Research on the Activity of Components in Fundamental System of Iron Blast Furnace Slag. IV : The Activity of Lime in the System CaO-SiO_2-Al_2O_3

Our previous reports described the determination of the activity of SiO_2 and Al_2O_3 in the slag of CaO-SiO_2-Al_2O_3 system by using the e. m. f. method of double cell. As it is difficult to construct the cell with reversible calcium electrode at high temperature, the authors tried to determine the activity of CaO with solid lime at 1630°as the standard state using Gibbs-Duhem equation. First, the activity of CaO on the system CaO-Al_2O_3 was determined. Then the same calculation was extended to CaO-SiO_2-Al_2O_3 and CaO-SiO_2 systems. From these values, the iso-activity lines were drawn on the ternary coordinates of CaO-SiO_2-Al_2O_3. The course of iso-α_ line was similiar to the so-called sulphur capacity lines. From the activity-composition diagram on the system CaO-SiO_2, α_ saturated with 2CaO・SiO_2 was given as 0.25