Tantalum's mechanical and physical properties depend largely on its purity. The purity of tantalum is mainly related to the presence of non-metals (such as carbon, oxygen, nitrogen and hydrogen, etc.). Even very low concentration of these impurities in tantalum will cause great changes in its properties. Tantalum compact metal has different structure and morphology due to different production methods (such as sintering or electron beam melting). Tantalum structure and deformation rate are very important properties. The outstanding mechanical and physical characteristics of 99.9% pure tantalum are high melting point, high density, excellent formability, thermal conductivity, toughness and weldability.
Tantalum has the capacity to absorb hydrogen, oxygen, nitrogen and carbon in its lattice gaps. The actual solubility can reach quite large values. Tantalum metal can dissolve 20(atomic)% oxygen at room temperature. If this solubility is exceeded, hydrides and very hard oxides, nitrides, carbides and their mixed phases are formed. In order to remove the absorbed nonmetal, high temperature and high vacuum or very pure inert gas protection is required.
Hardness is a sensitive indicator of non-metal content in tantalum, and can also be used as a standard to measure the purity of tantalum metal. There is an industrial hardness difference of 100 to 200% between pure tantalum 99.5(by weight)% (the limit of hot deformation) and cold-forged tantalum with purity greater than 99.95%(by weight)%.
Pure tantalum produced from crude tantalum by different methods - electron beam melting, vacuum arc melting or sintering - varies in purity and structure. Electron beam smelting produces tantalum with the highest purity and the most complex structure.
The effect of cold deformation also depends on the content of various nonmetals. Tantalum with high purity obtained by electron beam smelting has little effect on deformation, while tantalum obtained by arc smelting has a larger deformation rate of 99%.
