An electrochemical method was tested in order to find a suitable experimental technique for the determinations of the activities of P2O5 in molten fluxes used for external dephosphorization of hot metal. This technique consists of equilibrating phosphorus‐containing copper with molten slag and measuring the equilibrium oxygen partial pressure by means of solid state galvanic cells. The activities of P2O5 in MgO—P2O5 were determined with this technique.

Coulometric titration technique has been employed for the determination of the parameter, Pe, defined as the oxygen partial pressure at which the n-type and ionic conductivities are equal, for various commercial zirconia electrolytes in the temperature range from 1243 to 1873 K. Measured values of the parameter, P, have been expressed by a formula, logP=A+B/T, where A and B denote constants. The P values for CaO-stabilized ZrO2 have shown negligible dependence on the conMeasured values of P for MgO-stabilized ZrO2 have shown a slight decrease with an increase in the concentration of cubic ZrO2 from 40% to 100%.

The oxygen partial pressures of the equilibrium among solid magnesia, phosphorus-containing liquid copper and trimagnesium phosphate were measured by means of solid-oxide galvanic cells. These cells incorporated magnesia-stabilized zirconia as solid electrolyte and Mo +Mo0 2 as reference electrode at 1473,1 523 and 1 573 K.Then the activities of phosphorus in liquid copper, and the free energy of dissolution of diatomic phosphorus gas into liquid copper at infinite dilution refered to 1 wt. pet. were determined. Untersuchungen derPhosphoraktivitaten in fliissigem Kupfer mit galvanischen Zellen. Die Sauerstoff-Partialdrucke im Gleichgewicht zwischen festem Magnesium, phosphorhaltigem, ftussiqern Kupfer und Trimagnesium-Phosphat werden mit galvanischen Zellen gemessen. Diese Zellen beinhalten magnesiumstabilisierten Zirkon als festen Elektrolyten und Mo + Mo0 2 als Referenzelektrode bei 1473, 1523 und 1573 K. Anschlielsend werden die Phosphoraktivitaten in flussiqern Kupfer bestimmt. Die freie Enthalpie der Auflosunq von zweiatomigem Phosphorgas in flussiqem Kupfer bei unendlicher Verdunnunq bezieht sich auf 1Gew.-%.(1)

The activities of FexO in CaO + CaF2 + SiO2 + FexO quaternary slags were measured by means of solid‐oxide galvanic cell. The FexO activities in the slags are influenced by CaF2 as well as SiO2. At constant FexO mole fractions, e.g., , at low SiO2 mole fractions i.e., , the substitution of CaF2 for CaO has an effect of raising the FexO activity. At higher SiO2 mole fractions, e.g., , however, such an effect becomes insignificant.

The activity data at I 073K after Fischbach almost agree with those after Delcet and Egan, however, the