Synthesis and characterization of chemical vapour deposited pyrolytic graphite

Pyrolytic graphite (PyG) is the candidate process crucibles material (containers/liners) in pyro reprocessing applications of spent metallic nuclear fuels. In the present work, the chemical vapor deposition (pyrolysis) temperature effects on the density, texture, degree of preferred orientation, defects, graphitization and growth kinetics of PyG were investigated. The sink and float technique, polarized light microscopy, X-ray diffraction, laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), and electron microscopy techniques were used. The near theoretical density (>2.2 g/cm3) was achieved at pyrolysis above 2100 °C. The preferred orientation by extinction angle and orientation density measurement reveals an increasing degree of texture and anisotropy with increasing pyrolysis temperature. The residual strain and defects concentration inferred from the blue shift of the G band position and integrated ratio ID/IG in LRS analysis shows that intermediate temperature pyrolysis at 1800 °C is more defective. The degree of graphitization defined by sp2:defect ratio in the peak fit analysis of C1s XPS peak show 2400 °C processed PyG is highly graphitized while at 1800 °C show higher fractions for sp3, CO content. The crystallite domain sizes parallel and perpendicular to the c-axis show an increasing ordering with pyrolysis temperature. The activation energy calculated for the surface pyrolysis reaction is ∼60 kJ/mol for the surface kinetics controlled regime between 1400 and 2200 °C, producing a conformal, smooth, and uniform PyG growth as evident by the Volmer-Weber 3D island growth model.