Barium metal

Why are barium- and iodine-based materials selected for contrast media The production of X-ray images depends on the differences between the X-ray absorbing power of various tissues. This difference in absorbing power is called contrast and is directly dependent on tissue density. To artificially enhance the ability of a soft tissue to absorb X-rays, the density of that tissue must be increased. The absorption by targeted soft tissue of aqueous solutions of barium sulfate and iodized organic compounds provides this added density through the heavy metal barium and the heavy nonmetal iodine. 

Chemists did not discover the mineral witherite (BaCO ) until the eighteenth century. Carl Wilhelm Scheele (1742—1786) discovered barium oxide in 1774, but he did not isolate or identify the element barium. It was not until 1808 that Sir Humphry Davy used molten barium compounds (baryta) as an electrolyte to separate, by electrolysis, the barium cations, which were deposited at the negative cathode as metallic barium. Therefore, Davy received the credit for bariums discovery. 

Asg ° by applying the valence bond concept (Fig. 9a). The bonding situation of the electron-deficient chains shown in Fig. 9b is not as trivial. In these cases, on one hand, multiple element-element bonding is discussed, and on the other hand, the possibility of partial protonation cannot be excluded completely, especially for compounds of the sometimes hydrogen-contaminated metal barium. 

The A2 structure is seen from Table 11-2 to be the preferred one for the alkali metals, barium, the fifth-group metals, and the sixth-group metals it is also observed as one aiiotropic form for titanium, zirconium, iron, and thallium. The factors determining the choice of the A2 structure by certain elements are not known. 

The nohle gases and most metals crystallize in either the hep or the ccp structure as would be expected for neutral atoms. The alkali metals, barium, and a few transition metals crystallize In the body-centered cubic system, though the reasons for this choice are unknown. 

Barium occurs chiefly as sulfate (barite, barytes, heavy spar, H.iSO(i. and. of less importance, carbonate (witherite. RaCf)3). Georgia and Tennessee are the principal producing states. The sulfate is transformed into chloride, and the electrolysis of the fused chloride yields barium metal. See also Barite and Witherite. Barium ores are mined chiefly as a source of barium compounds because very little metallic barium is consumed commercially. The metal is obtained by thermal reduction of the oxide, using aluminum metal at a high temperature and under vacuum in a closed retort 4BaO + 2A1 > BaOAI Ot+ 3Ba. The gaseous barium produced is recovered by condensation. 

Protactinium metal is prepared (1) by reducing the tetrafluoride witli metallic barium at about 1,500 0 (2) by heating the halide, usually the iodide, under a high vacuum and (3) by bombardment of the oxide under high vacuum with 35-keV electrons for hours at a current strength of 0.005 0.010 Amperes. 

Titanium forms a series of oxides called titanates, which are prepared by heating Ti02 with a stoichiometric amount of the oxide or carbonate of a second metal. Barium titanate (BaTi03) is piezoelectric, which means that it becomes electrically charged when it is mechanically distorted. This property leads to its use for underwater sound detection, in which a mechanical vibration is converted into an electrical signal. 

Compound (a) is composed of a metal (barium) and a nonmetal (fluorine) and is likely to be ionic. Compounds (b)-(d) are composed entirely of nonmetals and therefore are probably molecular. 

See Carbon dioxide, above Ammonium nitrate Metals Barium peroxide Metals Dinitrogen tetraoxide Metals Hydrogen peroxide Metals Lead(IV)oxide Metals Nitric acid Metals Oxygen (Liquid) Metals Potassium chlorate Metals Potassium perchlorate Powdered metals Sodium iodate Metals Sodium nitrate Magnesium See Halogens etc., above See Metal oxides, above See Metal oxosalts, above See Sulfur, etc., below... 

The alkali metals barium (Ba) and uranium (U) are atomic crystalline solids. Their atoms pack in a body-centered cubic arrangement. 

