Molecularly Designed Ultrafine/Nanostructured Materials. Materials ResearchSociety Symposium Proceedings Held in San Francisco, California on April 4-8, 1994. Volume 351

摘要

Nanostructured materials are usually defined as having some length scale smallerthan 100 nm in at least one dimension. An important subset of this group of materials is powders with particle size less than 100 nm, and polycrystalline materials, made by consolidating these powders in such a way as to retain a grain size below this limit. The choice of 100 nm stems from the fact that many physical, optical, and magnetic properties have characteristic lengths in this range. As grain or particle size is reduced below this characteristic length, the properties associated with these phenomena are radically altered. A frequently cited example is the freezing out of mechanisms for generating glissile dislocations. Another reason for expecting remarkable properties in nanostructured polycrystalline materials is the very high proportion of atoms at, or near, grain boundaries (as high as fifty percent or greater for grain sizes below five or ten nanometers). This leads, for example, to very rapid diffusion coupled with very short diffusion distances.