The Fluorosulfuric Acid Solvent System. IV. The Solutes Water and Potassium Nitrate

Gillespie, R. J.; Milne, J. B.; Senior, J. B.

doi:10.1021/ic50041a034

Cited by 9 publications

(4 citation statements)

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“…The NMR results that we present in Table IV show that water can simply be added to the EP solution to force the remaining fluorosulfonic acid to supply additional fluorine. Via conductivity measurements, Gillespie et al 22 determined that the equilibrium constant for [5] decreases with increasing temperature. Increasing the temperature also decreases the viscosity of the solution, therefore the free fluorine available for polishing is increased, and subsequently the etch rate, by two mechanisms.…”

Section: Discussionmentioning

confidence: 99%

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Chemical Analysis of Fluorine in Niobium Electropolishing

Ford

Cooper

Cooley

et al. 2013

J. Electrochem. Soc.

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Surface topography and chemical purity are important factors in niobium superconducting radio-frequency (SRF) cavity performance. Electropolishing (EP) is currently being used to minimize the surface roughness and to remove the damaged surface layer created during cavity manufacturing. This process is not ideal for reasons such as safety and performance consistency, so research and development is ongoing. Furthermore, the EP process specifications have been developed empirically, and a molecular level understanding of the process is not complete. The currently employed polishing solution is composed of sulfuric and hydrofluoric acids, where the fluorine ion is active in polishing the niobium. We used vibrational and nuclear magnetic resonance (NMR) spectroscopies to analyze the standard solution, and show that fluorine is bound and released by the reaction of the acid components in the solution: HF + H 2 SO 4 <-> HFSO 3 + H 2 O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction, which provides a route to improve the safety and effectiveness of EP. We also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard EP recipe.

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Section: Discussionmentioning

confidence: 99%

“…Via conductivity measurements, Gillespie et al [22] determined that the equilibrium constant for (5) decreases with increasing temperature. Increasing the temperature also decreases the viscosity of the solution, therefore the free fluorine available for polishing is increased, and subsequently the etch rate, by two mechanisms.…”

Section: Nmr Spectramentioning

confidence: 99%

Chemical Analysis of Fluorine in Niobium Electropolishing

Ford

Cooper

Cooley

et al. 2013

J. Electrochem. Soc.

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“…The presence of fluorosulfonic acid in EP solution is also confirmed with 19 The NMR results presented in Table 4.4 show that water can simply be added to the EP solution to force the remaining fluorosulfonic acid to supply additional fluorine. Via conductivity measurements, Gillespie et al [86] determined that the equilibrium constant for (R16) decreases with increasing temperature. Increasing the temperature also decreases the viscosity of the solution, therefore the free fluorine available for polishing is increased, and subsequently the etch rate, by two mechanisms.…”

Section: Nmr Spectramentioning

confidence: 99%

Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques

Ford

2013

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Insights to the fundamental processes that occur during the manufacturing of niobium superconducting radio-frequency (SRF) cavities are provided via analyses of density functional theory calculations and Raman, infrared, and nuclear magnetic resonance (NMR) spectra. I show that during electropolishing fluorine is bound and released by the reaction of the acid components in the solution: HF + H 2 SO 4 <−> HFSO 3 + H 2 O. This result implies that new recipes can possibly be developed on the principle of controlled release of fluorine by a chemical reaction. I also show that NMR or Raman spectroscopy can be used to monitor the free fluorine when polishing with the standard electropolishing recipe.Density functional theory was applied to calculate the properties of common processing impurities -hydrogen, oxygen, nitrogen, and carbon -in the niobium. These impurities lower the superconducting transition temperature of niobium, and hydride precipitates are at best weakly superconducting. I modeled several of the niobium hydride phases relevant to SRF cavities, and explain the phase changes in the niobium hydrogen system based on the charge transfer between niobium and hydrogen and the strain field inside of the niobium. I also present ACKNOWLEDGEMENTS 5LIST OF ACRONYMS AND SYMBOLS 7 TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES 1. INTRODUCTION 2. BACKGROUND Superconducting Radio-Frequency Cavity Design and Material Fundamentals Impurities in Niobium Superconducting Radio-Frequency Cavity Processing Superconducting Radio-Frequency Cavity Performance Limitations 3. METHODS Calculations Based on Density Functional Theory Experimental Tools 4. ELECTROPOLISHING SOLUTION ANALYSES Abstract Introduction Methods Results Raman Spectra Infrared Spectra Nuclear Magnetic Resonance Spectra Discussion

