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外観
暗灰色の粉末
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溶解性
水, 有機溶剤に不溶。フッ化水素酸に少し溶ける。硝酸に不溶。ふっ化水素酸に溶けるが、水にほとんど溶けない。
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解説
ニオブ,原子番号41の元素．電子配置[Kr]4d45s1の周期表5族遷移金属元素．原子量92.90638(2)．天然には，質量数93の同位体のみが存在する単核種元素．81～113の放射性核種が知られている．
森北出版「化学辞典（第2版）
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特性
金属ニオブは灰白色で軟らかく，展延性をもつ．等軸晶系に属する．密度8.570 g cm－3．融点2468 ℃，沸点4930 ℃．9.25 K 以下で超伝導となる．仕事関数は3.96 V と小さい．原子半径0.143 nm．イオン半径0.069 nm(Nb5＋，六配位)．0.074 nm(Nb4＋，六配位)．標準電極電位 Nb3＋/Nb－1.1 V．第一イオン化エネルギー663.7 kJ mol－1(6.88 eV)．空気中では表面に酸化膜をつくって不動態となり，きわめて安定である．高温では水素を吸収してもろくなる．1000 ℃ 以上で窒素と反応して窒化物となる．塩素と200 ℃ 以上で反応して五塩化ニオブを生じる．常温では水に侵されないが，熱水蒸気と反応して水素を発生する．硝酸，熱濃硫酸に可溶，フッ化水素酸に微溶，アルカリに不溶．ニオブには，通常，酸化数2～5が知られており，酸化数5がもっとも安定である．これらの酸化数に相当する化合物のほかに，酸化数1に相当する(C5H5)Nb(CO)4や，[Na((CH3OCH2CH2)2O)2][Nb(CO)6]も知られている．
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用途
標準液、合金添加剤、ゲッター(残留気体収着除去剤)。
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応用
用途は，量的にはほとんど高張力鋼(自動車・造船用)，ステンレス鋼，耐熱超合金(航空機エンジン)用で，鉄との合金フェロニオブの形で供給され，鋼に添加される．希少資源で価格・供給に問題があるタンタルのかわりにニオブを使った小型コンデンサー(キャパシター)がパソコン・携帯電話機用に用いられる．高屈折率高級レンズ材料としても使用される．そのほか，Nb3Geは23 K，Nb3Snは18.1 K，Nb0.6Ti0.4は9.8 K，Nb自身も9.25 K で超伝導となるので，最近，MRI(磁気共鳴映像法)用超電導磁石や大型加速器用超伝導加速空洞用材料としての需要が加わり，とくにITER(国際熱核融合実験炉)用の超伝導コイル材料としての大口需要がある．資源エネルギー庁・要注視鉱種に指定されている．
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発見
1801年，イギリスのC. Hatchettが大英博物館所在の北米産のコルンブ石(columbite)と名づけられた鉱物中から新金属元素を発見し，コロンビウムと命名したが，ともに産出するタンタルの間違いであるとされた．1844年，ドイツのH. RoseはHatchettの新元素がタンタルとは別物であることを明らかにし，新元素をタンタルとともに産出することから，ギリシア神話のタンタルスの娘ニオベにちなんでニオブと命名した．1949年，niobiumがIUPACにより採用されたが，最近でもアメリカの金属鉱業界などではコロンビウムという名称も用いられている．日本語の元素名はドイツ語の元素名を採用した．宇田川榕菴は天保8年(1837年)に出版した「舎密開宗」で，格綸彪母(コリュムビウム)としている．比較的広く存在する元素であるが，産出量は少ない．資源的に極端に偏在していて，ブラジルに世界の埋蔵量の90％ 以上，ついでカナダである．地殻中の存在度11 ppm．
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使用上の注意
純度は金属ベースで差数法によって算出したもので、重量又は容量分析等の化学的方法によるものではありません。使用目的により、正確な含量が必要な場合は、それらの方法によって測定する必要があります。
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化学的特性
Niobium was discovered by Charles Hatchett in 1801 and isolated by Christian Blomstrand of Sweden in 1964. Its name was given after the Greek mythological ?gure Niobe, the daughter of Tantalos; tantalum always was associated with niobium. For many years, the terms “niobium” and “columbium”wereusedinterchangeably;however,thename “niobium” was of?cially adopted by International Union of Pure and Applied Chemistry (IUPAC) in 1950. Niobium is not a very rare element; its crustal abundance is 24ppm, which is similar or greater than those of many common elements, such as lead or cobalt.
Niobium is a shiny white, soft, and malleable metal. The element is inert to HCl, HNO3, or aqua regia at room temperature, slightly soluble in HF, but is attacked by alkali hydroxides or oxidizing agents at all temperatures. In pure
form, niobium is ductile, unless it is allowed to associate at elevated temperatures with common gases such as N2,H 2, or O2. Thus, when processed, it must be placed in a protective environment
No data were found in the literature; however, it might be assumed that niobium and most of their compounds are odorless. Niobium pentachloride (NbCl5) has pungent odor, because it decomposes slowly when heated, with Cl2 formation. Niobium in the form of dust is moderately explosive when exposed to ?ame or by chemical reaction.
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物理的性質
Niobium is a soft grayish-silvery metal that resembles fresh-cut steel. It is usually found inminerals with other related metals. It neither tarnishes nor oxidizes in air at room temperaturebecause of a thin coating of niobium oxide. It does readily oxidize at high temperatures(above 200°C), particularly with oxygen and halogens (group 17). When alloyed with tin andaluminum, niobium has the property of superconductivity at 9.25 Kelvin degrees.
