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.
Chemical properties of tantalum
Tantalum also 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. However, tantalum can be corroded in hot concentrated sulfuric acid. Under 150 ℃, tantalum will not be corroded by concentrated sulfuric acid. Only when the temperature is higher than this, it will react. In concentrated sulfuric acid at 175 ℃, the thickness of the corroded is 0.0004mm. When tantalum is immersed in sulfuric acid at 200 ℃ for one year, the surface is only damaged by 0.006mm. At 250 ℃, the corrosion rate increased to 0.116 mm per year, and at 300 ℃, the corrosion rate increased even faster. After immersion for 1 year, the surface was corroded by 1.368 mm. The corrosion rate in fuming sulfuric acid (containing 15% so?) is more serious than that in concentrated sulfuric acid. The corrosion thickness of the surface is 15.6 mm when immersed in 130 ℃ solution for 1 year. Tantalum will also be corroded by phosphoric acid at high temperature, but the reaction usually takes place at 150 ℃ or above. In 85% phosphoric acid at 250 ℃, it will be soaked for one year, and its surface will be corroded for 20 mm. In addition, tantalum can be rapidly dissolved in the mixed acid of hydrofluoric acid and nitric acid, and it can also be dissolved in hydrofluoric acid.  But tantalum is more afraid of strong alkali. In the caustic soda solution with the concentration of 110 ° 40%, tantalum will be rapidly dissolved. In the potassium hydroxide solution with the same concentration, as long as 100 ° C, it will be rapidly dissolved. In addition to the above situation, General inorganic salt can not corrode tantalum below 150 ℃. Experiments show that tantalum has no effect on alkali solution, chlorine, bromine water, dilute sulfuric acid and many other reagents at room temperature, but only react with hydrofluoric acid and hot concentrated sulfuric acid. Such a situation is rare in metals.
However, at high temperature, the oxide film on the surface of tantalum is destroyed, so it can react with a variety of substances. At normal temperature, tantalum can react with fluorine. At 150 ℃, tantalum is inert to chlorine, bromine and iodine. At 250 ℃, tantalum is still resistant to dry chlorine. When it is heated to 400 ℃, it still keeps bright. At 500 ℃, it begins to be corroded. Above 300 ℃, tantalum reacts with bromine. When the temperature of iodine vapor reaches red heat, it is inert. Hydrogen chloride reacts with tantalum at 410 ℃ to produce pentachloride, while hydrogen bromide reacts with tantalum at 375 ℃. When heated to 200 ℃ or lower, s can interact with TA, and carbon and hydrocarbon can interact with tantalum at 800-1100 ℃.