Monte carlo simulation of clustering of alumina particles in turbulent liquid aluminum
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I.
INTRODUCTION
PARTICLES suspended in liquid metals tend to form clusters that may be harmful or beneficial depending on the application.[1] For example, in liquid state processing of metal matrix composites (MMCs) containing ceramic particles, the formation of particle clusters results in a nonuniform microstructure that may reduce the ductility of the material but enhance its strength and work hardening capacity.[2] In liquid metal purification processes, formation of clusters may promote separation of undesirable particles from the liquid metal by enhancing sedimentation, flotation, or filtration.[3] An understanding of the mechanisms of clustering is of considerable importance from both the academic and industrial points of view. While clustering of second-phase particles in MMCs has been observed in many systems, there have been few studies of the kinetics of this process. Zou et al.[4] employed a Monte Carlo technique to simulate the clustering phenomena of small (0.1 and 1.0 mm) alumina particles in a stagnant liquid aluminum melt under the influence of Brownian motion and gravity. They found that 0.1-mm particles had a stronger tendency to form clusters than 1.0-mm particles and that only the larger particles were affected by gravity. In addition, they found that Brownian motion was significant for both particle sizes. Normally, the size of particles incorporated into commercial MMC materials is around 10 to 15 mm.[1] For such large particles, Brownian motion is expected to be negligible. Furthermore, in most liquid state processing, the melts are in motion, either from natural convection or mechanical mixing. To simulate the clustering phenomena under these conditions, appropriate models must be developed to take into account the turbulent nature of the melt. In this article, a model aimed at describing the clustering phenomena under turbulent flow conditions was developed and tested. C. TIAN, formerly Postdoctoral Fellow, Department of Materials Science and Engineering, McMaster University, is Research Scientist, Division of Manufacturing Technology, CSIRO, Preston, Victoria 3072, Australia. G.A. IRONS, holder of the Dofasco/NSERC Industrial Research Chair in Process Metallurgy, and D.S. WILKINSON, Chair and Professor, are with the Department of Materials Science and Engineering, McMaster University, Hamilton, ON, Canada L8S 4L7. Manuscript submitted October 29, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
II.
LITERATURE REVIEW
A. Cluster Formation Clustering of particles in liquids is encountered in many fields of science and engineering and takes on various names such as flocculation, agglomeration, coagulation, or aggregation, depending on the area of application.[5] Research has shown that formation of clusters is essentially governed by two processes, transportation and adhesion. For a cluster to form, the particles must first collide with each other, and then they must be held together by attractive or adhesive forces. The collisions can be considered as the kinetic condition, governed by
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