Metallic oxide microphases in fly ashes: An ultrastructural investigation

Fly ashes from fuel oil combustion consist almost entirely of hollow, spheroidal formations, cenospheres, with sizes ranging from about 10 to 100 mu m. These particles, produced during microdrop fuel oil combustion, look like droplet skeletons with numerous holes irregularly distributed on their surface. Heavy metals are present in fly ashes mostly like crystalline sulphate or oxide phases located into the cenosphere hollow. In this paper oxide phases were studied. They turned out to be prevalently composed of small particles with irregular shapes and sizes ranging from less than 0.1 mu m to about 1 mu m. Oxide microparticles were classified by cluster analysis; the atomic percentages of eight metallic elements-Fe, Ni, V, Al Cr, Mg, Zn, Ti, that represent virtually all the cations revealed in the composition of the oxides-were used to evaluate the ''degree of similarity''. On the basis of the obtained chemical, compositional and morphological data the structure of the major metallic oxide phases was defined.