With calcium, reduction

Pu (86 years) is formed from Np. Pu is separated by selective oxidation and solvent extraction. The metal is formed by reduction of PuF with calcium there are six crystal forms. Pu is used in nuclear weapons and reactors Pu is used as a nuclear power source (e.g. in space exploration). The ionizing radiation of plutonium can be a health hazard if the material is inhaled. 

It is recovered commercially from monazite sand, which contains about 3%, and from bastnasite, which contains about 0.2%. Wohler obtained the impure element in 1828 by reduction of the anhydrous chloride with potassium. The metal is now produced commercially by reduction of the fluoride with calcium metal. It can also be prepared by other techniques. 

Metallic cerium is prepared by metahothermic reduction techniques, such as reducing cerous fluoride with calcium, or using electrolysis of molten cerous chloride or others processes. The metahothermic technique produces high-purity cerium. 

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... 

L. Holmia, for Stockholm). The special absorption bands of holmium were noticed in 1878 by the Swiss chemists Delafontaine and Soret, who announced the existence of an "Element X." Cleve, of Sweden, later independently discovered the element while working on erbia earth. The element is named after cleve s native city. Holmia, the yellow oxide, was prepared by Homberg in 1911. Holmium occurs in gadolinite, monazite, and in other rare-earth minerals. It is commercially obtained from monazite, occurring in that mineral to the extent of about 0.05%. It has been isolated by the reduction of its anhydrous chloride or fluoride with calcium metal. 

Vanadium metal can be prepared either by the reduction of vanadium chloride with hydrogen or magnesium or by the reduction of vanadium oxide with calcium, aluminum, or carbon. The oldest and most commonly used method for producing vanadium metal on a commercial scale is the reduction of V20 with calcium. Recently, a two-step process involving the alurninotherniic reduction of vanadium oxide combined with electron-beam melting has been developed. This method makes possible the production of a purer grade of vanadium metal, ie, of the quaUty required for nuclear reactors (qv). 

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Hydrides. Zirconium hydride [7704-99-6] in powder form was produced by the reduction of zirconium oxide with calcium hydride in a bomb reactor. However, the workup was hazardous and many fires and explosions occurred when the calcium oxide was dissolved with hydrochloric acid to recover the hydride powder. With the ready availabiHty of zirconium metal via the KroU process, zirconium hydride can be obtained by exothermic absorption of hydrogen by pure zirconium, usually highly porous sponge. The heat of formation is 167.4 J / mol (40 kcal/mol) hydrogen absorbed. 

Good yields of phenylarsine [822-65-17, C H As, have been obtained by the reaction of phenylarsenic tetrachloride [29181-03-17, C H AsCl, or phenyldichloroarsine [696-28-6], C3H3ASCI25 with lithium aluminum hydride or lithium borohydride (41). Electrolytic reduction has also been used to convert arsonic acids to primary arsines (42). Another method for preparing primary arsines involves the reaction of arsine with calcium and subsequent addition of an alkyl haUde. Thus methylarsine [593-52-2], CH As, is obtained in 80% yield (43) ... 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

In the production of metallic uranium the fluoride UF4 is used for magnesium reduction since die reduction of UCI4 does not produce sufficient heat. The chloride can be reduced with calcium, when a signihcantly greater amount of heat is generated to reach die desired temperature. 

The above series of alcohols are exceedingly difficult to manufacture, hence their expense. The general method of their preparation would theoretically be by distilling the calcium salts of the corresponding fatty acid with calcium formate, in vacuo. This would yield the corresponding aldehyde, which on reduction would yield the corresponding alcohol. In practice, however, many technical difficulties arise, and special processes have to be used which are kept carefully as trade secrets. 

About 250 ml of a reaction mixture obtained by the electrolytic reduction of nitrobenzene in sulfuric acid solution and containing about 23 grams of p-aminophenol by assay is neutralized while at a temperature of 60° to 65°C, to a pH of 4.5 with calcium carbonate. The calcium sulfate precipitate which forms is filtered off, the precipitate washed with hot water at about 65°C and the filtrate and wash water then combined. The solution is then extracted twice with 25 ml portions of benzene and the aqueous phase is treated with 0.5 part by weight, for each part of p-aminophenol present, of activated carbon and the latter filtered off. The activated carbon is regenerated by treatment with hot dilute caustic followed by a hot dilute acid wash, and reused a minimum of three times. 

The first difference of normal stresses (tr, t) may serve as an indirect index of the highly elastic properties of polymeric systems [199]. C. D. Han [200] related (ru with the residual pressure at outlet Pt)dt. Han, who observed its reduction in polypropylene filled with calcium carbonate [201], concluded that filling decreases the normal stresses. Note that addition of fibrous fillers, vice versa, somewhat increases Pexi, [180]. 

The anode residues must be chemically processed to recover the plutonium remaining in the residues. This may amount to about 10% of the feed mass if delta alloy is the feed metal. Either aqueous or pyrochemical processes may be used for anode recovery. One pyrochemical process used for recovery utilizes oxidation of the plutonium with zinc chloride to form plutonium chloride salt, followed by calcium reduction of the PUCI3 contained in the salt phase to produce pure plutonium metal (the impurities follow the zinc metal obtained from the oxidation reaction and are discarded to waste). Impurities more stable than calcium chloride remain in the salt phase and are also... 

Direct Oxide Reduction. In DOR, plutonia is reduced with calcium metal to form plutonium metal and calcium oxide.2 3 The reaction takes place in a CaCl2 solvent which dissolves the calcium oxide and allows the plutonium metal to coalesce in the bottom of the crucible. 

The CaB can be obtained by reduction of boric oxide with calcium aluminide at 800°C... 

Several other useful modifications of calciothermic reduction have been successfully developed for the preparation of this neodymium-bearing magnetic alloy. One of these is reduction-extraction which involves the reduction of neodymium sesquioxide (Nd203) with calcium in a molten calcium chloride-sodium chloride salt bath at 750 °C and the simultaneous extraction of the reduced metal into a molten neodymium-zinc or neodymium-iron alloy pool. The neodymium-zinc alloy product is treated in vacuum to remove zinc and produce neodymium metal, while the neodymium-iron alloy is itself the end product of... 

One of the important differences between calciothermic and aluminothermic reduction of oxides concerns the interaction between the reduced metal and the reductant. Calcium does not form stable solid solutions or alloys with the reduced metals calcium contamination in the metal is, therefore, relatively small. Aluminum, on the other hand, readily forms solid solutions with the reduced metals, and the product generally contains appreciable quantities of residual aluminum. This is not a serious problem because in many cases either a certain aluminum content is desired in the reduced metal or the residual aluminum can be effectively removed in post-reduction purification operations. The extent of the contamination of a reduced metal with the reductant can be related to factors such as the reaction temperature, the standard free energy change associated with the reaction, and the slag composition. Let the following generalized reaction be considered ... 

Figure 4.24 Reactor for uranium fluoride reduction with calcium.

All the rare earth metals except samarium, europium, and ytterbium can be prepared in a pure form by reducing their trifluorides with calcium. Magnesium fluoride is less stable than the rare earth fluorides and so magnesium does not figure as a reductant. Lithium forms a fluoride which is stabler than some of the rare earth fluorides and thus finds some use as a reductant. 

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