THERMOPHYSICAL PROPERTIES EFFECTS ON SEGREGATION DURING SOLIDIFICATION

The phenomenon of particles segregation by a solidification front is v ery important in several areas like metallurgy, materials science, bio logy, soils freezing, etc. When a particle is close to a freezing fron t, it may be trapped in the solid region or may be repulsed by the mov ing freezing interface. The behaviour of the particle depends essentia lly on its size and on the distance between the particle and the inter face. In this contribution, we develop a theoretical investigation of the different forces exerted on a solid particle and make comparisons with recent observations. The results should apply also to gas bubbles and droplets. The involved forces, i.e. the hydrodynamic force which favours capture, and the van der Waals forces which may induce rejecti on are determined for various sets of conditions and assumptions: idea l case (pure liquid, planar interface, smooth particle); and realistic cases (curved interface, different surface properties of the particle ). Moreover, the boundary conditions for viscous drag are time depende nt and clearly expressed. This represents a first step towards the dev elopment of a dynamical model. (C) 1998 Elsevier Science B.V.