rhodium

Rh. Element with atomic number 45. Group 9 precious metal or platinum group element of the periodic table with ^electron configuration [Kr] ^4d85s1 . Atomic weight 102.90550(2). Mononuclear element with only one stable nuclide, an isotope with mass number 103. Radioactive isotopes with mass numbers between 89 and 122 are known. It was discovered in 1804 by the British WH Wollaston in a crude platinum sample, and was named after the Greek word ροδον (rodon) for "rose color" due to the red color of the chloride _RhCl3 . Udagawa Yoan described rhodium as a new metal in volume 15 of "Semitsu Kaisou" published in 1837.
Among the platinum group metals, which are rare in the earth's crust, Rh is found in extremely low abundance, below ppb. South Africa holds approximately 90% of the world's known reserves, followed by Russia and Canada. The element is a silvery-white metal with a cubic close-packed structure. It is separated from platinum group metal concentrates by solvent extraction, extracted as (NH ₄ ) ₃ RhCl ₆ , and the metal is obtained by hydrogen reduction. Melting point 1966 °C, boiling point 3695 °C, density 12.41 g cm ^-3 , first ionization energy 7.46 eV, oxidation number 1-4, usually 3. It is extremely stable chemically, and although there are few binary compounds, there are many complexes. It is oxidized to Rh ₂ O ₃ by reacting with oxygen at temperatures above 600 °C, but decomposes back to Rh at temperatures above 1200 °C. It also reacts with chlorine at 300°C to _form Rh ^ⅢCl3 , but undergoes a reverse reaction at 318°C to form Rh. The lumps are insoluble in aqua regia. They are soluble in hot sulfuric acid.
It is essential as a component for reducing _NOx in three-way catalysts used to purify automobile exhaust gas, and accounts for 80% of demand in Japan. It is also used as a raw material for Pt-Rh alloys (10%), which are used as crucibles for the manufacture of high-grade glass for liquid crystal displays, and as catalysts for the chemical industry. In 2005, of Japan's total imports of 9.5 t, 6.5 t came from South Africa, 0.8 t from the United States, and 0.7 t from Russia. [CAS 7440-16-6][See other terms] Rhodium catalyst

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

Rh．原子番号45の元素．電子配置[Kr]4d⁸5s¹の周期表9族貴金属または白金族元素．原子量102.90550(2)．安定核種が質量数103の同位体のみの単核種元素．質量数89～122の放射性同位体が知られている．1804年，イギリスのW.H. Wollastonが粗白金試料中に発見，塩化物RhCl₃の赤色から，ギリシア語の“バラ色”ροδον(rodon)をとって命名．宇田川榕菴は天保8年(1837年)出版の「舎密開宗」巻十五で，新金属として羅冑母(ロヂウム)と記載している．
地殻中の存在度の低い白金族中でもきわめて存在度が低く ppb 以下とされる．世界の知られている埋蔵量の約90％ を南アフリカが占め，ついでロシア，カナダの順である．単体は立方最密構造の銀白色の金属．白金族精鉱から溶媒抽出法で相互分離し，(NH₄)₃RhCl₆としてとりだし，水素還元して金属を得る．融点1966 ℃，沸点3695 ℃．密度12.41 g cm^－3．第一イオン化エネルギー7.46 eV．酸化数1～4，通常3．化学的にきわめて安定で，二元化合物の数は少ないが錯体は多数存在する．酸化して600 ℃ 以上で酸素と反応してRh₂O₃となるが，1200 ℃ 以上で分解してRhに戻る．塩素とも300 ℃ で反応してRh^Ⅲ Cl₃となるが，318 ℃ で逆反応を起こしてRhとなる．塊は王水にも不溶．熱硫酸に可溶．
自動車排気ガス浄化用3元触媒のNO_x還元用成分として不可欠で，わが国の需要の80％ を占める．ついで液晶ディスプレイ用高級ガラス製造用るつぼ材のPt-Rh合金原料として10％，ほか化学工業用触媒に用いられる．2005年には，わが国は全輸入量9.5 t 中，6.5 t を南アフリカ，0.8 t をアメリカ，0.7 t をロシアから輸入した．[CAS 7440-16-6][別用語参照]ロジウム触媒

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