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

Abstract

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. $$ {\text{CaO}}\left( s \right) + \underline{\text{S}} = {\text{CaS}}\left( s \right) + \frac{1}{2}{\text{O}}_{2} $$ $$ 2{\text{CaO}}\left( s \right) + \underline{\text{Si}} + {\text{O}}_{2} = {\text{Ca}}_{2} {\text{SiO}}_{4} \left( s \right) $$ 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. $$ {\text{CaO}}\left( s \right) + \underline{\text{S}} = {\text{CaS}}\left( s \right) + \frac{1}{2}{\text{O}}_{2} $$ $$ 3{\text{CaO}}\left( s \right) + \underline{{2{\text{Al}}}} + \frac{3}{2}{\text{O}}_{2} = {\text{Ca}}_{3} {\text{Al}}_{2} {\text{O}}_{6} \left( {\text{s}} \right) $$