タンタル

外観

灰黒色の粉末

溶解性

水に不溶。酸化性の酸、ふっ化水素酸、融解アルカリに反応し溶ける。ふっ化水素酸に溶け、水にほとんど溶けない。

解説

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)％)．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．

主な性質

1. 単体タンタルは光沢のある灰色の色調を持つ金属である
2. 金属タンタルはほとんどの試薬に侵されず、極めて酸化し難い金属である
3. タンタルはかなり硬いが、延性に富む。しかし高温で容易に酸化して燃焼する為、高温加工及び溶接を大気中で行う事が出来ない
4. 金属タンタルは融点がタングステンに次いで高い
5. タンタルは窒素、酸素、水素などの気体を吸収する性質を持つ
6. 人体への反応がほとんど無いので、医療器具に用いられる

用途

電解コンデンサー材料、耐熱耐食材料 (化学工業日報社)

用途

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．

主な用途

1. 高温度ヒーター（真空熱処理炉、熱交換器具）
2. タンタルコンデンサー（携帯電話、ビデオ、デジカメ、パソコン）
3. 光学ガラス添加剤（携帯電話、ビデオ、デジカメ、パソコン）
4. 超硬工具の成分（超硬バイト、ドリル）
5. スパッタターゲット（磁気ディスク）

存在

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．

化学的特性

Tantalum is a refractory metal in Group V-B of the periodic table. The pure metal is ductile, steel-blue to gray solid or black, odorless powder.

物理的性質

Tantalum has properties similar to niobium and vanadium above it in group 5. It is a veryhard and heavy metal with a bluish color when in its rough state, but if polished, it has a silveryshine. It is ductile, meaning it can be drawn into fine wires, and also malleable, meaningit can be hammered and worked into shapes. Thin strips and wires of tantalum will ignite inair if exposed to a flame.
Tantalum’s melting point is 2,996°C, which is almost as high as tungsten and rhenium. Itboiling point is 5,425°C, and its density is 19.3 g/cm³.

同位体

There are 49 isotopes of tantalum. Only the isotope Ta-181 is stable andaccounts for 99.988% of the total mass of the element on Earth. Just 0.012% of the element’s mass is contributed by Ta-180, which has a half-life of 1.2×10⁺¹⁵ years and isthus considered naturally stable. The remaining 47 isotopes are all artificially producedin nuclear reactions or particle accelerators and have half-lives ranging from a few microsecondsto few days to about two years.

名前の由来

Tantalum was named after Tantalus, who was the father of Niobe, the queen of Thebes, a city in Greek mythology. (Note: The element tantalum was originally confused with the element nobelium.)

天然物の起源

Tantalum is the 51st most abundant element found on Earth. Although it is found in afree state, it is usually mixed with other minerals and is obtained by heating tantalum potassiumfluoride or by the electrolysis of melted salts of tantalum. Tantalum is mainly obtainedfrom the following ores and minerals: columbite [(Fe, Mn, Mg)(Nb, Ta)₂O₆]; tantalite [(Fe,Mn)(Ta, Nb)₂O₆]; and euxenite [(Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)₂O₆]. Tantalum’s oresare mined in South America, Thailand, Malaysia, Africa, Spain, and Canada. The UnitedStates has a few small native deposits but imports most of the tantalum it uses.
Since tantalum and niobium are so similar chemically, a solvent process must be employedto separate them from the common ores. They are dissolved in a solvent, resulting in 98% pure niobium oxide being extracted during this part of the process. This is followed by 99.5%pure tantalum oxide being extracted in a second solvent process.

特性

Tantalum is almost as chemically inert at room temperatures (it has the ability to resistchemical attacks, including hydrofluoric acid) as are platinum and gold. It is often substitutedfor the more expensive metal platinum, and its inertness makes it suitable for constructingdental and surgical instruments and artificial joints in the human body.

使用

In pen points; analytical weights; apparatus and instruments for chemical, surgical, and dental use instead of platinum, in tantalum capacitors (a type of electrolytic condenser, trademarked "Tantalytic").

