A new strategy to prepare ammonium aluminum carbonate hydroxide using plasma electrolytic oxidation in electrolyte containing carbon nanotubes

In this work, a plasma electrolytic oxidation (PEO) technique was used to prepare ammonium aluminum carbonate hydroxide (AACH) in an electrolyte containing carbon nanotubes (CNTs). CNTs were also involved in the composite coating on the surface of 6063 aluminum alloy. The formation mechanism of AACH and effects of CNTs on the microstructure and corrosion behavior of the PEO coatings were investigated. The surface morphology, pore distribution, phase composition, functional groups and electrochemical characteristics of the PEO composite coatings were examined using scanning electron microscopy (SEM), Image Pro software, X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR) and electrochemical workstations, respectively. Results showed that the rod-like AACH was generated around the discharge channel by reacting between ammonia, carbon dioxide and AlOOH under transient high temperature and high pressure environment with the presence of CNTs. The surface micropores of the composite coatings were enlarged due to the excellent electrical conductivity of CNTs. With the by addition of CNTs of 1.5 g/L, the self-corrosion current of the coating was the smallest, and the polarization resistance Rp was larger than that of 1.0 g/L and 2.0 g/L CNTs.