Corrosion Tests of Noble Metals and Ti/IrO₂-Ta₂O₅ in Supercritical and Sub-critical Water Oxidation with Hydrochloric Acid

Abstract

The corrosion resistance of noble metals and Ti/IrO₂-Ta₂O₅ in hydrochloric acid was evaluated to develop a material for a supercritical water oxidation reactor. The results of the corrosion tests in 20 wt% hydrochloric acid with the autoclaves showed Ir had good corrosion resistance between 300ºC and 600ºC. Although Ti-Pd showed active dissolution at 300ºC, the corrosion rate of Ir was less than 1.8 mm/y. This value was superior to that of Rh (26 mm/y) and Ru (14mm/y). The mass change of Ti/IrO₂-Ta₂O₅ was little. Ti/IrO₂-Ta₂O₅ has superior corrosion resistance to Ti-Pd. Using the continuous flow reactor for 893 h, the detachment of Ti/IrO₂-Ta₂O₅ coatings was observed at 550-580ºC. The detachment of coatings was not observed at 400-450ºC. At 550-580ºC, the thickness of oxide layer on Ti grew greater than 100 μm and the Vickers hardness of it was 660-772. High temperature and long time would cause the growth and brittle of oxide layer on Ti substrate. The study on the growth and the brittle of the oxide layer on Ti substrate is expected to use Ti/IrO₂-Ta₂O₅ at greater than 550ºC for a supercritical water oxidation reactor.