ユウロピウム

解説

Eu．原子番号63の元素．電子配置[Xe]4f 76s2の周期表3族ランタノイド元素．希土類元素の一つで，ランタノイドの中間に位置するので，イットリウム族，セリウム族の両者にに含まれることがある．62Sm～66Dyを中希土類ともいう．原子量151.964(1)．質量数151(47.81(6)％)，153(52.19(6)％)の2種の安定同位体と，質量数130～167の放射性同位体が知られている．1896年，E-A. DemarçayがSmから分離し(スペクトル中の発見は，1889年，W. Crookes)，ヨーロッパ大陸にちなんでeuropiumと命名した．地殻中の存在度1.1 ppm．存在度の低い希土類元素の一つ．微量に含まれるモナズ石，バストネス石などを原料に，溶媒抽出法で希土類相互分離後，溶融塩電解により金属が得られる．銀白色，体心立方格子構造．融点822 ℃，沸点1597 ℃．密度5.243 g cm－3(25 ℃)．第一イオン化エネルギー5.670 eV．標準電極電位C/Eu－1.99 V，Eu3＋/Eu2＋－0.35 V．熱水，酸に溶けて水素を発生する．酸化数2，3．イオン半径 Eu2＋0.131 nm，Eu3＋0.109 nm．Eu3＋ は淡紅色，Eu2＋ は無色．150 ℃ 以上では空気中で発火してEu2O3となる．電子配置が4f殻半分充満(4f 7)の EuⅡは希土類元素の酸化状態(Ⅱ)中でもっとも安定である．Eu2＋ のイオン半径は Sr2＋(0.132 nm)と非常に近いので，EuⅡ化合物はSr化合物と似た性質を示す．硫酸ユウロピウム(Ⅱ)は，Srの硫酸塩と同様に水に難溶．Eu2＋ による Sr2＋ の同形置換もよく見られる．EuⅢ化合物はほかの希土類元素と同様に，炭酸塩，シュウ酸塩，フッ化物が水に不溶．用途は，Eu3＋ はブラウン管用赤色蛍光体の賦活材．YVO4Eu3＋，Y2O2S：Eu3＋，Y2O3：Eu3＋ など．Eu2＋ は青色蛍光体の賦活材．YSr5Cl(PO4)3：Eu2＋ など．中性子捕獲断面積が大きいところから原子炉制御棒にも利用される．[CAS 7440-53-1]
森北出版「化学辞典（第2版）

化学的特性

grey ingots

物理的性質

Europium is one of the most rare of the rare-earths. Its abundance on Earth is only 1.1ppm. It is a soft, shiny, steel-gray metal that is quite ductile and malleable, which means it canbe worked and formed into many shapes. It looks like and feels like the element lead (Pb), butis somewhat heavier. It is the most chemically active of all the rare-earths.
Europium’s melting point is 822°C, its boiling point is 1,529°C, and its density is 5.243g/cm³.

同位体

There are a total of 45 isotopes of europium. Two are considered stable andaccount for 100% of the europium found on Earth: Eu-151 (47.81%) and Eu-153(52.19%). All the other 53 isotopes are radioactive and artificially produced, primarily through electron capture.

名前の由来

Named for the continent of Europe.

天然物の起源

Europium is the 13th most abundant of all the rare-earths and the 55th most abundantelement on Earth. More europium exists on Earth than all the gold and silver deposits. Likemany other rare-earths, europium is found in deposits of monazite, bastnasite, cerite, andallanite ores located in the river sands of India and Brazil and in the beach sand of Florida.It has proven difficult to separate europium from other rare-earths. Today, the ion-exchange process is used to extract europium from the other rare-earths found in monazite sand(ore).

特性

Pure europium will slowly oxidize in air at room temperature and will produce hydrogenwhen placed in water. It will ignite spontaneously if the air temperature is over 150°C. Insome ways europium resembles the elements calcium, strontium, and barium found in group2 of the periodic table.

来歴

In 1890 Boisbaudran obtained basic fractions from samarium-gadolinium concentrates that had spark spectral lines not accounted for by samarium or gadolinium. These lines subsequently have been shown to belong to europium. The discovery of Europium is generally credited to Demarcay, who separated the rare earth in reasonably pure form in 1901. The pure metal was not isolated until recent years. Europium is now prepared by mixing Eu₂O₃ with a 10% excess of lanthanum metal and heating the mixture in a tantalum crucible under high vacuum. The element is collected as a silvery-white metallic deposit on the walls of the crucible. As with other rare-earth metals, except for lanthanum, europium ignites in air at about 150 to 180°C. Europium is about as hard as lead and is quite ductile. It is the most reactive of the rare-earth metals, quickly oxidizing in air. It resembles calcium in its reaction with water. Bastnasite and monazite are the principal ores containing europium. Europium has been identified spectroscopically in the sun and certain stars. Europium isotopes are good neutron absorbers and are being studied for use in nuclear control applications. Europium oxide is now widely used as a phosphor activator and europium-activated yttrium vanadate is in commercial use as the red phosphor in color TV tubes. Europiumdoped plastic has been used as a laser material. With the development of ion-exchange techniques and special processes, the cost of the metal has been greatly reduced in recent years. Natural europium contains two stable isotopes. Thirty-five other radioactive isotopes and isomers are known. Europium is one of the rarest and most costly of the rare-earth metals. It is priced at about $60/g (99.9% pure).

使用

There are only a few commercial uses for europium. Europium oxide, (Eu₂O₃), a compoundof europium, is added to infra-sensitive phosphors to enhance the red colors on TVand computer-monitor picture tubes. It is also added to fluorescent light tubes to increasetheir efficiency, as well as to some materials to make lasers. Since it is a good neutron absorber,it is part of nuclear reactor control rods. Europium is an additive to the glue used on postagestamps, thus making it possible for the electronic sorting machines in U.S. postal offices to“read” the stamps.

定義

A silvery element of the lanthanoid series of metals. It occurs in association with other lanthanoids. Its main use is in a mixture of europium and yttrium oxides widely employed as the red phosphor in television screens. The metal is used in some superconducting alloys. Symbol: Eu; m.p. 822°C; b.p. 1597°C; r.d. 5.23 (25°C); p.n. 63; r.a.m. 151.965.

危険性

Europium is very reactive and, in powder form, may burst into flames spontaneously atroom temperature. Most of the salts of europium are toxic when inhaled or ingested.