Alternative electrolytes for Nb Electropolishing:

1. Alternative electrolytes for Nb Electropolishing: Magic Powders for Magic Cleaning M. Brichese, V. Rampazzo, F. Stivanello and V. Palmieri ISTITUTO NAZIONALE DI FISICA NUCLEARE Laboratori Nazionali di Legnaro and UNIVERSITÀ DEGLI STUDI DI PADOVA Science Faculty – Material Science Dept.

2. Standard Nb Etching Technology: • Buffered Chemical Polishing:HF : HNO3 : H3PO4(ratio 1:1:1 or 1:1:2) • HNO3: Is the Oxyding agent • HF: Transforms the Nb2O5 in a water soluble salt • H3PO4: Reaction moderator • ElectroPolishing:HF : H2SO4(ratio 1:9)

3. Alternatives for BCP: • Standard BCP:HF : HNO3 : H3PO4 • Modified BCP:HF : HNO3 : H2SO4 (ratio 1:1:2) at 78°C • Y. Uzel, K. Schnitzke, N. Krause: Appl. Phys., A30 (1983) p.185 • Remodified BCP:HF : HNO3 : H2SO4 (ratio 1:1:1) room T • C. Z. Antoine, A. Aspart, J.P. Charrier, H. Safa, B.Visentin, Proc 9° Workshop on SC RF, (1999) Santa Fé

4. T. Higuchi, K. Saito, Proc. Of the 11th Workshop SC RF, 2003, Travelmunde Development of Hydrogen-free EP and Hydrogen Absorption Phenomena Abstract We developed a hydrogen-free electropolishing method for superconducting Nb cavities……….. ….We prevent hydrogen absorption in barrel polishingreplacing the water from a liquid without hydrogen component……. ……..Thus we finally invented the hydrogen-free electropolishing by putting one drop of Nitric acid into the EP acid

5. V. Palmieri, F. Stivanello, C. Roncolato, M. Valentino Proc, 10th SC RF workshop, 2001 Tsukuba investigated the system BCP HF : HNO3 : H3PO4(ratio l, m, n)

6. V. Palmieri, F. Stivanello, C. Roncolato, M. Valentino Proc, 10th SC RF workshop, 2001 Tsukuba investigated the system BCP HF : HNO3 : H3PO4(ratio l, m, n)

7. V. Palmieri, F. Stivanello, C. Roncolato, M. Valentino Proc, 10th SC RF workshop, 2001 Tsukuba The introduction of LESS HAZARDOUS COMPONENTS in the standard BCP was proposed For example: HF NH4F HNO3 H2O2 NH4F + HCl + H2O2 + H3PO4at room temperature was found Several percentages studied, the best results were obtained with the NH4F : HCl : H2O2 : H3PO4 in the 2:2:4:1 ratio with (60g/lt) of NH4F

8. 1. Alternatives for EP: lactic acid 2° International TESLA Workshop, DESY, Hamburg ,August 1991 Improved Methods for Electrochemical Polishing of Nb Superconducting cavities V.M. Efremov, L.M. Sevryukova, M. Hein, L. Ponto 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

9. 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 Liquid Composition for ElectroPolishing Niobium Material and its preparation Abstract: PURPOSE: To obtain a polshing solution which prevents the reduction of the polishing power and the pollution of work environment due to the evaporation of HF by using a mixed solution consisting of concentrated sulfurc acid, fluosulfuric acid and water as an electropolishing solution when Nb material is electropolished to form a mirror finished surface See also: K. Saito, Proceedings of the 4th workshop on RFSC, Tsukuba 1989

10. Nb ELECROPOLISHING 3. Alternatives for EP:getting rid of sulphuric (Palmieri et al., Tsukuba SRF Workshop 2001) We automatically find the working point (I 0, V0), by locking the minimum of dI/dV. This idea allows us the possibility to investigate new solution, finding by ourselves the working parameters This approach has permitted the author 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.

