On Measurements of Oxidation-Reduction Rate of Iron and of Oxygen Pressure in Oxide Melts

Study on the oxygen concentration cells at high temperature-IV

Abstract

The change of oxygen pressure in the waste gas of CO-CO₂ mixture after the oxidation or reduction of iron or iron oxides has been continuously measured. From this change, the rate of oxidation or reduction has been calculated, knowing the initial gas composition of CO-CO₂ mixture flown into the reaction chamber.
It is shown that the oxygen concentration cells or the oxygen gauge can be used for the continuous measurement of the change in the gas compositon. Thus, the rates of the reactions relating to the change of oxygen pressure, in general, can be determined by the oxygen concentration cells with a solid electrolyte, Zr0₂ CaO. The used cell is:_??_
The equilibrium oxygen pressure in a liquid PbO-Si0₂ binary solution equilibrated with liquid lead has been measured at 800°C, 900°C, 1000°C, and 1100°C by the following cell:_??_EMF
The equilibrium oxygen pressure in the PbO-SiO₂ binary solution increased at higher temperatures, and decreased with anincrease in the silica content of the solution.
The chemical activity of PbO was calculated from the equilibrium oxygen pressure.
The activity of PbO deviated in a negative direction from the Raoultian law, with the deviation increasing with a lowering temperature. The activity of SiO₂ was determined by the Gibbs-Duhem equation.
The activity of SiO₂ deviates in a negative direction from ideality if the silica content is less than 0.38 mole fraction, above which the activity of silica deviates in a positive direction. The deviation becomes less at higher temperatures.
The free energy of mixing of PbO-Si0₂ system has minimum values at Nsio₂ 0.38, asΔF^mix=-2.2Kcal/mole, -2.3Kcal/mole, and -2.45Kcal/mole at 900°C, 1000°C, and 1100°C, respectively.
The minimum enthalpy of mixing is about-700 Cal/mole at Nsio₂=0.32 and the maximum entropy of mixing is about 1.3 entropy units/mole at Nsio₂=0.38.