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
Standard Nb Etching :
• Buffered Chemical Polishing:
• ElectroPolishing:
HF : HNO3 : H3PO4
(ratio 1:1:1 or 1:1:2)
HF : H2SO4 (ratio 1:9)
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
in the ratio
HF : H2SO4 : Lactic acid
18 :
21
:
61
Current Density = 90-110 mA/cm2
Voltage = 15-18 V
Temperature = 50-60 °C
Note: Lactic
acid solutions can be explosive
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
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
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
4. Alternatives for EP: perchlorate salts
The electrolyte is 0.05 mole/liter Mg(ClO4)2 in
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
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
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
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
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
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!!
….. But Choline Chloride is an ingredient of chicken feed !?!
Choline Chloride
Urea
Campione 47 - Densità di corrente = 0,18 A/cm2
350
300
Choline Chloride-Urea
mixture melting point
Tm °C
250
200
150
Campione 51 - Densità di corrente = 0,10 A/cm2
100
50
0
0
20
40
60
80
100
mol % Urea
Campione 52 - Densità di corrente = 0,05 A/cm2
We first succeeded in electropolishing Nb
by a mixture of Choline Cloride, Urea,
NH4Cl at 80°C
Optical Microscope
Untreated Surface
Urea/Choline Chloride 3/1 +
10g/L Ammonium Chloride
(190 °C; 200 mA/cm2)
80 μm
80 μm
Bare Surface
Standard Electropolishing
Urea/Choline Cloride 3/1 +
Ammonium Chloride 10g/L
(190 °C; 200 mA/cm2).
Sample 71
Mirror-like finishing
•Current Density = 0,46 A/cm2
•Temperature = 165°C
•Time = 25 min
Application to 6 GHz Cavities still in progress
6 GHz seamless monocells
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)
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)