Interaction of oxygen with nanocrystalline metals

Nanocrystalline Ni and Fe specimens with a low oxygen content and mass-densities up to 98 and 93%, respectively, were produced by gas-phase condensation. The oxygen contents were determined by nuclear-reaction analysis (NRA) in the as-prepared state and after exposition to different oxygen partial pressures. NRA measurements in combination with serial sectioning by ion-beam sputtering show that the penetration of oxygen along open porosity is suppressed in the case of specimens with a high mass-density. Neither by NRA measurements nor by secondary-ion mass spectrometry (SIMS), performed after thermal treatments in oxygen in the temperature regime between 100 and 200°C, oxygen penetration can be detected in high-density nanocrystalline Ni specimens. This may indicate a low oxygen diffusion in interfaces of n-Ni. However, a low oxygen solubility may not be excluded.