Some chemical, physical, and optical properties of fly ash particles

Fly ash samples from two different generating plants have been examined by laser light scattering techniques. Individual particles below approximately 3-microm diam, found to be primarily spherical, were electrostatically levitated in a single-particle light scattering photometer while their differential light scattering (DLS) patterns were recorded. During this measurement period, the relative humidity within the scattering cell could be varied to study the water accretion properties of the suspended particle. The recorded DLS patterns are used to derive the complex refractive index, size, and accreted layer thickness of the particle. Each particle appears to have a different refractive index, probably indicative of the varied microscopic conditions of formation. Even at very high relative humidities, the fly ash particle surface does not appear to have a natural affinity for water, contrary to popular expectations.