Hafnium hydrides

Hafnium hydride is brittle and easily cmshed to very fine particle sizes. It is usually produced as an intermediate in the process of making hafnium powder from massive hafnium metal. The hydrogen can be removed by high vacuum pumping above 600°C. 

Zirconium, titanium, and hafnium hydrides can activate the C-H bonds of several alkanes at low temperatures (even at room temperature) because they are very electrophilic and reactive. Moreover, the surface complex is immobilized by the strong metal-silica bonds, and this immobilization can prevent the coupling reactions leading to the deactivation of the complex. 

Zirconium and hafnium hydrides can catalyze the olefin polymerization under olefin pressure and the polyolefin hydrogenolysis under hydrogen pressure.260 It is potentially interesting for plastic recovery and transformation into valuable products. 

Hafnium-free zirconium alloys, 26 6351 Hafnium halides, 73 91-93 Hafnium hydride, 73 93 Hafnium hydroxide chloride heptahydrate, 13 92... 

In contrast to the extensive zirconium series, there have been relatively few hafnium hydride compounds reported (Table III). The... 

Titanium hydride (cubic) (27) Zirconium hydride (cubic) (28) Zirconium hydride (tetrag.) (28) Hafnium hydride (cubic) (46) Hafnium hydride (tetrag.) (46)... 

The homogeneity ranges of the lower cubic hydrides also change appreciably with temperature. At 550° C., cubic zirconium hydride exists from ZrHj 3 to ZrH17, while cubic hafnium hydride extends down to HfH0 4 at 800° C. (9). 

Scheme 2. Pathways for the formation of the hafnium amides from azides and hafnium hydrides. Reprinted with permission from Organometallics 1, 1025. Copyright (1982) American Chemical Society.

Band Structure Calculations of Titanium, Zirconium, and Hafnium Hydrides",J. Less-Common Metals, 103, 317 (1984). 

Hafnium can no longer be used as a neutron absorber in fast neutron reactors, due to insufficient absorption efficiency. However, due to the strong moderation effect of hydrogen (concentration in metal hydrides is comparable to water), hafnium hydride has an initial absorption efficiency comparable to enriched boron carbide, with much slower decrease during operation (Fig. 15.18, [52]). 

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