Magnetite scale cluster adhesion on metal oxides surfaces: atomistic simulation study

Magnetite scale (Fe3O4) cluster adhesion on stainless steel, Ni-alloy tube surface oxides (FeCr2O4 or NiFe2O4) and chromium coating tube surface oxides (Cr2O3 or FeCr2O4) has been studied using static atomistic simulations and molecular dynamics (MD) simulations with new modi®ed embedded atom method (MEAM) potentials developed to describe interatomic interactions in the metal oxide systems. We calculated total energies and the work of adhesion at Fe3O4(1 1 0)/ NiFe2O4(1 1 0), FeCr2O4(1 1 0), Cr2O3(1 0 0), Cr2O3(1 1 0), Cr2O3(0 0 1) interfaces where a cluster-surface interfacial model is adopted with consideration of an orientation of the cluster. In addition, the magnetite scale cluster adhesion behavior on the metal oxide surfaces was studied by MD simulations. As the results of the simulations, it was found that there is an energy barrier which prevents a magnetite scale cluster from approaching a tube surface due to an interaction of interfacial oxygen atoms in a potential energy curve versus a separation only between the cluster and the chromium coating surfaces without iron atoms, Cr2O3. We observed that the more following conditions were satis®ed in the metal oxide surfaces, the easier the energy barrier is to be made: (i) crystal structures different from magnetite scale crystal structure, (ii) surface directions with asymmetrical surface oxygen positions, (iii) inclusions of surface chromium atoms. The energy barrier formation on Cr2O3 surfaces was also con®rmed by density-functional-theory calculations using a simple interfacial model. # 2001 Elsevier Science B.V. All rights reserved.