Controlling the shear thinning property of calcium silicate melts by addition of Si3N4

Calcium silicate melts at high temperature are valuable as a lubricant for continuous casting of steel. They are limited by the contradictory situation in that high viscosity is required under low shear rate whereas low viscosity is needed under high shear rate. To resolve such problem, we conducted a rheological study to generate a strong shear thinning behavior of a calcium silicate melts which is an ideal thermal property for continuous casting of steel. We found that a small amount of silicon nitride leads to a strong shear thinning property, allowing a high viscosity at low shear rate without significant changes in the viscosity at higher shear rates. Such trend is completely opposite to the one previously suggested with a borate additive. This improvement of the shear thinning property arises because each additive enables these calcium silicate melts to have a shear thinning favorable structure in thoroughly different manner.