EQUILIBRIUM STUDIES IN THE SYSTEM FeO‐AI ₂ O ₃ ,‐SiO ₂ *

A bstract Equilibrium relationships on the liquidus surface in the system Fe0‐Al 2 O 3 SiO 2 have been established by a modified quenching procedure. The crystal phases which separate from melts heated in iron crucibles are fayalite (2FeO·SO 2 ), hercynite (FeO·Al 2 O 3 ), tridymite and cristobalite (SiO 2 ), mullite (3Al 2 O 3 ·2SiO 2 ), corundum (Al 2 O 3 ), and wastite (approximately FeO). A considerable portion of this system is liquid at 1400°C. Diagrams show the isotherms and the index of refraction of the glasses formed. Two quintuple points have been established in this investigation. One point is at the composition, SiO 2 42% by weight, Al 2 O 3 13%, and FeO 45%, and is a eutectic involving the phases fayalite, hercynite, and tridymite at 970°C. ± 200C. The preferred composition of the second quintuple point is 48% of SO 2 , 23% of Al 2 O 3 , and 29% of FeO; it is a peritectic, and the crystal phases are mullite, hercynite, and tridyrnite. Crystallization from this melt without a change in the weight composition calls for the resorption of mullite at a temperature of 1100°C. ±20°C.