Thorium vaporization

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Complex ions of Th(IV) have been studied and include M2 ThClg] [21493-66-3] where M = Li—Cs, (CH2)4N, or (C2H ) N. Under more extreme conditions, eg, molten KCl or vapor phase, ThCL [51340-85-3] ThCh [51340-84-2] ThCl g [53565-25-6] and ThCh are known to be important. Additional information on thorium chlorides can be found in the Hterature (81). 

In a chemical vapor deposition (CVD) variant of conventional powder metallurgy processing, fine chromium powder is obtained by hydrogen reduction of Crl2 and simultaneously combined with fine thorium(IV) oxide [1314-20-17, H1O2, particles. This product is isostaticaHy hot pressed to 70 MPa (700 atm) and 1100°C for 2 h. Compacts are steel clad and hot roUed to sheets (24). 

Thorium oxide on activated carbon was prepared by absorption of thorium nitrate from its solution in anhydrous acetone on the activated carbon Supersorbon. The excess solution was decanted, the catalyst was dried at 80 °C, and the adsorbed thorium oxide was decomposed by excess 5% ammonium hydroxide solution. After repeated washing and decanta-nation with distilled water and acetone, the catalyst was dried at 180°C. It was then stabilized by heating to 360°C for 5 hr in a stream of nitrogen. The content of thorium oxide was 2.9% (wt.). The BET surface area was 870 m2/g. Prior to kinetic measurements, the catalyst was modified by passing over acetic acid vapors (100 g acid/1 g catalyst). 

The last reaction is the most favored of these three. The actual occurrence of the reactions with elemental phosphorus or phosphorous trichloride as products has been explained to be due to kinetic reasons. The thorium present in the ore volatilizes in the form of thorium tetrachloride (ThCl4) vapor other metallic impurities such as iron, chromium, aluminum, and titanium also form chlorides and vaporize. The product obtained after chlorination at 900 °C is virtually free from thorium chloride and phosphorous compounds, and also from the metals iron, aluminum, chromium, and titanium. 

Multidentate V-heterocyclic ligands, thorium and, 24 767 Multidimensional gas chromatography, 4 617-618 6 433-434 Multidrug resistant bacteria, 18 252 Multi-effect distillation (ME), 26 65—67 Multi-effect vapor-compression submerged-tube desalination plant, 26 70 Multielevation piperacks, 19 515 Multifeed fractionation, 10 616 Multifilamentary superconductor, 23 846 Multifilament sutures, 24 218 threads for, 24 207 Multifilament yarns, 11 177-178 Multifile patent searches, 18 244 Multifunctional aliphatic epoxies, 10 376 Multifunctional coatings, 1 714-716 Multifunctional epoxy resins, 10 367-373, 418, 454... 

This article presents a general discussion of actinide metallurgy, including advanced methods such as levitation melting and chemical vapor-phase reactions. A section on purification of actinide metals by a variety of techniques is included. Finally, an element-by-element discussion is given of the most satisfactory metallurgical preparation for each individual element actinium (included for completeness even though not an actinide element), thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, and einsteinium. 

The light actinide metals (Th, Pa, and U) have extremely low vapor pressures. Their preparation via the vapor phase of the metal requires temperatures as high as 2375 K for U and 2775 K for Th and Pa. Therefore, uranium is more commonly prepared by calciothermic reduction of the tetrafluoride or dioxide (Section II,A). Thorium and protactinium metals on the gram scale can be prepared and refined by the van Arkel-De Boer process, which is described next. 

Proceeding from thorium to plutonium along the actinide series, the vapor pressure of the corresponding iodides decreases and the thermal stability of the iodides increases. The melting point of U metal is below 1475 K and for Np and Pu metals it is below 975 K. The thermal stabilities of the iodides of U, Np, and Pu below the melting points of the respective metals are too great to permit the preparation of these metals by the van Arkel-De Boer process. 

Isobutyronitrile has been prepared by a number of catalytic vapor-phase reactions at elevated temperatures isobutylamine over copper 2 or nickel,3 isobutyramide over alumina,4 a mixture of ammonia and isobutyraldehyde over thorium dioxide,5 and a mixture of ammonia and isobutyl alcohol over copper. Isobutyronitrile also has been obtained by decarboxylation of 2-methyl-2-cyanopropanoic add 7 and from the reaction of iso-butyric acid with potassium thiocyanate.8 The above procedure is a modification of the method used by Walter and McElvain.9... 

Metals. Beryllium, manganese, thorium, copper, and zirconium react with incandescence when heated with phosphorus.19 Cerium, lanthanum, neodymium, and praseodymium react violently above 400°C. Osmium incandesces in phosphorus vapor and platinum burns vividly.20... 

The old method of heating the calcium salts of formic and a second carboxylic acid for aldehyde formation has been modified by the use of a catalytic decomposition technique. By this scheme, the acid vapors are passed over thorium oxide, titanium oxide, or magnesium oxide at 300° or the acids are heated under pressure at 260° in the presence of titanium dioxide. In the latter procedure, non-volatile acids can be used. With aliphatic acids over titanium oxide, reaction occurs only when more than seven carbon atoms are present, the yields increasing with increase in the molecular weight (78-90%). Aromatic-acids having halo and phenolic groups are converted in high yields to aldehydes, e.g., salicylaldehyde (92%) and p-chlorobenzaldehyde (8S>%). Preparation of a thorium oxide catalyst has been described (cf. method 186). 

Thorium. Th02 is one of the most thermally stable oxides known, but it forms a slightly oxygen-deflcient, congruently-vaporizing solid ThOi.998 (3) at temperatures of about 2500°C. Th02 is a fluorite-type dioxide with a = 5.999A. 

An exception involves the passage of hot alcohol vapors over thorium oxide at 350-450°C, under which conditions Hofmann s mle is followed, and the mechanism is probably different. Cyclobutanol derivatives can be opened in the presence of a palladium catalyst. 2-Phenylbicyclo[3.2.0]octan-2-ol, for example, reacted with a catalytic amount of palladium acetate in the presence of pyridine and oxygen to give phenyl methylenecyclohexane ketone. ... 

Thorium and Pa are most conveniently prepared from carbides, but at low temperatures made possible by an iodide intermediate in the iodine vapor process, based on the reaction of carbide with iodine vapor at 300 C. The actinoid iodide is transported to a hot surface (such as a W wire or sphere at 1200°C), where it decomposes and deposits the actinoid metaF". The overall reaction sequence is... 

Thorium oxide would not be expected to react with molten alkali metal nitrates. Brambilla claims, however, that a soluble thorium species is produced in the molten phase when nitric acid vapor is combined with fluoride ion in molten nitrates (10). 

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