Atomistic Simulations of the Work of Adhesion at Metal Oxide Interfaces
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ABSTRACT In this work we have studied magnetite scale adhesion on a tube made from some different type materials, and treated metal oxide interfaces between magnetite scales (Fe 30 4) and stainless steel tube surface oxides (NiFe 20 4) or chromium coating tube surface oxides (Cr 20 3, FeCr 20 4). In this paper we have defined new MEAM (Modified Embedded Atom Method) parameters for Fe0, Cr-O, Ni-0, Fe-Ni, and Fe-Cr pair interactions based on experimental information such as lattice constants, cohesive energies, bulk moduli of those metal oxides, and have calculated the work of adhesion at Fe 30 4 (110) / Fe 30 4 (110), NiFe2 0 4 (110), Cr 20 3(110), Cr 20 3(100), FeCr 20 4(1 10) interfaces where a cluster-surface interfacial model is adopted. As the results of the calculation, it was found that there is an energy barrier, which prevents scales from approaching a tube surface, in a potential energy curve vs. a separation between scales and chromium coating surfaces. We further discuss the effect of surface directions at interfaces on the work of adhesion. INTRODUCTION Evaluation of the work of adhesion at metal oxide interfaces is very important technologically in various fields such as a development of composite materials, catalysts and materials preventing impurity adhesion, etc. Experimental measurements of the work of adhesion by a scratch method [1] etc., however, have a problem that there is little reliability in the measured values even if the same apparatus and materials are used. Hence, it is necessary to predict it by simulation methods. In this paper adhesion at technologically important metal oxide interfaces on scales, problem has been studied by atomistic simulations with interatomic potentials, the Modified Embedded Atom Method (MEAM) developed by Baskes et al. [2,3]. The MEAM was used to calculate the geometry and the work of adhesion between magnetite scales (Fe 30 4) and stainless steel tube surface oxides (NiFe 20 4) or chromium coating tube surface oxides (Cr 2 0 3 , FeCr 204). The MEAM follows the EAM concept [4,5] in that the energy of a given atom is taken as one half the energy in two-body bonds with its neighboring atoms plus the energy to embed the atom in the electron density at its site arising from all the other atoms. In the EAM, this background electron density is a simple sum of radially dependent contributions from the other atoms, while in the MEAM the background electron density includes angular dependence. Also, the most recent implementation of the MEAM [2] incorporates a strong screening function so that the model is very short ranged for a structure that is reasonably tight packed, but can be long ranged in open structures such as at a surface. MEAM potentials are now available [2,3] for 44 elements in the periodic table including materials with fcc, bcc, hcp, and diamond cubic crystal structures. In addition, the MEAM has been recently applied to an interface between a metal and an ionic material, AI/A120 3 [6]. In this study, in order to calculate the work of adhesion at Fe 3
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