Crystallinity and selected properties of fly ash particles

The morphology, composition and crystallinity of both precipitator (solid) and cenosphere (hollow) fly ash particles of different sizes were studied with scanning electron microscopy (SEM), EDX, and X-ray diffraction (XRD). Bulk density, tap density and real density of both precipitator and cenosphere particles of different sizes as well as the wall thickness to diameter ratio of cenosphere particles were measured. The microhardness of individual fly ash particles embedded in the matrix of aluminum alloy was also measured. The crystalline to amorphous ratio weight percentage in fly ash particles, and the weight or volume fraction of each crystalline component varies with the particle size. The crystallinity of precipitator particles increased as the particle size increases, whereas the crystallinity of cenosphere decreased as the particle size increases. The elastic modulus of fly ash was estimated from the crystallinity of fly ash and the volume fraction of each component, using the rule of mixtures. The calculated upper limits for Young's modulus of precipitator particles were 126 GPa for particles in the size range 150–250 μm and 98 GPa for particles in the size range 5–10 μm. Young's modulus of cenosphere particles was estimated to be approximately in the range of 13–17 GPa in all particle size ranges. The hardness of the larger precipitator fly ash particles (120 μm) exhibited a wide scatter in the range of 160–400 kg mm−2, while the hardness of the smaller size precipitator particles (20 μm) were in a narrow range from 250 to 270 kg mm−2.