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.

In Japanese steelworks, hot metal is now being produced by a scrap melting process. With this process, removals of sulphur is very much handicapped because of very high sulphur levels (0.04‐ to 0.09‐ pct by weight) and relatively low tapping temperatures (1623 to 1723 K). In order to overcome such handicaps, the authors explored on the respective phase diagrams. These explorations revealed that {CaO‐SiO2‐Al2O3‐MgO} slags with Al2O3 contents of 30‐ to 35‐pct by weight would be good candidates as reagents for sulphur removal from high sulphur hot metal at relatively low temperatures. For better understanding of the thermodynamic properties of the candidate slags, in this study, sulphide capacities were determined through gas/slag equilibrium technique. The experimental results suggest that there would be, at least, a “window” to remove sulphur from high sulphur hot metal as relatively low temperatures.

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%.

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