Alternative electrolytes for Nb Electropolishing:

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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
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• Standard Nb Etching
• Buffered Chemical Polishing HF HNO3
  H3PO4 (ratio 111 or 112)
• ElectroPolishing HF H2SO4 (ratio
  19)

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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
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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
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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
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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
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4. Alternatives for EP perchlorate salts
The electrolyte is 0.05 mole/liter Mg(ClO4)2 in
CH3OH EP Voltage 50-70 V, Temperature
-5C 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
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• 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
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• 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

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

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For Niobium One such system that could be
explored is that formed from 1-ethyl-3-methylimida
zolium (EMIC) and anhydrous AlCl3 However
Anhydrous AlCl3 can give rise to unpleasent
exothermic reactions! Glow box is mandatory!!
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.. But Choline Chloride
is
an ingredient of chicken feed !?!
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Choline Chloride
Urea
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We first succeeded in electropolishing Nb by a
mixture of Choline Cloride, Urea, NH4Cl at 80C
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Optical Microscope
Untreated Surface
Urea/Choline Chloride 3/1 10g/L Ammonium
Chloride (190 C 200 mA/cm2)
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Bare Surface
Urea/Choline Cloride 3/1 Ammonium Chloride
10g/L (190 C 200 mA/cm2).
Standard Electropolishing
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Sample 71

• Current Density 0,46 A/cm2
• Temperature 165C
• Time 25 min

Mirror-like finishing
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Application to 6 GHz Cavities still in progress
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6 GHz seamless monocells
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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)
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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)