PREPARATION AND PROPERTIES OF NANOCRYSTALLINE POWDERS OBTAINED BY CRYOGENIC MELTING

Authors
Citation
J. Bigot, PREPARATION AND PROPERTIES OF NANOCRYSTALLINE POWDERS OBTAINED BY CRYOGENIC MELTING, Annales de chimie, 18(5-6), 1993, pp. 369-378
Citations number
23
Categorie Soggetti
Chemistry,"Material Science
Journal title
ISSN journal
01519107
Volume
18
Issue
5-6
Year of publication
1993
Pages
369 - 378
Database
ISI
SICI code
0151-9107(1993)18:5-6<369:PAPONP>2.0.ZU;2-7
Abstract
We have produced nanocrystalline powders from iron, nickel, cobalt and alloys, by fusion in a cryogenic medium. The use of refractory crucib les being incompatible with the temperatures required we have used ele ctromagnetic levitation. This process enables these metals to be broug ht up to around 2000-degrees-C, and to obtain a powder production of s everal grammes per minute. We have studied the parameters acting on th e average particle diameter: temperature, height and nature of the cry ogenic medium. The powders obtained are characterized by X-rays and Tr ansmission Electron Microscopy. Their crystalline structure is compara ble to that of powders obtained by conventional evaporation-condensati on methods. We have also studied the compaction of powders obtained as a function of pressure. The maximum relative density of the iron powd ers was of 0.7 for a pressure of 2.56 GPa which is far less than that obtained with micrometric powders under identical conditions. The sint ering of powders starts from 160-degrees-C with a very large shrinkage .