Crystal structure: The cell is a body-centered cubic cell, each cell contains 2 metal atoms.
Cell parameters: a=330.13pm, b=330.13pm, c=330.13pm, α=90°, β=90°, γ=90°, Mohs hardness: 6.5, melting point: 2996℃. Tantalum is very hard, with a hardness of 6-6.5. Its melting point is as high as 2996 ° C, ranking fifth after carbon, tungsten, rhenium and osmium. Tantalum is malleable and can be drawn into fine wires. Its coefficient of thermal expansion is very small, only 6.6 parts per million per degree Celsius rise. In addition, its toughness is very strong, even better than copper.
Physical properties: Very hard and malleable.
Chemical properties: Tantalum also has excellent chemical properties and high corrosion resistance. Under hot and cold conditions, it does not react with hydrochloric acid, concentrated nitric acid and aqua regia. But tantalum is corroded in hot concentrated sulfuric acid. Below 150 ° C, tantalum will not be corroded by concentrated sulfuric acid, and the reaction will only occur at temperatures above this temperature. 175℃ concentrated sulfuric acid for 1 year, the thickness will be corroded. Tantalum is soaked in sulfuric acid at 200℃ for one year, and the surface layer is only damaged 0.006 mm. At 250℃, the corrosion rate increases and the corrosion thickness is SDS mm per year. At 300°C, the corrosion rate is faster. After soaking for 1 year, the surface corrosion is 1.368mm. The corrosion rate in fuming sulfuric acid (containing 15%SO3) is more serious than that in concentrated sulfuric acid. After soaking in this solution at 130 degrees for 1 year, the corrosion surface thickness is 15.6mm. Tantalum will also be corroded by phosphoric acid at high temperatures, but the reaction generally occurs above 150 degrees. Soak in 250% phosphoric acid at 85 degrees for 1 year and corrode the surface by 20 mm. In addition, tantalum is corroded, can quickly dissolve in nitric acid mixed acid, can also dissolve in hydrofluoric acid. But tantalum is more resistant to strong alkali. In a caustic soda solution of 110 degrees and 40% concentration, tantalum will dissolve quickly. In the same concentration of potassium hydroxide solution, 100 degrees will quickly dissolve. In addition to the above, the general inorganic salt can not corrode tantalum below 150 degrees. Experiments show that tantalum has no effect on alkaline solution, chlorine gas, bromine water, dilute sulfuric acid and many other reagents at room temperature, and only reacts under the action of hydrofluoric acid and hot concentrated sulfuric acid.
