The Anodization Behavior Of A1Substrate Coated By Pre-existed Anodic Aluminum And Fabrication Of AAO Films With Hierarchiral Pore Structure

With the development of nanotechnology, the structure of functional nano-devicesbecomes more complicated. As one of the most important ways to preparenano-materials, complex nanostructured templates have great advantages in this field.Due to lots of advantages, such as controlled structural parameters, simple preparationprocess and low cost, anodic aluminum oxide (AAO) has been one of the mostimportant hard templates to prepare nano-materials. In this paper, through changingelectrolytic solution and electrolytic parameters, we explored successive anodizationbehavior of aluminum with a pre-existed anodic alumina, and fabricated ofself-ordered AAO and AAO template with changed pore diameter. The main results areas follows:1. Subsequent anodization behaviors of aluminum respectively in H2C2O4solution, malonic acid solution and H2C2O4solution with a pre-existed anodic aluminaformed by anodizing in H2SO4solution, H2C2O4solution and malonic acid solutionwere respectively investigated systematically. The result shows that, a pre-existedanodic alumina has great effect not only on controlling the degree of difficulty that Alwas anodized in different electrolytic solution under condition of high filed, ie. highcurrent density, but on broadening the windows of subsequent anodization voltage. Asstructure parameters of pre-existed anodic alumina were similar to those of subsequentanodic alumina, the pre-existed anodic alumina greatly affected nucleation and degreeof order in the subsequent anodic alumina. Otherwise, the phenomena were notobvious.2. We present an improved fast two-step anodization to prepare self-ordered AAOfilms. The first step is hard anodization (HA) in H2SO4and the second step is mildanodization (MA) in H2C2O4. HA in H2SO4at a wide range of anodization voltageprovided a fast formation of ordered arrays of pits on Al sheet, and in the second step,arrays of pits on Al substrate affected nucleation initially, and the anodization voltagein H2C2O4MA affected the degree of AAO obviously later. The best anodizationvoltage in H2C2O4MA was validated to be around40V. The improved combination ofHA and MA not only shortens the time of the first anodization step relative toconventional two-step anodization, and keeps the good degree of order of AAO withinlarge area, but also decreases the high mechanical stress in AAO formed in HA which limits practical application. Moreover, the relationship between the size of arrays ofpits formed in H2SO4HA and degree of order of AAO formed in H2C2O4MA wasinvestigated in detail.3. AAO films with changed pore diameter were obtained by different ways. First,AAO with changed pore diameter or pore density could be prepared under condition ofstep changed voltage in H2C2O4solution, including low-to-high and high-to-lowalternating voltage; Second, according to the relationship between unit cell size andvoltage (ζHA=2.0nm V-1, ζMA=2.5nm V-1) under HA and MA, AAO with periodicchange in pore diameter could be obtained by the combination of HA and MA throughanodizing Al alternately in H2C2O4solution, H3PO4solution or more appropriate acidsolutions.