Carbide Capacity of CaO-SiO₂-CaF₂(-Na₂O) Slags at 1 773 K

Abstract

The influence of CaF₂, Na₂O, and basicity on the solubility of carbon in the CaO-SiO₂-CaF₂-Na₂O slag at 1 773 K was investigated on the basis of carbide capacity concept. The carbide capacity of the CaO_satd-SiO₂-CaF₂ system increases with increasing CaF₂ content up to about 40 mass%, followed by nearly constant value. The capacity of the slags saturated with Ca₂SiO₄ also increases with increasing the content of CaF₂ and this trend can be explained from the depolymerization reaction of silicate network by F⁻ ions. The carbide capacity of the slags increases by increasing the ratio of (%CaF₂)/(%SiO₂) up to about 0.8, followed by slight increase or nearly constant value at a fixed CaO content. The capacity also increases by increasing the ratio of (%CaO)/(%SiO₂) at a fixed CaF₂ content. The carbide capacity of the Na₂O-containing slags linearly increases with increasing the basicity, B (≡{(%CaO)+(%Na₂O)}/(%SiO₂)) and the dependence of the capacity on the basicity decreases by increasing the CaF₂ content. On the other hand, the capacity decreases with increasing CaF₂ content at basicity, B of the slags greater than about 2.0 and vice versa in the composition of B≤2.0. The capacity of the slags containing CaF₂ and Na₂O could quantitatively be described by the activity of CaO rather than optical basicity.