SYNTHESIS OF IRON(III) OXIDE ULTRAFINE POWDERS BY LASER-INDUCED VAPOR-PHASE REACTION

Iron(III) oxide ultrafine powders have been synthesized by laser-induced vapour-phase reaction using an IR pulsed CO2 laser as light source and a mixture of Fe(CO)(5)-O-2 as reactant without adding any sensitizer. The optimum experimental conditions were presented. A single laser pulse can initiate an explosive reaction provided that the total Fe(CO)(5)-O-2 pressure exceeds 5 kPa and the O-2-Fe(CO)(5) partial pressure ratio is greater than or equal to 1. The reaction results in the complete disappearance of iron carbonyl and the energy consumption is very low compared with the conventional chemical process. The maximum quantum efficiency is ca. 10(2), suggesting that the explosive reaction may proceed according to a chain reaction mechanism. The relationships between the total pressure and the quantum efficiency and laser fluence threshold were both derived. IR, XRD, TEM and XPS were used to characterize the powders. The experimental results showed that the powders consisted of both crystalline gamma-Fe2O3 and amorphous Fe2O3. The former phase is 50-100 nm in diameter while the latter is 5-12 nm in diameter. This is the first time that crystalline gamma-Fe2O3 prepared in this way has been found to be present as regular polyhedra and not spherical particles.