Surface chemical analysis on the corrosion of alloys in the supercritical water oxidation of halogenated hydrocarbon

A surface chemical analysis on the corrosion of various alloys under supercritical water oxidation (SCWO) conditions with relatively high concentrations of halogenated compounds and hydrogen peroxide was conducted using an Auger electron spectroscopy/scanning Auger-electron spectroscopy. The tested alloys (Inconel 600, Hastelloy C-276, Monel 400, stainless steel (SUS 316), Titanium G2, and Zirconium 702) were exposed to the same conditions: 4000 mg/L of 2,4-DCP at 400 °C and 250 bar, with 700% stoichiometric H ₂O₂ in a Hastelloy C-276 batch reactor. Even under the supercritical water (SCW) condition of 4.8 pH without H₂O ₂, a certain degree of corrosion was observed on the surface of all the alloys, especially SUS 316. Under the severe SCWO condition with excess H₂O₂, the surface corrosion of all the alloys was significant, but the types of corrosion on the alloy surfaces differed. Chromium in the SCWO process that contained H₂O₂ for halogenated compounds could potentially lead to the corrosion type and degree of alloys, but a certain amount of nickel depletion was also observed. Among the alloys tested, Titanium G2 was the most resistant to corrosion, under the conditions of the experiment. Considering that the surfaces of the alloys were covered by a carbon-contaminated layer, it may be concluded that the metal oxides or metal ions on the surface of the alloy have a role in forming the carbon-contaminated layer in the decomposition of halogenated compounds under SCWO.