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

Standard Nb Etching : Buffered Chemical Polishing : HF : HNO 3 : H 3 PO 4 (ratio 1:1:1 or 1:1:2) ElectroPolishing : HF : H 2 SO 4 ( ratio 1:9 )

Composition HF : H 2 SO 4 : Lactic acid in the ratio 18 : 21 : 61 Current Density = mA/cm 2 Voltage = V Temperature = °C Note: Lactic acid solutions can be explosive Improved Methods for Electrochemical Polishing Nb Superconducting cavities by V.M. Efremov, L.M. Sevryukova, M. Hein, L. Ponto, 2° TESLA Workshop, DESY, Aug Alternatives for EP: lactic acid

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

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

Working point (I 0, V 0 ) 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 + H 3 PO 4 30% HF, 15% H 3 PO 4, 30 gr/lt Oxalic acid, 10 gr/lt Boric acid (Palmieri et al., Tsukuba SRF Workshop 2001) 3. Alternatives for EP: getting rid of sulphuric

The electrolyte is 0.05 mole/liter Mg(ClO 4 ) 2 in CH 3 OH EP Voltage = 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 4. Alternatives for EP: perchlorate salts

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 (CaF 2 and MgF 2 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-NbCl n ) - AlCl 3 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 AlCl 3 However Anhydrous AlCl 3 can give rise to unpleasent exothermic reactions! Glow box is mandatory!!

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

Urea Choline Chloride

Choline Chloride-Urea mixture melting point mol % Urea T m °C

We first succeeded in electropolishing Nb by a mixture of Choline Cloride, Urea, NH 4 Cl at 80°C

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

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

Sample 71 Current Density = 0,46 A/cm 2 Temperature = 165°C Time = 25 min Mirror-like finishing

Application to 6 GHz Cavities still in progress

6 GHz seamless monocells

Choline Chloride Drink Dosage and Use_ Take 1 to 3 teaspoons daily. (best if mixed with fruit-juice) 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.

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