A Study on the Formation Mechanism of the Interfacial Layer Between Solid CaO and Molten Iron Alloys

The present study aims to clarify the formation mechanism of the interfacial layer between solid CaO and molten iron through SEM–EDS analysis. The interfacial layer formed between CaO and molten iron is observed by SEM–EDS for different compositions of molten iron (CaO/Fe–C–S interface: CaS layer; CaO/Fe–C–Si–S interface: CaS and Ca₂SiO₄ layers; CaO/Fe–C–Si interface: no interfacial layer; CaO/Fe–S–Si interface: Ca₂SiO₄ and CaS layers). The effect of S and Si concentrations on layer formation is discussed using the following proposed mechanism.$$\text{CaO}\left(s\right)+\underset{\_}{\text{S}}=\text{CaS}\left(s\right)+\frac{1}{2}{\text{O}}_2$$$$2\text{CaO}\left(s\right)+\underset{\_}{\text{Si}}+{\text{O}}_2={\text{Ca}}_2{\text{SiO}}_4\left(s\right)$$ In the case of the Fe–C–Si–Al–S/CaO interface, CaS and Ca₃Al₂O₆ layers are observed. The formation mechanism of a reaction layer for Al-containing iron melts is also proposed as below.$$\text{CaO}\left(s\right)+\underset{\_}{\text{S}}=\text{CaS}\left(s\right)+\frac{1}{2}{\text{O}}_2$$$$3\text{CaO}\left(s\right)+\underset{\_}{2\text{Al}}+\frac{3}{2}{\text{O}}_2={\text{Ca}}_3{\text{Al}}_2{\text{O}}_6\left(\text{s}\right)$$