Study On The Anodic Oxidation Of Porous Alumina Membrane

Porous alumina membrane has attracted great attention due to its interesting porous structure and potential applications in many fields. In the thesis, high-purity aluminum foil was used as anode. Porous alumina membrane was fabricated by constant-voltage anodic oxidation, then characterized by scanning electron microscopy. According to the experiments and analysis, the internal stress, slight boundaries and other microscopic defects on the high-purity aluminum foil can be decreased by annealing. The disordered layer of immersing can be eroded and the size of pores can be widened in phosphate. In the same kind of the electrolyte, if concentration increases, the aperture becomes larger, but shape of the hole is more irregular. In 0.3mol/L sulfuric acid, porous alumina membrane with 40-60nm diameter can be obtained when the voltage is 25V constantly; the sickness of disordered layer is 3μm, and the length of nano-wire is about 4-7μm. In the mixture of 6g/L C₂H₂O₄ and 2ml/L H₃PO₄, porous alumina membrane with 160-190nm diameter can be obtained when the voltage is 140V constantly by the two-step oxidation method.At present, as the porous alumina membrane is thin and crispy, its surface morphology and structure may be destroyed easily by the peel membrane process. So aluminum is deposited on the substrate directly to avoid stripping film. In the experiments, high purity aluminum film is obtained using magnetron sputtering and vacuum evaporation respectively. And the effect of pretreatment process on the porous alumina membrane is discussed.In the mixture as the electrolyte system, the best process of porous alumina membrane prepared by magnetic sputtering aluminium film was: sputtered aluminium film at 450℃, annealed at this temperature for 2 hours; anodized in the electrolyte of 560mg/L oxalic acid, 3.0ml/L phosphoric acid and 1.0g/L sodium molybdate; and the diameter of pores is 130-160nm. And the best process to porous alumina film with prepared by vacuum evaporation aluminium film was: aluminium powder as evaporation source, evaporated 30mg one time, four times in all; then anodized in the mixture of 350mg/L oxalic acid and 2ml/L phosphoric acid for 4 hours; and the density of pores is about 1.4×10⁹ ind /cm².The curve of current density was drawn during anodic oxidation, and the mechanism analysis of anodic oxidation was discussed. No linking of individual pore was seen in the cross-section of porous alumina membrane. And it was verified that formation of highly ordered nano-pore channels was related to oxygen precipitation.