Surface modelling of crystalline non-metallic inclusions

Non-metallic inclusions such as corundum and spinel-type compounds are crystalline at steelmaking temperatures. The crystal structure and the configuration of the atoms at the crystal surfaces affect the surface related energies and thus the growth forms of the inclusions near equilibrium. Potential growth layers in spinel are described by the application of the Hartman–Perdok theory (HPT). Four different periodic bond chains (PBCs) have been found, i.e., 〈12 12 0〉, 〈0 0 1〉, 〈12 12 1〉 and 〈0 12 112〉. These PBCs give rise to five F faces, which are in order of decreasing slice thickness: {1 1 1}, {2 2 0}, {1 1 3}, {4 0 0} and {3 3 1}. Electrostatic point charge computations, taking into account the short-range interactions as well, were carried out to compute the attachment energies and specific surface energies of the F faces to derive the theoretical growth form and the theoretical equilibrium form, respectively. For spinel the growth form is an octahedron, while the equilibrium form is a combination of an octahedron with a minor rhombic dodecahedron. These theoretical forms are rather similar to the growth forms observed as non-metallic inclusions.