Factors Affecting the Formation of Anodic Oxide Coatings

Hunter, M. S.; Fowle, P.

doi:10.1149/1.2781147

Cited by 55 publications

(31 citation statements)

References 4 publications

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“…Also, Mason [131] and Li [132,133] found that the temperature rise at the pore bottom was higher at about 25°C, but even with this magnitude of temperature rise, the associated Joule heat would still be far insufficient to result in the observed high growth rate at the pore base. In fact Hunter and Fowle [134,135] demonstrated that the electrolyte would have to reach boiling temperature in order for such fast growth to occur. Thus, the contribution of heat assisted dissolution of oxide should only play a minor role on pore growth during anodization [130].…”

Section: Electric Field Assisted Pore Growthmentioning

confidence: 99%

Theoretical Pore Growth Models for Nanoporous Alumina

Cheng

Ngan

2015

Nanoporous Alumina

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Nanoporous alumina has been extensively used in a wide range of applications, including template materials for various types of nanomaterials, high surface-area structures for energy conversation and storage, bio/chemo sensors, electronic/photonic devices, and so on. However, the formation mechanism of the nanopores and the subsequent pore growth process towards self-ordered pore arrangements have been under investigation for several decades without clear conclusions. The present models may be divided into two main groups in terms of the driving force for pore initialization, as well as the subsequent pore growth process. One group considers that the driving force is the high electric field across the oxide barrier layer at the bottom of the pore channels, which assists metal oxidation at the metal/oxide interface, and oxide dissolution at the oxide/electrolyte interface. The other group of models assumes that the driving force is mechanical stress originating from the volume expansion of the metal oxidation process. This chapter reviews the development of these models for nanoporous alumina formation, and discusses their advantages and shortcomings. A recent model proposed by us is also described, and potential directions for further development are discussed.

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Section: Electric Field Assisted Pore Growthmentioning

confidence: 99%

Theoretical Pore Growth Models for Nanoporous Alumina

Cheng

Ngan

2015

Nanoporous Alumina

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“…For steady-state pore growth, the velocity of the m/o-and o/e-interfaces should be balanced, keeping the barrier layer thickness (t b ) constant. This balance has long been attributed to an equilibrium between the oxide formation at the m/o-interface and the removal of oxide at the o/e-interface either by Joule's heat-induced chemical dissolution [24][25][26][27][28] or by field-assisted oxide dissolution [26,[29][30][31][32][33]. But, recent studies have indicated that the dissolution-based pore formation model is operative for the initial stage of pore formation [34][35][36], whereas it does not adequately account for the steady-state pore formation.…”

Section: Structure Of Porous Anodic Aluminum Oxide (Aao) and Its Formmentioning

confidence: 99%

Structural Engineering of Porous Anodic Aluminum Oxide (AAO) and Applications

Lee

2015

Nanoporous Alumina

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Porous anodic aluminum oxide (AAO) films can be conveniently produced by anodization of aluminum. Porous oxide layer formed on aluminum contains a large number of mutually parallel pores. Each cylindrical nanopore and its surrounding oxide constitute a hexagonal cell aligned normal to the metal surface. Under proper conditions, the oxide cells are self-organized to form a hexagonally close-packed structure. The novel and tunable structural features of porous AAOs have been intensively exploited for templated synthesis of a variety of functional nanostructures and also for fabrication of nanodevices. On the other hand, porous AAOs with modulated pores may provide an additional degree of freedom in templated synthesis. In addition, they can be used as model systems for systematically investigating structure-property relations of nanostructured materials. Based on the anodization techniques developed recently, one can fabricate porous AAOs with tailor-made internal pore structures. This chapter is devoted to conveying the most recent advances in structural engineering of porous AAOs and nanotechnology applications. In order to provide context, a brief description is given of the general structure and fundamental electrochemical processes associated with pore formation. Subsequently, two common anodizing techniques (i.e., mild and hard anodizations) that have been explored for nanotechnology applications are discussed. Next, various nanostructuring approaches for custom-designed porous AAOs are reviewed. The chapter covers the properties of porous AAOs derived from structural engineering and their applications to various nanotechnology researches and finally presents the challenges and future prospects.

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“…Mason [166] and Li [162,167] found that the temperature rise at the pore bottom was higher at about 25°C, but even with this magnitude of temperature rise, the associated Joule heat would still be far insufficient to result in the observed high growth rate at the pore base. In fact Hunter and Fowlep [168,169] demonstrated that the electrolyte would have to reach boiling temperature in order for such fast growth to occur.…”

Section: Formation Mechanisms Of Anodic Porous Aluminamentioning

confidence: 99%

Research Background and Motivation

Cheng

2015

Electro-Chemo-Mechanics of Anodic Porous Alumina Nano-Honeycombs: Self-Ordered Growth and Actuation

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Anodic porous alumina, which exhibits a characteristic nano-honeycomb structure, has received increasing attention both experimentally and theoretically . Due to the quasi-periodic arrangement of the nanopore channels, narrow distribution of pore sizes, and interpore distances, relative ease to control the porous scales and self-ordering qualities by anodization conditions, excellent thermal stability, and very low-cost anodic porous alumina has been extensively used as templates for fabrication of various nanostructured materials such as nanodots [22][23][24], nanowires [25][26][27][28][29], nanotubes [30][31][32], and many other types [33][34][35], especially to realize the collective functioning of arrays of nanoelements which may not be realized by individual nanoelements [5,36], for applications in high-density magnetic media [37][38][39][40][41][42] [95,96]. For neutral electrolytes with pH in the range of 5-7, such as boric acid solution, ammonium borate, or tartrate aqueous solution, only barrier-type anodic alumina films with a uniform thickness will be formed by anodization [1,97]. The configuration of anodic porous alumina is composed of closely packed arrays of nanopore channels perpendicular to the aluminum substrate with pore diameters on the order of several to hundreds of nanometers [58,[93][94][95]98]. When viewed from the top, the nanopores are usually arranged in a quasi-hexagonal porous pattern. The in-plane arrangement of pore channels generally exhibits local variations with ordered zones separated with disordered zone boundaries, which is much similar to the crystallographic grains and grain boundaries of the Al substrate. However, the perfect ordered zones are at most several micrometers big even for highly self-ordered patterns, while the grain

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Factors Affecting the Formation of Anodic Oxide Coatings

Cited by 55 publications

References 4 publications

Theoretical Pore Growth Models for Nanoporous Alumina

Theoretical Pore Growth Models for Nanoporous Alumina

Structural Engineering of Porous Anodic Aluminum Oxide (AAO) and Applications

Research Background and Motivation

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