ISSN:
1434-6079
Keywords:
75.60.J
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract In the preparation of ultrafine metal particles (Cu, Ti, Ni or Al) by opposed-targets dc sputtering, a substrate cooled by liquid helium flow was used, on which the metal clusters and argon atoms were condensed simultaneously, forming a solid layer of the mixture. By raising the temperature of the substrate and the argon pressure in the chamber, the solid argon melts and evaporates, remaining the metal-particle aggregates. After complete evaporation of the argon, a phenomenon was observed in which the metal-particle aggregates shrank and suddenly changed their colour from black to bulk-metal colour, followed by an explosion-like noise. We offer an explanation for this phenomenon by the mechanism of spontaneous coalescence due to the large surface energy of the ultrafine particles. From our observation and analysis, we conclude that a certain particle size exists, below which the spontaneous coalescence may occur in a very fast way, leading to melting of the particles. The fast process of coalescence, melting and cooling introduces large internal stress which splits the sintered particle, giving the explosion-like noise. This phenomenon may imply a size limitation in forming nanocrystalline solid materials of pure metals.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01543994
Permalink