Hello Gulam,

Because it is essential for formation of C3S and protection of the kiln bricks, I would say that the quantity of liquid phase is of critical importance. The other physical properties of liquid phase such as viscosity and surface tension are more useful in fine tuning such things as clinker granulometry and stabilizing coating.

Normally you need about 25 +/- 5% of liquid phase (@ 1450 deg. C) for economic kiln operation. Within this broad general range,  the optimum quantity and viscosity of liquid phase will be slightly different for each plant, and for each type of cement. This optimum can be determined through plant trials by fine tuning the raw meal silica ratio and alumina ratio.

Best Regards,

Ted.