Capillary Interaction Between Micron-Sized Ce₂O₃ Inclusions at the Ar Gas/Liquid Steel Interface

The agglomeration behavior of Ce₂O₃ inclusions was observed in situ on a 20 pct Cr liquid steel surface (i.e., the argon gas/liquid steel interface) using high temperature confocal scanning laser microscopy (CSLM). The inclusions are electrolytically extracted from the steel sample. These inclusions are heterogeneous in chemical composition and are shaped irregularly with a rough surface, suggesting pinning (undulating) three-phase contact lines around the inclusion particles on the liquid steel surface. To understand the interactions between Ce₂O₃ inclusions deeply, the particles are treated either as capillary ‘charges’ with planar contact lines or as capillary ‘multipoles’ with undulating contact lines through the analogy with 2D electrostatics. These capillary interactions include ‘charge’–‘charge’, ‘charge’–‘quadrupole’, ‘charge’–‘hexapole’, ‘quadrupole’–‘quadrupole’ and ‘hexapole’–‘hexapole’. It is found that the interaction between capillary ‘quadrupoles’ performs best in interpreting the strong pairwise attractive force between Ce₂O₃ inclusions. However, there are apparent deviations between the attractive force derived from the CSLM test and that predicted from the capillary ‘quadrupoles’ model. These deviations might be caused by the more complex undulation of the real contact lines rather than the rotational symmetry assumption in the capillary ‘quadrupole’ model. Based on the present analysis, the resistive drag force is larger compared to the inertial force by 3 or 4 orders of magnitude.