lanthanum

La. Atomic number 57. Electron configuration [Xe] ^5d16s2 . A member of the lanthanide group ³ of the periodic table. A member of the cerium group of rare earth elements. Atomic weight 138.90547(7). Two stable isotopes, with mass numbers 138 (0.090(1)%) and 139 (99.901(1)%), and radioactive isotopes with mass numbers 117-155, are known. It was isolated in cerium salts by CG Mosander in 1839. Mosander's teacher, JJ Berzelius, suggested the name lanthanum, derived from the Greek word λανθανω (lanthan) for "hidden," as it was found hidden in cerium salts. The Japanese name for the element is a transliteration of the German name for the element Lanthan.
Abundance in the earth's crust: 16 ppm. Ranked first in China's total rare earth reserves (30%) and production (98%) (2007). Found in rare earth ores such as monazite and bastnaesite. Crushed ore is treated with alkali, converted to chloride with concentrated hydrochloric acid, separated by solvent extraction, and the metal is produced by molten salt electrolysis. A soft, tin-white metal. Melting point: 921 °C, boiling point: 3457 °C. Density: 6.145 g cm ^-3 (25 °C). There are three modifications: hexagonal α, cubic close-packed β at temperatures above 310 °C, and body-centered cubic γ at temperatures above 863 °C. Soluble in acid. Strongly alkaline, it also reacts with hot water. Rapidly oxidizes in air. Oxidation state: 3. All of the compounds are La ^III compounds; the oxide, hydroxide, fluoride, phosphate, carbonate, and oxalate are sparingly soluble in water, while the chloride, nitrate, and acetate are soluble in water. In the lanthanides, basicity decreases with increasing atomic number. Lanthanum hydroxide is the strongest base in the series and the strongest of the hydroxides of trivalent metals.
The alloy LaNi ₅ with Ni absorbs large amounts of hydrogen, and is used as a hydrogen storage alloy in nickel-hydrogen batteries installed in hybrid and electric vehicles. The oxide La ₂ O ₃ is added to the support and promoter of three-way catalysts for purifying automobile exhaust gas to improve heat resistance, and to high-refractive-index, low-dispersion optical lens glass. It is also used in La-Co ferrite magnets and ceramic capacitors. The chloride is used in petroleum catalytic cracking catalysts. Of Japan's total import of lanthanum oxide of 1,800 tons, 97% was imported from China (2005). [CAS 7439-91-0]

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

La．原子番号57の元素．電子配置[Xe]5d¹6s²の周期表3族ランタノイド元素．希土類元素セリウム族の一つ．原子量138.90547(7)．質量数138(0.090(1)％)，139(99.901(1)％)の2種の安定同位体と，質量数117～155の放射性同位体が知られている．1839年，C.G. Mosanderがセリウム塩中から分離した．Mosanderの師J.J. Berzelius(ベルセリウス)がセリウム塩中に隠されていたところから，ギリシア語の“隠された”λανθανω(lanthan)をとってlanthanumを提案した．日本語の元素名はドイツ語の元素名Lanthanの音訳．
地殻中の存在度16 ppm．中国の全希土類埋蔵量(30％)・生産量(98％)でともに一位(2007年)．モナズ石，バストネス石など希土類元素の鉱石中に含まれている．粉砕鉱石をアルカリで処理し，濃塩酸で塩化物に転換，溶媒抽出法で分離して，溶融塩電解法で金属がつくられる．スズ白色の軟らかい金属．融点921 ℃，沸点3457 ℃．密度6.145 g cm^－3(25 ℃)．六方晶のα，310 ℃ 以上で立方最密のβ，863 ℃ 以上で体心立方のγの3変態がある．酸に可溶．塩基性がかなり強いので熱水とも反応する．空気中ではすみやかに酸化される．酸化数3．化合物はすべて La^Ⅲ化合物で，酸化物，水酸化物，フッ化物，リン酸塩，炭酸塩，シュウ酸塩は水に難溶，塩化物，硝酸塩，酢酸塩は水に可溶．ランタノイドでは原子番号の増大とともに塩基性が減少する．ランタンの水酸化物は，この系列でもっとも強い塩基で，また三価の金属の水酸化物中でももっとも強い．
Niとの合金LaNi₅は大量の水素を吸蔵するので，水素吸蔵合金としてハイブリッド・電気自動車搭載のニッケル-水素電池に利用されている．酸化物La₂O₃は，自動車排気ガス浄化3元触媒の担体・助触媒耐熱性向上用に，また高屈折率・低分散の光学レンズ用ガラスに添加される．La-Co系フェライト磁石，セラミックコンデンサーにも使用される．塩化物は石油接触分解触媒に使われる．わが国は酸化ランタン全輸入量1800 t のうち97％ を中国から輸入した(2005年)．[CAS 7439-91-0]

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