pyrolytic synthesis of nanopowders
otherwise
nanopowder synthesis by pyrolysis
(rus. пиролитическое получение нанопорошков)
—
synthesis of nanopowders of metals, alloys or chemical compounds (oxides, borides, nitrides, carbides) by thermal decomposition of heteroorganic and metal-organic compounds, hydroxides, carbonyls, formiates, nitrates, oxalates, amides, imides and other compounds that break down at a certain temperature, producing the synthesised substance and gas.
Description
One of the common methods of pyrolytic synthesis of nanopowders is aerosol spray pyrolysis.
Another pyrolysis technique is the decomposition of metal-organic compounds in an impact tube, followed by the condensation of free metal atoms from supersaturated vapour. A long steel tube capped on both ends is separated into two sections of unequal length by a thin membrane made from a film of foil. The shorter section is filled with argon containing 0.1 to 2.0 mol % of a metal-organic compound to the pressure of 1,000 to 2,500 Pa. The other section is filled with helium or a helium and nitrogen mix until the membrane breaks. The breakage of the membrane is followed by an impact wave, with the temperature reaching 1000-2000 K at the wave front. Shock-wave heating of gas causes the decomposition of the metal-organic compound in several microseconds and the formation of a supersaturated vapour that can quickly condense.
The major shortcoming of thermal decomposition is the poor selectivity of the process, while the reaction product is usually a mix of the target product with other compounds. The mean grain size of powders synthesised by pyrolysis depends on the nature of the precursors, and may be between 50 and 300 nm.
Another pyrolysis technique is the decomposition of metal-organic compounds in an impact tube, followed by the condensation of free metal atoms from supersaturated vapour. A long steel tube capped on both ends is separated into two sections of unequal length by a thin membrane made from a film of foil. The shorter section is filled with argon containing 0.1 to 2.0 mol % of a metal-organic compound to the pressure of 1,000 to 2,500 Pa. The other section is filled with helium or a helium and nitrogen mix until the membrane breaks. The breakage of the membrane is followed by an impact wave, with the temperature reaching 1000-2000 K at the wave front. Shock-wave heating of gas causes the decomposition of the metal-organic compound in several microseconds and the formation of a supersaturated vapour that can quickly condense.
The major shortcoming of thermal decomposition is the poor selectivity of the process, while the reaction product is usually a mix of the target product with other compounds. The mean grain size of powders synthesised by pyrolysis depends on the nature of the precursors, and may be between 50 and 300 nm.
Author
- Gusev Alexander I.
Sources
- Gusev A. I. Nanomaterials, Nanostructures, and Nanotechnologies (in Russian) // Fizmatlit, Moscow (2007) - 416 pp.
- Gusev A. I., Rempel A. A. Nanocrystalline Materials. — Cambridge: Cambridge International Science Publishing, 2004. — 351 p.