A monte carlo simulation study of dissolution of graphite in iron-carbon melts
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I. INTRODUCTION
A clear understanding of the dissolution behavior of various carbonaceous materials into molten Fe-C alloys and the reactions taking place across the carbon/melt interface is of fundamental importance in a number of iron making processes.[1–4] The dissolution behavior of coals, added either as lump or fines, is highly complex and involves volatile reactions and possible particle breakup. While there have been some studies on the dissolution behavior of coke and coal,[5–9] most of the investigations have focused their attention on the dissolution behavior of graphite.[10–15] These studies, both experimental and theoretical, have provided a great deal of information about the reaction kinetics and various factors affecting the graphite dissolution rate and have generally concluded that the dissolution of graphite is governed by mass transfer in the melt. This implies that the reactions at the interface are much faster than mass transfer and, therefore, do not control the dissolution kinetics. This, however, may not be the case for less ordered materials such as coals, and interfacial reactions could play an increasingly important role in their dissolution. An understanding of the processes occurring at the carbon/melt interface is therefore of crucial importance. Even for graphite, various theoretical studies have been basically analytical in nature, and an atomic level understanding of the interfacial region is far from complete. We have developed an atomic model of the graphite/Fe-C interfacial region and report our main results in this article. In an attempt to understand various atomic reactions taking place at the graphite/Fe-C interface, we developed a theoretical model of the melt and the interfacial region[16] and carried out a Monte Carlo (MC) simulation study. The atoms in graphite and Fe-C melt were arranged on a rigid V. SAHAJWALLA, Senior Lecturer, and R. KHANNA, Research Associate, are with the School of Materials Science and Engineering, The University of New South Wales, Sydney, NSW 2052, Australia. Manuscript submitted July 6, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS B
hexagonal lattice (space group: P63/mmc). The sites in the melt were occupied by Fe and C atoms distributed randomly. Pairwise, short-range interaction was assumed between the atoms. While the interactions were an-isotropic in graphite, they were chosen to be isotropic in the liquid phase. Preliminary results of these simulations showed a good qualitative agreement with experimental trends.[17,18] The main assumption of this model was regarding the structure of the liquid phase. There have been a few studies of the Fe-C solution phase where the atoms were assumed to occupy rigid lattice sites. In the interstitial model,[19] carbon atoms occupy the octahedral interstitial sites with Fe atoms arranged on a regular fcc lattice. Using this model, MC simulations of the a/g phase boundary have been reported in the literature.[20] A two sublattice model using defects[21] and an associated solution model[22] postulating
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