Tantalum TA, a metal element, occurs mainly in tantalite and coexists with niobium. The hardness of tantalum is moderate and it is malleable. It can be drawn into thin foil of filament type. Its coefficient of thermal expansion is very small. Tantalum has excellent chemical properties and high corrosion resistance. It does not react with hydrochloric acid, concentrated nitric acid and aqua regia under cold and hot conditions. It can be used to make evaporating utensils and so on. It can also be used as electrodes, rectifiers and electrolytic capacitors of electronic tubes. Used medicinally to make thin sheets or threads to repair damaged tissue. Although the corrosion resistance of tantalum is very strong, its corrosion resistance is due to the formation of stable tantalum pentoxide protective film on the surface.