Reactor corrosion in ceria production by hydrothermal synthesis under supercritical conditions

Abstract

Type 316 (UNS S31600) stainless steel (SS) is used for reactor tubes in a hydrothermal process under supercritical water oxidation (SCWO) conditions for the production of fine ceria particles in a large scale. Reliability of this reactor material depends upon corrosion resistance under SCWO. To assess this, a case study was analyzed and simulated tests on Type 316 SS in 3% cerium(III) nitrate (Ce[NO3](3)(.)6H(2)O) at 400 degrees C and 300 atm were carried out. Case study analysis and characterization of the exposed specimen were performed using x-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive x-ray (EDX), and x-ray photoelectron spectroscopy (XPS) measurements. Dissolution of cations was analyzed by induction-coupled plasma spectroscopy (ICP-MS). Type 316 SS was well protected under SCWO conditions despite the absence of a protective Cr-oxide/hydroxide layer on the alloy surface. Corrosion protection was mainly due to the formation of a Ce oxide layer on the surface of the tube.