is viscosity, A is an empirical constant, E is activation energy, T is temperature and R is gas constant. For a given temperature, addition of basic oxides decreases rapidly the viscosity of a slag which contains  and . The decrease in viscosity is greater with alkaline oxides like  and fluorides like as compared with CaO and MgO for the reasons discussed in lecture 4.

Alumina acts as a network breaker in an acidic slag and network former in a basic slag.

Presence of solid particles in slag increases the viscosity of slag as shown in the following expression:

(2)

                                                                   
Where  is volume fraction of solids in slag

If volume fraction of the solid is in between 5% to 10%, viscosity of slag increases by 114% to 130%.