The well-known fact, that γ=Fe
3+/ (Fe
2++Fe
3+) 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= Fe
2++ Fe
3+and ΣM=Ca
2++ Si
4++Ti
4++Al
3+. 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, SiO
2, TiO
2 (2) binary slags CaO-SiO
2, CaO-TiO
2, SiO
2-TiO
2, CaO-Al
2O
3, SiO
2-Al
2O
3, and (3) ternary slags CaO-SiO
2-TiO
2, CaO-SiO
2-Al
2O
3. 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 CO
2/CO=133 at a temperature of 1480°C. The basicity (
B) was determined from the results of analyses for Fe
2+ and Fe
3+.
The values of
B for CaO, SiO
2 and TiO
2 are such as would be expected from the metaloxygen bond strength. In the systems CaO-510
2 and CaO-TiO
2,
B changes approximately linearly with mol %, but in the system SiO
2-TiO
2 a maximum appears. The basicity of CaO is decreased by the additions of Al
2O
3, while that of SiO
2 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/SiO
2=1/3-4 and TiO
2 (or Al
2O
3) =0-35%. At a certain CaO/SiO
2 the basicity does not change with additions of TiO
2 or Al
2O
3. The basicity corresponding to this CaO/SiO
2 is termed the isoelectric point (B
i). At lower ratios of CaO/SiO
2 B is increased and at higher ratios decreased by additions of TiO
2 or Al
2O
3. 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.
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