Pronounced corrosion damage occurs in supercritical water oxidation reactors, and few materials are immune to attack. In this paper, we describe a phenomenological mode] for the corrosion process, and we discuss the effect of electrolyte dissociation and water density, as influenced by temperature and pressure, upon the kinetics of corrosion of metals and alloys in supercritical.water. The corrosion process at near-critical temperatures is believed to involve acid attack, with the concentration of H § being a function of the dissociation constant of HC1, which is a major product of the oxidation of chlorinated organic waste, and of the density of the solution. We show that the competing effects of temperature on the heterogeneous rate constant and on the concentrations of H § and 02 leads to a pressure (and hence density)-dependent maximum in the corrosion rate in the vicinity of the critical temperature. This result is in general agreement with experimental data on corrosion in aqueous solutions at near-critical temperatures.
The tungsten/tungsten oxide electrode was investigated as a pH sensor over a wide range of pH at temperatures from 200 to 300°C and was compared with the yttria‐stabilized zirconia membrane electrode. The tungsten/tungsten oxide electrode shows a Nernstian pH response within the pH range of 2 to 11 and exhibits stable and reproducible potentials. In solutions with pH values lower than 2 were observed deviations from Nernstian behavior. The potential of the electrode is not significantly affected by the redox properties of the system, as established by the presence of oxygen or hydrogen in the solution.
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