Microtopography of high-calcium fly ash particle surfaces

Tapping mode atomic force microscopy (TM-AFM) has been used to image the surfaces of glassy spheres from high-calcium fly ash (HCFA). TM-AFM provides high-resolution images of such spheres under ambient conditions (e.g. no vacuum and no conductive coating), showing topographic details which were not accessible with conventional electron microscopy. Combined single-particle X ray diffraction and TM-AFM allows identification of nanometre-sized anorthite, gehlenite, anhydrite and magnetite crystals attached to the glassy spheres. Furthermore, the TM-AFM technique revealed that the glassy matrix is quite inhomogeneous even on the lower nanometre scale. The spatial distribution of reactive and inert mineral phases attached to fly ash particle surfaces provides information about their high-temperature formation, which may be relevant to their subsequent reactivity during hydration.