In recent years, a lot of work has been performed to interpret corrosion during the process of supercritical water oxidation (SC WO). For a better understanding of the corrosion mechanisms, the initiation processes of corrosion have to be known. The corrosion resistance of two ahunina (Al2O3) ceramics and sapphire in hydrochloric acid (HCI) solutions was investigated at T = 240°C – 500°C and p = 27 MPa. For the alumina ceramics, intergranular corrosion and dissolution of the grains were identified as corrosion mechanisms. The corrosion experiments with the nickel-base alloy 625 (UNS N06625) and its main constituents nickel, chromium, and molybdenum were performed in oxygenated HCl solutions at T = 350°C and p = 24 MPa. Nickel and molybdenum showed severe weight loss after only 5 h of reaction. The attack on chromium started with grain boundary etching and proceeded via the formation of thick, spalling oxide layers on the surface. Initial corrosion phenomena observed on alloy 625 were intergranular attack and pit formation. At longer reaction times, a complete surface attack was observed.
Keywords: alloy 625, nickel, molybdenum, chromium, alumina, sapphire, high-temperature water, HCl, Supercritical Water Oxidation, SCWO