Abstract:
A chemical vapour deposition process using radio frequency induction heating operating at atmospheric pressure
was developed for the deposition of ZrC coatings. The precursors utilised in this process were zirconium tetrachloride
and methane as zirconium and carbon sources respectively, in an excess of hydrogen. Additionally, a
stream of argon was used to, first, remove oxygen from the reactor and then to sweep the vapourised ZrCl4 at
300 °C to the reaction chamber. The ZrC coatings were deposited on graphite substrates at substrate temperatures
in the range of 1200 °C–1600 °C. The molar ratio of CH4/ZrCl4 was varied from 6.04 to 24.44. Before the
start of the deposition process, thermodynamic feasibility analysis for the growth of ZrC at atmospheric pressure
was also carried out. Response surface methodology was applied to optimise the process parameters for the deposition
of ZrC coatings. A central composite design was used to investigate the effects of temperature and molar
ratio of CH4/ZrCl4 on the growth rate, atomic ratio of C/Zr and crystallite size of ZrC coatings. Quadratic statistical
models for growth rate and crystallite size were established. The atomic ratio of C/Zr followed a linear trend. It
was found that an increase in substrate temperature and CH4/ZrCl4 ratio resulted in increased growth rate of
ZrC coatings. The carbon content (and concomitantly the atomic ratio of C/Zr) in the deposited coatings increased
with temperature and molar ratio of CH4/ZrCl4. The substrate temperature of 1353.3 °C and the CH4/ZrCl4 molar
ratio of 10.41 were determined as the optimal condition for growing near-stoichiometry ZrC coatings. The values
were 1.03, 6.05 μm/h and 29.8 nm for C/Zr atomic percentage ratio, growth rate and average crystallite size
respectively.
