Metallic Thorium

Because the thorium atom density is higher in thorium metal than in any thorium compound, metal is the preferred form of thorium where the hipest nuclear reactivity or hipest density is wanted. One likely nuclear application is in a sodium-cooled fast reactor where thorium would capture a neutron and be converted to 

The phases of thorium metal and their transition temperatures are listed in Table 6.4. Equations for the vapor pressure of thorium metal are [11 ] 

The theoretical density of thorium at 25°C, from x-ray crystal measurements, is 11.72 g/cm . The density of cast metal is between 11.5 and 11.6 g/cm . 

The mean thermal expansion coefficient is given in Table 6.5. Because thorium crystallizes in the cubic system, it expands equally in all directions and is not subject to as much distortion on thermal cycling as uranium. For this reason, and because the a- transition temperature in thorium is much hi er than in uranium, thorium metal reactor fuel has much better limensional stability than uranium metal. 

1360+ 10 1750 10 4702(1 atm) Solid a SoUd 3 Liquid Vapor Face-centered cubic Body-centered cubic 

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In 1789 M. H. Klaproth examined pitchblende, thought at the time to be a mixed oxide ore of zinc, iron and tungsten, and showed that it contained a new element which he named uranium after the recendy discovered planet, Uranus. Then in 1828 J. J. Berzelius obtained an oxide, from a Norwegian ore now known as thorite he named this thoria after the Scandinavian god of war and, by reduction of its tetrachloride with potassium, isolated the metal thorium. The same method was subsequendy used in 1841 by B. Peligot to effect the first preparation of metallic uranium. 

Metallic thorium can be obtained by reduction of Th02 with Ca or by reduction of ThCU with Ca or Mg under an atmosphere of Ar (like Ti, finely divided Th is extremely reactive when hot). 

Bonnelle, C. Band and Localized States in Metallic Thorium, Uranium and Plutonium, and in Some Compounds, Studied by X-ray Spectroscopy. Vol. 31, pp. 23-48. 

Trank AL. 1980. Diseases associated with exposure to metals-thorium. In Last JMM-R, ed. Public health and preventive medicine. 11th ed. New York, NY Appleton-Century-Crofts, 681-682. 

R. Ferreira Paradoxial Violations of Koop-man s Theorem with Special Reference to the 3 d Transition Elements and the Lanthanides. Cfionne/fe.-Band and Localized States in Metallic Thorium, Uranium, and Plutonium, and in some Compounds, Studied by X-Ray Spectroscopy V. Gutmann, H Mayer The Application of the Functional Approach to Bond Variations under Pressure... 

H. A. Wilhelm, The Metal Thorium, American Society for Metals, Novelty, Ohio, 1958, pp. 78-103. 

Various borides, sulfides, carbides, nitrides, etc., have been obtained by direct interaction of the elements at elevated temperatures. Like other actinide and lanthanide metals, thorium also reacts at elevated temperatures with hydrogen. Products with a range of compositions can be obtained, but two definite phases, ThH2 and TlqH, have been characterized. 

The vast majority of the studies reported have concerned the metals thorium and uranium, particularly the latter, due to accessibility of raw materials, ease of handling, and the long lifetimes of the relatively weakly a-emitting elements Th and U. In many cases, compounds of neptunium and plutonium with similar formulae to U and Th analogues have been made and found to be isomorphous and thus presumably isostructural. This chapter will therefore commence with, and concentrate largely on, the chemistry of complexes of these elements, followed by sections on the other actinides. 

In titanium, at the left end of the transition series, the 3d states will be much more like. S and p valence states and will contribute to the bonding. Even at the far left of the 5/ series, the / levels will behave as valence states and will form bands in metallic thorium (Freeman and Koelling, 1974). These two trend.s—a decrease in the extent of localization as we move left in each series and as we move down in the periodic table constitute the two most important trends in the transition series. They will show up in different ways in different systems, but have the same origin. 

Under working conditions, thoria is reduced and the released thorium atoms act as an emitter [6.21]. The reason for the formation of a monoatomic layer of metallic thorium is still not yet fully understood. It is assumed that the reduction of thoria by tungsten according to... 

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