Efficient growth of anodic films on magnesium in organic electrolytes containing fluoride and water

Habazaki, H.; Kataoka, Fumitaka; Tsuji, Etsushi; Aoki, Yoshitaka; Nagata, Shinji; Skeldon, P.; Thompson, G.E.

doi:10.1016/j.elecom.2014.06.011

Cited by 10 publications

(17 citation statements)

References 24 publications

(24 reference statements)

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“…The film is 300 ± 20 nm thick, which indicates a formation ratio of 1.1 ± 0.1 nm V −1 . The formation ratio compares with values of ∼1.24 nm V −1 for an anodic film formed on magnesium in a fluoride/ethylene glycol electrolyte, 18 and ∼1.2 to 1.4 nm V −1 for an anodic film formed at the matrix region of a commercial magnesium alloy in a similar electrolyte to the present one. 19 The elemental maps extracted from the EDXS data show the presence of magnesium, fluorine and oxygen throughout the film.…”

Section: Resultsmentioning

confidence: 94%

“…5,7,[15][16][17] Barrier-type films can also be formed using non-aqueous electrolytes and the formation of uniform films in such electrolytes provides the opportunity for systematic studies of the anodizing behavior. 18,19 From previous work, anodizing of magnesium alloys can result in the enrichment of alloying elements beneath the anodic film. Such enrichments have been reported for copper, tungsten and zinc beneath oxide/hydroxide films formed on model alloys in an aqueous electrolyte 20,21 and of zinc beneath fluoride-based films formed on a cast commercial alloy in an organic electrolyte of the composition used in the present work.…”

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confidence: 99%

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Behavior of Alloying Elements during Anodizing of Mg-Cu and Mg-W Alloys in a Fluoride/Glycerol Electrolyte

Palagonia

Němcová

Kuběna

et al. 2015

J. Electrochem. Soc.

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Anodizing of sputtering-deposited magnesium and Mg-0.75at.%Cu and Mg-1.23at.%W alloys has been carried out in a fluoride/glycerol electrolyte. The aims of the study were to investigate the enrichment of alloying elements in the alloy immediately beneath the anodic film and the migration of alloying element species in the film. The specimens were examined by electron microscopy and ion beam analysis. An enrichment of copper is revealed in the Mg-Cu alloy that increases with the anodizing time up to ∼6×10 15 Cu atoms cm −2 . Copper species are then incorporated into the anodic film and migrate outwards. In contrast, no enrichment of tungsten occurs in the Mg-W alloy, and tungsten species are immobile in the film. Anodizing treatments have long been used for the protection of magnesium alloys against corrosion and wear and interest still remains in improving and extending the range of available technologies. [1][2][3][4][5][6] Nevertheless, fundamental knowledge of anodizing of magnesium, 7 for instance relating to the migration rates and transport numbers of film species, is comparatively limited, in part due to the difficulty of forming films of uniform composition and thickness, and also to their reactivity to water. The formation of barrier-type anodic films has been extensively investigated on the valve metals, especially for aluminum, niobium, tantalum, titanium and zirconium.8 These studies have shown that oxide films of uniform thickness are formed under a high electric field that depends upon the film composition and the rate of film growth. [8][9][10] The films on aluminum, tantalum and niobium are usually amorphous, 8 and their formation involves migration of metal ions and oxygen ions, with significant contributions of both types, e.g. the transport numbers of Al 3+ , Nb 5+ and Ta 5+ are ∼0.40, 0.24 and 0.24 respectively. 8 Further, an outer region of the oxide films often contains a low concentration of species derived from the anions of the electrolyte.11 In contrast, the films on zirconium are usually nanocrystalline and form mainly by migration of O 2− ions, 12,13 while films on titanium undergo a transition from amorphous oxide to a mixture of amorphous and crystalline oxide.14 Barrier-type films can also be formed on magnesium, although such films have received much less attention and, consequently, less is known of the details of their composition, structure and growth mechanism. Films formed in aqueous electrolytes are often reported to consist of MgF 2 , MgO and/or Mg(OH) 2 . 5,7,[15][16][17] Barrier-type films can also be formed using non-aqueous electrolytes and the formation of uniform films in such electrolytes provides the opportunity for systematic studies of the anodizing behavior. 18,19 From previous work, anodizing of magnesium alloys can result in the enrichment of alloying elements beneath the anodic film. Such enrichments have been reported for copper, tungsten and zinc beneath oxide/hydroxide films formed on model alloys in an aqueous electrolyte 20,21 and of zinc beneath fluoride-...

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Section: Resultsmentioning

confidence: 94%

mentioning

confidence: 99%

Behavior of Alloying Elements during Anodizing of Mg-Cu and Mg-W Alloys in a Fluoride/Glycerol Electrolyte

Palagonia

Němcová

Kuběna

et al. 2015

J. Electrochem. Soc.

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“…In the present study, the effect of current density on the formation of the films on a cast Mg-Zn-RE alloy is investigated, contrasting with the single current density used in the previous studies [19,20]. Further, the oxidation of Zn-Zr phases of the alloy is examined in order to shed light on ionic migration in the film.…”

Section: Introductionmentioning

confidence: 99%

“…Mechanistic investigations of film growth are made easier when the films are of uniform thickness and relatively unreactive in the electrolyte. Such films have recently been formed using a fluoride/glycol/water electrolyte [19]. The films were nanocrystalline and grew by outward migration of cations and inward migration of anions, with a formation ratio of ∼1.24 nm V −1…”

