Reoxidation

Reoxidation is the process by which a material that has been reduced or has lost its oxide layer re-forms an oxide when exposed to an oxidizing environment. It is common in metals, alloys, oxides, ceramics, semiconductors, and nanomaterials, and represents the oxidation half of redox cycles. The rate and extent depend on temperature, oxygen availability, and material structure.

In metallurgy and corrosion, reoxidation occurs when a reduced metal surface contacts air or O2-rich gas. An oxide film forms, which may be protective or deleterious if porous or adherent poorly. Oxide growth is generally diffusion-controlled, with oxygen moving through the oxide and metal ions diffusing in the opposite direction.

In semiconductor fabrication, reoxidation often means regrowing silicon dioxide after oxide removal to repair interfaces or form a gate dielectric. Thermal oxidation can use dry O2 or water vapor, yielding different film properties. Growth is influenced by temperature, time, and ambient composition, and the process is used to tune interface quality.

In catalysis and redox chemistry, reoxidation regenerates reduced active sites or oxygen-storage materials, restoring catalytic performance. It is performed by heating in oxygen or air and is integral to redox cycles in processes like exhaust treatment, solid oxide fuel cells, and chemical looping.

Mechanistically, reoxidation involves oxygen diffusion and redox equilibria and is sensitive to temperature, the partial pressure of oxygen (pO2), and microstructure. It can be reversible under mild conditions but may induce phase changes, stresses, or spallation under aggressive conditions. Characterization methods include thermogravimetric analysis and X-ray spectroscopy.