The Effect of the Slag Formation on the Impurity Removal for the Floating Zone Melting of Iron

The zone melting method is often adopted to achieve ultra‐high‐purity materials. Herein, ultra‐high‐purity irons (>5 N) are prepared by the floating zone melting method. Two major purification effects during the zone melting, i.e., segregation and evaporation, are clearly confirmed. Besides, another purification effect, related to the formation of the slag layer at the surface of the melting‐zone tail, is also found. The insoluble particles, which are most composed of the Al and Si oxidizes, can be accumulated together under the forced convection in the melting zone, and finally lead to the formation of the slag layer at the surface. Therefore, this purification effect, based on the movement of this slag layer from the head into the end of the whole melting zone, can partly remove the elements like Al and Si, which are normally difficult to be removed by the segregation and evaporation process.