ultradisperse (rus. ультрадисперсный) — 1) ultradisperse are the systems that contain particles of submicron scale, particularly, nanoscale; 2) in today’s metal powder industry, the microstructure of alloys shall be ultradisperse if the grain size ranges from 200 to 500 nm.

Description

Ultradisperse systems typically have a significant amount of atoms on the surface (up to tens of percent) and that percentage grows higher as the dispersion goes up. Due to the size effect, ultradisperse materials can have a unique combination of chemical, electrical, magnetic, thermal, mechanical, sorption, radio absorption and other properties, which are extrinsic to macroscopic objects.

There have been developed a large number of methods aimed at generating ultradisperse systems allowing very fine control of the particle size, shape and structure. Those methods can be divided into two groups: dispersion-type (mechanical, thermal, electrical grinding or spraying of the macroscopic phase) and condensation-type (chemical or physical condensation). Examples of ultradisperse systems are nanopowders, many colloid systems, microemulsions, etc.

There are no strict dimensions to determine the boundary of ultradisperse systems, and various fields of knowledge mean different quantities under this concept. The two most common ways to treat the notion are given in the definition. According to the second definition, submicron materials include alloys and powders with grain (crystallite) size from 500 nm to 1.2 microns, and nano-structured materials refer to the grain size below 200 nm, whereas ultradisperse materials occupy an intermediate position between the two.

Authors

  • Smirnov Andrey V.
  • Shlyakhtin Oleg A.

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