The synthesis and characterization of CVD ZrB2 coating from ZrCl4-BCl3-H2-Ar system

Abstract By conducting thermodynamics calculations and chemical vapor deposition (CVD) experiments, the synthesis and characterization of CVD ZrB 2 from ZrCl 4 -BCl 3 -H 2 -Ar system at low pressure were investigated. Cauliflower-shaped, dense ZrB 2 coating was successfully deposited on graphite substrates and carbon fibers under appropriate parameters. Calculation results indicate that the yield of ZrB 2 increases with increasing temperature. The amount of ZrB 2 increases to a broad maximum with increasing H 2 flux and then remains constant when H 2 flux reaches above 40 mol. BCl 3 concentration significantly affects phase composition of CVD ZrB 2 . Three phases are involved, namely, Zr+ZrB 2 , ZrB 2 , and ZrB 2 +B. Experimental results show that the temperature and H 2 and BCl 3 fluxes significantly affect surface roughness, growth rate, and phase composition of ZrB 2 coating. The thickness and particle size of ZrB 2 coating increase with the increase in temperature. However, at high temperatures, particle size decreases because particles do not have enough time to grow at high reaction rate. Morphologies of ZrB 2 coating vary from porous and rough to dense and smooth with the increase in H 2 flux. BCl 3 reduction by H 2 dominates deposition process at low BCl 3 concentration, and deposition mechanism changes to the codeposition of B and ZrB 2 at high BCl 3 concentration.