Investigation of Metal–H2O Systems at Elevated Temperatures: Part I. Development of a Solubility Apparatus Specialized for Super-Ambient Conditions

Abstract

Metals used in aqueous environments where high temperatures and pressures are present are susceptible to corrosion. This is the case for nuclear power plants, especially CANDUTM reactors, where the liquid water systems can reach over 300 °C at pressures well above 101.325 kPa (1 atm). In such situations, failure to control corrosion has economic and safety consequences. To extend corrosion modeling tools, such as Pourbaix diagrams, to harsh aqueous conditions, there is a need for experimental thermochemical data performed at elevated temperatures. This is particularly true for metal and alloy systems where such information is unavailable or unreliable. A relatively simple approach to obtaining temperature dependent thermodynamic properties is the investigation of solid–liquid phase, or solubility, equilibria. However, this requires specially designed instrumentation that can withstand harsh temperatures and extreme pH conditions, while providing accurate data. In this work, an apparatus developed for super-ambient highly acidic and alkaline solubility experiments is presented. Solubility measurements were made in the zinc oxide system, which has been extensively studied. Using these equilibrium data and comparing to the literature, allowed the instrumentation and analysis process to be validated. In situ pH measurements using a constant volume, batch reactor system are described along with a brief presentation of the ZnO dissolution equilibria results at 85 °C (358.15 K).