Calcium hydride reduction

The most useful commercially available titanium powders are made by calcium hydride reduction, and are furnished in a variety of particle sizes, generally coarser than zirconium. The latter is made by calcium metal reduction and is of an average particle size of only 2-5 ju, measured by the permeation method, though coarser grades also exist. The differences of manufacture and grain sizes do not permit a fair comparison of the two as to intrinsic hazardousness, but at present in this country, zirconium is frequently the cause of serious accidents, while to the author s knowledge titanium rarely is. Conversely, the subsieve-sIze zirconium affords advantages in. performance that cannot be duplicated by the other metal. 

TiH2 is prepared on an industrial scale by dkect combination of hydrogen and the metal (sponge, ingot, scrap, etc) at 200—650°C, followed by cooling in an H2 atmosphere. An alternative method is the reduction of the oxide using calcium hydride under hydrogen ... 

MetaHic potassium and potassium—sodium alloys are made by the reaction of sodium with fused KCl (8,98) or KOH (8,15). Calcium metal and calcium hydride are prepared by the reduction of granular calcium chloride with sodium or sodium and hydrogen, respectively, at temperatures below the fusion point of the resulting salt mixtures (120,121). 

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. 

An estimate of world calcium consumption in 1986 indicated that lead refining uses 30% alloys, eg, with Pb, Al, and Si, 25% steel treatment, 20% calciothermic reduction, 10% calcium hydride, 10% and miscellaneous usage is 5%. More recent evidence, however, has suggested that increasing consumption of calcium in battery manufacture has made this the most significant use. 

Calciothermic reduction of samarium oxide, in the presence of cobalt powder, yields samarium-cobalt alloys in the powder form. The process is popularly known as reduction diffusion. Samarium oxide, mixed with cobalt powder and calcium hydride powder or calcium particles, is heated at 1200 °C under 1 atm hydrogen pressure to produce the alloys. Cobalt oxide sometimes partly replaces the cobalt metal in the charge for alloy preparation. This presents no difficulty because calcium can easily reduce cobalt oxide. A pelletized mixture of oxides of samarium and cobalt, cobalt and calcium, with the components taken in stoichiometric quantities, is heated at 1100-1200 °C in vacuum for 2 to 3 h. This process is called coreduction. In reduction diffusion as well as in coreduction, the metals samarium and/or cobalt form by reduction rather quickly but they need time to form the alloy by diffusion, which warrants holding the charge at the reaction temperature for 4 to 5 h. The yield of alloy in these processes ranges from 97 to 99%. Reduction diffusion is the method by which most of the 500 to 600 t of the magnetic samarium-cobalt alloy (SmCOs) are produced every year. 

The checkers used 40-mesh calcium hydride, from Metal Hydrides, Inc. The submitters report that there may also be used freshly ignited lime (22 g., 0.39 mole), but with a reduction of 10-20% in the yield. 

Alternatively, calcium hydride may be prepared by the reduction of calcium oxide with magnesium in the presence of hydrogen ... 

A successful laboratory method is reduction of the dioxide with an excess of calcium hydride in a molybdenum boat. The reaction is carried out at 900 °C in a vacuum or in an atmosphere of hydrogen5 (equation 1). Most of the hydrogen present can be removed by heating the metal in a vacuum at 1100 °C. 

Weber and coworkers reported the synthesis of novel substituted borazoles. The reaction of boron trichloride with 1,2-diimines 367 provide a mixture of products. The formation of dimeric borazole 369 was explained based on a nucleophilic attack of the chloroborane 370 on the ate complex 368 followed by dehydrohalogenation. Alternatively, a controlled addition of BCR to the diimine 367 results in a clean formation of the imine-borane complex 373 that upon reduction with sodium amalgam and calcium hydride provided the chloroborazole 375 (Scheme 59) <2006EJI5048>. 

Refractory metals such as titanium and zirconium can be won from their oxides by reduction with metals which have oxides with a high heat of formation. Of these, only calcium (or calcium hydride) is capable of producing refractory metals in purities approaching those required for metallurgical uses. 

Derivation Direct combination of titanium with hydrogen, reduction of titanium oxide with calcium hydride in the presence of hydrogen above 600C. 

USE To prepare rare metals by reduction of their oxides as a drying agent for liquids and gases to generate hydrogen 1 g of calcium hydride in water liberates 1 liter of hydrogen at STP in organic syntheses. 

Lithium cyanotrihydridoborate reduces aldehydes in hot dioxan, e.g., pyrenecarbaldehyde in 85% yield, but does not affect aliphatic or aromatic ketones.380 Of the alkaline-earth boron hydrides, only calcium hydridotrimethoxyborate has been mentioned it is prepared from calcium hydride and trimethyl borate and its preparative use for reduction of carbonyl compounds has been investigated by Hesse and Jager.381... 

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