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Unusual Alternatives for Nb Electropolishing

This article explores unconventional methods for Nb electropolishing, including lactic acid, fluosulfuric acid, and perchlorate salts, as alternatives to standard etching techniques. It also discusses the use of molten salts and ionic liquids for electrochemical polishing of Nb surfaces. The potential advantages, risks, and applications of each method are examined.

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Unusual Alternatives for Nb Electropolishing

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  1. ISTITUTO NAZIONALE DI FISICA NUCLEARE Legnaro National Laboratories PADUA UNIVERSITY Science Faculty Material Science Dept. HF free solutions for Nb Electropolishing: Something Unusual !! M. Ceccato, G. Mondin, V. Rampazzo, A.A. Rossi and V. Palmieri

  2. Standard Nb Etching : • Buffered Chemical Polishing:HF : HNO3 : H3PO4(ratio 1:1:1 or 1:1:2) • ElectroPolishing:HF : H2SO4(ratio 1:9)

  3. 1. Alternatives for EP:lactic acid Improved Methods for Electrochemical Polishing Nb Superconducting cavities by V.M. Efremov, L.M. Sevryukova, M. Hein, L. Ponto, 2° TESLA Workshop, DESY, Aug 1991 Composition HF : H2SO4 : Lactic acid in the ratio 18 : 21 : 61 Current Density = 90-110 mA/cm2 Voltage = 15-18 V Temperature = 50-60 °C Note:Lactic acid solutions can be explosive

  4. 2. Alternatives for EP:fluosulfuric acid Japanese Patent office Publication number 60092500 A Date of filing 26.10.83 Date of Application Publication 24.05.85 Applicant Mitsubishi heavy Ind LTD., Nomura Tokin: KK Inventor : Yoshisuke Keisuke; Nomura Hirotoshi See also: K. Saito, Proceedings of the 4th workshop on RFSC, Tsukuba 1989 PATENT PURPOSE: To obtain a polishing solution which prevents HF evaporation to form a mirror finished surface Note: Fluosulfuric acid is suspected cancerousgenic

  5. 3. Alternatives for EP:getting rid of sulphuric (Palmieri et al., Tsukuba SRF Workshop 2001) Working point (I 0, V0) automatically found by locking the minimum of dI/dV

  6. 3. Alternatives for EP:getting rid of sulphuric (Palmieri et al., Tsukuba SRF Workshop 2001) Working point (I 0, V0) automatically found by locking the minimum of dI/dV This approach has permitted the authors to easily find other electrolytes for Nb, i.e.: HF + OXALIC ACID + BORIC ACID + H3PO4 30% HF, 15% H3PO4, 30 gr/lt Oxalic acid, 10 gr/lt Boric acid

  7. 4. Alternatives for EP:perchlorate salts The electrolyte is 0.05 mole/literMg(ClO4)2in CH3OH EP Voltage = 50-70 V, Temperature = -5°C by Schober and Sorajic, extrapolating what proposed by Epelboin [Rev. Met. 49 (1952) 863.] The electrolyte does not contain Hydrogen radicals, so no Hydrogen intake is possible

  8. for its remarkable solubility of numerous metallic perchlorates in non aqueous media, … • An EP mixture of • perchloric acid, • ethylic acid, • acetic anhydride • would be the solution! However, in the technical literature, many explosions caused by perchloric acid solutions have been reported. Some authors claim that ethyl-perchlorate is as dangerous as Nitroglycerin

  9. If Percloric acid gives rise to explosive mixtures, under other aspects Hydrofluoric acid is not less dangerous : • (refineries using HF acid have a plethora of devastating histories) • On contact, HF passes through skin and tissue. • Because its action can be delayed for many hours, it can distribute throughout the body, causing the erosion of bone. • F- ions bind to Ca++ and Mg++ ions to form insoluble salts (CaF2 and MgF2 salts form some natural gemstones). • Contact with HF does not cause immediate pain, so systemic poisoning begins before the person is aware • In the body, Ca and Mg ions are used to mediate a variety of physiological processes, such as muscle movement. • Cardiac arrests have been reported from concentrated acid burns to as little as 2.5% of exposed body surface area

  10. 5. Alternatives for EP:molten salts Anodic dissolution of Nb is possible in (NaCl-KCl-NbCln) - AlCl3 melts at 710°C In molten salts, electrical conductance is due to ionic mobility, but high temperatures are necessary for salt melting

  11. 6. Alternatives for EP:Ionic liquids • ‘‘Ionic liquids’’ are molten salts • having a melting point less than 100 °C • which solely consist of cations and anions

  12. For Niobium: One such system that could be explored is that formed from 1-ethyl-3-methylimidazolium (EMIC) and anhydrous AlCl3 However Anhydrous AlCl3 can give rise to unpleasent exothermic reactions! Glow box is mandatory!!

  13. ….. But Choline Chloride is an ingredient of chicken feed!?!

  14. Choline Chloride Urea

  15. 350 300 Choline Chloride-Urea mixture melting point 250 200 Tm °C 150 100 50 0 0 20 40 60 80 100 mol % Urea

  16. We first succeeded in electropolishing Nb by a mixture of Choline Cloride, Urea, NH4Cl at 80°C

  17. 80 μm 80 μm Optical Microscope Untreated Surface Urea/Choline Chloride 3/1 + 10g/L Ammonium Chloride (190 °C; 200 mA/cm2)

  18. Bare Surface Urea/Choline Cloride 3/1 + Ammonium Chloride 10g/L (190 °C; 200 mA/cm2). Standard Electropolishing

  19. Sample 71 • Current Density = 0,46 A/cm2 • Temperature = 165°C • Time = 25 min Mirror-like finishing

  20. Application to 6 GHz Cavities still in progress

  21. 6 GHz seamless monocells

  22. Choline Chloride Drink The brain has a voracious appetite for Choline. Choline is required for synthesis of the key neurotransmitter acetylcholine, and it is used for the building and maintenance of brain cell membranes. Dosage and Use_ Take 1 to 3 teaspoons daily. (best if mixed with fruit-juice)

  23. Work supported by the European Community Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3 CT-2003-506395) Conclusions Best Recipe at the moment: Urea : Choline Chloride in ratio 3 : 1 + Ammonium Chloride 10g/L (165 °C; 460 mA/cm2)

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