Interaction of particles with an advancing solid/liquid interface

The interaction of particles with an advancing solid/ liquid interface has been studied considering mechanical forces and forces arising from the nature of the particle, liquid and solid materials. Experiments were carried out on lead and lead alloys containing iron particles to determine whether the particles were rejected or encompassed by an advancing interface. The distribution of particles in the solid as a function of the morphology of the interface was also examined. It was found that particles were not rejected by an advancing interface and were primarily segregated into cell walls and interdendritic zones for a non planar interface. For a planar interface the particle distribution was uniform both on a macroscopic and microscopic level. This was also the case for solidification in different directions, vertical and horizontal. A water model system was examined to observe directly how particles interact with a solid surface under different velocities and surface conditions. The results clearly demonstrated how spheres segregate to cell walls on a solid cellular interface as a result of mechanical forces. The present results are compared to theories for particle interface interactions in both metal and non metallic systems. Calculations of Lifshitz-Van der Waals forces in a metal show that an attractive force exists between the metal particle and metal surface. As a result particles are not rejected by an interface in a metal system in agreement with the present results. The observed distribution of particles in the solid can be accounted for on the basis of buoyancy forces, convection in the liquid, and the interface morphology.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat