2. The surface of 2.Nb is treated by electrophoretic coating, which can't be covered by ordinary coating.
3. The surface scratches of niobium can be treated with metal restorer. This is a composite material composed of polymer, metal powder, ceramic powder, fiber and curing agent, which can repair various surface defects. It should be sold in chemical stores or supermarkets, and is suitable for repairing metal defects such as wear, scratch, corrosion and cracking.