Redox Potential Measurements in High Temperature Aqueous Systems

Redox potential measurements on platinum and Type 304 stainless steel in equilibrium ( or ) and nonequilibrium boric acid/lithium hydroxide solutions at 275°C are reported. For equilibrium systems containing hydrogen, good agreement was obtained between the measured potentials on platinum and calculated equilibrium potentials for pH . For highly basic systems , however, the observed potentials tended to be more positive than the calculated values; the difference was probably due to trace amounts of oxygen remaining in the system. In oxygenated equilibrium systems, good agreement was found between the observed and calculated potentials for the solution for , but the observed potentials tended to be less positive than the calculated values for more acidic solutions and for lower oxygen concentrations. Steady‐state measurement on nonequilibrium boric acid solutions at 275°C showed that the redox potential on platinum becomes more negative as the ratio increases. Transient studies on nonequilibrium boric acid solution revealed that the redox potential can vary over a wide range on cycling the relative concentrations of oxygen and hydrogen. The experimental findings are interpreted in terms of mixed potential model from which numerical simulations have reproduced the essential features of the data.