OVERVIEW

The problem of production of ultrafine powders of metals, alloys and compounds and submicrocrystalline materials for different areas of technology, has been discussed in literature for many years now. In the last couple of decades, the interest in this subject has greatly increased because it was found (primarily, in metals) that a decrease in the size of crystals below some threshold value may result in a large change of the properties [1 16]. These effects form when the mean size of crystalline grains does not exceed 100 nm, and are most evident when the grain size is smaller than 10 nm. When examining the properties of superfine materials, it is necessary to take into account not only their structure and composition but also dispersion. Polycrystalline superfine materials with a mean grain size of 300 to 40 nm are referred to as submicrocrystalline, and those with a mean grain size of less than 40 nm as nanocrystalline. The conditional classification of materials on the basis of the size D of particles (grains) is shown in Fig. 1.1. Nanomaterials can also be classified on the basis of their geometrical form and the dimensionality of structural elements from...