molybdenum

Mo. Atomic number 42. A transition metal element in group ⁶ of the periodic table with the electron configuration [Kr] ^4d55s1 . Atomic weight 95.94(2). Naturally occurring isotopes exist with mass numbers 92 (14.77(31)%), 94 (9.23(10)%), 95 (15.90(9)%), 96 (16.68(1)%), 97 (9.56(5)%), 98 (24.19(26)%), and 100 (9.67(20)%). ^100Mo is a radioactive nuclide that undergoes double beta decay with a half-life of 7.3× ¹⁰¹⁸ y to ^100Ru . Other radioactive nuclides with mass numbers between 83 and 115 are known. In 1778, CW Scheele discovered it as a substitute for lead in molybdenite, which was thought to be a lead ore at the time, and PJ. Hjelm isolated it in 1781. Chemically pure metallic molybdenum (99.98%) was not obtained until 1895 by H. Moissan through reduction with carbon in an electric furnace. Scheele named the element after the Greek word μολυβδο (molybdos), which means lead. Udagawa Yoan wrote it as molybternium in his book "Semitsu Kaisou" published in 1837.
Its abundance in the earth's crust is 1000 ppm. Its main mineral is molybdenite (MoS2 ₎ , but it also occurs as molybdate minerals such as pyrite (PbMoO4 ₎ and powellite (Ca(Mo,W)O4 ₎ . Of the world's confirmed reserves of 19 million tons, China accounts for 44%, the United States for 28%, and Chile for 13%, while the total production (187,000 tons in 2007) is 31% for the United States, 25% for China, and 22% for Chile, each accounting for approximately 80% of the world's total. Japan's main import sources are Chile, Mexico, Canada, and China. Approximately 90% of Japan's demand is consumed in the iron and steel sector. As an extremely important rare metal for industry, it is one of the minerals subject to the national stockpiling system. In smelting, _MoS2 is first roasted at 650 °C, below the sublimation temperature of _MoO3 , to convert it into industrial grade (85-90%) molybdenum trioxide _MoO3 . For steel alloys, it is put into the furnace as is, or in the form of ferromolybdenum alloyed with iron. Ferromolybdenum is obtained by reducing _MoS2 with carbon and iron in an electric furnace, or by thermite reduction with aluminum, iron, and ferrosilicon. For chemical uses, industrial grade molybdenum trioxide is sublimated at over 1200 °C to refine it into high-purity (99.95%) _MoO3 , which is then dissolved in ammonia water to produce ammonium molybdate ( _NH4 ) _2MoO4 . The metal is obtained by reducing high-purity _MoO3 or ( _NH4 ) _2MoO4 in an electric furnace or muffle furnace _with a hydrogen gas stream. The powder is a gray or silvery-white metal (body _- centered cubic lattice). It has a melting point of 2617 °C and a boiling point of 4612 °C, both of which are very high. Density is 10.22 g cm ^-3 (20 °C). Resistivity is 5.2 × 10 ^-8 Ω m. First ionization energy is 7.099 eV. Standard electrode potential Mo ³⁺ /Mo-0.2 V. It is superconducting below 0.915 K. It is known to have oxidation states of -2, 0 to 6, but is usually 1 to 6. It is chemically inert and highly acid-resistant, and does not react with hydrofluoric acid, hydrochloric acid, or dilute sulfuric acid. It reacts with concentrated nitric acid, but a passive state is formed. It is soluble in aqua regia, hot concentrated sulfuric acid, and a mixture of concentrated nitric acid and hydrofluoric acid. It is readily attacked by oxidizing melts such as molten KNO ₃ -NaOH or Na ₂ O _2. It is soluble in aqueous ammonia in the presence of air. It does not react with nitrogen, but reacts with phosphorus, arsenic, carbon, silicon, and boron in the red-hot state. It is stable against oxygen and sulfur at room temperature, but is oxidized to MoO ₃ and MoS ₂ in the red-hot state. It reacts with fluorine even at room temperature to form MoF _6. It reacts with chlorine, bromine, and iodine in the red-hot state to form MoCl ₅ , MoBr ₄ , and MoI ₂ .
Molybdenum is one of the biochemically active transition elements and is an essential trace element for humans. When added to steel, it increases the hardness and strength, so almost all special steels contain molybdenum. Structural alloy steels, high-tensile steels, heat-resistant steel plates, and alloy tool steels contain 0.15-1.5% Mo by weight, while stainless steels and high-speed steels contain 0.5-9.5% Mo by weight. Structural alloy steels are used for machine parts (bearings, gears, pressure vessels, bolts, etc.), high-tensile steels are used for aircraft parts that require high strength, engine parts, and automobiles, high-speed steels are used for tools and dies, heat-resistant steels are used for structural materials, steam and gas turbines, boilers, high-temperature pressure vessels and heat exchangers, and stainless steels are used in the chemical industry and in household appliances. It is also added to petroleum refining (hydrodesulfurization) and oxidation catalysts for petrochemicals. As an inorganic chemical, it is used in the high-temperature lubricant molybdenum sulfide _MoS2 , as well as in paints and pigments. Metallic molybdenum is used in lighting fixtures, electron tube cathodes, microwave oven magnetron parts, and in IT-related semiconductor elements for mobile phones. Approximately 90% of demand in Japan is for the steel industry. "Molybdenum and its compounds" are designated as Class 1 chemical substances under the PRTR Law, with an oral chronic toxicity of 3 and a water quality standard of 0.07 mg/L. [CAS 7439-98-7][See other terms] Molybdenum catalyst