11. 4. Alternatives for EP:perchlorate salts A well known hydrogen free electrolite for Nb: An electrolyte for Nb was introduced by Schober and Sorajic, extrapolating what proposed by Epelboin [Rev. Met. 49 (1952) 863.] The electrolyte is 0.05 mole/liter Mg(ClO4)2 in CH3OH EP Voltage is 50-70 V, bath temperature -5°C Since the electrolyte does not contain a hydrogen radical, no intake of hydrogen is possible

12. Perchloric acid has been largely used as constituent of electropolishing baths for its peculiar properties, for its easy dissolution in non aqueous media, for its powerful dissolution action of metals and alloys for the remarkable solubility of numerous metallic perchlorates in acid milieu

13. However, in the technique literature, many explosions caused by perchloric acid solutions have been brought to notice Polishing baths perchloric acid-based can be divided into two main classes: Strong solutions, containing perchloric acid mixed with anhydride or with acetic acid Less concentrated solutions containing perchloric acid mixed with ethylic acid, acetic acid or acetic anhydride Notice!!!!! Some authors maintains that ethyl perchlorate is as dangerous as Nitroglycerin

14. Mixes containing less than 55% in weight of perchloric acid cannot explode Unfortunately they are the less interesting for the EP use The convenient polishing baths are just located in the flammable field

15. If Percloric acid gives rise to explosive mixtures, under other aspects Hydrofluoric acid is not less dangerous : • hydrofluoric acid is a highly corrosive solution • if it is accidentally released, it forms an aerosol acid cloud which can cause serious bone damage and death by burns to the skin, tissue or lungs o even minor exposure can cause skin burns and blindness • - refineries using hydrofluoric acid have a long and devastating history: • ExxonMobil had 1,133 releases from the years 1990-2003; Roughly translates into one accident every five days • March 2, 2003, 13 employees at the Marathon Ashland oil refinery in Minnesota were hospitalized after a pump leaked hydrofluoric acid4 • January 1, 2005, a train car carrying hydrogen fluoride derailed into the Allegheny River, releasing the gas into the river in Pennsylvania at the Norfolk Southern Refinery • 5October 20, 2000, 1 person was hospitalized after a disk ruptured on a storage tank in Delaware, at the General Chemical Corporation • 6 October 30, 1987, 1,037 people were sent to the hospital and 3,000 residents were forced out of their homes after a crane accidentally dropped its load on a storage tank, rupturing a pipe and releasing 30,000 pounds of hydrofluoric acid

16. There are a lot of horror stories about HF: • On contact, HF very easily passes through skin and tissue. Because its action can be delayed for many hours, it can distribute throughout the body. • Negatively charged fluorine ions bind very easily to positively charged calcium and magnesium ions to form insoluble salts (CaF2 and MgF2 salts form some natural gemstones.) In the body, Ca and Mg ions are used to mediate a variety of physiological processes, such as muscle movement. Calcium is also a chief component in bone. • Local tissue damage (and the point of contact) results from free hydrogen ions which causes corrosive chemical burns and free fluorine ions which cause deep tissue damage including erosion of bone. • Systemic damage can occur when fluorine becomes distributed throughout the body. These conditions include hypocalcemia (loss of calcium) and hyperkalemia (too much potassium). Since calcium and potassium regulate the heart, irregular beating and cardiac arrest are manifestations. "Deaths have been reported from concentrated acid burns to as little as 2.5% BSA [body surface area exposed to skin contact]

