Slag Characteristics and Composition

To work within a reasonable and practical melting temperature range, at or below 1200°C, it is necessary to operate within a restricted region within the following boundaries of an idealised ternary 

This will give average ratios as follows  

The basicity index = molar ratio of (CaO + MgO + FeO + ZnO + PbO) to (2Si02 + 3 AI2O3). The fluidity index = mass ratio of (CaO + MgO + FeO) to (S1O2 + AI2O3). 

The concept of slag basicity is analogous to pH in aqueous systems and is useful in characterising general behaviour of the slag as it affects the following  

Most simply, basicity can be expressed as the Ca0 Si02 ratio or by the more complete basicity index as shown in Table 5.2. The fluidity index also shown in Table 5.2 is clearly a closely related empirical guide, demonstrating that viscosity is influenced by basicity. A more basic slag will have a higher fluidity or lower viscosity. 

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