CHARACTERIZATION OF CALCIUM-RICH STEEL SLAG WITH FLUORINE-BEARING MICRODOMAINS

Abstract

In this study, steel slag particles were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) to clarify how micro-scale morphology relates to local chemical composition. High-magnification secondary-electron images showed that the slag consists predominantly of angular, brittle fragments with sharp edges and irregular particle outlines, which is typical of rapid fracture of heterogeneous, hard phases. Many surfaces exhibited lamellar, stepped, or cleavage-like features, indicating preferential crack propagation along phase boundaries or crystallographic planes. In addition, numerous fine particles were observed adhering to larger fragments and accumulating in surface recesses, suggesting either mechanical attrition during handling/grinding or the presence of weakly bonded secondary phases. The coexistence of smooth, plate-like regions and more granular, porous zones supports the interpretation of a multi-phase material with localized differences in toughness and fracture mechanisms.

Elemental characterization was performed using an EDS map-sum spectrum collected from a representative area of the particle surface. The spectrum was dominated by calcium, evidenced by a strong Ca Kα peak, accompanied by oxygen as the second major component, consistent with a matrix rich in Ca-bearing oxides and/or silicates. A noticeable fluorine contribution was also detected, implying the presence of fluoride-containing phases or residual flux-related compounds intro-duced during steelmaking and slag conditioning. Silicon and magnesium appeared as minor constituents, which may reflect limited amounts of silicate phases and Mg-bearing oxides/spinels dispersed within the Ca-rich matrix. Manganese was detected only at trace level, suggesting either dilute substitution in oxide phases or small inclusions below the spatial resolution of the map-sum area.