Electron Current Generation And The Formation Of Porous Anodic Aluminum Oxide Mechanism

To understand the nature of porous anodic alumina (PAA) growth, the generation of electronic current (Je) in the anodizing process of aluminium was studied. Through calculating the current efficiency and alumina growth efficiency, the generation of je and the transitional mechanism between je and ion current (jion) were studied. The present work determined the Voltage-time (V-t) curves in the anodizing process of aluminum. The types of alumina membrane formed in various electrolytes were characterized by scanning electron microscopy (SEM).First, the forming processes of barrier anodic alumina (BAA) were studied. The BAA growth can be divided into two stages:before sparking and after sparking. Through calculating the current efficiency in the forming process of BAA, the transitional mechanism between je and jion within oxide was studied after BAA sparking. The avalanche electronic current resulted form the dissociation of anion within oxide. SEM images of BAA at different growth stages showed that the release of oxygen gas was the reason of holes forming within BAA. Second, we added the phosphoric acid solutions of different concentrations to typical BAA electrolytes. The "horseback-shape" curve and "three-structure" alumina film were discovered as aluminium was anodized in this mixed electrolyte. The "horseback-shape" curve and "three-structure" alumina were resulted form the generation of je within oxide. Third, the disciplines of V-t curves were studied and the current efficiency and alumina growth efficiency in the forming process of PAA were analyzed. Combined SEM images of PAA, the thickness of PAA bottom barrier layer corresponded to the anodizing voltage was found. Anodizing current (jT) within the oxide included jion and je during anodizing process. The jion was used to form oxide and the je was used to the release of oxygen gas. At last, the transitional mechanism between je and jion within alumina in the anodizing process of aluminium was analyzed and the internal relationship between the generation of je and the forming of nanopores in PAA was proposed. When the ratio of je/jT exceeded the critical value, the PAA film was formed. When the ratio of je/jT was less than the critical value, the BAA film was formed.