Tantalum, previously known as tantalium, is a chemical element with the symbol Ta and atomic number 73. A rare, hard, blue-grey, lustrous transition metal, tantalum is highly corrosion resistant and occurs naturally in the mineral tantalite, always together with the chemically similar niobium. It is part of the refractory metals group, which are widely used as minor component in alloys. The chemical inertness of tantalum makes it a valuable substance for laboratory equipment and a substitute for platinum, but its main use today is in tantalum capacitors in electronic equipment
The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150 °C tantalum is almost completely immune to attack by the normally aggressive aqua regia. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulphur trioxide, as well as with a solution of potassium hydroxide. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded only by tungsten and rhenium for metals, and carbon.
It is able to form oxides with the oxidation states +5 (Ta2O5) and +4 (TaO2), The most stable oxidation state is +5, tantalum pentoxide. Tantalum pentoxide is the starting material for several tantalum compounds. The compounds are created by dissolving the pentoxide in basic hydroxide solutions or by melting it in another metal oxide. Such examples are lithium tantalate (LiTaO3) and lanthanum tantalate (LaTaO4). In the lithium tantalate, the tantalate ion TaO−3 does not occur; instead, this part of the formula represents linkage of TaO7−6 octahedra to form a thensional perovskite framework; te contains lone TaO3−4 tetrahedral The fluorides of tantalum can be used for its separation from niobium. Tantalum forms halogen compounds in the oxidation states of +5, +4, and +3 of the type TaX5, TaX4aX3, although multi core complexes and substoichiometric compounds are also known. Tantalum pentafluoride (TaF5) is a white solid with a melting point of 97.0 °C and tantalum pentachloride (TaCl5) is a white solid with a melting point of 247.4 °C. Tantalum pentachloride is hydrolysed by water and reacts with additional tantalum at elevated temperatures by forming the black and highly hygroscopic tantalum tetrachloride (TaCl4). While the trihalogen compounds can be obtained by reduction of the pentahalogenes with hydrogen, the dihalogen compounds do not exist. A tantalum-tellurium alloy forms quasicrystals. Tantalum c with oxidation states as low as -1 have been reported. Like most of the other refractory metals, the hardest known compounds are the stable nitrides and carbides. Tantalum carbide, TaC, like the more commonly used tungsten carbide, is a very hard ceramic that is used in cutting tools. Tantalum (III) nitride is used as a thin film insulator in some microelectronic fabrication processes. There are two tantalum aluminides, TaAl3 and Ta3Al. These are stable, refractory, and reflective, and they have been proposed as coatings for use in infrared wave mirrors.
The base value of each unit of ranges between 10 and 40Ð per unit, with up to 4 units being found at any one time.
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|Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6|
|Group 3|||Antimony | Astatine | Barium | Bismuth | Cesium | Francium | Hafnium | Indium | Iodine | Iridium | Lanthanum | Lead | Mercury | |Osmium | Platinum | Polonium | Radium | Radon | Rhenium | Tantalum | Tellurium | Thallium | Tin | Tungsten | Xenon||