Dual roles of Cr2O3 in preparation of glass-ceramics from ferronickel slag

The dual effects of Cr2O3 in the fabrication of glass-ceramics from ferronickel slag (FNS) with the addition of coal fly ash (CFA) were investigated by varying the content of Cr2O3 from 0 wt % to 2.0 wt %. The crystallization kinetics results showed that as the Cr2O3 content increased from 0 wt % to 1.6 wt %, the crystallization activation energy of the parent glass decreased from 448.23 kJ/mol to 232.65 kJ/mol with the change of crystallization mode from surface crystallization to bulk crystallization. When the content of Cr2O3 reached 1.6 wt %, there existed the highest degree of depolymerization of the glass network and the strongest crystallization tendency. The prepared glass-ceramic was composed of enstatite as the main crystalline phase and spinel as the secondary crystalline phase. The microstructure changed from a loose tabular structure to a dense spherical structure. As the Cr2O3 content further increased to 2.0 wt %, the crystallization activation energy increased to 304.21 kJ/mol and the spherical structure became inhomogeneous due to the coexistence of enstatite particles with different sizes. By controlling the Cr2O3 content of 1.6 wt %, an optimal glass-ceramic with density of 3.17 g/cm3, bending strength of 175 MPa, Vickers microhardness of 9.51 GPa, acid resistance of 99.99% and alkali resistance of 99.97% was obtained. This study provided a novel method for promoting conversion of FNS to glass-ceramics.