Abstract
ABSTRACTPyrolytic graphite (PyG) coatings on high-density graphite (HDG) substrates were deposited by chemical vapour deposition using propane and methane as precursor gas at aprocess temperature of 1800°C. Upon cooling to room temperature, cracking and delamination were observed in the PyG layer at certain edges of flat substrates deposited in propane cycle, attributed to large thermal expansion mismatch stresses. The PyG coatings deposited using different precursor hydrocarbon sources were characterised using polarised light microscopy, scanning electron microscope, X-Ray diffraction analysis, Laser Raman Spectroscopy and X-ray Photoelectron Spectroscopy. Microstructure analysis revealed coarse structure cones grown with larger cone angles. The large deposition rate, associated growth and thermal stress in the case of propane cycle have led to the cohesive delamination of the PyG coating. Nickel melting studies to simulate the uranium melting was carried out in PyG coated HDG crucibles whichshowed reactive dissolution of PyG at the Ni/crucible interface.
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