Superabundant Vacancy Formation in Iron under High Hydrogen Pressures: Thermal Desorption Spectroscopy

Abstract

Thermal desorption of hydrogen from high-purity iron was observed after heat treatments at 470–870 K under a hydrogen pressure of 1.7 GPa. A total of 0.1–1.5 at% trapped hydrogen, with its amount increasing at higher holding temperatures, was desorbed in five stages. The most prominent one, occurring at 400–440 K, was identified as being due to the release from vacancy-hydrogen complexes, VacH6. The binding energy of a vacancy is estimated to be 44±4 kJ/mol.Possible implications of the result for hydrogen embrittlement are discussed.