Thorium metal

Several methods are available for producing thorium metal it can be obtained by reducing thorium oxide with calcium, by electrolysis of anhydrous thorium chloride in a fused mixture of sodium and potassium chlorides, by calcium reduction of thorium tetrachloride mixed with... 

Properties. Pure thorium metal is a dense, bright silvery metal having a very high melting point. The metal exists in two allotropic modifications. Thorium is a reactive, soft, and ductile metal which tarnishes slowly on exposure to air (12). Having poor mechanical properties, the metal has no direct stmctural appHcations. A survey of the physical properties of thorium is summarized in Table 1. Thorium metal is diamagnetic at room temperature, but becomes superconducting below 1.3—1.4 K. 

Thorium metal alloys readily with a large number of metals, including Fe, Co, Ni, Cu, Au, Ag, B, Pt, Mo, W, Ta, Zn, Bi, Pb, Hg, Na, Be, Mg, Si, Se, and Al. Like many electropositive metals, finely divided thorium metal is pyrophoric in air, and bums to give the oxide. Massive metal, chips, and turnings... 

Most mineral acids react vigorously with thorium metal. Aqueous HCl attacks thorium metal, but dissolution is not complete. From 12 to 25% of the metal typically remains undissolved. A small amount of fluoride or fluorosiUcate is often used to assist in complete dissolution. Nitric acid passivates the surface of thorium metal, but small amounts of fluoride or fluorosiUcate assists in complete dissolution. Dilute HF, HNO, or H2SO4, or concentrated HCIO4 and H PO, slowly dissolve thorium metal, accompanied by constant hydrogen gas evolution. Thorium metal does not dissolve in alkaline hydroxide solutions. 

Chlorides. Anhydrous ThCl [10026-08-1] has usually been prepared by direct interaction of thorium metal, hydride, or carbide with chlorine. 

Thorium is potentially hazardous. Einely divided thorium metal and hydrides can be explosive or inflammatory hazards with respect to oxygen and halogens. Einely divided Th02 and other inorganic salts also present an inhalation and irritation hazard. The use of standard precautions, skin covering, and a conventional dust respirator should be sufficient for handling thorium materials. 

Thorium metal, 24 759-761 in alloys, 24 760-761 preparation of, 24 759-760 properties of, 24 760-761 reactions of, 24 761 Thorium nitrate, 24 757, 766 Thorium oxalates, 24 768-769 Thorium oxide, 21 491 Thorium oxides, 24 757, 761-762 Thorium oxyhalides, 24 762 Thorium perchlorate, 24 764 Thorium phosphates, 24 765-766 Thorium pnictides, 24 761 Thorium sulfate, 24 764 Thorium-uranium fuel cycle, 24 758-759 Thorocene, 24 772 Thorotrast, 24 775-776 3A zeolite. See Zeolite 3A Three-boiling beet sugar crystallization scheme, 23 463-465 Three-color photography, 19 233-234 3D models, advantages of, 19 520-521 3D physical design software, 19 519-521 3D QSAR models, 10 333. See also QSAR analysis... 

Large single crystals (54 mm ) of ultrapure thorium metal have been prepared by this technique (99). 

Thorium metal is generally prepared by the metallothermic reduction of its halides (Section II,A). Very high-quality metal containing a total of 250 ppm impurities has been prepared at the Ames Laboratory of the Department of Energy (98, 99). These workers reduced ThCl4 with excess Mg metal to yield a Th-Mg alloy, which was then heated in vacuo to remove the excess Mg (55) ... 

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

Finely divided thorium metal is pyrophoric in air, and thorium ribbon burns in air to give the oxide. The metal also reacts vigorously with hydrogen, nitrogen, the halogens, and sulfur. Thorium compounds are stable in +4 oxidation state (Katzin 1983). Details of thorium chemistry are given by Katzin (1983). 

Thorium metal may be produced from its salts— usually the oxide or a hahde—by several methods that include electrolysis and reduction with calci-... 

Thorium metal also can he prepared hy thermal reduction of its hahdes with calcium, magnesium, sodium, or potassium at elevated temperatures (950°C), first in an inert atmosphere and then in vacuum. Fluoride and chloride thorium salts are commonly employed. Berzehus first prepared thorium by heating tetrachloride, ThCh, with potassium. Magnesium and calcium are the most common reductant. These metals are added to thorium halides in excess to ensure complete reduction. Excess magnesium or calcium is removed by heating at elevated temperatures in vacuum. One such thermal reduction of hahdes produces thorium sponge, which can be converted into the massive metal by melting in an electron beam or arc furnace. 

Thorium dioxide is obtained as an intermediate in the production of thorium metal from monazite sand (See Thorium). 

The compound also can be prepared by many other methods including thermal decomposition of thorium oxalate, hydroxide, carbonate, or nitrate. Heating thorium metal in oxygen or air, and hydrolysis of thorium halides also yield thorium dioxide. 

Thorium nitrate is obtained as an intermediate in making thorium metal from monazite sand. Also, the salt is prepared by heating thorium metal or its oxide or hydroxide with nitric acid, followed by evaporation of the solution and crystaUization. 

The Valence Band Spectra of Light Actinides a. Thorium Metal a. XPS and BIS Results... 

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