Self-ordered porous anodic TIO2 nanotubes and other porous anodic oxides (PAO) have received considerable attention because of their potential for high technological application in a number of fields. The anodization of valve metals has been widely investigated over the last eight decades. The formation mechanisms of hexagonal cells and nanotubes, however, have remained unclear until now. Simply reviewing the mechanisms of PAO formation was not the aim of this research and we were more interested in reviewing the forming processes of compact anodic oxides (CAO) and investigating the relationship between the PAO and CAO, to better understand the pore generating mechanisms. The present work introduces the differences between PAO and CAO films, as well as reviewing the traditional theories of PAO films and their deficiencies. Recent progress in the formation mechanism of PAO, including the viscous flow, breakdown, equifield strength, and oxygen bubbles models has been reviewed in detail. The perspective on future developments for the PAO forming mechanism has been tentatively discussed. Based on sufficient analysis of the latest findings, it has been proposed that several approaches may be employed for investigating the pore forming and self-ordering mechanisms. These new approaches include ultrasound-assisted anodizing, anodizing under vacuum or high pressure and adding sodium carbonate or a reducing agent to the PAO-forming electrolytes. An investigation of changes in the current and anodizing efficiencies would also be an effective approach for better understanding the physical nature of field-assisted dissolution (FAD).%自组织有序的TiO2纳米管和多孔型阳极氧化膜(PAO)因其潜在的应用价值而倍受关注.阀金属的阳极氧化研究了80多年,但是六棱柱元胞结构和多孔纳米管的形成机理至今尚不清楚.本文不是简单地综述PAO的形成机理,而是从更宽的视角综述了致密型阳极氧化膜与PAO的本质联系和形貌差异.对比两种膜的形貌差异和生长过程有助于孔洞形成本质的认识.简要综述了PAO的传统“场致助溶(FAD)”理论和局限性,重点综述了PAO形成机理的最新研究进展,包括粘性流动模型、阻挡层击穿模型、氧气气泡成孔模型、等电场强度模型等.在充分对比分析最新成果的基础上,对PAO机理研究的发展趋势进行了展望:采用超声氧化、真空或高压条件下氧化以及对电解液中添加碳酸钠或还原剂等方法,对揭示孔洞形成和自组织的本质将会有很大帮助；从电流和阳极氧化效率角度入手,是探究传统FAD理论的物理本质的有效途径.
展开▼
