Tantalum 1826 INDEX

Gmelin s Handbook of Inorganic Chemistry, System Nos. 48/49/50, Vanadium-Niobium-Tantalum, Index, Gmelin Institute, Max Planck Institute, 1973. VI. 

Antireflection coatings are used over the silicon surface which, without the coating, reflects ca 35% of incident sunlight. A typical coating consists of a single layer of a transparent dielectric material with a refractive index of ca 2, which is between the index of siUcon and ait or cover material. Materials such as titanium dioxide, tantalum pentoxide, Ta20, or siUcon nitride, Si N, ca 0.08-p.m thick are common. The coating and a physically textured... 

Tantalum pentoxide is used in making high refractive index optical glass as a dielectric film on tantalum for its use as a capacitor component and rectifier and for preparing tantalum metal, its carbide, and many other tantalum compounds. 

Optical Properties.—The refractive index of tantalum is 2-05, the coefficient of absorption 2-31, and the reflexion capacity 43-8 per cent, when measured with yellow light of wave-length A=5790.5 The spectral emissivity and the radiation intensity and their variation with temperature have been measured by Worthing.6 For a comparison of the radiation constants of tantalum, platinum, osmium and carbon, see the references cited.7 The flame spectrum of tantalum between carbon electrodes consists of a blue cone with a reddish-yellow edge.8... 

The first single crystal results were therefore surprising (9,10), a band at 2085 cm-1 being reported for Cu(100) and a band at 2076 cm-1 for Cu(lll). The absence of appreciable absorption at these positions in the spectra of CO on silica- or alumina-supported copper, or in the RAIR spectra of CO on copper films deposited on glass (11,12) and on tantalum ribbons (13), led to the unexpected conclusion (4) that the major low index faces were conspicuous by their scarcity in polycrystalline copper surfaces. 

Properties Dark, reddish-brown liquid irritating fumes.Bp 58.8C, fp-7.3C, d 3.11 (20/4C), vap d vs. air (at 15C) 5.51, wt/gal 25.7 lb, specific heat 0.107 cal/g, refr index 1.647, dielectric constant 3.2. Soluble in common organic solvents very slightly soluble in water. Attacks most metals, including platinum and palladium aluminum reacts vigorously and potassium explosively. Dry bromine does not attack lead, nickel, magnesium, tantalum, iron, zinc, or (below 300C) sodium. 

Tantalum is a gray, very hard, malleable, and ductile metal, with an atomic mass of 180.95 and atomic number 73 (Merck Index Online 2002). The boiling point of 5429°C and a melting point of 2996 °C are exceeded only by those of rhenium and tungsten (Hammond 1986, Merck Index Online 2002). Numerous forms of tantalum exist, including pentachloride, pentafluoride, and pent-oxide salts, which are insoluble in water. The most stable oxidation state is + 5. Tantalum is almost twice as dense as iron (density 16.6 gcm ) and about 90% as stiff, with a modulus of elasticity value, E = 2.7x10 psi (Taylor 1969, Merck Index Online 2002). 

Tantalum occurs almost invariably with niobium, although it is the less abundant of the two elements. Tantalum occurs with other metals in the minerals columbite-tan-talite [(Fe, Mn) (Ta, Nb)20J and microlite [(Na, Ca)2Ta20g(0, OH, F)] (Merck Index Online 2002). The metal is present at about 1 mgkg in the Earth s crust (Saager 1984, Merck Index Online 2002). There is very little geographical variability or environmental mobilization of tantalum, possibly because it is highly insoluble (Fbr-stner 1984, Merck Index Online 2002). Instack coal fly ash has been shown to contain... 

Meeck Index Online (2002) Tantalum. Merck and Co., Inc., Whitehouse Station, NJ. 

Introduction.—The m.p. of 99.7% pure niobium has been measured as 2469 + 9°C. The crystal structure of p-tantalum appears to be isomorphous with that of P-uranium, and its X-ray powder diffraction pattern has been indexed in terms of a tetragonal unit cell. The absorption spectra of niobium atoms isolated in Ar, Kr, and Xe matrices at 14 K have been recorded. The absorptions observed in the u.v. region correlate well with those expected from known gas-phase data, but this was not the case for the visible and i.r. spectral regions. Spectral features observed upon annealing an Ar matrix containing Nb... 

Properties M.w. 184.31 sp.gr. 0.993-0.997 b.p. 95-97 C (13 mm Hg) ref. index 1.579 Toxicology TSCA listed Uses Reducing agent for prep, of silyl-substituted alkylidene complexes of tantalum, in ionic reduction of enones to sat. ketones, in reductive cyclization of unsat. ketones, for esters in presence of zinc hydride catalyst, for o-halo ketones in presence of Mo(0), reduction of thio esters to ethers, esters to alcohols with Rh catalysis, in assym. reduction of methyl ketones, reductive cleaving of allyl acetates Manuf./Distrib. ABCR http //www.abcr.de, Alfa Aesar http //www.aifa.com-. Digital Spec. Chems. http //www.digHaichem.com, Fluorochem USA... 

Dielectric used in film supercapacitors. Tantalum oxide is a high-refractive index, low-absorption material usable for making optical coatings from the near-UV (350 nm) to the IR (8 p.m). Insoluble in most chemicals except HF, HF—HNO3 mixtures, oleum, fused alkaU metal hydroxides (e.g. NaOH and KOH) and molten pyrosulfates. Tantalum pentoxide (tantalite, tantala)... 

In this paper we describe, for the first time, a self-assembly technique that employs alkyl phosphoric acid esters to produce dense, highly ordered monolayers in a tails-up configuration, on a TazOs surface. Tantalum oxide was chosen because of its high refractive index, which renders it ideal for application in a planar-waveguide-based bioaffinity sensor. Upon appropriate m-function-alization, alkanephosphate-based SAMs have the potential to be used as the interface that anchors active sensing elements or as the basis of passive, biomolecule-resistant regions on the sensor surface. 

Oxides of transition metals, such as niobium, tantalum, or titanium, are suitable as waveguiding layers on optical (grating coupler) waveguides due to their high refractive index and transparency. Therefore, oxide-coated chips are used as sensing devices in technology based on the interaction of a laser-induced evanescent field with analyte constituents adsorbed on or immobilized at the waveguide/ fluid interface. ... 

In plasmon resonance gas sensors, which also usually operate at room temperatures, we have another situation. In these devices, in order to shift the operating point of the surface plasmon resonance toward an aqueous environment, a thin high-refractive index dielectric overlayer can be employed. The use of overlayers with higher refractive indexes allow for thinner overlayers and potentially better sensor sensitivity. Analysis of results obtained indicates that tantalum pentoxide, which has high refractive index (see Table 2.18) and good environmental stability, may be used for this purpose (Dostalek et al. 2001 Boozer 2003). 

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