tantalum

Ta. An element with atomic number 73. It is a transition metal element (d-block) in group ⁵ of ^the periodic table with the electron configuration [Xe] ^4f145d36s2 . Its atomic weight is 180.9479(1). It has isotopes with mass numbers between 155 and 190, with stable isotopes of 180 (0.012(2)%) and 181 (99.988(2)%). In 1802, Swedish chemist AG Ekeberg discovered it in two minerals from Finland and Sweden, and named it tantalum after the Greek mythological character "Tantalus" because its oxide does not dissolve in acid. In his book "Semitsu Kaisou" published in 1837, Udagawa Yoan called it Tantalum. Because of its similar properties to niobium, there was considerable controversy before it was confirmed that the two were different elements.
Its abundance in the earth's crust is 1.0 ppm. Its main ores are tantalite (Fe, Mn)Ta ₂ O ₆ and microlite (Na, Ca) ₂ Ta ₂ O ₆ (O, OH, F). It is produced together with the niobium ores columbite and pyrochlore. Its resources are highly unevenly distributed, with Australia, Brazil, and Canada accounting for almost 100% of the world's reserves. The minable reserves are 40,000 tons in Australia and 3,000 tons in Canada, and the total reserves are 80,000 tons in Australia and 73,000 tons in Brazil (2006). Japan imports all of it in the form of metal, semi-finished products, and finished products from the United States, Germany, and China. As it is a rare metal, its price fluctuates greatly. In the United States, it is a target for stockpiling as a strategically important mineral, and in Japan, it is a mineral of particular interest (Agency for Natural Resources and Energy). Tantalum is smelted in an alkali, then dissolved in hydrofluoric acid and extracted in the form of a fluoro complex salt with a solvent (such as isobutyl methyl ketone). The simple substance can be obtained by reducing the fluoride K ₂ TaF ₇ with magnesium or sodium, or by molten salt electrolysis. Metallic tantalum is silver in color and has a cubic cubic crystal system. Its density is 16.65 g cm ⁻³ (0 °C). Its melting point is 2996 °C, its boiling point is 5425 °C. Its atomic radius is 0.143 nm. Its first ionization energy is 714 kJ mol ⁻¹ (7.40 eV). It is a fairly hard metal, but highly ductile. It becomes brittle with a small amount of impurities. It can have oxidation numbers 2 to 5, with oxidation number 5 being the most stable. It has extremely high chemical resistance, and is insoluble in aqua regia, let alone hydrochloric acid or nitric acid. It is also not affected by chlorine, concentrated sulfuric acid, or strong alkalis at temperatures below 200 °C. However, it is soluble in hydrofluoric acid and molten alkali. At high temperatures, it also reacts directly with fluorine, chlorine, oxygen, nitrogen, and carbon. It has an unusually large affinity for hydrogen, and when heated to 600°C, it absorbs and releases hydrogen in an amount 740 times its own volume, forming a fragile hydride.
Its main use is in small, high-capacity capacitors (condensers) that use tantalum powder sintered bodies as the positive electrode, and are resistant to high temperatures and voltage surges. They are used in computer CPUs, mobile phones, automotive electrical equipment, aircraft, missiles, and weapon systems. Its excellent resistance to heat, corrosion, and acidity makes it a material for chemical plants, a component of superalloys used in aircraft structures and jet engines, a sputtering material used in hard disk magnetic layers, and it does not react with biological tissues, so _it is used as a material for medical instruments, artificial bones, and artificial tooth roots. Tantalum oxide _Ta2O5 is used as a raw material for the manufacture of lithium tantalate _LiTaO3 , which is used in noise filters for mobile phones, and as an additive for optical lenses, while tantalum carbide TaC is used as an additive for cemented carbide used in cutting tools. [CAS 7440-25-7]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Ta．原子番号73の元素．電子配置[Xe]4f ¹⁴5d³6s²の周期表5族遷移金属元素(d-ブロック)．原子量180.9479(1)．質量数155～190の同位体が知られているが，安定同位体は180(0.012(2)％)，181(99.988(2)％)．1802年，スウェーデンの化学者，A.G. Ekebergがフィンランドおよびスウェーデン産の2種類の鉱物中に発見し，酸化物が酸に溶けないことからギリシア神話の“Tantalus”にちなんでタンタルと命名した．宇田川榕菴は天保8年(1837年)に出版した「舎密開宗」で，これを旦荅律母(タンタリュム)としている．ニオブと性質が類似していることから，両者が異なる元素であることを確認するまでにかなりの論争があった．
地殻中の存在度1.0 ppm．主要鉱石は，タンタル石(Fe，Mn)Ta₂O₆やマイクロ石(Na,Ca)₂Ta₂O₆(O，OH，F)など．ニオブの鉱石コルンブ石，パイロクロアとともに産出する．資源的にいちじるしく偏在していて，オーストラリア，ブラジル，カナダが世界の埋蔵量のほぼ100％ を占める．採掘採算性埋蔵量はオーストラリア4万t，カナダ3千 t，全埋蔵量ではオーストラリア8万t，ブラジル7万3千 t(2006年)．わが国は全量を金属，半製品，製品の形でアメリカ，ドイツ，中国から輸入している．希少金属であるため，価格変動が激しい．アメリカでは戦略上重要鉱物として備蓄の対象で，わが国では要注視鉱種(資源エネルギー庁)とされている．製錬はアルカリ融解したのち，フッ化水素酸に溶かしてフルオロ錯塩の形で溶媒(イソブチル=メチル=ケトンなど)抽出する．単体はフッ化物K₂TaF₇をマグネシウム，ナトリウムで還元するか，融解塩電解を行うことにより得られる．金属タンタルは銀色で，結晶系は等軸晶系体心立方格子．密度16.65 g cm^－3(0 ℃)．融点2996 ℃，沸点5425 ℃．原子半径0.143 nm．第一イオン化エネルギー714 kJ mol^－1(7.40 eV)．かなり硬い金属であるが展延性に富む．少量の不純物によりもろくなる．酸化数2～5の状態をとり，酸化数5がもっとも安定である．化学的にはきわめて抵抗力が大きく，塩酸，硝酸はもとより王水にも不溶．また，200 ℃ 以下の温度では，塩素，濃硫酸，強アルカリにも侵されない．ただし，フッ化水素酸，融解アルカリに可溶．また高温においては，フッ素，塩素，酸素，窒素，炭素とも直接反応する．水素に対して異常に大きい親和力を示し，加熱すると600 ℃ で自己の体積の740倍の水素を吸放し，もろい水素化物を生成する．
最大の用途は，タンタル粉末焼結体を正極とする大容量で高温・電圧サージに強い小型コンデンサー(キャパシター)で，パソコンCPU，携帯電話，自動車電装品，航空機，ミサイル，兵器システムなどで用いられる．耐熱，耐食，耐酸性にすぐれるので化学プラント用材料，航空機構造材やジェットエンジンに使われる超合金の成分，ハードディスク磁性層などに使われるスパッター材料，生体組織と反応しないので医療器具・人工骨・人工歯根材料として使われる．酸化タンタルTa₂O₅は，携帯電話などのノイズフィルターに使われるタンタル酸リチウムLiTaO₃製造の原料および光学レンズ用添加材，炭化タンタル TaCは，切削工具に用いられる超硬合金用添加材に用いられる．[CAS 7440-25-7]

出典　森北出版「化学辞典（第2版）」化学辞典 第2版について　情報