The higher hydrides of vanadium and niobiua of approximate coapost- 

 tioa VH~ and Kb 11, are relatively unstable. By decreasing the system 

 pressure to atmospheric at about 100 F, the v&aediua dlhydridr gives up 

 some of the hydrogen slowly and stabilizes at a composition of VH . 

 Further release of hydrogen from VH Q g„ at atmospheric pressure is* 

 possible if its temperature is raised substantially. For instance, 

 raising the temperature to about 775 F utll reduce the hydrogen to metal 

 ratio to 0.27, whereat- a temperature of 1,100°F is required to further 

 reduce this ratio to C.062 [9]. 



The hydriding behavior of niobium is similar to vanadium in most 

 respects. By decreasing the system pressure to atmospheric at about 

 100OF, niobium dihydride gives up hydrogen until the hydrogen-to-metal 

 atomic ratio reaches about 1.1. Raising the temperature of the system 

 could further release hydrogen until the hydtogen-to-metal ratio reaches 

 about 0.15 at 1,100°F [9]. 



It is more difficult to release hydrogen from tantalum hydride. At 

 atmospheric pressure, the temperature of the hydride has to be raised to 

 about 785 F to reduce the hydrogen- to-metal ratio from 0.9 to 0.38. 



The dissociation pressures in each of the above three cases could 

 be raised if small amounts of catalytic metals are added to pure metals 

 prior to hydriding. This aspect will be discussed in the intersetallic 

 section of this report. 



A hazard of these hydrides, which have dissociation pressures of 1 

 atmosphere or greater at ambi^ut temperatures, is that they generally 

 will release hydrogan when exyosed to the atmosphere. If a fire is 

 allowed to start it can burn the hydrogen which is further released by 

 the heat. 



Because these metals are expensive, are not widely available, are 

 hazardous, give up hjdrogen below the hydrogen-to-metal ratio of 0.9 

 only with difficulty, and absorb and release hydrogen more readily in 

 the presence of catalysts, pure vanadium, niobium, and tantalum are not 

 considered suitable for hydrogen storage applications. 



Summary. No pure metal appears completely suitable for the 

 hydrogen storage applications under consideration. The pure 

 met'ls are either too stable, or they don't hold enough 

 hydrogen; they are either not widely available and thus cost 

 a great deal, or they react too slowly with hydrogen. On 

 the other hand, as described in the next section, some 

 intermetallic compounds have recently been discovered which 

 absorb and release hydrogen very easily, are not very 

 expensive, and are widely available. 



Hydrides of Int'irmetallic Compounds 



In recent years many intermetallic compounds have been tested to 

 determine their hydrogen storage capabilities. As mentioned earlier 

 this search has been rewarded by the discovery of several satisfactory 



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