Evaluation of Yttria Coated High Density Graphite with Silicon Carbide Interlayer for Uranium Melting Applications

Yttrium Oxide (Y2O3) deposited over High Density Graphite (HDG) by Atmospheric Plasma Spray (APS) process is highly desirable as a chemical barrier coating for reusable Uranium (U) melting crucibles in the pyrochemical reprocessing of spent metallic fuels. In the present study, an oxidation protective Silicon Carbide (SiC) interlayer coating over HDG has been achieved by pack cementation process. The high-temperature oxidation resistance and resistance to thermal fatigue failure of Y2O3 coating with and without SiC interlayer were evaluated by performing repeated thermal cycling studies at 1450, 1500 and 1550 degrees C. The durability performance of Y2O3 coating with SiC interlayer in the actual working environment was simulated by performing U melting studies using miniature size HDG coated crucibles. The microstructural, chemical and phase characterization of coatings prior and post thermal cycle failure were carried out by SEM/EDS and XRD techniques. It is observed that the SiC interlayer developed by novel pack cementation technique for the Y2O3 top coat extended the thermal cycling and life of the coating with U melting in inert argon gas environment significantly. The occurrence of micro-cracking over Y2O3 top coat with SiC interlayer perceived after 33, 30 and 25 thermal cycles at 1450, 1500 and 1550 degrees C, respectively.