Metal vapor synthesis, large scale

As more sophisticated metal hydrides are developed (nanocrystalline, multicomponent systems, composites and nanocomposites, graphite/metals or similar hybrid systems, clusters, etc.), it is important to be a vare that, for practical applications, a large volume of material should be processed in a fast, inexpensive and reliable vay, for example casting. Techniques such as cold vapor deposition may be impossible to scale up but this does not mean they should be discarded as a means of studying new metal hydrides. On the contrary, laboratory techniques allow much better control of the end product and permit the elaboration of new compounds. Once an attractive compound is found then another challenge w ill have to be faced scaling up the synthesis. In this respect, it is important for the community of metal hydrides researchers to also study large-scale production techniques in order to make the transition from laboratory to industrial scale easier. 

The catalytic decomposition of carbon-contaming compounds is an extensively investigated method, also known as catalytic chemical vapor deposition (CCVD). One of the advantages of this method is the potential for large-scale production at a lower energy consumption and overall cost than with other methods. The CCVD method is essentially the same as that used for a long time in the synthesis of other filamentous forms of carbon, such as nanofibers or fibrils. The CCVD method involves the catalytic decomposition of hydrocarbons or carbon monoxide on transition metal particles. The major difference with those processes that produce nanofibers is in the structure of the catalyst. To produce SWNT, the size of the metal cluster needs to be very small. Therefore, the success of a CCVD method lies in the design of the catalyst. 

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