Amorphous alloys hydrogen embrittlement

Inspection of this list suggests that amorphous metallic alloys satisfy many of these criteria. This is partially true. Amorphous materials are a possible choice in some applications, and this list is growing with the advent of bulk metallic glasses. However, in many cases where conventional crystalline alloys must serve as the best available choice, they are either unavailable in the product form needed or lack some other desired properties. A slightly different set of attributes might be desired for resistance of hydrogen embrittlement. 

As already said, the power equation was used, for example, by Itoh et al. (1998) in determining the Hj permeability in amorphous alloys, at elevated temperatures up to 390°C. It should also be added that the main conclusions of their work were (a) H2 permeability strongly depends on the Si content and increases with it (b) the amorphous alloy shows higher hydrogen permeability than the crystallized one and shows resistance to hydrogen embrittlement and (c) the amorphous membrane must be used below its crystallization temperature, due to the strong reduction of Hj permeability in the crystallization state. 

In the case of metallic systems, there were early indications that metallic glasses and disordered alloys may be more corrosion resistant, less susceptible to embrittlement by hydrogen and have a higher hydrogen mobility than ordered metals or intermetallics. All of these properties are desirable for hydrogen storage. Subsequent research has shown that thermodynamic instability is a severe problem in many amorphous metal hydrides. The present ASI has provided an appropriate forum to focus on these issues. 

The metal alloys studied for hydrogen separation usually have either a binary or ternary composition. In particular, alloys from the highly permeable groups IV and V are used to reduce the susceptibility to hydride formation and increase the resistance to H2 embrittlement, while alloying with Cu, Ni, Ag or Fe usually reduces surface susceptibility and subsequent surface contamination. Moreover, due to the compositional flexibility of metal alloys (and amorphous metals), it is possible to increase the catalytic surface activity in order to enhance H2-surface interactions. Because of their relatively high Hj permeability and low cost, most of the alloys considered for Hj-separation are Nb-, V- and Ni-based Table 4.6 summarizes the permeability data of these alloys. 

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