Inert Gas Condensation Method

Inert Gas Condensation Method:

The inert gas evaporation–condensation (IGC) technique, in which nanoparticles are formed via the evaporation of a metallic source in an inert gas, has been widely used in the synthesis of ultrafine metal particles since the 1930s.

A similar method has been used in the manufacture of carbon black, an ink pigment, since ancient times. The technique employed now for the formation of nanopowders, in reality, differs from that used to produce carbon and lampblack primarily in the choice of atmospheric composition and pressure and in the use of a chemically reactive source.

Thus, although the technology is old, the application to the production of truly nanoscaled powders is relatively recent.

 

In its basic form, the method consists of evaporating a metallic source, using resistive heating (although radio frequency heating or use of an electron or laser beam as the heating source are all equally effective methods) inside a chamber which has been previously evacuated to about 10 power -7 torr and backfilled with inert gas to a low pressure.

The metal vapour migrates from the hot source into the cooler inert gas by a combination of convective flow and diffusion and the evaporated atoms collide with the gas atoms within the chamber, thus losing kinetic energy. Ultimately, the particles are collected for subsequent consolidation, usually by deposition on a cold surface.

Most applications of the inert gas condensation technique carry this approach to extremes by cooling the substrate with liquid nitrogen to enhance the deposition efficiency.

Particles collected in this manner are highly concentrated on the deposition substrate. While the particles deposited on the substrate have complex aggregate morphology, the structure tends to be classified in terms of the size of the crystallites that make up these larger structures.

The scraping and compaction processes take place within the clean environment to ensure powder surface cleanliness (i.e., to reduce oxide formation) and to minimise problems associated with trapped gas.