Determination of Area Fraction of Free Lime in Steelmaking Slag Using Cathodoluminescence and X-ray Excited Optical Luminescence

Determining the free lime (f-CaO) content in steelmaking slag is critical for road construction because f-CaO is likely to cause road expansion. Herein, we present a method to determine an area fraction of f-CaO from fractions of illuminated areas related to f-CaO in cathodoluminescence (CL) or X-ray excited optical luminescence (XEOL) image of industrial steelmaking slag, which is simpler and quicker than the commonly employed ethylene glycol extraction method. A heat-treatment in which the industrial steelmaking slag was quenched from 1000 °C was needed to obtain intense luminescence from f-CaO, which originated from a peak at 600 nm. Other mineral phases, such as Ca₂SiO₄, free magnesia, and 2CaO·Al₂O₃·SiO₂, were distinguishable from f-CaO from their luminescent colors. When we analyzed three types of industrial steelmaking slag with different f-CaO contents, the order of the fractions of the illuminated areas originating from f-CaO in the CL images was consistent with that of the f-CaO content measured applying the ethylene glycol extraction method. The average exposure times it took the CL and XEOL images to detect the luminescence from f-CaO were 5 and 30 seconds, respectively. In particular, acquiring XEOL images is promising for on-site analysis.