Abstract
The e. m. f. measurement of double cells was applied in order to determine directly the activity of CaO in CaO-SiO2 slags at 1, 600°C.
The electrodes used in the cell were of two tungsten rods, which had been treated in a molten slag bath by passage of direct current as cathodes and confirmed to be capable of using for a calcium electrode by electrode potential measurement, spectroanalysis and X-ray diffraction.
The e. m. f. of eight CaO-SiO2 slags against a reference slag and the e. m. f. of one of them against the CaO-Al2O3 molten slag coexisting with solid lime were measured at 1, 600°C. From these observed values the activities of CaO at 1, 600°C relative to solid lime were calculated.
The activity of SiO2 in the system was also found from that of CaO relative to solid silica by means of the Gibbs-Duhem relation.
Even a small amount of the sulfur in slags lowered very rapidly the activity of CaO in them.
