THE ACTIVITY OF CALCIUM IN CALCIUM-METAL-FLUORIDE FLUXES

The standard Gibbs energy of reaction Ca (1) + 0 (mass pct, in Zr) CaO (s) has been determined as follows by equilibrating molten calcium with solid zirconium in a CaO crucible: Delta G degrees = -64,300(+/-700) + 19.8(+/-3.5)T J/mol (1373 to 1623 K) The activities of calcium in the CaOsatd-Ca-MF(2) (M: Ca, Ba, Mg) and CaOsatd-Ca-NaF systems were measured as a function of calcium composition at high calcium contents at 1473 K on the basis of the standard Gibbs energy. The activities of calcium increase in the order of CaF2, BaF2, and MgF2 at the same calcium fraction of these fluxes. The observed activities are compared with those estimated by using the Temkin model for ionic solutions. Furthermore, the possibility of the removal of tramp elements such as tin, arsenic, antimony, bismuth, and lead from carbon-saturated iron by using calcium-metal-fluoride fluxes is discussed.