EQUILIBRIUM POTENTIALS OF LEAD OXIDE (II) IN AN EQUIMOLAR MIXTURE OF KCl-PbCl2

Abstract

The electromotive forces (EMF) of the electrochemical system (GC)Pb|(1-N)·KCl-PbCl2+N·PbO|ZrO2(Y2O3)|O2(Pt) in the concentration range of PbO 0.16-7.32 % mol. were measured at temperatures 776, 821 and 874 K. From the experimental values of EMF activities, coefficients of the activity and basic thermodynamic functions of lead oxide for dilute solutions were calculated. It is shown that PbO activities in the KCl-PbCl2 melt have moderate negative deviations from Raoul's law for ideal solutions. The activity coefficients of PbO at each temperature within the calculation errors are constant, that is, the diluted solutions of PbO in KCl-PbCl2 obey Henry's law. In the studied area of dilute solutions of PbO solvent activity coefficients are constant within the error, and their value is close to 1, as a consequence of the solvent activity within the calculation error will be equal to its molar fraction. This confirms the rule of Kubashevskii-Alcock about the obedience behavior of the solvent KCl-PbCl2 to Raoult's law for ideal solutions. Partial thermodynamic functions of the solvent - melt KCl-PbCl2 and integral thermodynamic functions of the KCl-PbCl2-PbO system are calculated using the standard equations. The interaction of lead oxide with chloride melts is caused by the formation of oxychloride compounds. According to the literature, there is a compound {[Pb2OCl]++Cl-} in the ion melt. The results of x-ray phase analysis show the presence of Pb2OCl2 compound in the frozen electrolyte melt. Using the device LECO ONH836 the concentration of oxygen in the metal lead was determined. It is shown that the oxygen concentration was 0.031 wt. % after the long-term exposure, which also exceeds the values in the Pb-O diagram almost twice.