate within the interlayers at distinct reaction fronts, which can be locally resolved by atomic force microscopy (AFM). Thus, AFM enables to investigate both the reaction kinetics and the front kinematics. The present study shows that the front kinematics depends strongly on the crystal structure and solution composition. The observed kinematics can accurately be described by kink-nucleation and kink-propagation processes. In this way, the reaction kinematics within the apophyllite interlayer consequently follows a terrace-ledge-kink model pattern, which has initially been developed for the growth and dissolution of crystals on free uncovered surfaces. Thus the results imply that the occurrence of processes with terrace–ledge–kink-type kinematics is not restricted to surfaces but well extends into the confined spaces of phyllosilicate interlayers.