Experiments were carried out to investigate the effect of surface roughness of MgO substrate on the formation and size distribution of inclusion particles employing new experimental methodology. The reaction of MgO refractory with Al deoxidised liquid Fe can take place, which results in forming both MgO and spinel type of inclusions. The number density of inclusions increases with increasing surface roughness of the substrate, which could be explained by Gibbs-Thompson effect. Activated interfacial reactions between the substrate and liquid Fe are believed to be more dominant than the effect of increased surface roughness of the substrate on the number density of inclusions. It is recommended to use Al 2 O 3 based nozzle than MgO based one of similar surface roughness from a viewpoint of the generation of lower number density of inclusions.

In the current investigation, the thin film method was employed to clarify the formation mechanism of inclusions at the interface between refractory and liquid Fe. According to the electron probe microanalysis (EPMA) mapping of the interface, a Si peak corresponding to SiO 2 was significant at the interface between the refractory and Fe and a small amount of Fe oxide existed. A reacted layer was formed in a way that initially FeO enriched liquid layer was widely distributed on the Fe surface and FeO and SiO 2 in the liquid layer were reduced by Al in liquid Fe to develop solid Al 2 O 3 enriched layer of inclusions. Some inclusions in the liquid Fe might be produced by the remaining oxygen in Ar gas which was supplied through the nozzle to prevent the adherence of inclusions onto it. Thermodynamic prediction was carried out to confirm if the oxygen partial pressure with increasing the oxygen activity on Fe surface could closely be related to the formation of reacted layer.

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