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Thomas R. P. Gibb, Jr. [60], zirconium-nickel hydride has a dissociation 

 enthalpy and a plateau temperature and pressure similar to that of 

 magnesium-nickel, but it can hold only a small fraction of the hydrogen 

 that magnesium-nickel holds. In addition, it costs about three times 

 more per pound. Thus, zirconium-nickel hydride appears to have all the 

 disadvantages of magnesium-nickel hydride with none of tbe advantages. 



Vanadium-niobium Hydride. Not much is presently vritten about 

 vanadium-niobium hydride. This report relies on the paragraph included 

 in Reference 61. From this information one can see that this hydride 

 contains only 1.25% hycrogen and that nearly 1,700 pounds of vanadium- 

 niobium hydride would be needed to store 21.2 pounds of hydrogen. In 

 Figure 7b one cm see that vanadium-niobium hydride has a dissociation 

 plateau of 4 atmospheres at 158 F (70°C). A consideration of cost shows 

 that one should not expect a cost of much less than $20 per pound. This 

 hydride, then, can probably be discarded from consideration as a hydro- 

 gen storage system due to its high cost and heavy weight. 



CeMgg.S, LaMg8.5» YgMg2&. The next three intermetallic hydrides 

 listed in Table 3 were studied by Drs. Reilly and Wiswall and reported 

 in 1972. They are mentioned because they all contain fairly high per- 

 centages by weight of hydrogen. They have dissociation pressures and 

 temperatures similar to magnesium hydride and are all expensive. In 

 addition, they are all pyrophoric and therefore, generally undesirable. 



LaCuNl/j. This hydride is a variation of the lanthanum-pentanickel 

 hydride. It was investigated by Drs. Reilly and Wiswall [28] in 1971-2. 

 As shown in Tabid 3, it has dissociation plateaus similar to lanthanjaa- 

 pentanickel, but it stores only 1.14% hydrogen by weight and thus requires 

 a larger amount of hydride to store the seme amount of hydrogen — 1,860 

 pounds of hydride to store 21.2 pounds of hydrogen. As such, it has no 

 advantages over lanthanum-pentanickel. 



Vanadium with Impurities. Not mentioned in T?ble 3 is the inter- 

 metallic hydride of vanadium with impurities. Drs. Reilly and Wiswall 

 have ascertained [62] that an impure vanadium will form a hydride with a 

 higher dissociation pressure than a pure vanadium. This fact was discov- 

 ered when the results of experiments made on a hydride of zone-refined 

 vanadium were compared to those made on a hydride of commercial -grade 

 vanadium. Further, it was shown that the less pure vanadium reacts 

 faster with hydrogen. Other characteristics are the same as zone- 

 refined vanadium, so only the zone-refined characteristics included in 

 Table 3. 



Vanadium hydride suffers the problems of being expensive and 

 containing & very low percentage weight of hydrogen. 



Summary. The best hydride storage medium in terms of cost and 

 weight appears to be the magnesium-nickel hydride. In terms 

 of volume, judgment is difficult because the void fraction 

 is unknown and the hee.t exchanger volumes will depend upon 



26 



