Crystalline Anodic Oxide Growth on Aluminum Foil in an Aqueous Ammonium Dihydrogen Phosphate Anodization Electrolyte

Chen, C. T.; Hutchins, Gudrun A.

doi:10.1149/1.2114166

Cited by 18 publications

(15 citation statements)

References 16 publications

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“…It has been reported that the thermally formed crystalline ␥-Al 2 O 3 could act as the nucleation site for forming ␥Ј-Al 2 O 3 in Al anodizing. 10,11 The presence of the outer layer of crystalline ␥Ј-Al 2 O 3 , as revealed in Fig. 2a, was probably associated with the thermal oxide formed during pre-heat-treatment.…”

Section: Resultsmentioning

confidence: 95%

Effect of Heat-Treatment on Characteristics of Anodized Aluminum Oxide Formed in Ammonium Adipate Solution

Chang

Lin

Liao

et al. 2004

J. Electrochem. Soc.

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The effects of heat-treatment ͑before and after anodization͒ on the microstructure and electrochemical characteristics of anodized aluminum oxide films formed in 85°C aqueous ammonium adipate electrolyte were investigated. The morphology and crystal structure of the anodized oxide were examined by transmission electron microscopy. The capacitance, relative dielectric constant, electrochemical impedance spectroscopy, and I-V behavior of the oxide film were also determined. Both pre-and post-heattreatment at 500°C could induce the formation of crystalline ␥Ј-Al 2 O 3 in the outer layer of anodized oxide and consequently increase the relative dielectric constant of the film. The differences in the morphology and crystalline characteristics between the anodized oxide subjected to pre-and/or post-heat-treatments led to variations in the electrochemical properties. The pre-heattreatment could economize the required charge to anodize the oxide and retard the growth of film thickness during anodizing. Thermal-induced phase transformation from amorphous to crystalline oxide of the anodized film due to post-heat-treatment, could leave some defects and substantially decrease the electrical resistance of the oxide layer. The reanodization further developed and extended the crystalline oxide formation, which subsequently increased the relative dielectric constant of the oxide film.Barrier aluminum oxide finds many applications in the integrated circuit process, 1 thin film transistor/liquid crystal display fabrication, 2 metal-insulator-metal cathodes for electron-beam lithography, and electrolytic capacitors. 3 Depending on the anodizing conditions, either amorphous or crystalline barrier aluminum oxide can be formed. Because the crystalline oxide can sustain a higher voltage, 4 has a higher relative dielectric constant, 5,6 and possesses a lower ionic conductivity than that of the amorphous oxide film, work on developing an anodized film with a high degree of crystallinity is of continuous interest to researchers. 7 Crystalline oxide growth may be promoted by the presence of a thin layer of thermal oxide on the surface of aluminum. 5,[8][9][10][11][12] The thermal oxide, which contains ␥-Al 2 O 3 13,14 crystals, becomes incorporated into the growing barrier oxide and acts as nuclei for the amorphous to ␥Ј-Al 2 O 3 transformation. 10,11 But the development, during the anodization, of ␥Ј-Al 2 O 3 within the anodized oxide film formed on aluminum covered with a thin thermal oxide is strongly influenced by the nature of the anion species of the electrolytes. 15 Although the film morphology, crystalline characteristics, and growing mechanism of dielectric oxides anodized in borate and phosphate electrolytes had been extensively reported, 10-12,15-17 those formed in ammonium adipate solution, a common medium to anodize the aluminum for use in lowvoltage electrolytic capacitors, were rarely explored.In a recent study, the dependence of the microstructure of aluminum anodized film on the forming voltage in ammonium adipate solution...

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Section: Resultsmentioning

confidence: 95%

Effect of Heat-Treatment on Characteristics of Anodized Aluminum Oxide Formed in Ammonium Adipate Solution

Chang

Lin

Liao

et al. 2004

J. Electrochem. Soc.

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“…This scenario satisfies the conditions of thermodynamic equilibrium of different species on the Pourbaix diagram. However, the proposed scenario does not follow a scenario of anodic electropolishing of metals 35 37 38 39 which does not take into account thermodynamic constrains. These constrains are set on by the Pourbaix diagrams.…”

Section: Discussionmentioning

confidence: 99%

“…These constrains are set on by the Pourbaix diagrams. To the best of our knowledge, while the two-layer model has been sugested for almost half a century ago, the current literature dealing with electropolishing does not address the thermodynamic limitations associated with incorporation of electrolyte anions such as groups into the oxide structure 35 37 38 39 .…”

Section: Discussionmentioning

confidence: 99%

In situ X-ray nanotomography of metal surfaces during electropolishing

Nave

Allen

Chen-Wiegart

et al. 2015

Sci Rep

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A low voltage electropolishing of metal wires is attractive for nanotechnology because it provides centimeter long and micrometer thick probes with the tip radius of tens of nanometers. Using X-ray nanotomography we studied morphological transformations of the surface of tungsten wires in a specially designed electrochemical cell where the wire is vertically submersed into the KOH electrolyte. It is shown that stability and uniformity of the probe span is supported by a porous shell growing at the surface of tungsten oxide and shielding the wire surface from flowing electrolyte. It is discovered that the kinetics of shell growth at the triple line, where meniscus meets the wire, is very different from that of the bulk of electrolyte. Many metals follow similar electrochemical transformations hence the discovered morphological transformations of metal surfaces are expected to play significant role in many natural and technological applications.

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“…Since the oxide obtained by anodic oxidation consists of -alumina, which can be only partially transformed in -alumina by heating to 6003C (Chen & Hutchins, 1985) this method cannot be applied for the present study. Therefore, a washcoating method was developed to deposit the needed -Al O layer in the microchannels of the stainless-steel reactor.…”

Section: Catalytic Coatingmentioning

confidence: 99%

Microchannel reactors for fast periodic operation: the catalytic dehydration of isopropanol

Rougé

Spoetzl

Gebauer

et al. 2001

Chemical Engineering Science

137

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A microchannel reactor specially designed for periodic operation and a process to deposit a catalyst, -alumina, inside the reactor channels were developed. The hydrodynamics of the reactor was characterised. Although the #ow in the microchannels is laminar, a uniform radial concentration pro"le and consequently a narrow residence time distribution were obtained. Depending on the manufacturing method the Bodenstein number was found to be Bo"ud/D K 70. The catalytic coating had no in#uence on this distribution indicating a uniform deposition of the catalyst within the microchannels. As the inlet function was only slightly modi"ed in the reactors, frequencies of up to 1 Hz could be imposed for periodic operation. The dehydration of isopropanol to propene was chosen as model reaction to study the dynamic behaviour of a microreactor under periodic concentration variations. The kinetics was "rstly studied in a conventional "xed-bed reactor with the catalyst developed for the microreactor. Experimental results con"rmed the theoretically predicted increase of the reactor performance under periodic operation exceeding the maximum obtainable performance under steady-state conditions.

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Crystalline Anodic Oxide Growth on Aluminum Foil in an Aqueous Ammonium Dihydrogen Phosphate Anodization Electrolyte

Cited by 18 publications

References 16 publications

Effect of Heat-Treatment on Characteristics of Anodized Aluminum Oxide Formed in Ammonium Adipate Solution

Effect of Heat-Treatment on Characteristics of Anodized Aluminum Oxide Formed in Ammonium Adipate Solution

In situ X-ray nanotomography of metal surfaces during electropolishing

Microchannel reactors for fast periodic operation: the catalytic dehydration of isopropanol

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