Terbium

Terbium is a chemical element; it has symbolTb and atomic number 65. It is a silvery-white, rare earthmetal that is malleable and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime and euxenite.

Swedish chemist Carl Gustaf Mosander discovered terbium as a chemical element in 1843. He detected it as an impurity in yttrium oxide (Y₂O₃). Yttrium and terbium, as well as erbium and ytterbium, are named after the village of Ytterby in Sweden. Terbium was not isolated in pure form until the advent of ion exchange techniques.

Terbium is used to dopecalcium fluoride, calcium tungstate and strontiummolybdate in solid-state devices, and as a crystal stabilizer of fuel cells that operate at elevated temperatures. As a component of Terfenol-D (an alloy that expands and contracts when exposed to magnetic fields more than any other alloy), terbium is of use in actuators, in naval sonar systems and in sensors. Terbium is considered non-hazardous, though its biological role and toxicity have not been researched in depth.

Most of the world's terbium supply is used in green phosphors. Terbium oxide is used in fluorescent lamps and television and monitor cathode-ray tubes (CRTs). Terbium green phosphors are combined with divalent europium blue phosphors and trivalent europium red phosphors to provide trichromatic lighting technology, a high-efficiency white light used in indoor lighting.

SwedishchemistCarl Gustaf Mosander discovered terbium in 1843.^[43][44] He detected it as an impurity in yttrium oxide, Y₂O₃, then known as yttria. Yttrium, erbium, and terbium are all named after the village of Ytterby in Sweden.^[45][46] Terbium was not isolated in pure form until the advent of ion exchange techniques.^[47]

Mosander first separated yttria into three fractions, all named for the ore: yttria, erbia, and terbia. "Terbia" was originally the fraction that contained the pink color, due to the element now known as erbium. "Erbia", the oxide containing what is now known as terbium, originally was the fraction that was yellow or dark orange in solution.^[43][45] The insoluble oxide of this element was noted to be tinged brown,^[48][49][39] and soluble oxides after combustion were noted to be colorless.^[50] Until the advent of spectral analysis, arguments went back and forth as to whether erbia even existed. Spectral analysis by Marc Delafontaine allowed the separate elements and their oxides to be identified,^[47] but in his publications, the names of erbium and terbium were switched,^[51] following a brief period where terbium was renamed "mosandrum", after Mosander.^[52] The names have remained switched ever since.^[45]

テルビウム（酸化テルビウムとして）の製造の初期は困難でした。ガドリナイトとサマルスカイトからの金属酸化物を硝酸に溶解し、溶液をさらにシュウ酸と硫酸カリウムで分離しました。エルビアとテルビアの分離は非常に困難で、1881年には両者を分離する満足のいく方法はないと指摘されました。^{[ 50 ]} 1914年までに、テルビウムを母鉱物から分離するためにさまざまな溶媒が使用されましたが、テルビウムを隣接する元素であるガドリニウムとジスプロシウムから分離するプロセスは「面倒」だが可能だと説明されました。^{[ 53 ]}現代のテルビウム抽出法は、1937年にヴェルナー・フィッシャーらが開発した液液抽出法に基づいています。 ^{[ 54 ]}

テルビウムは、モナザイト（テルビウム含有量最大0.03%の(Ce,La,Th,Nd,Y)PO ₄ ）、ゼノタイム（YPO ₄） 、ユークセナイト（テルビウム含有量1%以上の( Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti) ₂ O ₆ ）など、多くの鉱物中に他の希土類元素とともに存在します。テルビウムの地殻存在量は1.2 mg/kgと推定されています。 ^{[ 31 ]}テルビウムが主成分の鉱物はまだ発見されていません。^{[ 55 ]} 

テルビウム（Tb IIとして）は、太陽系外のホットジュピター型惑星KELT-9bの大気中で検出されている。^{[ 56 ]}

現在、テルビウムの最も豊富な商業的供給源は中国南部のイオン吸着粘土です。^{[ 40 ]}重量比で約3分の2の酸化イットリウムを含む濃縮物には、約1%のテルビウムが含まれています。バストネサイトとモナザイトには少量のテルビウムが含まれており、これらを溶媒抽出によって処理して貴重な重ランタニドをサマリウム-ユーロピウム-ガドリニウム濃縮物として回収する際に、テルビウムも回収されます。イオン吸着粘土に比べて処理されるバストネサイトの量が多いため、世界のテルビウム供給量のかなりの割合がバストネサイトから得られています。^{[ 10 ]}

