Electrochemical measurement of oxygen activity in lead glass by means of a stabilized ZrO2 sensor Part 2. Determination of the equilibrium constants in the redox systems arsenic and antimony

Abstract

The influence of the redox systems Sb3+/Sb5+ and As3+/As5+ on the lead glass refining is shown. This is achieved through the determination of the equilibrium constant, K, and the thermodynamic standard quantities, ΔG^0, ΔH^0, ΔS^0, by means of chemical analysis as well as electrochemical measurement. A discussion of the results yields the thermodynamic standard quantity ΔH^0 as determined by electrochemical measurement and the transition temperature, T, as determined by chemical analysis, in turn resulting in ΔS^0 = ΔH^0/T. For the redox system As2O3/As2O5 the following thermodynamic standard quantities are determined: ΔH^0 = - 193 kJ/mol, ΔS^0 = - 112 J/(mol K) with T = 1725 K. The respective quantities for the system Sb2O3/Sb2O5 are: ΔH^0 = - 325 kJ/mol, ΔS^0 = - 226 J/(mol K) with T = 1435 K.