Researches On The Forming Process And Forming Mechanism Of Anodic Alumina Films With Ordered Nano-pore Structure

In this paper, the anodic alumina films with ordered nano-pore array structurewere prepared by anodic oxidation of aluminum under the optimum conditions indifferent electrolytes and their pore diameters were in the range of 20nm to 200nm.The forming mechanism and the self-organized process of the anodic alumina filmswith ordered nano-pore array structure were studied thoroughly by ESEM, TEM,X-ray diffraction and XPS. The effects of the technical conditions, such as electrolyte,voltage, concentration, states of Al-substrate, pretreatment of aluminum surface andtemperature, on the self-organized process were studied systematically. The mainresults are as following:For the first time, We proposed a new mechanism about the self-organizedprocess of the anodic alumina film, which was concerned tightly with two kinds offorces including the internal tensive stress and the surface tension. The self-organizedprocess of the anodic alumina film progresses under the control of these two oppositeforces. During the self-organized process, the configuration of the pore changes fromirregular to regular round with excellent uniformity in diameter and the spacing amongpores.In different electrolytes, the anodic alumina films with nano-pore array structurewere formed only under certain range of voltages, which were 5-25 V for 15%H₂SO₄,10-50 V for 3%H₂C₂O₄ and 40-150 V for 2%H₃PO₄. The optimum conditions forpreparing anodic alumina film with regular pore morphology and ordered nano-porearray structure in the different electrolytes were as following: anodizing under 20Vcondition for4h in 15%H₂SO₄,anodizing under 40V condition for 6h in 3%H₂C₂O₄,anodizing under 150V condition for 40h in 2%H₃PO₄. The thickness of the anodicalumina films were about 60⁷0μm in the optimum conditions.The crystalline structures of the anodic alumina films formed at the differentvoltages were studied by X-ray diffraction. The influence of the voltage on the porediameter of the anodic alumina film was investigated, and internal factor of the matchbetween voltage and concentration of the electrolyte was studied. The results showed thatthe voltage was the most important parameter to the pore diameter of the anodicalumina film.The effect of the concentrations of the electrolytes on the self-organized processof anodic alumina film was researched. Theoretical analysis showed that only in theoptimal condition, the self-organized process of the anodic alumina film could becompleted at the shortest time.The microstructure of Al-substrates used to prepare alumina film was analysed byTEM. For the first time, the relationship between the morphology of the nano-pore andthe microstructures of Al-substrates was presented. The results showed that the range withregular nano-pore array structure was consistent with the size of the subgrain inaluminium matrix.The influence of the temperature on the self-organized process was alsoresearched. The results showed that the lower the temperature was, the quicker theself-organizing process was.