The role of ZrCl4 partial pressure on the growth characteristics of chemical vapour deposited ZrC layers

ZrC layers were deposited in a chemical vapour deposition (CVD) reactor on graphite substrates using a ZrCl4-Ar-CH4-H-2 precursor mixture. The deposition was conducted at different ZrCl4 partial pressures at a constant substrate temperature of 1400 degrees C for 2 h at atmospheric pressure. The deposited ZrC layers were characterised using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The effect of ZrCl4 partial pressure on the growth rate, microstructure and surface morphology of the deposited layers was studied. The ZrCl4 partial pressure was manipulated by changing the flow rate of the argon carrier gas through the sublimation chamber. The boundary layer thickness decreased as ZrCl4 partial pressures increased due increased argon flows. The increased ZrCl4 partial pressure increased the growth rate of ZrC layers linearly. It was found that the transport process of the source materials was laminar and forced convection flow. The flow process of source materials through the boundary layer to the reacting surface was also illustrated using a model. The average crystallite size increased with ZrCl4 partial pressures, whereas the lattice parameter, lattice strain and dislocation density decreased as ZrCl4 partial pressure increased. The surface morphology of the as deposited ZrC layers varied with the ZrCl4 partial pressure. The size of crystals grew larger and the cavities surrounding them decreased in number and size as the ZrCl4 partial pressure increased.