Zirconium, hydride formation

AHoy M16630 (ZE63A) which contains rare-earth metals and zinc, is designed to take advantage of a newer he at-treatment technique involving inward diffusion of hydrogen and formation of zirconium hydride [7704-99-6]. The alloy is heated in hydrogen at 480°C for 10, 24, or 72 hours for 6.3,... 

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. 

Water as an impurity is known to promote the breakaway corrosion of a number of metals in addition to iron in CO2 the effect has been reported for magnesium (hydrocarbons have more effect on the oxidation of this metal), beryllium, zirconium and sodium. In the latter case water is known to convert the oxide to deliquescent NaOH but acceleration of beryllium oxidation probably results from hydride formation and mechanical damage to the oxide. 

Note that the main difference between zirconium hydride and tantalum hydride is that tantalum hydride is formally a d 8-electron Ta complex. On the one hand, a direct oxidative addition of the carbon-carbon bond of ethane or other alkanes could explain the products such a type of elementary step is rare and is usually a high energy process. On the other hand, formation of tantalum alkyl intermediates via C - H bond activation, a process already ob-... 

Reaction of this well-characterized species with dry hydrogen at 150°C leads to the formation of zirconium hydride and the evolution of alkanes.257 Hafnium and titanium monohydride can be obtained in the same way.258... 

The marked difference in reaction efficiency that arises when different sources of metallocene are employed in the (ebthi)Zr-catalyzed hydrogenation is illustrated in Table 6.5. The mechanism by which MAO converts the zirconium(IV) salts to the active zirconium hydride species remains unclear [122]. However, it has been proposed that a chlorine atom may form an q2-bridge between aluminum and zirconium when the dichloride salt is used, thereby preventing formation of the active cationic metal center. 

Sublimation of tetraneopentyl zirconium onto the surface of silica dehydroxylated at 500 °C results in the electrolytic cleavage of one Zr-C bond by a surface proton, with the formation of the tris neopentyl zirconium [Si]-0-Zr(CH2CMc3)3 grafted species. Reaction of this supported Zr alkyl with hydrogen at 150°C leads to the formation of a zirconium hydride. Interestingly, this reaction does not yield neopentane, but rather the formation of methane and ethane are observed. These products are in fact the result of the hydrogenolysis of evolved neopentane catalyzed by the silica-supported zirconium hydride. ... 

Enthalpy of formation values at 298.15 K for other zirconium hydride stoichiometries have been either measured, or calculated from earlier data at higher temperatures, by [64TUR] and are listed in Table V-13. 

When zirconium is oxidized in water, a considerable fraction of the corrosion product hydrogen enters the metal. There is evidence that the oxide recrystallization and the transition in kinetics that were shown in Figure 19 are related to a buildup of hydrogen in the surface of the metal. It has been suggested that at that time some zirconium hydride forms beneath the film. The addition of alloying elements which form active cathodes for hydrogen liberation have reduced hydrogen uptake, have delayed transition, and have resulted in the formation of more coherent oxide after transition. There has been no clear resolution as to mechanisms (29). 

Because of their tendency to hydride formation, the embitterment of Ti, zirconium (Zr), and tantalum (Ta) by hydrogen is particularly pronounced. The proneness to gas absorption restricts the use of these metals. They are not only attacked by nascent hydrogen they also become brittle at... 

As the above-mentioned formation of zirconium hydride shows, not only metals but also various compounds can be the end product of a thermitic process. Silicides, such as the compound BaSi from the peroxide and oxide with silicon, have been quoted by Ullmann from German patents. The lower oxide of titanium (TiO) has been described as obtainable from the dioxide and magnesium. A very hard form of artificial corundum (crystalline aluminum oxide) of superior quality for grinding and polishing operations is the byproduct of the above-described production of chromium metal. ... 

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