Figure 4.3 Doctors illuminate the intestines of a patient with the help of the alkaline earth metal barium. The patient drinks a concoction of barium sulfate that lines the stomach and intestines. Barium s chemical properties allow it to absorb X-rays, highlighting any problem areas.

Precisely the last condition explains the fact that mainly ICC have been obtained by the immediate interaction of ligands and zero-valent metals. Thus, a large series of metal p-diketonates was synthesized in the absence of a solvent [513,634-638], for example, iron bis- and tra-acetylacetonates [635]. It was shown that other ligands can serve as activators or promoters in these processes. In particular, the introduction of a,a or y,y -bipy into the reaction mixture gives the possibility of isolating copper acetylacetonates and adducts of similar complexes of cobalt and nickel [636], meanwhile the p-diketonates of the metals above are not formed under conditions similar to those reported in Ref. 635. Under dissolution of more active metallic barium in the mixture of another p-dikctone - dipivaloyl-methane (DPM) - with dyglime (DG) or tetraglime (TG) in absolute pentane, the mononuclear complex [Ba(DPM)2(TG)] and binuclear complex [Ba2(DPM)4 ( t-H20)(DG)] were isolated and structurally characterized [637]. 

As with other metals, barium is probably very poorly absorbed from the gastrointestinal tract. The International Commission for Radiation Protection (ICRP) estimates that the gastrointestinal absorption of barium is less than 5% (ICRP 1973). This percentage is supported by studies of two men whose daily input and fecal excretion were monitored for 50 weeks (Tipton et al. 1969). 

Physical and Chemical Properties. The physical and chemical properties of metallic barium and its inorganic compounds have been well characterized (DOT 1986 EPA 1980a, 1984, 1985c, 1987d Hawley 1981 Hayes 1982 HSDB 1989 Kirkpatrick 1985 Kunesh 1985 Meister 1989 NIOSH/OSHA 1978 OHM/TADS 1989 Parmeggiani 1983 Perry and Chilton 1973 RTECS 1989 Sax and Lewis 1987, 1989, Sax et al. 1984 Stokinger 1981 Weast 1989 Windholz 1983). Physical and chemical properties of organic compounds of barium have not been comprehensively examined... 

For example, metallic barium has a bcp lattice with a = 502.5 pm (Table 10.3.2). From these results, the metallic radius of Ba atom can be calculated ... 

When metallic barium is dissolved in liquid sodium or K/Na alloy in an inert atmosphere of nitrogen, an extensive class of mixed alkali metal-barium... 

Ammonia dissolves alkali metals, barium, calcium and strontium and forms an unstable blue solution. This solution contains the metal ion and free electrons that slowly decompose, release hydrogen and form the metal amide. Compared to water, liquid ammonia is less likely to release protons (H+ ions), is more likely to take up protons (to form NH4+ ions) and is a stronger reducing agent219. 

Barium. The metal "barium has no significant use. Its principal compounds arc barium sulfate, BaSO, which is only very slightly soluble in water and dilute acids, and barium chloride, BaCl2 2H20, which is soluble in water. 

Metallic barium is little used industrially, its worldwide production being estimated to be a few tons (30 to 40 t). It is utilized in the manufacture of vacuum tubes (television tubes) and as a getter-material for removing undesirable trace gases. 

The vapour pressure of metallic barium has been determined, and over the temperature range 983—1408 K is given by... 

The metals (excluding radionuclides) currently identified for regulation under RCRA/SDWA are listed in Table I. The original list of 13 metals was defined in the 1986 revision of the SDWA. These Include two group II metals (barium and beryllium), eight transition metals (cadmium, chromium, copper, lead, mercury, nickel, silver, and thallium), and three near-transltlon metals (selenium, arsenic, and antimony). 

Like other alkaline earth metals, barium is a soft, silvery white metal. Discovered by Humphrey Davy in 1808, its primary sources are witherite, which is a type of barium carbonate (BaC03), and baryte, a type of barium sulfate (BaS04). 

Dimethylformamide is required for the corresponding reaction of Sr metal. Barium metal... 

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