Plasma Electrolytic Oxidation of Aluminium in Electrolytes Containing Various Concentrations of Carbon Black Nanoparticles

Incorporation of carbon-based nanoparticles into ceramic coatings during plasma electrolytic oxidation (PEO) is promising for the synthesis of new composite layers on lightweight metals. Specifically, the present study focuses on the incorporation of carbon black (CB) nanoparticles into PEO alumina layers. For this purpose, PEO of aluminium is performed in silicate-based electrolytes containing various concentrations of dispersed carbon black nanoparticles (from 0 to 6 g center dot L (-1)). The influence of this concentration on the microstructure of the achieved PEO coatings is investigated by combining complementary characterization techniques (scanning electron microscopy, X-ray diffraction and Raman spectroscopy). Results show that using concentrations up to 6 g center dot L (-1) tend to limit the morphological inhomogeneity between the edges and the centre of the treated samples. Moreover, the addition of carbon black nanoparticles results in a sponge-like outermost sublayer covering larger areas of the surface with abilities to host a higher amount of these nanoparticles. It is also evidenced that CB nanoparticles do not suffer any further structural degradation during their incorporation. In addition, cross-checked results show that the presence of dispersed CB nanoparticles slightly affect the coating average growth rate. As for potential future applications, the electrical volume conductivity of grown carbon-alumina composite coatings is also measured.