Its melting point is 2,468°C, its boiling point is 4,742°C, and its density is 8.57 g/cm3.
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同位体
There are 49 isotopes of niobium, ranging from Nb-81 to Nb-113. All are radioactiveand made artificially except niobium-93, which is stable and makes up all of theelement’s natural existence in the Earth’s crust.
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名前の由来
Niobium is named after the Greek mythological figure Niobe who was
the daughter of Tantalus. Tantalus was a Greek god whose name is the source of the
word “tantalize,” which implies torture: he cut up his son to make soup for other gods.
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天然物の起源
Niobium is the 33rd most abundant element in the Earth’s crust and is considered rare.It does not exist as a free elemental metal in nature. Rather, it is found primarily in severalmineral ores known as columbite (Fe, Mn, Mg, and Nb with Ta) and pyrochlore [(Ca,Na)2Nb2O6 (O, OH, F)]. These ores are found in Canada and Brazil. Niobium and tantalum[(Fe, Mn)(Ta, Nb)2O6] are also products from tin mines in Malaysia and Nigeria. Niobium is a chemical “cousin” of tantalum and was originally purified by its separation through theprocess known as fractional crystallization (separation is accomplished as a result of the differentrates at which some elements crystallize) or by being dissolved in special solvents. Todaymost of the niobium metal is obtained from columbite and pyrochlore through a complicatedrefining process that ends with the production of niobium metal by electrolysis of moltenniobium potassium fluoride (K2NbF7).
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来歴
Niobium was discovered in 1801 by Hatchett in an ore sent to England
more that a century before by John Winthrop the Younger,
first governor of Connecticut. The metal was first prepared
in 1864 by Blomstrand, who reduced the chloride by heating
it in a hydrogen atmosphere. The name niobium was adopted
by the International Union of Pure and Applied Chemistry in
1950 after 100 years of controversy. Most leading chemical societies
and government organizations refer to it by this name.
Some metallurgists and commercial producers, however, still
refer to the metal as “Niobium.” Niobium is found in
niobite (or columbite), niobite-tantalite, pyrochlore, and euxenite.
Large deposits of niobium have been found associated
with carbonatites (carbon-silicate rocks), as a constituent of
pyrochlore. Extensive ore reserves are found in Canada, Brazil,
Congo-Kinshasa, Rwanda, and Australia. The metal can be
isolated from tantalum, and prepared in several ways. It is a
shiny, white, soft, and ductile metal, and takes on a bluish cast
when exposed to air at room temperatures for a long time. The
metal starts to oxidize in air at 200°C, and when processed at
even moderate temperatures must be placed in a protective
atmosphere. It is used in arc-welding rods for stabilized grades
of stainless steel. Thousands of pounds of niobium have been
used in advanced air frame systems such as were used in the
Gemini space program. It has also found use in super-alloys
for applications such as jet engine components, rocket subassemblies,
and heat-resisting equipment. The element has
superconductive properties; superconductive magnets have
been made with Nb-Zr wire, which retains its superconductivity
in strong magnetic fields. Natural niobium is composed
of only one isotope, 93Nb. Forty-seven other isotopes and isomers
of niobium are now recognized. Niobium metal (99.9%
pure) is priced at about 50￠/g.
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特性
Some of niobium’s characteristics and properties resemble several other neighboring elementson the periodic table, making them, as well as niobium, difficult to identify. This isparticularly true for tantalum, which is located just below niobium on the periodic table.
Niobium is not attacked by cold acids but is very reactive with several hot acids such ashydrochloric, sulfuric, nitric, and phosphoric acids. It is ductile (can be drawn into wiresthrough a die) and malleable, which means it can be worked into different forms.
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使用
In ferrous metallurgy: Ferroniobium (produced by silicon reduction of columbite) is used to alloy stainless steels and metals for welding rods. In niobium base alloys for high temperatures and nuclear reactions. Niobium has some use as a getter in electronic vacuum tubes.
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調製方法
Theextractingandre?ningprocessesforniobiumfromore are extremely complex and consist of a series of operations,
starting from upgrading the ores by concentration. Disruption of the niobium-containing matrix is then performed by an ore-opening procedure with hot HF or fusion with alkali ?uxes. The next steps include pure niobium compound preparation and reduction to metallic niobium, followed by re?ning, consolidation, and fabrication of the metal. Niobium is so closely associated with tantalum that they must be separated by fractional crystallization or by solvent extraction before puri?cation.
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定義
The name niobium is officially approved by chemical authorities, but columbium is still used chiefly
by metallurgists. Metallic element, atomic number
41, group VB of the periodic table, aw 92.9064,
valences of 2, 3, 4, 5; no stable isotopes
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危険性
Niobium is not considered reactive at normal room temperatures. However, it is toxic in itsphysical forms as dust, powder, shavings, and vapors, and it is carcinogenic if inhaled or ingested.
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製法
主たる用途である FeNb はパイロクロア（(Na,Ca)2Nb2O6(OH,F)）鉱石を選鉱濃縮し、この精鉱と高品位ヘマタ イト（酸化鉄）にアルミ粉と石灰など造滓剤を混合し、テルミット法で製造される。残りの精鉱は、湿式で不純物 を除去し高純度酸化ニオブとした後、テルミット還元、更には電子ビーム溶融により金属ニオブとなる。
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発がん性
No evidence was found that niobiumiscarcinogenic.Indeed,therearesomestudiessuggesting its antitumor activity. In the mouse study of Schroeder et al., occurrence of 23.6% of tumors in the niobiumtreated group (5–6.62ppm niobium in drinking water and diet for a lifetime) versus 34.8% for the controls was documented.
