On the Measurement of Oxygen Pressure in Liquid Iron

Study on the oxygen concentration cells at high temperature-V

Abstract

The following four measurements have been carried out by the oxygen concentration cells with the solid electrolyte, ZrO₂·CaO at the temperature range of 1000°C-1550°C.
(1) Oxygen pressure in the iron equilibrated with Fe_xO by
Ni+NiO|ZrO₂·CaO|Iron+Fe_xO.
(2) Oxygen pressure in the liquid iron saturated with graphite by Ni-NiO|ZrO₂·CaO|Liquid Iron+Graphite.
(3) Oxygen pressure in the liquid iron of intermediate carbon range by Graphite |ZrO₂·CaO|Liquid Fe-C-O System at 1550°C.
(4) Change of Oxygen pressure in liquid iron during deoxidation by Al, Si, or Mn at 1550°C by Graphite |ZrO₂·CaO| Liquid Fe-O System.
From the results of these measurements, the following conclusions have been obtained;
(a) The standard free energy for formation of Fe_xO, calculated from the measured EMF agreed very well with the data in literatures. This agreement suggested a 100% ionic conduction at least up to 1550°C for the ZrO₂·CaO electrolyte (P_O2≈10^-8 atm at 1550°C).
(b) The measured EMF was smaller than the calculated EMF for the iron saturated with graphite, possibly due to some electronic conduction.
(c) This cell can be used to determine the oxygen content dissolved in liquid iron of intermediate carbon range at steel-making temperature.
(d) From the very rapid decrease of the EMF after the addition of dleoxidizers, it was known that the rate-determining step of deoxidation of steel was separation of the reaction products, such as Al₂O₃, SiO₂ and FeO-MnO.
In addition, the solid electrolyte MgO was used to compare the performance as an anion conductor.