Control of oxygen concentration in liquid lead and lead–bismuth

Conditions for control of the oxygen concentration in liquid lead alloys are described using the gas phase as a control medium. Calculation of the Gibbs energy of oxygen in liquid Pb45Bi55 is conducted using the data for the binary Pb–O and Bi–O systems. The data obtained are employed to estimate the solubility of oxygen in the Pb45Bi55 melt between 200 and 650 °C which is given by log cO,s(Pb45Bi55)=2.52–4803/T with T in K. Above 500 °C, agreement is satisfactorily of calculated solubilities with a measurement reported in literature. However, deviations of calculated and measured data increase with decreasing temperatures. Calculated solubilities at 200 °C are 2 × 10−8 wt% compared to 10−6 wt% obtained by extrapolation of the measured ones. The obtained solubility data are used to calculate oxygen concentrations at which oxide scales appear that protect steel against dissolution attack by the Pb45Bi55 melt without precipitation of PbO. Those concentrations have constant values between 8 × 10−7–10−4 wt% in Pb at 400–600 °C and 4 × 10−10–10−8 wt% in Pb45Bi55 at 200–400 °C. These conditions can be established by equilibration with a gas phase containing H2/H2O ratios between 10−4 and 1.5.