Investigation into the Corrosion of NITE-SiC/SiC in Molten FLiNaK Salt

The study presented is part of a wider effort to evaluate NITE-SiC/SiC as a candidate structural material in the Liquid Sandwich Vacuum Vessel (LSVV) concept for ARC-class fusion energy devices. The LSVV design proposes the use of a non-conductive structural material shell made of NITE-SiC/SiC enclosing a conductive liquid (like molten lead). This assembly is contained within the liquid immersion blanket, thereby exposing the outer walls of the shell to LiF-BeF2 (FLiBe) for extended periods. Given the difficulty in using FLiBe owing to the toxicity of Beryllium, FLiNaK is chosen as a surrogate salt in this preliminary study.<br/>SiC/SiC composites - silicon carbide (SiC) matrix reinforced with unidirectional SiC fibers - fabricated by a nano infiltration and transient eutectic-phase (NITE) have been chosen as the leading candidate material for this application owing to the decreased porosity in the matrix as compared to the composite fabricated by Chemical Vapor Infiltration (CVI).<br/>We will present the results of a comprehensive investigation into the effects of static corrosion on NITE - SiC/SiC composites after exposure to LiF-NaF-KF, typically referred to as FLiNaK. Existing studies have looked at the corrosion of stoichiometric SiC in such salts, however, through this study, emphasis is put on understanding the effect of the sintering additives (Al2O3, Y2O3 and SiO2) on the corrosion behavior. The microstructure of the samples will be characterized before and after corrosion through Scanning Electron Microscopy and Energy-dispersive X-ray spectroscopy. X-Ray Photoelectron Spectroscopy will be used to probe the charged states on the surface and shed light on the corrosion mechanisms of the material in presence of the sintering additives. X-Ray Diffraction will then be used to study the phases present on the surface.<br/>Static corrosion tests are conducted in a dedicated, argon-filled glovebox using high purity salt held in glassy-carbon crucibles for 100 and 400 hours at 800C .