Niobium

Niobium is a refractory metal that has characteristics very similar to tantalum, which is located below it on the Periodic Table. It oxidizes readily, especially in air above 200°C, and forms a protective oxide film that provides good corrosion resistance.

Embrittlement of niobium is a problem in hydrogen, nitrogen, oxygen, or carbon at temperatures greater than 300°C. Niobium reacts with nitrogen at temperatures greater than 350°C, water vapor at temperatures greater than 300°C, chlorine at temperatures greater than 200°C, and hydrogen, carbon monoxide and carbon dioxide at temperatures greater than 250°C.

In general, niobium has a good resistance to both mineral and organic acids, but is susceptible to alkaline solutions. Specifically, it is resistant to hydrochloric, hydroiodic, hydrobromic, nitric, sulfuric and phosphoric acids; it is susceptible, however, to corrosion in hydrofluoric acid, and strong sulfuric and hydrochloric acids at higher temperatures. It is also less resistant to hot mineral acids compared to tantalum.

Niobium exhibits a good resistance to most gases at temperatures up to 100°C. It is also resistant to liquid and vaporous metals and molten salts. Furthermore, neither salt solutions nor seawater readily attack niobium.