Thermal formation mechanism and size control of spherical hematite nanoparticles

Hematite nanoparticles were prepared by a FeCl2 solution. The whole thermal formation mechanism as well as the size and dispersity control of hematite nanoparticles was studied. It has been found that goethite nanoparticles were firstly produced through the mix and oxidation of 0.5 M ferrous salt and 2.1 M bicarbonate and then hematite nanoparticles were obtained directly by thermal transformation of the goethite samples. At higher temperatures, nanopores were observed in the goethite nanocrystals and then merged into slits due to the high water pressure in the nanopores. The morphology of hematite particles with regular texture was changed due to recrystallization and then spherical nanoparticles were formed in the end. The particle size and dispersity of hematite nanoparticles could be controlled by different charging rates. From the second particle size distribution diagrams measured by the laser dynamic scatter method, not only the hematite particle size became small but also the dispersity of hematite nanoparticles was improved as the charging rate increased. (C) 2004 Elsevier B.V. All rights reserved.