調製方法

It was identi?ed that tantalum minerals exists in over 70 differentchemicalcompositions.Thoseofgreatesteconomic importance are tantalite, microlite, and wodginite; however, it is common practice to name any tantalum-containing mineral concentrate as “tantalite”. Tantalum resources are widespread, with the most important known resources being found in Brazil and Australia. In mid-2008, the main mining operations were in Australia, Brazil,Canada,Mozambique,andEthiopiaandinmid-2009, in Brazil, Ethiopia, and China, with additional quantities originating in central Africa, Russia, and Southeast Asia. There is continued interest in exploration of this element in other countries, primarily in Egypt, Canada, Mozambique, and Saudi Arabia.
The major world mine producers of tantalum in 2010 were Brazil (180 tons), Mozambique (110 tons), Rwanda (100 tons), and Australia (80 tons). Other countries produced around 170 tons, so the total world production of tantalum was approximately 670 tons. The major producers of tantalum mineral concentrates are Australia, Brazil, and Canada.

定義

A silvery transition element. It is strong, highly resistant to corrosion, and is easily worked. Tantalum is used in turbine blades and cutting tools and in surgical and dental work. Symbol: Ta; m.p. 2996°C; b.p. 5425 ± 100°C; r.d. 16.654 (20°C); p.n. 73; r.a.m. 180.9479.

一般的な説明

Tantalum dust is a black odorless powder. Mp: 2996°C; bp: approx. 5250°C. Density: 16.65 g cm-3. Insoluble in water. Tantalum oxide dust is a white, microcrystalline powder Mp: 1800°C. Density: 7.6 g cm-3. Insoluble in water. The mixture is listed as a toxic inhalation hazard by OHSA.

危険性

The dust and powder of tantalum are explosive. Several tantalum compounds are toxic ifinhaled or ingested, but the metal itself is nonpoisonous.

健康ハザード

Tantalum has a low order of toxicity but has produced transient inflammatory lesions in the lungs of animals. Surgical implantation of tantalum metal products such as plates and screws has not shown any adverse tissue reaction, thus demonstrating its physiological inertness.

安全性プロファイル

An inhalation hazard. Some industrial skin injuries from tantalum have been reported. Systemic industrial poisoning, however, is apparently unknown. Questionable carcinogen with experimental tumorigenic data. The dry powder iptes spontaneously in air. Incompatible with bromine trifluoride, fluorine, lead chromate. See also specific tantalum compounds.

特性

酸化物は安定した酸化被膜を形 成し耐食性に優れる 

酸化物の誘電率がアルミニウム 酸化物の 2.7 倍と高い 

融点がタングステンの次に高い

発がん性

Although Oppenheimer et al., using embedded metal foil technique, have elicited two malignant ?brosarcomas in 50 embeddings of tantalum metal in 25Wistar rats aftera latent period of714days, these results remain a controversial issue. Miller et al. have studied tumorigenic transforming potential of tungsten, iron, nickel, and cobalt with tantalum as a comparison on an immortalized nontumorigenic human osteoblast-like cell line. No tumorigenic activity of Ta was reported, but data are not shown.
In the recent study, intramuscularly pellets (1mm 2mm cylinders) of weapons-grade WA were implantedtosimulateshrapnelwounds.Ratswereimplanted with 4 (low dose) or 20 pellets (high dose) of WA. Tantalum (20 pellets) and nickel (20 pellets) served as negative and positive controls, respectively. Rats implanted with tantalum (n=46) did not develop tumors.

輸送方法

UN3089 Metal powders, flammable, n.o.s., Hazard Class: 4.1; Labels: 4.1-Flammable solid.

不和合性

A flammable solid; the dry powder can ignite spontaneously in air. Incompatible with lead chromate. A strong reducing agent; incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, bromine trifluoride, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoacids, epoxides. Tantalum metal is attacked by hydrogen fluoride, fused alkalis, fuming sulfuric acid.

廃棄物の処理

Sanitary landfill if necessary; recover if possible because of economic value. Technology exists for tantalum recovery from spent catalysts, for example.