Motion of Fine Particles under Interfacial Tension Gradient in Relation to Continuous Casting Process

In front of the solidifying interface of a water solution, in the case of NaCl water solution, fine bubbles (10~100 μm in diameter) were just moving upward, no matter how close they were from the solidifying interface. However, in front of the solidifying interface of C₈H₁₇SO₃Na water solution, once the distance between the bubbles and the solidifying interface became less than 90~100 μm, rising bubbles were found to move horizontally toward the solidifying interface quickly, and then to be engulfed by the interface. This effect can be attributed to the surface tension gradient around the bubbles induced by the concentration gradient in the boundary layer formed in front of the solidifying interface. The phenomenon is taken as a kind of the Marangoni effect in a broad sense. The movement of fine particles driven by the interfacial tension gradient is found to have a close relationship to certain phenomena in continuous casting processes, such as the occurrence of bubble or inclusion‐related defects in steel and nozzle clogging.