In the present study, we measured the viscosity change with the melting time (melting temperature: 1873 K, 1773 K or 1673 K, atmosphere: air) of calcium ferrite (CaO·Fe₂O₄(CF)) based slags (CF, CF–5wt%SiO₂ and CF–5wt%Al₂O₃) by the rotating crucible method. Moreover, the viscosity changes were discussed from the viewpoints of the iron oxidation states (Fe²⁺ and Fe³⁺) and the coordination number of Fe³⁺.
Viscosity of the CF based slags decreased with the melting time at all the temperature (1673 K, 1773 K or 1873 K). Viscosities of the slags became constant after the melting time of 120 min at 1873 K and at 1773 K. In the case of the melting at 1673 K, the viscosity of the slags became constant after 240 min. The results of the chemical analysis indicated that the oxidation state of iron ions in the quenched CF slag was not changed during the viscosity measurements. We could not directly observe the change in the coordination structure of Fe³⁺ in CF based slags during the melting time, because the CF based slag could not be vitrified due to the limitation of quenching rate in the present study. However, the data of the viscosity and the structural information for 40CaO–40SiO₂–20Fe₂O₃ (mol%) slag indicated that the coordination structure of Fe³⁺ strongly affect the viscosity of iron-containing slags. The decreases in the viscosity of the CF based slags would be also controlled by the change in the coordination number of Fe³⁺.