17. Hydrofluoric acid (HF) is a corrosive inorganic acid [Himes, 1989]. It is used in industry for etching glass, electronics, and semiconductor manufacturing, and in the petroleum industry to produce high octane fuels [Bertolini,1992]. It is also a component of some consumer products, such as rust removers [Saadi et al., 1989]. With regard to human toxicity, HF is of particular concern because not only does its contact with skin cause local burns, but the fluoride ions readily penetrate the skin to cause systemic poisoning. Skin penetration by HF is retarded by the lipid layer of intact skin and accelerated by abrasions or minor trauma [Noonan et al., 1994]. Death can occur from a splash of as little as 2.5% of the body surface with concentrated HF [Tepperman, 1980]. Inhaling HF vapors (boiling point 68F) leads to pulmonary edema, and in high enough concentrations, death [O'Neil, 1994]. Fluoride ions that penetrate the skin into systemic circulation bind to divalent cations, primarily calcium and magnesium, leading to electrolyte imbalance, cardiac arrhythmia, and death [Sadove et al., 1990]. Fluoride also inhibits glycolysis and oxidative phosphorylation with the same results [DeLauder et al., 1994]. Contact with HF in concentrations less than 50% does not cause immediate pain, so systemic poisoning can begin before the person is aware they have had contact with the acid [U.S. Department of Energy, 1986].

18. A brief summary of individual cases identified from Occupational Safety and Health Administration (OSHA) reports follows: Case 1 occurred on 20 August 1984. A 53-year-old worker was exposed to HF in the process of using methyl chloroform to unclog a line leading to a storage tank of HF. In the process of connecting a hose to the tank valve, the coupling came loose, splashing him with methyl chloroform (the cleaning agent), and HF (from the tank), resulting in burns to the arm, face, and neck covering 30% of his body. He was showered and was transported to the plant's first aid area, arriving approximately 30 min following the accident. He was transferred to a hospital where he developed seizures and then cardiac arrest, dying 7±8 min after arrival. Case 2 occurred on 20 September 1985. A 51-year-old worker entered an area where there had been an HF spill and cleanup efforts were underway. The worker entered the spill area with only rubber gloves, rubber boots, and a self contained breathing apparatus. A sump pump was being used to pump the spilled acid back into a tank for storage. As the employee moved the pump to a lower level to continue the process, the hose came off of the pump and the worker was sprayed with HF across 40% of his body (face and chest) and died shortly after. A review of pump specifications revealed that this pump was not recommended for use with corrosive material.

19. Case 3 A woman etching computer chips developed a pin-hole in her glove during the four hours that she was working in a dip tank with 5% hydrogen fluoride. She went to a doctor's office where a non-specific burn ointment was applied (no calcium gluconate was applied). She continued to have pain during the next four days. At that time she had severe pain under the finger nail and the subungual tissues were black. There was mild erythema around the proximal cuticle. Upon removal of the finger nail at a burn treatment center where she was referred, exposed and necrotic bone was identified. The distal phalanx was demineralized and the patient required distal amputation of the finger (Edelman, 1986). Hydrofluoric acid (HF) differs from other acids because the fluoride ion readily penetrates the skin, causing destruction of deep tissue layers, including bone. Pain associated with exposure to solutions of HF (1-50%) may be delayed for 1-24 hours. If HF is not rapidly neutralized and the fluoride ion bound, tissue destruction may continue for days and result in limb loss or death. … Do you really want I continue with case 4?

20. The chemical/Electrochemical Polishing of 20,000 cavities would require several hundred Tons of HF The phase out of HF and the enactment of a safer alternative would be mandatory NH4F is not less dangerous when dissolved in water, but at least it is a fluorine compound with a lower volatility and a reduced risk of acid vaporization

21. 5. Alternatives for EP: alcaline media V. Brichese, V. Rampazzo, S. Stivanello, V. Palmieri Nb Electrodissolution in basic environment: Solution1: KOH 1 M Solution1: KOH 1 M T ~ 70° Stirring T ~ 70° Stirring E = 1,38 V E = 1,38 V Etching rate: 66 g/m2min Etching rate: 132 g/m2min

22. 6. Alternatives for EP: Niobium Electrodissolution in molten salts Anodic dissolution of Nb alloys in NaCl-KCl and NaCl-KCl-NbCln melts, as well as cathodic reduction of niobium from molted NaCl-KCl-NbCln-AlCl3 at 710 °C

