Binder free boron nitride-based coatings deposited on mild steel by chemical vapour deposition

Abstract

Boron nitride-based coating was deposited on mild steel (MS) substrate by the chemical reaction of boron powder and ammonia gas in a chemical vapour deposition setup at 1200 °C. The effect of reaction temperature and time were studied to obtain uniform coating on MS. A uniform BN-coating was obtained for the reaction time of 1 and 3 h at 1200 °C. The as-deposited boron nitride (BN) coating was characterized by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The anti-corrosion performance of the coating was studied by Tafel analysis and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. XRD analysis confirmed that the coating consisted of hexagonal BN. SEM analysis revealed presence of mainly boron nitride nanosheets (BNNS). However, some tubular and ribbon like structures along with some pores were also observed in the as-deposited coating. AFM analysis confirmed that coating consisted of BNNS with thickness of 5–6 nm. EIS analysis showed charge transfer resistance of bare MS and BNNS coated-MS were 298.8 and 1996.3 Ωcm2, respectively, suggesting BNNS coating had 6 × times higher resistance to saline corrosion than bare MS. Show more