Oxidation Behaviors of Co, Cr, and Ni Nanopowders: A Real-Time Synchrotron X-ray Scattering Study.

We have studied the oxidation behaviors of Co, Cr, and Ni nanopowders for applications in biomedicine using a real-time synchrotron X-ray scattering in air. The Co nanopowders have a crystal domain size of 70 nm at room temperature (RT). The surface of the Co nanopowders was oxidized to CoO phase at RT. The interior of the Co nanopowders was rapidly oxidized at above 300 °C and was mostly oxidized above 550 °C. The Cr nanopowders have a crystal domain size of 92 nm at RT. The surface of the Cr nanopowders was oxidized to Cr₂O₃ phase at RT, but the interior of the nanopowders was present as Cr phase without being oxidized up to 650 °C. On the other hand, the Ni nanopowders have a crystal domain size of 93 nm at RT. The surface of the Ni nanopowders began to oxidize to Ni₂O₃ phase at 300 °C, and the interior of the nanopowders was mostly oxidized above 600 °C.