Metallic Nanopowders: An Overview
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It is now widely recognized that the fundamental properties of materials strongly depend on the size of crystallites, especially if they are in the nanometer regime. Most of the physical, optical, and electronic properties of a bulk solid vary when the crystallites are in the nanoscale regime. If the grain size can be maintained at nanoscale dimensions, this creates major opportunities to design advanced materials with enhanced properties.
The emerging nanometals industry encompasses nanoparticles, nanolayers, thin films, nanofibers, and bulk nano-structured metals and alloys. This chapter focuses on metal nanoparticles, their properties and uses, with special emphasis on those manufactured by the electroexplosion of metal wire (EEW), a process that is the most commercialized and has produced the greatest diversity of metal nanopowders.
Nanometals are in the process of becoming one of the major feedstocks for a host of emerging technologies and industries. The body of knowledge on nanosize particles has grown throughout the latter part of the twentieth century as various processes for producing them were developed. With the exception of precious metals, most of the focus has been on ceramics and nonmetallic materials. More recently, there has been an increasing interest in other metallic nanoparticles. Handling them is problematic because they are highly reactive and difficult to produce, handle, and ship.
Nanosize precious metals have already had a long history of development and use as catalysts and in photography because of their chemical stability in water and air. Precious metal catalysts in a ceramic matrix, as in automotive catalysts, or dispersed homogeneously in media have had a profound affect on industrial processes. The increasing availability of other nanosize metals should lead to a plethora of new applications from composites to chemicals.