NIOBIUM COLUMBIUM

Niobium (also known as columbium) is a soft, ductile, refractory metal with good strength retenti on at high temperature, and a low capture cross-section for thermal neutrons. Itis readily attacked by oxygen and other elements above 200°C. CVD is used to produce coatings or free standing shapes. The properties of niobium are summarized in Table 6.8. 

Cubic structure cubic(b.c.c) Density (g/cm ) 8.57 Melting point (°C) 2468 

Niobium is generally deposited by the hydrogen reduction of its chloride which is accomplished at 900-1300°C and at pressure up to 1 atm as follows  

The chloride is usually prepared by direct chlorination in situ by heating the metal chips to 300°C (see Ch. 4, Sec. 3.1). 

Deposition is also feasible by the hydrogen reduction of the bromide at 1200°C as follows  

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Stainless Steel There are more than 70 standard types of stainless steel and many special alloys. These steels are produced in the wrought form (AISI types) and as cast alloys [Alloy Casting Institute (ACI) types]. Gener y, all are iron-based, with 12 to 30 percent chromium, 0 to 22 percent nickel, and minor amounts of carbon, niobium (columbium), copper, molybdenum, selenium, tantalum, and titanium. These alloys are veiy popular in the process industries. They are heat- and corrosion-resistant, noncontaminating, and easily fabricated into complex shapes. 

Niob, Niobium, n. niobium (columbium). Niobat, n. niobate (columbate). 

Niob-saure,/. niobic (colutnbic) acid, -wasser-stoff, m. niobium (columbium) hydride. Nippel, m. nipple. nippeQ, v.i. sip. 

Hafnium had lain hidden for untold centuries, not because of its rarity but because of its dose similarity to zirconium (16), and when Professor von Hevesy examined some historic museum specimens of zirconium compounds which had been prepared by Julius Thomsen, C. F. Rammelsberg, A. E. Nordenskjold, J.-C. G. de Marignac, and other experts on the chemistry of zirconium, he found that they contained from 1 to 5 per cent of the new element (26, 27). The latter is far more abundant than silver or gold. Since the earlier chemists were unable to prepare zirconium compounds free from hafnium, the discovery of the new element necessitated a revision of the atomic weight of zirconium (24, 28). Some of the minerals were of nepheline syenitic and some of granitic origin (20). Hafnium and zirconium are so closely related chemically and so closely associated in the mineral realm that their separation is even more difficult than that of niobium (columbium) and tantalum (29). The ratio of hafnium to zirconium is not the same in all minerals. 

The metals and alloys that have been under test at National Northern were before the publication of Ref 7 the following plain carbon steels, alloy steels, stainless steels Ni, Al, Mg, Ti Cu alloys Zircalloy—2 Ta, U, Ber, Niobium (CoLumbium), W (Wolfram or Tungsten) and Mo. They have been in either one or more of the following starting forms sheet, plate, cylinders, cones, powders and pellets... 

Tantalum is found in a number of oxide minerals, which almost invariably also contain niobium (columbium). The most important tantalum-bearing minerals are tantalite and columbite. which are variations of the same natural compound (Fe, Mn)(Ta, Nb Og. Much of the tantalum concentrates has been obtained as a byproduct from tin mining in recent years, tin slags, which are a byproduct of the smelting of cassiierite ores, such as those found in the Republic of Congo. Nigeria, Portugal. Malaya, and Thailand have been an important raw material source for tantalum. 

TTTANTTE. A yellow or brown calcium silicotitanite, C aTi Si05, having a waxy luster, and often containing niobium (columbium), chromium, fluorine, and other elements. Titanite occurs in wedge-shaped monodime crystals, usually as an accessory mineral in granitic rocks and in calcium-rich metamorphic rocks. See also Sphene. 

The atoms of the vanadium group metals have five valence electrons. In vanadium (Z — 23) and niobium (columbium, Z = 41), these valence electrons lie beyond ra re-gas cores, whereas in tantalum (Z = 73), they lie beyond the xenon core which has been augmented by fourteen 4/ electrons. The +5 oxidation state is characteristic of this family for niobium and tantalum it is the only oxidation state of importance. Oxidation is often regarded as removal of five valence electrons, followed by coordination of the pentapositive ion (which cannot exist for appreciable time in chemical systems) to basic groups which are present (H2O, OH, Cl, etc.). Although such a description almost certainly has very little resemblance to the actual path of oxidation of these metals, it is clerically convenient and may be used if not taken literally. In the same way, the lower oxidation states of vanadium may be considered vanadium atoms with the two 4s electrons removed, and with additional removal of one or two 3d electrons. 

As a result of this lanthanide contraction the radius and therewith the properties of the next elements hafnium, tantalum and tungsten are practically the same as those of the elements zirconium, niobium (columbium) and molybdenum which are situated above them. The same phenomenon is shown in the similarity of the metals of the platinum group with those of the palladium group. 

Niobium (columbium) High melting point nonvolatile oxide ductile moderate density Oxidizing rapidly... 

Niobium (Columbium)—From measurement of the rate of vaporization of niobium filamentthe N.B.S.529 derive A/f/(Nb g)25 c = 184-5 kcal. Only three determinations were made, so the reliability may not be very high. 

Vanadium, vanadinite, carnotite, KV(S04)2 12H20, VOg, VO+ +, V0O5, NH4VO3. Niobium (columbium), tantalum columbite, tantalite TaC. 

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