【作者】 任建军；

【导师】 左禹；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2012， 博士

【摘要】 本论文对丙二酸电解液中的铝阳极氧化进行了研究,作为比较,同时对硫酸电解液中的铝阳极氧化也进行了研究。由于丙二酸电解液酸性较弱,因此在氧化膜生长过程中的场致溶解相应地比较小。结果导致在阳极氧化过程中生长电压能够上升到一个较大的值,并且能够生成较大尺寸的多边形单元和较厚的阻挡层；与硫酸阳极氧化膜的情形相比,要大得多。在丙二酸电解液中,在恒电流的阳极氧化模式下,氧化膜的生长电压随时间的变化速率比较慢,这就为深入研究氧化膜在初期暂态阶段的生长情况提供了便利。在实验中使用扫描电镜对氧化膜的形貌演变进行了观察。研究结果表明在电压上升的线性阶段,氧化膜就显露出多孔型的初期形貌或胚胎；在电压到达顶峰之前,氧化膜多孔型的构型已经非常明确；当电压达到顶峰时,氧化膜的多孔型构型已经有了一定程度的发展,孔道及孔壁的形貌已经非常明显。所得到的实验结果与解释多孔型氧化膜生长过程的传统理论不太符合,因此该实验结果对传统理论做出了有益的补充,为传统理论的进一步完善提供了实验基础。在第二暂态阶段,多孔型的氧化膜继续发展,其多孔型结构逐渐趋于稳定。在多孔型氧化膜生长的暂态阶段,伴随有显著的横向自组织行为,随着氧化过程向稳定生长阶段的推移,横向自组织行为逐渐减弱。但是即使在稳定生长阶段,依然伴随有持续的自组织行为,自组织行为是氧化膜生长的内在调节机制,贯穿于氧化膜生长过程的始终。电解液浓度、氧化电流密度及氧化时间均是显著影响氧化膜构型的重要因素。但是在氧化过程中,丙二酸电解液的浓度不能太大,因为电解液粘度也会随着浓度的增大而增大,较大的粘度对氧化膜的生长有负面影响。在保证氧化膜能够正常生长的情况下,尽可能地提高电流密度能够非常有效地改善氧化膜的构型,并且还能显著地增大孔间距。在高温加热条件下(500-600℃),夹杂在膜层中的羧酸根阴离子会发生分解而放出C02。在800℃以上的高温条件下对丙二酸阳极氧化膜加热时,原来无定型的氧化铝会发生结晶而生成γ-Al2O3,结果会导致氧化膜耐酸性的显著提高。此外,经高温加热后还会导致氧化膜发光性质的改变。交流阻抗分析结果表明,丙二酸氧化膜的阻挡层厚度虽然比硫酸氧化膜的阻挡层厚度要大得多,但是其阻挡层电阻却比硫酸氧化膜阻挡层的电阻要小。更多还原

【Abstract】 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.更多还原