Characterisation of CVD carbon coatings on Nextel™440 fibres

Carbon coatings were deposited on Nextel™440 fibres using C₃H₆–Ar system by hot wall chemical vapour deposition (CVD) with a total pressure of 1·5 kPa. The morphology and structure of the coatings were characterised by SEM, XRD and Raman spectroscopy. As the deposition temperature increased from 1173 to 1373 K, the growth rate increased complying with the Arrhenius law, and the calculated apparent activation energy was 45·9 kJ mol⁻¹. The coating growth was controlled by surface reaction, and smooth coatings were obtained. Above 1373 K, the free energy barrier for the formation of critical nucleus in gas phase was so low that remarkable nucleation occurred, thereby leading to the growth of rough coatings. The grain size and orientation of the coatings both increased as the deposition temperature increased. Additionally, the strength of the fibres coated at 1173 K was the highest, owing to low fibre degradation and healing effect of the thin coatings.