Studies in the System Li ₂ O–Al ₂ O ₃ –Fe ₂ O ₃ ‐H ₂ O

Subsolidus equilibrium relations in a portion of the system Li2O‐Fe 2 O 3 ‐Al 2 O3 in the temperature range 500° to 1400°C. have been determined near po 2 = 0.21. Of particular interest in this system is the LiFe 5 O 8 ‐LiAl 5 O 8 join, which shows complete solid solution above 1180°C. Below this temperature the solid solution exsolves into two spinel phases. At 600°C. approximately 15 mole % of each compound is soluble in the other. The high‐temperature solid solution and the low‐temperature exsolution dome extend into the ternary system from the 1:5 join. There is no appreciable crystalline solubility of LiFeO 2 or of α‐Fe 2 O 3 in LiFe 5 O 8 . An attempt to confirm HFe 5 O 8 as the correct formulation of the magnetic ferric oxide “γ‐Fe 2 O 3 ” was inconclusive, but in the absence of positive evidence, the retention of γ‐Fe 2 O 3 is recommended. All the metallic oxides of the Group IV elements increase the temperature of the monotropic conversion of ‐γ‐Fe 2 O 3 to α‐Fe 2 O 3 . Silica and thoria have a greater effect on this conversion than does titania or zirconia.