On the Mechanism of Niobium Electropolishing

Chandra, Ashwini

doi:10.1149/2.054211jes

Cited by 26 publications

(31 citation statements)

References 46 publications

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“…Similarly to [7], we have to consider in this study the viscous layer that is generated at the niobium surface during VEP. The benefits of improved electric field and fluid distribution are lowered by the macroscopic movement of the viscous surface film, highlighted on flat samples in [26][27]. The two half-cells should be distinguished during VEP: (i) in the upper half-cell, the layer runs or slides down the cavity due to the gravity.…”

Section: B Asymmetry Of the Processmentioning

confidence: 99%

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Éozénou

Boudigou

Carbonnier

et al. 2014

Phys. Rev. ST Accel. Beams

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An advanced setup for vertical electropolishing of superconducting radio-frequency niobium elliptical cavities has been installed at CEA Saclay. Cavities are vertically electropolished with circulating standard HF-HF-H 2 SO 4 electrolytes. Parameters such as voltage, cathode shape, acid flow, and temperature have been investigated. A low voltage (between 6 and 10 V depending on the cavity geometry), a high acid flow (25 L= min), and a low acid temperature (20°C) are considered as promising parameters. Such a recipe has been tested on single-cell and nine-cell International Linear Collider (ILC) as well as 704 MHz five-cell Super Proton Linac (SPL) cavities. Single-cell cavities showed similar performances at 1.6 K being either vertically or horizontally electropolished. The applied baking process provides similar benefit. An asymmetric removal is observed with faster removal in the upper half-cells. Multicell cavities (nine-cell ILC and five-cell SPL cavities) exhibit a standard Q 0 value at low and medium accelerating fields though limited by power losses due to field emitted electrons.

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Section: B Asymmetry Of the Processmentioning

confidence: 99%

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Éozénou

Boudigou

Carbonnier

et al. 2014

Phys. Rev. ST Accel. Beams

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“…SRF cavities can be manufactured by forming Nb sheets either by deep drawing or spinning (Padamsee,et al (1); Chandra, et al (2)). After the formation of the Nb half shells, they are trimmed on a lathe or milling machine to attain (2)).…”

Section: Introductionmentioning

confidence: 99%

Effects of Normal Load, Sliding Speed, and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

Khun

Frankel

Sumption

2014

Tribology Transactions

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The effects of normal load, sliding speed, and surface roughness on the friction and wear of high-purity niobium (Nb) during sliding without and with an introduction of water were systematically investigated. Increasing the normal load or sliding speed decreased the friction of the Nb under the both dry and wet conditions because the increased wear of the Nb decreased the interfacial shear strength between the steel ball and Nb by promoting the surface roughening and the production of wear debris. However, the Nb tested at the lowest sliding speed under the lowest normal load with water exhibited the lowest friction and wear due to the formation of oxide layer on the wear track. The friction and wear of the Nb tested under the dry condition decreased with increased surface roughness because the higher interfacial shear strength between the steel ball and smoother Nb resulted in the earlier breakdown of the native oxide layer and direct contact between the steel ball and Nb. However, increasing the surface roughness of the Nb increased its friction and wear under wet conditions, probably due to the easier breakdown of the oxide layer that formed on the rougher surface during sliding. The tribological results clearly showed that the introduction of water during sliding had a significant influence on the tribological properties of the Nb.

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“…The current density then increases slowly and finally reaches a peak value, which results from the competition between the thickening viscous film and the growing transport rate of ions during the increase of the applied potential. 15 The current density then falls down and levels off at a plateau value of 6 mA/cm 2 , which is relatively constant over the potential range from 1.3 V to 2 V (vs. Al). Literature reveals that the current density plateau of the electrochemical polarization curve is characterized by dissolution under mass transport control and the formation of a stable diffusion layer at the liquid/metal interface.…”

Section: Resultsmentioning

confidence: 96%

Fundamental Aspects of Uranium Electropolishing in AlCl₃-1-ethyl-3-Methylimidazolium Chloride Ionic Liquid

Jiang¹,

Fang²,

Luo³

et al. 2018

J. Electrochem. Soc.

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A smooth and flat uranium surface with trace of well-defined grain boundaries has been obtained by electropolishing in the Lewis acidic AlCl 3 -1-ethyl-3-methylimidazolium chloride ionic liquid. The surface roughness Ra and Ry of the uranium reduced substantially from 130.1 nm and 899.4 nm to 16.77 nm and 206.89 nm after electropolishing, respectively. The underlying mechanism of electropolishing has been investigated by the combination of electrochemical, spectroscopic and surface characterization methods. A current density plateau in the measured polarization curves of uranium is observed, which is directly related to the mass transport limit of U 3+ . The mass transport mechanism of the process follows the salt precipitation model, and the precipitate is proposed to be in the form of U(Al 2 Cl 7 ) x (AlCl 4 ) 3-x Uranium (U) has been used in military and civilian applications due to its high density and nuclear properties. Mechanical polishing is usually used to reduce the surface roughness of uranium, which could remove the mechanically damaged surface layer and determine the metallographic structure of uranium. However, typical mechanical polishing of uranium is problematic due to its radioactivity and toxicity produced by aerosol.1 Electropolishing is a more suitable method for the polishing of uranium, which could avoid the generation of aerosol. However, there are major limitations associated with the method -most notably that the extensive gas evolution with low current efficiency occurs, along with etch pits and environmental concerns.2 It is proposed that a non-aqueous solution could eliminate the above-mentioned difficulties.Ionic liquids (ILs) served as new non-aqueous solvents have been employed in the field of electropolishing.3-5 The advantage of using ILs is that high current efficiency could be obtained with negligible gas evolution at the anode/solution interface. The liquid used is comparatively benign and non-corrosive compared to the current aqueous acid solutions and bears the potential for repeated usage. Among a large variety of ILs, AlCl 3 -1-ethyl-3-methylimidazolium chloride (AlCl 3 -EMIC) is an appropriate alternative with the merits of high ionic conductivity, low viscosity and wide potential window. 6 We have previously shown that metal uranium can be oxidized to U 3+ and the corresponding products accumulated on the metal/ILs interface form a viscous layer, which could facilitate a uniform dissolution of the substrate surface. Normally, this uniform dissolution could lead to electropolishing under optimum parameters. 8 The study of mass transport mechanisms in electrodissolution systems is critical for the optimization of operating parameters. As reported, mass transport mechanisms of electrodissolution vary from mass transport limiting species. The mass transport limiting species could be the cations of the dissolving metal (salt precipitation mechanism), the anions from the electrolyte (acceptor mechanism), or the water (water mechanism). 9 The salt precipitation mechanism des...

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On the Mechanism of Niobium Electropolishing

Cited by 26 publications

References 46 publications

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Effects of Normal Load, Sliding Speed, and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

Fundamental Aspects of Uranium Electropolishing in AlCl₃-1-ethyl-3-Methylimidazolium Chloride Ionic Liquid

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On the Mechanism of Niobium Electropolishing

Cited by 26 publications

References 46 publications

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Development of vertical electropolishing process applied on 1300 and 704 MHz superconducting niobium resonators

Effects of Normal Load, Sliding Speed, and Surface Roughness on Tribological Properties of Niobium under Dry and Wet Conditions

Fundamental Aspects of Uranium Electropolishing in AlCl3-1-ethyl-3-Methylimidazolium Chloride Ionic Liquid

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Fundamental Aspects of Uranium Electropolishing in AlCl₃-1-ethyl-3-Methylimidazolium Chloride Ionic Liquid