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“…Bei der Herstellung der MeBproben mulJte die groI3e Hydrolyseempfindlichkeit und Ltjsungswarme der wasserfreien Siiure berucksichtigt werden. Das Gleichgewicht der Reaktion H,O+ + FSQ,-= H,SO, + HF liegt dagegen bei tieferen Temperaturen weit auf der linken Seite [7]. Es galt also, die Proben bei moglichst tiefen Temperaturen herzustellen und auch anschlieBend jede unnotige thermische Relastung zu vermeiden.…”

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Hydrate der Fluorsulfonsäure: Das Schmelzdiagramm des Systems FSO₃HH₂O und die Kristallstruktur des Monohydrats, (H₃O)FSO₃

Mootz¹,

Bartmann²

1991

Zeitschrift anorg allge chemie

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Das System FSO3HH2O wurde mit Differenzthermoanalyse untersucht. Durch Einhaltung ausschließlich tieferer Temperaturen bei Präparation und Manipulation der Meßproben konnte Hydrolyse der SF‐Bindung vermieden und ein quasibinäres Schmelzdiagramm erhalten werden. Dieses zeigt die Existenz von vier kristallinen Hydraten FSO3H · nH2O mit n = 1, 2, 3 und 4, die bei –12, –53 (Zers.), –46 bzw. −63°C (Zers.) schmelzen. Die Struktur des Monohydrats wurde bestimmt (Kristallsystem orthorhombisch, Raumgruppe Pnma, Z = 4 Formeleinheiten pro Elementarzelle; Gitterkonstanten a = 8,055, b = 6,465, c = 7,459 Å bei −50°C; abschließender R‐Wert mit 515 unabhängigen beobachteten MoKα‐Diffraktometerdaten bei 0,043). Es liegt ein typisches Oxoniumsalz vor, (H3O)FSO3, geprägt durch starke Wasserstoffbrücken nur der Art OH…︁O und mit interessanten Bezügen zur isosteren, dimorphen Verbindung (H3O)ClO4.

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The Fluorosulfuric Acid Solvent System. IV. The Solutes Water and Potassium Nitrate

Cited by 9 publications

References 0 publications

Chemical Analysis of Fluorine in Niobium Electropolishing

Chemical Analysis of Fluorine in Niobium Electropolishing

Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques

Hydrate der Fluorsulfonsäure: Das Schmelzdiagramm des Systems FSO₃HH₂O und die Kristallstruktur des Monohydrats, (H₃O)FSO₃

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The Fluorosulfuric Acid Solvent System. IV. The Solutes Water and Potassium Nitrate

Cited by 9 publications

References 0 publications

Chemical Analysis of Fluorine in Niobium Electropolishing

Chemical Analysis of Fluorine in Niobium Electropolishing

Insights to Superconducting Radio-Frequency Cavity Processing from First Principles Calculations and Spectroscopic Techniques

Hydrate der Fluorsulfonsäure: Das Schmelzdiagramm des Systems FSO3HH2O und die Kristallstruktur des Monohydrats, (H3O)FSO3

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Hydrate der Fluorsulfonsäure: Das Schmelzdiagramm des Systems FSO₃HH₂O und die Kristallstruktur des Monohydrats, (H₃O)FSO₃