The Preparation Of The Anodic Aluminium Oxide Film And Making Research For Its Self-organizing Behaviour

The anodization of aluminum in malonic acid electrolyte has been studied in this paper. In order to make a comparison, the conventional anodization performed in sulfuric acid solution has also been studied briefly. Due to the relatively weak acidity of malonic acid electrolyte, the field-assisted dissolution of the growing oxide film is accordingly weak, as a result, the formation voltage, cell dimension and barrier layer thickness can achieve a larger value as compared with the condition of sulfuric acid anodization. Under the galvanostatic mode, the voltage evolution with anodizing time is relatively slow in malonic acid electrolyte, which may be convenient for studying deeply the initial growing process of the anodic aluminum oxide (AAO)film by SEM observation. It was found that the embryo of the porous structure has been revealed within the linear range of voltage-time curve; the definite porous structure of the AAO film has been formed before reaching the voltage peak, i.e. the end of the first transient stage; and at the moment of voltage peak the porous structure has already achieved the obvious growth to a certain degree. So the experimental results do not greatly conform to the conventional theory that concerns the developing process of the porous AAO film, and the present results contribute to the improvement of the conventional theory. During the second transient stage, the porous AAO film develops continuously towards the even stable porous structure. The reorganizing behavior of the growing cells is very marked during the initial transient stages and decreases gradually as approaching the steady-state stage. But the reorganizing behavior still takes effect even during the course of film stable growth. The electrolyte concentration, the anodizing current density and anodizing duration are all important factors that can significantly influence the order of cell arrangement. But the concentration of malonic acid electrolyte cannot be too high because the simultaneous increase of electrolyte viscosity has the negative effect on the film development. Increasing the current density as high as possible can improve the cell order to a high degree and makes the interpore distance enlarge notably. At the high temperature, the dicarboxylic anions that incorporated into the film bulk during the anodizing process can decompose and produce CO2. When the malonic acid anodic oxide film is calcinated at the temperature higher than800℃, the crystallization of orginal amorphous film material occurs producing the γ-Al2O3. The formation of γ-Al2O3makes the anodic oxide film obtaining the high resistance to acid dissolution. Moreover, the treatment at high temperature can make the PL (photoluminescence) property of malonic acid AAO film to change greatly. According the electrochemical impedance spectroscopy measurement, it was found that the AAO film formed in malonic acid anodization with the larger barrier layer thickness has the lower electric resistance than the AAO film formed in sulfuric acid anodization with the thinner barrier layer thickness.