Formation of carbonaceous-coatings on aluminium using poly(vinyl alcohol)

Uniform and adhesive carbonaceous-coatings were formed on the aluminium by the following two-step process: first, aluminium specimens were anodized in acid solutions to form porous anodic oxide films; they were then heated with powder of poly(vinyl alcohol) (PVA) in flowing argon at 300°C for 30 min then at different temperatures of 450–550°C for 1 h. The coatings showed mirror-like smoothness on the electropolished and anodized specimens. The coating failed on specimens without the porous oxide films. The penetration of the fluid materials formed in the course of the decomposition of PVA into the pores of the porous oxide film was accordingly important for adhesion. This anchor effect was confirmed by scanning electron microscopy. The Vickers hardness of the surface was increased by coating and by increasing temperature of the coating process. The highest value was Hν50=850. The resistance to pitting corrosion in a NaCl solution was markedly increased in specimens coated at 450°C. The coating is resistant also to 1 mol l−1 HCl solution and to organic solvents such as acetone and hexane.