23. Niobium Electrodissolution in molten salts Electrical conductivity is a physical property reflecting the ability of a matter to transfer electrical charge. In molten salts conductance is due to ionic mobility which depends on many factors but the mostly the size of ions and ionic bond strength. Direct electrochemical reduction of Nb2O5 into Nb in molten CaCl2 is possible. The idea is that Calcium reacts at the cathode with the oxygen to form CaO, which is soluble in molten CaCl2. It remains however unsolved the problem that 800°C are needed for melting the salts. Lower temperatures are possible when reducing Niobium pentaoxyde with Al in an AlC13 melt

24. 7. Alternatives for EP: Ionic liquids Ionic liquids are defined today as liquids which solely consist of cations and anions and which by definition must have a melting point of 100 °C or below. In the middle of the 1990s the term ‘‘room temperature molten salt’’ was definitely replaced by ‘‘ionic liquid’’. The ‘‘room temperature molten salts’’ were regarded as uncommon and as a curiosity for a while. The situation has changed dramatically throughout the recent 3 years

26. The early history of ionic liquids began in 1914 when the first report of a room temperature molten salt was reported by Walden: Ethylammoniumnitrate, [C2H5NH3]NO3, which has a melting point of 12°C, was formed by the reaction of ethylamine with concentrated nitric acid. Then, Hurley and Weir stated that a room temperature ionic liquid could be prepared by mixing and warming 1-Ethylpyridinium Chloride with AlCl3. In 1970s and 1980s, Osteryoung et al. and Hussey et al. carried out extensive research on organic chloride–aluminium chloride ambient temperature ionic liquids. The ionic liquids based on AlCl3 can be regarded as the first generation of ionic liquids

27. Ionic liquids are going to represent a main stream in various fields of chemistry and physical chemistry! Imagine making a liquid just by mix ing two solids! And think what you could do with this liquid if it was non-toxic, biodegradable and could dissolve a wide range of materials.  The trend is to look for liquids that can be used to substitute the strong and corrosive acids traditionally used as solvents in many industrial chemical reactions.  By means of this non-aqueous media, the electroplating of Titanium, Alluminium, Niobium film can be attempted!

28. Salt flats in California: A lake has evaporated, leaving behind a layer of salt. In exactly the same way as common salt, liquid salts consist of positively charged and negatively charged ions, though they are not simple ions like sodium and chloride but are much larger and more complex, and unable easily to form a crystal lattice. If even a small amount of heat is applied to them, the solid crystalline structure disintegrates and bonds between the ions are broken. The salt becomes a liquid – an ionic liquid.

30. For Niobium: One such system that could be explored is that formed from 1-ethyl-3-methylimidazolium (EMIC) and anhydrous AlCl3 This system is a thermally stable liquid between –100 °C and ca. 200 °C, dependent on the molar ratio of EMIC to AlCl3 utilized …. But anhydrous AlCl3 can give rise to unpleasent exothermic reactions! Glow box is mandatory and …

31. ABBOTT Patent deposited by Shonix Surprisingly, however, we have now found that by forming the anion of an ionic compound from a hydrated metal salt and the cation from certain specific amine salts, it is possible 25 to produce compounds which are liquid at low temperatures (i.e. 50 °C and below), relatively inexpensive, and relatively water insensitive. Choline chloride and hydrated metal halides, as magnesium chloride, Copper nitrate, or Calcium chloride, … succeed in electropolishing a big variety of metals ….. But Choline Chloride is an ingredient of chicken feed!?! I don’t believe it will be ever useful for electropolishing Niobium? Cavities have nothing to do with chicken feed

33. Choline Chloride Drink The brain has a voracious appetite for choline. There are two main reasons for the brain's huge need for this nutrient: Choline is required for synthesis of the key neurotransmitter acetylcholine, and it is used for the building and maintenance of brain cell membranes. Acetylcholine is vital for thought, memory and sleep, and is also involved in the control of movements Dosage and Use Take 1 to 3 teaspoons daily. It is best mixed with approximately 2 oz. of juice per teaspoon.

36. On the basis of Abbott Patent, We succeeded in electropolishing Nb! by a mixture of Choline Cloride, Urea, NH4F at 80°C

37. THE END 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)