Slags with Na2O (2, 7, 7%)

Name: Slags with Na2O (2, 7, 7%)
Diagram No.: 1139
Type of diagram: TTT
Chemical composition in weight %: See the table
Group: Slag
Note: Effect of Na2O on incubation times of slags with CaO/SiO2 =1, and %Al2O3 in the range 6%-7% [42, 52].
Na2O has an important role related to crystallisation behaviour. The TTT diagrams show that it is possible to control the crystallisation tendency changing the Na2O content in CaO-SiO2-TiO2 slags. The effect of Na2O content on incubation times was shown in literature using the Hot Thermocouple Technique for some simple slags (%CaO/%SiO2 =1 and %Al2O3 in the range 6%-7%) [42, 52]. It can be observed in TTT diagrams that Na2O shortens the incubation times for these slags; see Figure.
Na2O has an important role regarding mould slag viscosity. It is known that the lower the viscosity the easier the crystallisation. In Figure 39 a summary for the viscosity measurements, which were performed with materials whose composition is close to that of the slags used for the SHTT analyses. It can be observed that: (i) When adding TiO2 in a CaO-SiO2 slag (43.3 %CaO, 56.7 %SiO2), the viscosity decreases for all the range of temperatures, and (ii) Afterwards, when adding Na2O in a CaO-SiO2-TiO2 slag (36.4 %CaO, 45.9 %SiO2, 17.7 %TiO2) obtaining in this way a CaO-SiO2-TiO2-Na2O slag (33.5 %CaO, 41.9 %SiO2, 16.3 %TiO2, 8.2 %Na2O, 0.1 %Al2O3) the viscosity decreases more, for all the range of temperatures, and the slope of the curve becomes lower.
Additional links: No. 1135, No. 1136, No. 1137, No. 1139, No. 1140
Reference: Not shown in this demo version.

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