Carbon Solubility in the CaO-SiO2-3MgO-CaF2 Slag System

The carbon solubility in the CaO-SiO2-3MgO-CaF2 slag system at 1773 K (1500 degrees C) was investigated under CO/Ar and CO/N-2 gases. Higher extended basicity [(CaO+MgO)/SiO2) increased the carbon solubility in the slag as the activity of free oxygen ions (a(O)(2-)] promoted the reaction of the free carbide mechanism. Higher CaF2 also resulted in higher carbon dissolution into the slag as fluorine ions interact with the bridged oxygen (O-0) in the melt structure to increase the activity of the free oxygen ions in the melt. Structural information obtained from the Fourier transformed infra-red (FT-IR) and Raman revealed a depolymerization of the network structure as the simpler structural units of NBO/Si = 4 increased and the Si-O-Si bending vibrations decreased with higher basicity and CaF2 content. This correlated well with higher free oxygen ions (O2-) in the slag system and subsequently higher carbon dissolution. A correlation of the theoretical optical basicity (A(th)) with the logarithm of the carbon content in slag showed a relatively similar trend and an increase of carbon was observed with higher optical basicity. (C) The Minerals, Metals & Materials Society and ASM International 2014