Characterization of an existing sample of cenospheres produced during residual-oil-fired steam power plant combustion included: scanning electron microscopy of surface structure; photomicrography of particle cross sections; measurement of porosity, surface area, and density; and measurement of chemical composition. The studies showed that typical large (100–200 μm) and small (20–40 μm) cenospheres were spheroidal and hollow and had at least one blowhole. The sizes of the blowholes range from 10 to 50 percent of the diameters of the cenospheres. The ratio of outer to inner diameter of the shell was of the order of 1.3–1.4. The shells are porous, the larger ones appearing spongelike, the smaller ones appearing smoother but containing many pores a few micrometers in diameter. The solid portions of the shell appear flaky and layered. A typical cenosphere contained only about 18 percent solid material on a volumetric basis. A relatively concentrated percentage content of elements S, Fe, Na, and V was indicative of the potential contribution to high-temperature corrosion from cenosphere deposition on heat exchanger surfaces.

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