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

Mo．原子番号42の元素．電子配置[Kr]4d⁵5s¹の周期表6族遷移金属元素．原子量95.94(2)．天然に質量数92(14.77(31)％)，94(9.23(10)％)，95(15.90(9)％)，96(16.68(1)％)，97(9.56(5)％)，98(24.19(26)％)，100(9.67(20)％)の同位体が存在する．¹⁰⁰Mo は半減期7.3×10¹⁸ y で二重β崩壊して ¹⁰⁰Ru になる放射性核種．このほか，質量数83～115の放射性核種が知られている．1778年にC.W. Scheele(シェーレ)が，当時，鉛の鉱石と思われていた輝水鉛鉱(molybdenite)中に鉛のかわりに発見し，1781年にP-J. Hjelmが分離した．化学的に純粋な金属モリブデン(99.98％)は1895年になってはじめて，H. Moissan(モアッサン)によって電気炉中の炭素による還元で得られた．元素名は鉛を意味するギリシア語μολυβδο(molybdos)からScheeleが命名した．宇田川榕菴は天保8年(1837年)出版の「舎密開宗」で，莫列貌達紐母(モレイフターニウム)と記載している．
地殻中の存在度1000 ppm．おもな鉱物は，輝水鉛鉱MoS₂であるが，黄鉛鉱PbMoO₄，パウエル鉱Ca(Mo,W)O₄などモリブデン酸塩鉱物としても産出する．世界の確認埋蔵量1900万t 中，中国44％，アメリカ28％，チリ13％，産出量(187千 t，2007年)はアメリカ31％，中国25％，チリ22％ でともに世界の約8割を占める．わが国のおもな輸入先はチリ，メキシコ，カナダ，中国．わが国の需要の約90％ が鉄鋼部門で消費される．産業上，きわめて重要なレアメタルとして，国家備蓄制度の対象鉱種の一つとなっている．製錬は，まずMoS₂をMoO₃の昇華温度以下の650 ℃ でばい焼して，工業用(85～90％)三酸化モリブデンMoO₃に転換する．鋼合金用にはこのまま，あるいは鉄との合金フェロモリブデンの形で炉中に投入する．フェロモリブデンは電気炉でMoS₂を炭素，鉄と還元するか，アルミニウム，鉄，フェロシリコンとテルミット法で還元すると得られる．化学的な用途には，工業用三酸化モリブデンを1200 ℃ 以上で昇華して高純度(99.95％)MoO₃に精製後，アンモニア水に溶かしてモリブデン酸アンモニウム(NH₄)₂MoO₄とする．金属は，高純度MoO₃または(NH₄)₂MoO₄を電気炉またはマッフル炉中で水素気流により還元すると得られる．粉末は灰色，銀白色の金属(体心立方格子)．融点2617 ℃，沸点4612 ℃ できわめて高い．密度10.22 g cm^－3(20 ℃)．抵抗率5.2×10^－8 Ω m．第一イオン化エネルギー7.099 eV．標準電極電位 Mo^3＋/Mo－0.2 V．0.915 K 以下で超伝導を示す．酸化数－2，0～6が知られているが，通常は1～6．化学的に不活性で，耐酸性がきわめて強く，フッ化水素酸，塩酸，希硫酸とは反応しない．濃硝酸とは反応するが，不動態が生成する．王水，熱濃硫酸，濃硝酸とフッ化水素酸の混合物に可溶．融解KNO₃-NaOHまたはNa₂O₂のような酸化融解剤にはただちに侵される．アンモニア水には空気の存在下で溶ける．窒素とは反応しないが，リン，ヒ素，炭素，ケイ素，ホウ素とは赤熱状態で反応する．酸素，硫黄に対しては常温では安定であるが，赤熱状態では酸化されてMoO₃，MoS₂となる．フッ素とは室温でも反応してMoF₆となる．塩素，臭素，ヨウ素とは赤熱状態で反応し，MoCl₅，MoBr₄，MoI₂となる．
モリブデンは生物化学的に活性な遷移元素の一つで，ヒトにとって必須微量元素である．鋼に添加すると硬度および強度が増加するので，ほとんどすべての特殊鋼はモリブデンを含む．構造用合金鋼，高張力鋼，耐熱鋼板，合金工具鋼はMo含有量0.15～1.5重量％，ステンレス鋼，高速度鋼では0.5～9.5重量％ 程度で，構造用合金鋼は機械部品(軸受，歯車，圧力容器，ボルトなど)に，高張力鋼は高い強度を要する航空機部品用材料，エンジン部品，自動車に，高速度鋼は工具や金型，耐熱鋼は構造用材，蒸気・ガスタービン，ボイラー，高温圧力容器・熱交換器に，ステンレス鋼は化学工業から家庭用器具まで使用される．石油精製(水素化脱硫)・石油化学用酸化触媒にも添加される．無機薬品としては，高温用潤滑剤の硫化モリブデンMoS₂や塗料・顔料にも使われる．金属モリブデンは，照明器具，電子管陰極，電子レンジ用マグネトロンの部品に，IT関連でも携帯電話用などの半導体素子に使用される．わが国の需要の約90％ は鉄鋼分野向けである．「モリブデン及びその化合物」はPRTR法・第一種指定化学物質で経口慢性毒性3，水質基準0.07 mg/L．[CAS 7439-98-7][別用語参照]モリブデン触媒

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