(144Pr)プラセオジム 化学特性,用途語,生産方法
解説
プラセオジム，元素記号 Pr ，原子番号 59，原子量 140.90765。周期表3族，希土類元素でランタノイド元素の1つ。セル石，モナズ石，ガドリン石などの中に，他の希土類元素に随伴して産出する。地殻における存在量は 8.2ppm，海水中の濃度 0.003μg/l 。 1885年 C.ウェルスバハにより，当時単一元素と考えられていたジジムがプラセオジムとネオジムに分離され，それぞれ元素として同定された。単体は銀白色の金属で，融点 935℃，比重 6.782，展性，延性がある。空気中 290℃で発火。酸と反応して溶ける。酸化数3。三酸化プラセオジムは黄緑色。塩類は結晶，水溶液ともに美しい緑色を呈する。常磁性。ミッシュメタル，鉄鋼，非鉄金属材料用添加剤として用いられる。
性質
モナズ石，バストネス石に含まれる．地殻中の存在度3.9 ppm．中国では全希土類の埋蔵量(30％)・生産量(98％)でともに一位(2007年)．溶媒抽出法で希土類相互分離後，塩化物・フッ化物のアルカリ金属塩化物・フッ化物との混合溶融塩電解により得られる金属は銀白色．六方最密構造のα態と，792 ℃ 以上の体心立方構造のβ態がある．融点931 ℃，沸点3512 ℃．密度はα態：6.773 g cm－3，β態：6.64 g cm－3．硬さ6.5．酸と熱水に易溶で，H2 を発生する．第一イオン化エネルギー5.464 eV．酸化数3，4．三価の化合物はほかの希土類と同じく，炭酸塩，シュウ酸塩，フッ化物などが水に不溶．塩類は結晶，水溶液ともに緑色．Pr3＋，Pr4＋ の電子配置は4f 2，4f 1で常磁性．PrⅣ化合物は非常に少なく，PrⅢ2O3を空気中で加熱すると得られる黒色の酸化物はPrⅣ O2と表されるが不定比化合物に近い．
化学的特性
grey powder
物理的性質
Praseodymium is a silvery-white, soft metal that is easily formed into various shapes. Whenthe pure metal is exposed to the air, a green oxide coating forms on its surface. To preventoxidation, praseodymium is usually kept in oil in a covered container.
Its melting point is 931°C, its boiling point is 3,520°C, and its density is 6.77g/cm
3.
同位体
There are 45 isotopes of praseodymium. All are artificially produced and radioactivewith half-lives ranging from several hundred nanoseconds to 23.6 days. Only oneis stable (Pa-141), and it makes up 100% of the praseodymium found in the Earth’scrust.
名前の由来
The name is derived from two Greek words, prasios and didymos,
which together mean “green twins.”
天然物の起源
Praseodymium is the 41st most abundant element on Earth and is found in the ores of monazite,cerite, bastnasite, and allanite along with other rare-earths. Praseodymium is also the stableisotope resulting from the process of fission of some other heavy elements, such as uranium.
Praseodymium is mainly found in monazite sands and bastnasite ores. The monazite sandscontain all of the rare-earths and are found in river sand in India and Brazil as well as inFlorida beach sand. A large deposit of bastnasite exists in California.
Praseodymium is separated from its ore and other rare-earths by a process called ionexchange, which exchanges one type of ion for another.
来歴
In 1879, Lecoq de Boisbaudran isolated
a new earth, samaria, from didymia obtained from the
mineral samarskite. Six years later, in 1885, von Welsbach separated
didymia into two others, praseodymia and neodymia,
which gave salts of different colors. As with other rare earths,
compounds of these elements in solution have distinctive
sharp spectral absorption bands or lines, some of which are
only a few Angstroms wide. Praseodymium occurs along with
other rare-earth elements in a variety of minerals. Monazite
and bastnasite are the two principal commercial sources of
the rare-earth metals. Ion-exchange and solvent extraction
techniques have led to much easier isolation of the rare earths
and the cost has dropped greatly. Thirty-seven isotopes and
isomers are now recognized. Praseodymium can be prepared
by several methods, such as by calcium reduction of the anhydrous
chloride or fluoride. Misch metal, used in making
cigarette lighters, contains about 5% praseodymium metal.
Praseodymium is soft, silvery, malleable, and ductile. It was
prepared in relatively pure form in 1931. It is somewhat more
resistant to corrosion in air than europium, lanthanum, cerium,
or neodymium, but it does develop a green oxide coating
that splits off when exposed to air. As with other rare-earth
metals it should be kept under a light mineral oil or sealed
in plastic. The rare-earth oxides, including Pr2O3, are among
the most refractory substances known. Along with other rare
earths, it is widely used as a core material for carbon arcs used
by the motion picture industry for studio lighting and projection.
Salts of praseodymium are used to color glasses and
enamels; when mixed with certain other materials, praseodymium
produces an intense and unusually clean yellow color in glass. Didymium glass, of which praseodymium is a component,
is a colorant for welder’s goggles. The metal (99.9% pure)
is priced at about $4/g.
特性
As a metal, Pr is hygroscopic (adsorbs water) and tarnishes in the atmosphere. It will reactwith water to liberate hydrogen. It is soluble in acids and forms greenish salts, along with someother rare-earths. It is used to fabricate the electrodes for high-intensity lights.
使用
Praseodymium salts, ingredient of mischmetal,
core material for carbon arcs, colorant in glazes and
glasses, catalyst, phosphors, lasers.
製造方法
Praesodymium may be recovered from its minerals monazite and bastanasite. The didymia extract of rare earth minerals is a mixture of praesodymia and neodymia, primarily oxides of praesodymium and neodymium. Several methods are known for isolation of rare earths. These are applicable to all rare earths including praesodymium. They include solvent extractions,ionexchange, and fractional crystallization. While the first two methods form easy and rapid separation of rare earth metals, fractional crystallization is more tedious. Extractions and separations of rare earths have been discussed in detail earlier (see Neodymium and Cerium).
Praesodymium metal can be obtained from its anhydrous halides by reduction with calcium. The metal also may be prepared by electrolysis of fused praesodymium chloride at elevated temperatures (about 1,000°C).Alternatively, an eutectic mixture of praesodymium chloride, potassium chloride, and sodium chloride may be electrolyzed. In such electrolysis graphite is the anode and tungsten the cathode.
定義
A soft ductile malleable silvery element of
the lanthanoid series of metals. It occurs in
association with other lanthanoids.
Praseodymium is used in several alloys, as
a catalyst, and in enamel and yellow glass
for eye protection.
Symbol: Pr; m.p. 931°C; b.p. 3512°C;
r.d. 6.773 (20°C); p.n. 59; r.a.m. 140.91.
危険性
If praseodymium gets wet or is submerged in water, the hydrogen released may explode. Itmust be kept dry and protected from the atmosphere.
(144Pr)プラセオジム 上流と下流の製品情報
原材料
準備製品