Mechanosynthesis of Nanophase Powders
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Among the different processes able to produce nanocrystalline powders in bulk quantities, mechanosynthesis, i.e., the synthesis of nanograined powders by means of mechanical activation, is one of the most interesting from an industrial point of view. Mechanosynthesis of nanophase powders is one of the less sophisticated technologies—and, in such a sense, also the most inexpensive—to produce nanophase powders; in fact, it exploits devices and processes that have many aspects in common with mixing, fine grinding, and comminution of materials. However, it does have interest for applications, as, in principle, this is a very low cost process and its potential for industrial applications is very significant. This article describes the basis of the process, some possible applications and perspectives of mechanosynthesized nanophase powders, and some simple ideas that are able to depict part of the process, with a specific mind to the mechanosynthesis of nanocrystalline materials starting from elemental powder precursors. Mechanosynthesis belongs to the family of process technologies known as mechanical alloying, which are basically using the same or very similar apparatuses, i.e., milling or size reduction devices, which could be generally described as ball mills. A recent thorough analysis by Suranarayana of the processes related to mechanical alloying defines mechanosynthesis as a mechanochemical synthesis, attributing most of the research work in this field of mechanical alloying to Dodd and McCormick, Takacs, and Matteazzi et al.; it is also necessary to quote the fundamental and pioneering work of Butyagin and Urakaev and Boldyrev and some important developments by Calka and Wexler. While, because of many different process parameters and conditions, a complete modeling of the mechanical alloying process and mechanosynthesis of nanophase materials would be an aim very difficult to reach, it is useful to identify the operating principle of the most common devices employed for the process, along with some kinematic aspects, some specific mechanical considerations, and thermodynamic and kinetic issues of the process as well. Finally, current production of mechanosynthesized powders and perspectives will be briefly discussed.