Tantalum physical properties

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

Occurrence. Niobium and tantalum usually occur together. Niobium never occurs as the metal, ie, ia the free state. Sometimes it occurs as a hydroxide, siUcate, or borate most often it is combiaed with oxygen and another metal, forming a niobate or tantalate ia which the niobium and tantalum isomorphously replace one another with Htde change ia physical properties except density. Ore concentrations of niobium usually occur as carbonatites and are associated with tantalum ia pegmatites and alluvial deposits. Principal niobium-beariag minerals can be divided iato two groups, the titano- and tantalo-niobates. 

The physical properties of tantalum are presented in Table 1 and represent the best values from several compilations (5—8). Original sources of the data are given in the Hterature. 

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. 

For a comparison of the physical properties of tantalum, tungsten, molybdenum, platinum, oopper and nickel, see Balke, Chem. Met. Mng., 1922, 27, 1273. 

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... 

In Chapter 1 we explain the motivation and basic concepts of electrodeposition from ionic liquids. In Chapter 2 an introduction to the principles of ionic liquids synthesis is provided as background for those who may be using these materials for the first time. While most of the ionic liquids discussed in this book are available from commercial sources it is important that the reader is aware of the synthetic methods so that impurity issues are clearly understood. Nonetheless, since a comprehensive summary is beyond the scope of this book the reader is referred for more details to the second edition of Ionic Liquids in Synthesis, edited by Peter Wasserscheid and Tom Welton. Chapter 3 summarizes the physical properties of ionic liquids, and in Chapter 4 selected electrodeposition results are presented. Chapter 4 also highlights some of the troublesome aspects of ionic liquid use. One might expect that with a decomposition potential down to -3 V vs. NHE all available elements could be deposited unfortunately, the situation is not as simple as that and the deposition of tantalum is discussed as an example of the issues. In Chapters 5 to 7 the electrodeposition of alloys is reviewed, together with the deposition of semiconductors and conducting polymers. The deposition of conducting polymers... 

The physical properties of tantalum are similar to those of mild steel, with the exception that its melting point (2996°C) is much higher. It is ordinarily used in the pure form, and it is readily fabricated into many different shapes. The corrosion-resistance properties of tantalum resemble those of glass. The metal is attacked by hydrofluoric acid, by hot concentrated alkalies, and by materials containing free sulfur trioxide. It is resistant to all other acids and is often used for equipment involving contact with hydrochloric acid. 

Major industrial uses of tantalum include the production of electrical components (mainly capacitors), superalloys, tantalum carbide, and in the chemical industry (Cunningham 2000). Its physical properties make tantalum an important component of superalloys (produced by combination with cobalt, iron, nickel, and titanium) commonly used in the aerospace industry. In the chemical industry, tantalum s corrosion resistance is taken advantage of in the production of heat exchangers, evaporators, condensers, pumps, and liners for reactors and tanks (Cunningham 2000). The recycling of industrial and obsolete tantalum-containing scrap represents approximately 20% of the total tantalum consumption in the US (Cunningham 2000). 

The usefulness of tantalum (and niobium) as container material derives from two physical properties of these elements. First, their ductility remains high even in the presence of significant nonmetallic impurities, as noted above. Sec-... 

PHYSICAL PROPERTIES The physical properties of metallic tantalum and tantalum pentoxide are provided for illustrative purposes, (metallic tantalum) steel-blue to gray solid or black powder very hard, malleable, ductile metal can readily be drawn in fine wires odorless insoluble in water insoluble in acids, except hydrofluoric and fuming sulfuric acids soluble in fused alkalies MP (2996"C, 5425"F) BP (5425 C, 9797T) DN/SG (16.65 (metal), 14.40 (powder)) CP (25.4 J/K-mol crystal at 25°C) VD (NA) VP (approximately 0 mmHg at 20 C) TS (130,000 psi) EC (8 x 10" over range 20 - 1500 C). (tantalum pentoxide) white, microcrystalline, infusible powder insoluble in water, acids, and alcohol soluble in hydrogen fluoride MP (1800 C, 3272 F) BP (NA) DN/SG (8.2) CP (135.1 J/K-mol crystal at 25"C) VD (NA) VP (approximately 0 mmHg at 20 C). 

That there are such differences between the structural chemistry of reduced Nb and Ta oxides is slightly surprising and two basic questions arise. Firstly, is there also a chemistry of condensed TaeO clusters as found for reduced oxoniobates and, secondly, how do the physical properties of such tantalum compounds compare with those of the niobates Future studies are required to answer this question. 

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