Preparation and characterization of glassy carbon powder modified with a thin layer of boron-doped ultrananocrystalline diamond (B-UNCD)

The surface of glassy carbon powder (4 μm diam, 2 m ²/g) was modified with a thin layer of borondoped ultrananocrystalline diamond (B-UNCD) for the purpose of improving the dimensional stability and corrosion resistance of the material. The UNCD layer was deposited by microwaveassisted chemical vapor deposition using a 1% CH ₄, 7% H ₂, 92% Ar and 1 x 10 ^-3 % B ₂H ₆ (10 ppm) source gas mixture at 800 W of microwave powder and a system pressure of 140 Torr. Each sample was coated twice using a 2 h growth period with powder mixing in between to increase the number of particles coated and the coverage over each particle. SEM, XRD, Raman spectroscopy, and electrochemical methods were used to characterize the as received and B-UNCD-GC powders before and after anodic polarization at 1.6 V vs Ag/AgCl (25 °C, 30-60 min) in 0.5 M H ₂SO ₄. Most particle surfaces were coated with a thin layer of UNCD and there was some particle aggregation due to diamond overlayer formation over multiple neighboring particles. The results demonstrate that the as received powder undergoes surface oxide formation, layer plane exfoliation and fracturing caused by the stress of the oxide formed and or the oxidation of an intercalation compound, and carbon corrosion during electrochemical polarization. On the other hand, negligible microstructural damage or corrosion was found for the B-UNCD-coated powder. The work demonstrates that modification of sp ² carbon powders with a thin layer of conducting diamond is a viable approach for creating a more durable and corrosion-resistant carbon powder.