Oxidation Resistant Coating for Niobium by Combining Hot Dipping in Molten Aluminum Coating and Anodize Oxidation

The combination of hot dipping in molten aluminum and the subsequent anodic oxidation to dense Al2O3 films was studied to prepare an oxidation-resistant coating on niobium surface. By immersing Nb into a molten Al bath, granular NbAl3 was precipitated and improved the coherency of the film to the substrate. Amorphous Al2O3 was formed by anodic oxidation of the Al layer and crystallized to corrosion resistant α-Al2O3 by the subsequent heat treatment. The Nb substrate after this combined treatment did not form any niobium oxides even after heating in air for 64.8 ks at 1073 K, and the oxygen increment in the Nb bulk was suppressed below 400 mass ppm