Microstructure evolution and diffusion of ruthenium in silicon carbide, and the implications for structural integrity of SiC layer in TRISO coated fuel particles

A thin film of ruthenium (Ru) was deposited on n-type 4H–SiC and 6H–SiC by electron beam deposition technique so as to study interface reaction of ruthenium with silicon carbide at various annealing temperatures, and in two annealing environments namely vacuum and air. The Ru–4H–SiC and Ru–6H–SiC films were both annealed isochronally in a vacuum furnace at temperatures ranging from 500 to 1000°C, and the second set of samples were also annealed in air for temperatures ranging from 100°C to 600°C. After each annealing temperature, the films were analysed by Rutherford Backscattering spectrometry (RBS). Raman analysis and X-ray diffraction analysis were also used to analyse some of the samples. RBS analysis of 4H–SiC annealed in a vacuum showed evidence of formation of ruthenium silicide (Ru2Si3) and diffusion of Ru into SiC starting from annealing temperature of 700°C going upwards. In the case of Ru–6H–SiC annealed in a vacuum, RBS analysis showed formation of Ru2Si3 at 600°C, in addition to the diffusion of Ru into SiC at 800°C. Raman analysis of the Ru–4H–SiC and Ru–6H–SiC samples that were annealed in a vacuum at 1000°C showed clear D and G carbon peaks which was evidence of formation of graphite. As for the samples annealed in air ruthenium oxidation started at a temperature of 400°C and diffusion of Ru into SiC commenced at temperatures of 500°C for both Ru–4H–SiC and Ru–6H–SiC. X-ray diffraction analysis of samples annealed in air at 600°C showed evidence of formation of ruthenium silicide in both 4H and 6H–SiC but this was not corroborated by RBS analysis.