Hydrogen metallic character

Table 5.2. Structures of a few selected hydrogen-metal compounds. The formulae very often have only an indicative character. Solid solution ranges are frequently observed.

It is unique because of its powerful hydrogen bonding character and its distinct polarity. However, in fuel systems, these characteristics of water make it a source of a variety of problems. Corrosion of metal fuel system components, emulsification with fuel performance additives, and ice formation in fuel lines are some of the problems directly related to the presence of water in fuel. 

Because of their diverse structure, one-third of the tubes are expected to possess metallic character and the remaining two-thirds to behave as semiconductors [2, 3]. CNTs represent potential candidates to be used in field emission [4-6] and nanoelectrical devices [6-10], components of electrochemical energy [11, 12] and hydrogen storage systems [13, 14] and as components in composite materials [15-17]. They represent the ultimate carbon fiber, exhibiting exceptional mechanical properties [18-21] by being up to 100 times stronger than steel [22]. 

It is mentioned in Section 13.4.2 that chemisorption of carbon monoxide or hydrogen from the gas phase, or adsorption of CO by electrochemical methods, does not change the metallic character of the surface of the platinum particles, since there... 

Fig, 6.7. a Site time yield in the processes described in the figure as a function of radius of the metal cluster involved in the catalytic processes. No particle size effect is observed down to small clusters, b Particle size effect for Pt clusters dispersed on Si02 in the recombination reaction of oxygen and hydrogen, c Particle size effect for Fe clusters dispersed on MgO for the ammonia synthesis at atmospheric pressure and 570° K. d Relationship between catalytic activity, dispersion of the metal cluster on support and bulk metal character of the cluster for metals of the group VIII... 

Attempts to impart metallic character to solid H2 have so far been unsuccessful. Under extremely high pressures, H2 (normally a non-polar molecule) undergoes a redistribution of electronic charge such that the ionic contribution to the bonding (represented by the resonance form H" -H ) becomes important. This remarkable finding may go some way to helping to explain why attempts to form metallic hydrogen in the solid state have not met with success. 

It is not very difficult to use this picture in explaining the dehydrogenation on semiconductors like ZnO, the hydrogenation activity of which is commonly attributed to the presence of interstitials (Zn or Zn+) with a metallic character, and the occurrence of Zn-H bonds on which has been definitely shown by Eischens et al. (97). 

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