Thermal signatures of Cu metal revealed through oxygen isotope fractionation

Cu metal, surrogate for metallic actinide materials, was subject to accelerated aging through thermal treatment. A multiphase oxide-layer (Cu 2 O, CuO) was detected, varying with temperature (250–400 °C) and aging time (1–3.5 h). Isotope ratio mass spectrometry revealed temperature-dependent isotopic fractionation of O, evidenced by the enrichment of Cu oxide in 16 O isotopes with increasing temperature. Isotopic fractionation occurred initially with atmospheric O, and later through exchange with water vapor. Raman spectra contributed insight on phase fraction and local bonding of Cu oxides. O isotopes could serve as a useful tracer for studying oxide layer growth from aging metallic systems.