A New Scale of Basicity in Oxide Slags and the Basicity of the Slags Containing Amphoteric Oxides

Abstract

The well-known fact, that γ=Fe³+/ (Fe²⁺+Fe³⁺) is increased by additions of basic oxides and decreased by acidic oxides under the constant oxygen pressure, has been selected to measure the basicity of slags. If the concentration of the slag, whose basicity is to be determined, is represented by C=ΣM/ (ΣFe+ΣM), where ΣFe= Fe²⁺+ Fe³⁺and ΣM=Ca²⁺+ Si⁴⁺+Ti⁴⁺+Al³⁺. c. c, and γ of the pure iron oxide by γ_o, the new scale of basicity is given by the equation B { (γ-γ_o) /C } x10.
The studied slags are (1) pure oxides CaO, SiO₂, TiO₂ (2) binary slags CaO-SiO₂, CaO-TiO₂, SiO₂-TiO₂, CaO-Al₂O₃, SiO₂-Al₂O₃, and (3) ternary slags CaO-SiO₂-TiO₂, CaO-SiO₂-Al₂O₃. Samples used in the experiment are of iron oxide with additions of the slag, whose basicity is to be determined. The slag sample is equilibrated under an atmosphere of CO₂/CO=133 at a temperature of 1480°C. The basicity (B) was determined from the results of analyses for Fe²⁺ and Fe³⁺.
The values of B for CaO, SiO₂ and TiO₂ are such as would be expected from the metaloxygen bond strength. In the systems CaO-510₂ and CaO-TiO₂, B changes approximately linearly with mol %, but in the system SiO₂-TiO₂ a maximum appears. The basicity of CaO is decreased by the additions of Al₂O₃, while that of SiO₂ is increased.
Isobasicity lines of the ternary systems are shown in the ternary diagrams, and einpirical equations of basicity were obtained for the concentration range CaO/SiO₂=1/3-4 and TiO₂ (or Al₂O₃) =0-35%. At a certain CaO/SiO₂ the basicity does not change with additions of TiO₂ or Al₂O₃. The basicity corresponding to this CaO/SiO₂ is termed the isoelectric point (B_i). At lower ratios of CaO/SiO₂ B is increased and at higher ratios decreased by additions of TiO₂ or Al₂O₃. Thus by the term of isoelectric point the amphoteric behaviour of slag constituents can be discussed quantitatively. It was found that B_i is decreased with increase of the metal-oxygen bond strength.