Conceptual Progress for Explaining and Predicting Self-Organization on Anodized Aluminum Surfaces

Abstract

Over the past few years, researchers have made numerous breakthroughs in the field of aluminum anodizing and faced the problem of the lack of adequate theoretical models for the interpretation of some new experimental findings. For instance, spontaneously formed anodic alumina nanofibers and petal-like patterns, flower-like structures observed under AC anodizing conditions, and hierarchical pores whose diameters range from several nanometers to sub-millimeters could be explained neither by the classical field-assisted dissolution theory nor by the plastic flow model. In addition, difficulties arose in explaining the basic indicators of porous film growth, such as the nonlinear current–voltage characteristics of electrochemical cells or the evolution of hexagonal pore patterns at the early stages of anodizing experiments. Such a conceptual crisis resulted in new multidisciplinary investigations and the development of novel theoretical models, whose evolution is discussed at length in this review work. The particular focus of this paper is on the recently developed electroconvection-based theories that allowed making truly remarkable advances in understanding the porous anodic alumina formation process in the last 15 years. Some explanation of the synergy between electrode reactions and transport processes leading to self-organization is provided. Finally, future prospects for the synthesis of novel anodic architectures are discussed.

Overview of Engineering Carbon Nanomaterials Such As Carbon Nanotubes (CNTs), Carbon Nanofibers (CNFs), Graphene and Nanodiamonds and Other Carbon Allotropes inside Porous Anodic Alumina (PAA) Templates

“…Very interesting review articles were published recently that provide an extensive description of the signs of progress made on the PAA fabrication [ 38 , 39 ], characterization [ 40 ], formation mechanisms [ 41 , 42 ] and applications [ 43 , 44 ]. All these works agree that the porous materials based on alumina templates are a very attractive platform to develop a wide range of applications but are still fundamental to get a better understanding of their growth mechanisms to gain more advanced control over their structure and the interaction with other materials.…”

Unraveling the six stages of the current–time curve and the bilayer nanotubes obtained by one-step anodization of Zr

“… 1,22–24 Pashchanka considered that in the self-organizing systems of PAA, the electroconvective ion transport mechanism prevails and helps overcome the diffusive transport limitations. 58 The growth of pores is assisted by the Coulomb forces that are responsible for the motion of electrolyte anions and entrained fluids toward the anode surface. 58 The process of self-organization on anodized aluminum is rather complex and multifaceted, and its numerous unique aspects still need to be clarified.…”

“… 58 The growth of pores is assisted by the Coulomb forces that are responsible for the motion of electrolyte anions and entrained fluids toward the anode surface. 58 The process of self-organization on anodized aluminum is rather complex and multifaceted, and its numerous unique aspects still need to be clarified. 58 …”

“… 58 The process of self-organization on anodized aluminum is rather complex and multifaceted, and its numerous unique aspects still need to be clarified. 58 …”

Incorporation of Ions into Nanostructured Anodic Oxides—Mechanism and Functionalities

“…Despite the countless amount of publications on applications of the nanostructured anodic metallic oxides, there are still certain fundamental aspects of anodizing that require deepened exploration. For example, there are still various, often contrary views on the mechanism of the anodic alumina growth [45]. Further development of more reliable tools is necessary for studying the initiation and evolution of the pores' arrangement throughout the anodization [46].…”