Evaluation of the propensity of niobium to absorb hydrogen during fabrication of superconducting radio frequency cavities for particle accelerators

Journal Article · 01 September 2010 · Journal of Research of the National Institute of Standards and Technology

DOI: https://doi.org/10.6028/jres.115.025 · OSTI ID:1628970

Ricker, R. E. ^[1]; Myneni, G. R. ^[2]

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1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States). Materials Science and Engineering Lab.
2. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

During the fabrication of niobium superconducting radio frequency (SRF) particle accelerator cavities procedures are used that chemically or mechanically remove the passivating surface film of niobium pentoxide (N_b2O₅). Removal of this film will expose the underlying niobium metal and allow it to react with the processing environment. If these reactions produce hydrogen at sufficient concentrations and rates, then hydrogen will be absorbed and diffuse into the metal. High hydrogen activities could result in supersaturation and the nucleation of hydride phases. If the metal repassivates at the conclusion of the processing step and the passive film blocks hydrogen egress, then the absorbed hydrogen or hydrides could be retained and alter the performance of the metal during subsequent processing steps or in-service. This report examines the feasibility of this hypothesis by first identifying the postulated events, conditions, and reactions and then determining if each is consistent with accepted scientific principles, literature, and data. Established precedent for similar events in other systems was found in the scientific literature and thermodynamic analysis found that the postulated reactions were not only energetically favorable, but produced large driving forces. The hydrogen activity or fugacity required for the reactions to be at equilibrium was determined to indicate the propensity for hydrogen evolution, absorption, and hydride nucleation. The influence of processing conditions and kinetics on the proximity of hydrogen surface coverage to these theoretical values is discussed. This examination found that the hypothesis of hydrogen absorption during SRF processing is consistent with published scientific literature and thermodynamic principles.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-06OR23177
• OSTI ID: 1628970
• Journal Information: Journal of Research of the National Institute of Standards and Technology, Vol. 115, Issue 5; ISSN 1044-677X
• Publisher: National Institute of Standards (NIST)Copyright Statement
• Country of Publication: United States
• Language: English