Section: Introductionmentioning

confidence: 99%

Effect of current density and behaviour of second phases in anodizing of a Mg-Zn-RE alloy in a fluoride/glycerol/water electrolyte

Němcová

Kuběna

Šmíd

et al. 2015

J Solid State Electrochem

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Anodizing of a Mg-Zn-RE alloy was carried out at constant current densities from 0.1 to 10 mA cm −2 in a fluoride/glycerol/water electrolyte. Rutherford backscattering spectroscopy, nuclear reaction analysis and analytical transmission electron microscopy revealed barrier-type films composed of oxide and fluoride species. The films were formed by outward migration of cations and inward migration of anions. The transport number of cations in the film above the matrix was in the range ∼0.5 to 0.6, and ∼0.1 in the film above the grain boundary Mg-Zn-RE phase. From the oxidation behaviour of the Zn-Zr phases, it is suggested that anions and cations migrate through short-circuit paths in the film.

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“…While not the subject of this report, studies of the role of water at anodic alkali and alkaline earth metal surfaces in non-aqueous electrolytes have been recently reported and confirm the role of water at electrode surfaces to remain a scientifically relevant topic. [11][12][13][14] This systematic study investigates the ORR activity of carbon (C), carbon-polypyrrole (C-cp), and carbon-polypyrrole-silver (C-cpAg) composite electrodes in hybrid nonaqueous-aqueous electrolytes (acetonitrile-water, tetrabutylammonium tetrafluoroborate). Two water loadings are selected, a moderate-water condition (500 ppm, 22 mM) and a higher-water condition (5000 ppm, 220 mM) more representative of operation in ambient air environment without rigorous exclusion of water.…”

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confidence: 99%

Progress toward Metal-Air Batteries: Mechanistic Investigation of the Effect of Water on the Oxygen Reduction Reaction at Carbon-Conductive Polymer-Silver Composite Air Electrodes

Lee

DeMayo

Takeuchi

et al. 2014

J. Electrochem. Soc.

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The oxygen reduction reaction (ORR) at the carbon-conductive polymer-silver (C-cp-Ag) composite electrode in non-aqueous electrolyte with small amounts of added water is the subject of this study. The contributions of the various components of the composite electrode were assessed by employing four electrodes: (1) glassy carbon (C), (2) polypyrrole coated glassy carbon (C-cp), (3) silver disk (Ag), and (4) carbon-polypyrrole-silver composite (C-cp-Ag). Notably, with 5000 ppm of water in non-aqueous solution, the ORR reaction at Ag and C-cp-Ag shows an n = 4 reduction, while ORR at C and C-cp display an n = 1 reduction. The results show that the use of a multilayer C-cp-Ag composite electrode provides the opportunity to achieve the four electron reduction of one O 2 molecule, with a low precious metal (Ag) loading. In metal air batteries, the cathode consists of the electroactive cathode material, oxygen (O 2 ) and the remainder of the inert electrode consisting of the current collector and oxygen reduction reaction (ORR) catalyst. Metal air batteries fall into a special category as the electroactive cathode material, oxygen (O 2 ), is available in excess from outside the battery. While the cathode current collector, the ORR catalyst and the oxygen reduction products all add mass, 1,2 metal air batteries still provide the opportunity for high energy densities relative to sealed battery technologies. 3,4 Notably, the structures and chemistries of the inert electrode (air electrode) can be varied to address ORR kinetic issues. Typically, a composite air electrode consists of an electrical conductor mixed with an ORR catalyst, often strengthened with a binder 5,6 and a support such as a metal mesh. 7,8 A disadvantage of the conventional air electrode fabrication strategy is that catalyst particles positioned within the electrode interior often have limited access to oxygen.With an earlier article, we introduced a new composite electrode paradigm for metal air batteries, and reported the preparation, characterization, and electrochemical activity of a carbon current collector-conductive polymer-silver (cc-cp-Ag) composite electrode. Enhanced oxygen reduction activity for our composite electrode was observed relative to coated glassy carbon or silver disk electrodes, at a low silver loading of < 0.3 mg cm −2 . Specifically, the role of the current collector toward the electrochemical reduction of oxygen, the role of the conductive polymer in improving the structural integrity of the composite electrode, and a quantitative study of the silver loading effect on ORR activity were all investigated. A notable advantage of the electrodeposition based strategy we developed is the ability to easily generate silver coated three-dimensionally structured composites via use of three dimensional electrically conductive substrates. Three dimensional electrodes can increase the active surface area, enabling reduction of more oxygen per unit planar area. This approach was utilized to prepare three-dimensionally structured carboncondu...

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Efficient growth of anodic films on magnesium in organic electrolytes containing fluoride and water

Cited by 10 publications

References 24 publications

Behavior of Alloying Elements during Anodizing of Mg-Cu and Mg-W Alloys in a Fluoride/Glycerol Electrolyte

Behavior of Alloying Elements during Anodizing of Mg-Cu and Mg-W Alloys in a Fluoride/Glycerol Electrolyte

Effect of current density and behaviour of second phases in anodizing of a Mg-Zn-RE alloy in a fluoride/glycerol/water electrolyte

Progress toward Metal-Air Batteries: Mechanistic Investigation of the Effect of Water on the Oxygen Reduction Reaction at Carbon-Conductive Polymer-Silver Composite Air Electrodes

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