Synergistic effect of PEG and hydrosol treatments of solution on preparing Al2O3coating by cathode plasma electrolytic deposition

Al2O3 coatings were prepared by cathode plasma electrolytic deposition (CPED) in the solutions containing Al(NO3)3 · 9H2O, polyethylene glycol (PEG) and hydrosol treated at different conditions. It was found that the deposition efficiency of Al2O3 coatings could be improved by adding PEG in Al(NO3)3 solution and hydrosol treatment of the Al(NO3)3 solution respectively, while the deposition efficiency was synergistically enhanced by both together. It was proved that Al2O3 gel was formed in the solution after hydrosol treatment. Therefore, there is a synergistic effect of PEG and Al2O3 gel on preparing Al2O3 coating by CPED. Such synergistic effect can be mainly attributed to the formation of thin gas sheath on the cathode surface under the action of PEG and Al2O3 gel together. Consequently, at 120 V, the over-potential in the gas sheath is decreased, while the over-potential in Al2O3 coating is increased. At the same time, the current density of the cathode is decreased, so a thick Al2O3 coating can be prepared by CPED in an effective way.