Microtopographic features and dissolution behavior of natural zeolite surfaces studied by Atomic Force Microscopy (AFM)

Atomic Force Microscopy (AFM) has been used to observe surface features at the micrometer scale in several zeolite samples. In zeolites exhibiting tabular habit, such as heulandite, yugawaralite, and stilbite, the AFM investigation of the well developed {010} form allowed direct mapping of the elementary steps visible on freshly cleaved surfaces. The steps have a thickness invariably corresponding to half-unit cell and they are commonly involved in growth spirals. Dissolution experiments using diluited acidic solutions have also been performed, both under in-situ and ex-situ conditions, in order to observe the structure and/or defect-controlled formation of dissolution pits. Regularly shaped etch pits have been observed on laumontite (both on the {110} prism and on the {-201} pinacoid) and in chabazite, whereas heulandite shows very irregular dissolution figures. In situ dissolution experiments on yugawaralite and chabazite showed anomalous surface swelling and deformation in proximity of structural defects prior to intensive fracturing of the surface layers.