thorium

Th. Atomic number 90. Transition metal element in group ³ of the periodic table with electron configuration [Rn] ^6d27s2 . One of the actinide elements. A naturally occurring radioactive element. Atomic weight 232.0381(1). Almost all naturally occurring radioactive nuclides are ^232Th (alpha-particle emission, half-life 1.40× ^1010y ), but there are also traces of ^234Th , ^230Th (uranium series), ^228Th (thorium series), ^231Th , and ^227Th (actinium series). In addition, artificial radioactive nuclides with mass numbers 209-238 are known. It was discovered in thorite by the Swede JJ Berzelius in 1829. Thor is the god of thunder in Norse mythology, and Berzelius had mistakenly given this name to another mineral, but he renamed it along with the name of the element after the discovery of the new element. In his book "Shemit Kaishu" published in 1837, Udagawa Yoan transliterated this as "Toriumu."
Known minerals include thorite and borosilicate, but monazite is the most widely used mineral. Its abundance in the earth's crust is 3.5 ppm. Australia, India, the United States, and Norway account for 80% of the world's reserves. The metal is obtained by reducing _ThO2 with calcium in argon or vacuum, or by molten salt electrolysis or thermal decomposition of the halide. It has a silvery-white cubic crystal system. Its density is 11.780 g cm ^-3 (20 °C). Its melting point is 1750 °C, its boiling point is 4790 °C (α form). It transforms to a body-centered cubic crystal at 1386 °C. Its density is 11.724 g cm- ³ (20 °C) (β form). It is not affected by water or alkali, but it dissolves easily in hydrochloric acid, dissolves slowly in perchloric acid and sulfuric acid, and becomes passive in nitric acid. Thorium forms a stable colorless compound with oxidation states of 2 to 4, usually oxidation state 4. Standard electrode potential Th ⁴⁺ /Th-1.83 V. First ionization energy 586.5 kJ mol ^-1 (6.08 eV), Th ^Ⅳ (hexacoordinate) ionic radius 0.108 nm. Reacts with halogens and nitrogen at high temperatures. Chlorides, bromides, iodides, chlorates, bromates, and sulfates are soluble in water, while hydroxides, fluorides, iodates, phosphates, and oxalates are insoluble in water. The salts are not as easily hydrolyzed as those of titanium and zirconium, but are easily hydrolyzed when the aqueous solution is heated. It easily forms complexes with many types of acid ions, such as [Th(NO ₃ ) ₆ ] ^2- and [Th(SO ₄ ) ₄ ] ^2- .
It is used in welding electrodes, high intensity discharge (HID) lamp electrodes, ship bottom paint, etc. It is also found in health clothing and bedding, home hot spring baths (bath additives), medical pillows, etc. Thorium is a "nuclear fuel material/nuclear source material" as defined by the Atomic Energy Basic Law, and according to the "Enforcement Order of the Law Concerning the Regulation of Nuclear Source Material, Nuclear Fuel Material, and Atomic Reactors," permission is required for use if it exceeds 900 g. [CAS 7440-29-1]

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

Th．原子番号90の元素．電子配置[Rn]6d²7s²の周期表3族遷移金属元素．アクチノイド元素の一つ．天然放射性元素である．原子量232.0381(1)．天然放射性核種として量的にはほとんどすべて ²³²Th(α線放出，半減期1.40×10¹⁰ y)であるが，微量の ²³⁴Th，²³⁰Th(ウラン系列)，²²⁸Th(トリウム系列)，²³¹Th，²²⁷Th(アクチニウム系列)が含まれる．そのほか，質量数209～238の人工放射性核種が知られている．1829年，スウェーデンのJ.J. Berzelius(ベルセリウス)によってトール石のなかから発見された．トールは北欧神話の雷神Thorで，Berzeliusはほかの鉱石に誤ってこの名称をつけていたが，新元素の発見により元素名とともに命名しなおした．宇田川榕菴は天保8年(1837年) に出版した「舎密開宗」で，これを音訳して多母(トリュウム)としている．
天然にはトール石，ホウトリウム鉱などの鉱物が知られているが，資源的にはモナズ石が利用される．地殻中の存在度3.5 ppm．埋蔵量はオーストラリア，インド，アメリカ，ノルウェイで世界の80％ を占める．ThO₂をアルゴン中または真空中でカルシウム還元するか，ハロゲン化物の融解塩電解または熱分解などにより金属を得る．銀白色の立方晶系．密度11.780 g cm^－3(20 ℃)．融点1750 ℃，沸点4790 ℃(α形)．1386 ℃ で体心立方晶．密度11.724 g cm^－3(20 ℃)(β形)に転移する．水，アルカリには侵されないが，塩酸に易溶，過塩素酸，硫酸に徐々に溶け，硝酸では不動態となる．トリウムの酸化数2～4，通常の酸化数4で，無色の安定な化合物をつくる．標準電極電位 Th^4＋/Th－1.83 V．第一イオン化エネルギー586.5 kJ mol^－1(6.08 eV)，Th^Ⅳ(六配位)のイオン半径0.108 nm．ハロゲン，窒素とは高温で反応する．塩化物，臭化物，ヨウ化物，塩素酸塩，臭素酸塩，硫酸塩などは水に可溶，水酸化物，フッ化物，ヨウ素酸塩，リン酸塩，シュウ酸塩などは水に不溶．塩類はチタンやジルコニウムの塩ほど加水分解しやすくはないが，水溶液を温めると容易に加水分解する．多種類の酸イオンと錯化合物をつくりやすく，たとえば，[Th(NO₃)₆]^2－，[Th(SO₄)₄]^2－ などがある．
溶接用電極棒，高輝度放電(HID)ランプ電極, 船底塗料などに利用されている．健康衣料・寝具，家庭用温泉器(入浴剤)，医療用枕などに含まれていることがある．トリウムは原子力基本法のいう「核燃料物質・核原料物質」で「核原料物質，核燃料物質及び原子炉の規制に関する法律施行令」により，900 g を超える場合は使用許可を要する．[CAS 7440-29-1]

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