Effect of Alkali Oxides on Crystallization in CaO–SiO₂–CaF₂ Glasses

Abstract

In the initial solidification stage in continuous steel casting, controlled crystallinity of the slag film is essential for regulating the horizontal heat flux from the strand to the mold. The effects of alkali oxides on the formation of cuspidine (3CaO·2SiO₂·CaF₂), which is the primary crystalline phase in the flux film in CaO–SiO₂–CaF₂–M₂O glasses (M=Li, Na, K), were investigated in both isothermal and heating conditions. Addition of alkali oxides enhances crystallization of cuspidine by lowering the glass transition temperature and lowering the apparent activation energy of crystal growth. However, single excess addition of alkaline oxide (M₂O) hinders the formation of cuspidine as CaF₂ is substituted by M₂O.