Action of Water on Calcium Aluminoferrites.

The action of water on seven preparations of the calcium aluminoferrite solid solution series, ranging in composition from 6CaO·2AlO·FeO to 2CaO Fe0, was studied (a) by leaching the powdered preparations with water, (b) by stirring in a large volume of water at different temperatures from 10 to 100 °C, and (c) by paste hydration at 1, 25, and 45 °C. The initial reaction occurring immediately on contact between the aluminoferrite and water is one of incongruent solution. The AlO, most of the CaO, and a trace of FeO pass into solution, and a residue of FeO, possibly hydrated and amorphous, remains. If the suspension is sufficiently concentrated to give a supersaturated solution, a hydrated precipitate will form. At room temperature the major precipitated phase is 2CaO·AlO 8HO, or a limited solid solution of the same. At 70 °C a solid solution of 3CaO·AlO3 6HO, in which about one-tenth of the AlO is replaced by FeO, is precipitated. The rate of reaction increases with temperature and with the proportion of alumina in the aluminoferrite. Hydration in paste form progresses in a different manner. The hydrogarnet phase produced varies in composition with the parent aluminoferrite, but is always somewhat poorer in FeO The hexagonal plate phase, 4CaO·(AlO,FeO)·HO is produced from the aluminoferrites high in F(eO, especially at the lower temperatures. Another platy phase, 2CaO·AlO·8HO (or its limited solid solution) is formed from preparations highest in AlO, also at lower temperatures. Intermediate members give chiefly the hydrogarnet phase even at 25 °C.