In 2018, a rich terbium supply was discovered off the coast of Japan's Minamitori Island, with the stated supply being "enough to meet the global demand for 420 years".^[57]

Crushed terbium-containing minerals are treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with caustic soda to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. The solution is treated with ammonium oxalate to convert rare earths into their insoluble oxalates. The oxalates are decomposed to oxides by heating. The oxides are dissolved in nitric acid that excludes one of the main components, cerium, whose oxide is insoluble in HNO₃. Terbium is separated as a double salt with ammonium nitrate by crystallization.^[31]

The most efficient separation routine for terbium salt from the rare-earth salt solution is ion exchange. In this process, rare-earth ions are sorbed onto suitable ion-exchange resin by exchange with hydrogen, ammonium or cupric ions present in the resin. The rare earth ions are then selectively washed out by suitable complexing agents. As with other rare earths, terbium metal is produced by reducing the anhydrous chloride or fluoride with calcium metal. Calcium and tantalum impurities can be removed by vacuum remelting, distillation, amalgam formation or zone melting.^[31][47]

In 2020, the annual demand for terbium was estimated at 340 tonnes (750,000 lb).^[40] Terbium is not distinguished from other rare earths in the United States Geological Survey's Mineral Commodity Summaries, which in 2024 estimated the global reserves of rare earth minerals at 110,000,000 tonnes (2.4×10¹¹ lb).^[58]

テルビウムは、固体素子に使用される材料であるフッ化カルシウム、タングステン酸カルシウム、モリブデン酸ストロンチウムのドーパントとして、また、二酸化ジルコニウム（ZrO ₂ ）とともに高温で動作する燃料電池の結晶安定剤として使用されます。^{[ 10 ] [ 59 ]}

テルビウムは合金や電子機器の製造にも使用されています。テルフェノール-Dの成分として、テルビウムはアクチュエータ、海軍ソナーシステム、センサー、その他の磁気機械装置に使用されています。テルフェノール-D は、磁場の存在下で膨張または収縮するテルビウム合金です。^{[ 60 ]}あらゆる合金の中で最も高い磁歪を持っています。^{[ 61 ]}長距離光ファイバー通信でベルデ定数を増加させるために使用されます。^{[ 62 ] [ 63 ]}テルビウムをドープしたガーネットは、反射光が光ファイバーに沿って戻るのを防ぐ光アイソレーターにも使用されています。^{[ 64 ]}

テルビウム酸化物は、蛍光灯、カラーテレビ管^{[ 10 ]}、フラットスクリーンモニター^{[ 65 ]}の緑色蛍光体に使用されています。テルビウムは、ランタンとルテチウムを除く他のすべてのランタニドと同様に、3+の酸化状態で発光します^{[ 66 ]} 。鮮やかな蛍光により、テルビウムは生化学のプローブとして使用でき、その挙動はカルシウムにいくらか似ています。テルビウム「グリーン」蛍光体（鮮やかなレモンイエローに蛍光します）は、二価のユーロピウム青色蛍光体と三価のユーロピウム赤色蛍光体と組み合わせて三色照明を提供します。これは、世界のテルビウム供給の最大の消費源です。三色照明は、白熱灯よりも一定量の電気エネルギーに対してはるかに高い光出力を提供します^{[ 10 ]}。

2023年には、テルビウム化合物を用いて単一の鉄原子を含む格子を作成し、それをシンクロトロンX線ビームで調べた。これは、単一原子を亜原子レベルで特性評価することに初めて成功した試みであった。^{[ 67 ]}

Terbium, along with many of the other rare earth elements, is poorly studied in terms of its toxicology and environmental impacts. Few health-based guidance values for safe exposure to terbium are available.^[68] No values are established in the United States by the Occupational Safety and Health Administration or American Conference of Governmental Industrial Hygienists at which terbium exposure becomes hazardous, and it is not considered a hazardous substance under the Globally Harmonized System of Classification and Labelling of Chemicals.^[69]

Reviews of the toxicity of the rare earth elements place terbium and its compounds as "of low to moderately toxicity", remarking on the lack of detailed studies on their hazards^[70] and the lack of market demand forestalling evidence of toxicity.^[71]

Some studies demonstrate environmental accumulation of terbium as hazardous to fish and plants.^[72][73] High exposures of terbium may enhance the toxicity of other substances causing endocytosis in plant cells.^[74]

• Terbium compounds
• List of elements facing shortage

• WebElements.com  – テルビウム
• それはエレメンタルです – テルビウム