Tantalum atomic properties

Systematic studies of the structural properties of TaS2 by Jellinek10 revealed the presence of several polymorphic forms of the compound as a function of temperature. Within a layer, the tantalum atom sits in the holes formed between two layers of sulfur atoms in the S—Ta—S sandwich. The coordination of the tantalum is trigonal prismatic or octahedral, depending on whether the two sulfur layers lie one on top of the other or are rotated by 60°. Thus the various poly-... 

Preparation of Motallic Tantalum—Colloidal Tantalum—Physical Properties of the Metal, Optical Properties, Are and Spark Spectra—Chemical Properties—Electromotive Behaviour—Atomic Weight—Alloys. 

Besides PTBs, A-site defective perovskite oxides are known to be formed when B = Ti. Nb.Ta and soon "13. Such compounds exhibit metallic properties and perovskite structures when the B atom occurs in a low oxidation stale. Compositions such as A0 5Nb03 (A = Ba. Pb etc.) where niobium is in the highest oxidation state adopt non-perovskite network structures. An interesting example20-21 of a A-site defective perovskite is Cu 5Ta03 which crystallizes in a pseudocubic perovskite structure. The unit cell is orthorhombic with a = 7.523, />= 7.525 and c = 7.520 A and eight formula units per cell. Tantalum atoms form... 

The lattice of vanadium expands approximately linearly with the addition of aluminum [64]. The aluminum intermetallic compound, V3AI (V-25 atom% Al), expands the lattice by about 1% from 0.3025 nm in unalloyed vanadium to 0.3054 nm [64]. Molybdenum, cobalt and titanium also expand the lattice of vanadium, whereas elements such as chromium and iron cause the lattice to contract [83]. Addition of these elements can increase the mechanical strength of alloys relative to unalloyed vanadium [85]. For niobium and tantalum, mechanical properties can also be improved by alloying [86]. Buxbaum has patented a number of alloys of niobium, tantalum and vanadium for membrane use, including Ta-W, V-Co, V-Pd, V-Au, V-Cu, V-Al, Nb-Ag, Nb-Pt, Nb-Pd, V-Ni-Co, V-Ni-Pd, V-Nb-Pt, and V-Pd-Au [45]. 

Thermal properties and decomposition mechanisms depend on the crystal structure type. Compounds with a crystal structure that includes shared octahedrons decompose forming tantalum- or niobium-containing gaseous components, while island-type compounds release light atoms and molecules into the gaseous phase. 

The 5th group metals a summary of their atomic and physical properties Vanadium, niobium and tantalum have only the bcc, W-type, structure no high-temperature or high-pressure polymorphs are known. 

Physical Properties.7—Tantalum is a white metal with a greyish tinge and is very similar to platinum in colour and general appearance. When it is heated to 1600° C. in vacuo it assumes a crystalline form.8 Examination of the powdered metal by X-ray analysis has shown that the arrangement of the atoms is on the plan of a body-centred cube of side 3 272 A, obtained by dividing the space of a crystal into equal closely packed cubes and placing an atom at each cube comer and each cube centre the distance between the nearest atoms is 2 883 A. The specific gravity of the fused metal is 16 6, - a sample drawn into wire 0 05 mm. diameter had a density of 16 5 10 the density calculated from X-ray data is 17 09.u... 

Ion implantation also has promise in other tields involv ino surface technology for example, new metallurgical phases w ith prior unknown properties can be I untied. In some eases. Mich as heav y implantations of tantalum irt copper of phosphorus in iron, amorphous or glassy phases can be formed. Or. if the implanted atoms ore mobile, inclusions and precipitates can he formed as. for example, implanted argon and helium atoms are insoluble in metals and may form bobbles. The composition of a surface layer can be changed by differential sputtering caused by the implanted ions. 

The GD plasma environment is an interesting vessel to study gas-phase chemical properties. The gettering qualities of carbon, silver, tantalum, titanium, and tungsten were compared by Mei and Harrison [40] on the basis of the atomic ion fraction of all of the observed lanthanum species R = La+/(La+ + LaO+) X... 

Niobium (formerly called columbium) and tantalum are Transition Metals having a considerable affinity for oxygen donor groups they are thus called oxophilic see Oxophilic Character). They occur as mixed-metal oxides such as columbites (Fe/Mn)(Nb/Ta)206 and pyrochlore NaCaNb206p. Their discovery in minerals extends back to the beginning of the nineteenth century, when they were believed to be identical and called tantalum. Rose showed that at least two different elements were involved in the minerals, and named the second one niobium. Their separation was resolved around 1866, especially by Marignac. These metals often display similar chemical behavior as a result of nearly identical atomic radii (1.47 A) due to the lanthanide contraction see Periodic Table Trends in the Properties of the Elements)... 

Another effect of lanthanide contraction is that the third row of the d-block elements have only marginally larger atomic radii than the second transition series. For example, zirconium and hafnium, niobium and tantalum, or tungsten and molybdenum have similar ionic radii and chemical properties (Zr + 80 pm, Hf + 81 pm Nb + 70 pm, Ta + 73 pm Mo + 62 pm, W + 65 pm). These elements are also found in the same natural minerals and are difficult to separate. 

The elements will be discussed in the order of increasing atomic number in the Periodic Table, i.e. nickel, zinc, technetium, ruthenium, silver, hafnium, tantalum, tungsten, rhem um, osmium, iridium, platinum, gold, and mercury. Full numerical data of the relevant nuclear properties are summarized, as for other elements, in Appendix 1. 

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