up a less cszspact configuration. Thus, during a ccnplete transition 

 from LaNi, to LaKigH^j, Reference 35 .gives the apparent density of the 

 fully expanded compound as 3.85 gm/cs and tl*en points out that if the 

 hydride could.be ccispressed to eliminate voids it should have a density 

 of 6.74 gra/ca . This last figure is derived by assuming that the lattice 

 structure expands 25% without fracturing. Tbese two values have been 

 included in Table 3 to indicate the hydrogen densities for both the 

 actual and the theoretically possible cases. 



With all of the previous hydrides, contact with C0 2 , CO, H.O, or 

 0. will deactivate the hydride; lanthanum-peatanickel, however, is able 

 to absorb hydrogen from gas mixtures containing these other gases. This 

 ability may make lanthanua-pectanickel and some related compounds conten- 

 ders with palladium for hydrogen purification applications. 



The only real disadvantages of the lanthanun-pentanickel hydride 

 are its low fraction of hydrogen and its high cost. This hydride 

 contains a aaxl~ m of 1.5% hydrogen by weight. Thus, to store 21.2 

 pounds of hydrogen one would need 1,415 pounds of the compound which would 

 cost $17,687 at §12.50 per pound. This would result in a volume of 5.89 

 cubic feet or 3.38 cubic feet, depending on whether one used the low or 

 the high density. The weight and cost are, therefore, major obstacles 

 in the use of this hydride for general mobile use. 



Lanthanun-cerium-pentanlckel Hydride. Van Vucht, et al. [58] point 

 out that by adding a small aisc-ant of cerium to create a compound of 

 Lag tCcq ^Kig, seven atoms of hydrogen can be combined with each formula 

 unit instead of the 6.7 atoms that LaNi5 is able to hold. This mixture 

 was shown to be the optimus-cerium-lanthinum mixture for holding hydrogen; 

 and, since cerium is cheaper than lanthanum, the economics are better, 

 too. It would take 1,320 pounds of this compound to store 21.2 pounds 

 of hydrogen at an estimated cost of $15,840— an improvement but still 

 too expensive. 



Mischiaetal-pentanickel Hydride. Another cousin to the lanthanum- 

 pentanickel is aischmetal-^entanickel. Mischaetal is a term which describes 

 a mixture of several rare-earth metals. The mixture is fairly uniform 

 containing 50% cerium, 27% Lanthanum, 16% Neodymium, 5% Praveodymium , 

 and 2% other rare-earth metals. This hydride delivers hydrogsn at 2 

 atmospheres at -24 F (-31 C); thus, it can conceivably take the heat it 

 needs for dissociation from its surroundings. 



Like the LaNi,, this hydride can be used to absorb hydrogen from 

 impure gas mixtures; but also, like LaNi,, the weight needed to store 

 21.2 pounds of hydrogen is 1,415 pounds. Again, the weight is a problem. 

 The Molybdenum Corporation of America estimates that in volume this 

 hydride can be supplied for $5.00 per pound which would mean that a 

 21.2-pound hydrogen storage unit would cost about $7,075. 



Zirconium-nickel Hydride. Of all the hydrides shown on Table 3, 

 zirconium-nickel hydride stores the least amount of hydrogen, 1% by 

 weight. Reported in 1957 by George G. Libowitz, Hertert F. Hayes, and 



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