The linear expansion coefficient of tantalum is 6, 5× 10-6k-1 between 0 ~ 100℃, the critical temperature of superconducting transition is 4, 38K, and the thermal neutron absorption cross section of the atom is 21, 3 target en. Tantalum is one of the most chemically stable metals at temperatures below 150℃. Only fluorine, hydrofluoric acid, fluorine-containing acidic solution and sulfur trioxide can react with tantalum. Reacts with a concentrated alkali solution at room temperature and dissolves in molten alkali. The compact tantalum was slightly oxidized at 200℃ and significantly oxidized at 280℃. Tantalum has a variety of oxides, the most stable of which is Ta2O5. Tantalum and hydrogen produce brittle solid solution and metal hydrides such as Ta2H,TaH,TaH2 and TaH3 at above 250℃. In the vacuum of 800 ~ 1200℃, the tantalum of hydrogen from tantalum precipitates and returns to plasticity. Tantalum reacts with nitrogen to form solid solution and nitrogen compound at about 300℃. At a high vacuum above 2000℃, the absorbed nitrogen is precipitated from tantalum. Tantalum and carbon exist in three phases above 2800℃ : carbon tantalum solid solution, low carbide and high carbide. Tantalum reacts with fluorine at room temperature and with other halogens above 250℃ to form halides.
Tantalum forms a stable anodic oxidation film in the acidic electrolyte. Electrolytic capacitors made of tantalum have the advantages of large capacity, small volume and good reliability. Capacitor making is the most important use of tantalum, accounting for more than 2/3 of the total tantalum consumption in the late 1970s. Tantalum is also used to make electronic emission tubes and high-power electron tube parts. Tantalum corrosion resistant equipment is used in the production of strong acid, bromine, ammonia and other chemical industries. Tantalum can be used as a structural material for the combustion chamber of aircraft engines. Tantalum tungsten, tantalum tungsten hafnium and tantalum hafnium alloys are used as heat-resistant and high-strength materials for rockets, missiles and jet engines, as well as parts for control and adjustment equipment, etc. Tantalum is easily machined and can be used as supporting accessories, heat shield, heater and heat sink in high temperature vacuum furnace. Tantalum can be used in orthopedics and surgery. Tantalum carbide is used in the manufacture of hard alloys. The borides, silicides and nitrides of tantalum and their alloys are used as heat release elements and liquid metal cladding materials in atomic energy industry. Tantalum oxide is used in the manufacture of advanced optical glasses and catalysts. In 1981, the proportion of tantalum consumed by all sectors in the United States was about 73% for electronic components, 19% for the machinery industry, 6% for transportation and other 2%.
