Spectral measurement of the complex refractive index of fly ashes of canadian lignite and sub‐bituminous coals

The complex spectral refractive index (absorption index) of fly ash from two generating stations burning Canadian lignite and sub‐bituminous coals have been examined by two different techniques. Ash samples collected at different combustion conditions were analyzed. It is shown that the absorption index of both ashes is in the range of 0.004 to 0.018 in the wavelength range of 0.7‐2.5 μm. The effects of presence of carbonaceous material in ashes, iron content and different operating (combustion) conditions are reported.