Tantalum

Tantalum is a fairly inert and expensive metal that is durable and long lasting with a very good resistance to corrosion in many environments including severe ones. Its corrosion resistance can be at least partially attributed to the thin, protective oxide film (usually Ta2O5) that forms when exposed to air or another oxidizing environment at 300°C. Its corrosion resistance, in general, is better than that of niobium. It is, however, embrittled in oxygen at temperatures greater than 350°C.

Tantalum is resistant to fresh water, mine water, deionized water and seawater; it is also resistant to steam at high pressures. It is highly resistant to most acids (e.g. sulfuric (H2SO4), nitric (HNO3), hydrochloric (HCl), hydrobromic (HBr), etc.), chemical solutions, salts and salt solutions, and organic compounds including alcohols, ketones, alkaloids and esters, and is fairly resistant to dilute alkaline solutions.

Tantalum reacts with gaseous oxygen, nitrogen, and hydrogen at higher temperatures. It is susceptible to corrosion in hydrofluoric acid, hot concentrated phosphoric acid, sulfite (SO3), strong alkalis, and strong sulfuric acid at higher temperatures. Tantalum is also susceptible to hydrogen embrittlement, if it is not protected from becoming cathodic in an electrochemical cell that produces atomic hydrogen. The reason for this is because tantalum will absorb hydrogen when it is galvanically coupled with anodic metals.