Crystallization behavior of Li₂O-SiO₂, Na₂O-SiO₂ and Na₂O-CaO-SiO₂ glasses

It has been known that crystallization of mold powder is effective on the disturbance of heat transfer between mold and solidified shell in production of middle carbon steel slabs in continuous casting process. But it has not yet been made clear which composition of mold powder is the most suitable for crystallization. The crystallization behavior of Li₂O-SiO₂, Na₂O-SiO₂ and Na₂O-CaO-SiO₂ glasses was observed by differential thermal analysis (DTA) and hot-thermocouple methods with DTA in the present work. As a result, addition of alkaline metal and alkaline earth metal oxides to SiO₂ increased the critical cooling rate for glass formation in binary system of Li₂O-SiO₂ and Na₂O-SiO₂, and Li₂O-SiO₂ system crystallized easier than Na₂O-SiO₂ system. In ternary system of Na₂O-CaO-SiO₂, addition of Na₂O hurried the critical cooling rate at CaO/SiO₂ = 0.93 mass ratio, but the rate was almost constant in the composition range of more than 15 mass% Na₂O. The slag of CaO/SiO₂ = 0.93 made the rate faster than the slag of CaO/SiO₂ = 0.47 at constant content of 10mass% Na₂O.