Tantalum and its alloys are midway between tungsten and molybdenum in density and melting points. Tantalum can be worked easily at room temperature. Its thermal conductivity is one-fourth that of molybdenum and its coefficient of expansion is one-third greater. Its elevated temperature strength is low compared with tungsten and molybdenum.
Tantalum is attractive for refractory environments because of its high melting point and corrosion resistance. Substances that can affect tantalum are fluorine, hydrofluoric acid, sulfur trioxide (including fuming sulfuric acid), concentrated strong alkalis, and certain molten salts. The corrosion resistance of tantalum is comparable to glass, although tantalum withstands higher temperatures and offers the machinable advantages of a metal. Tantalum is frequently used in conjunction with glass, glass-lined steel, and other nonmetallic materials. Due to its high cost and lack of strength, tantalum is usually used as a lining over a stronger, less expensive base material.
