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

Iron(III) oxide ultrafine powders have been synthesized by laser-induc ed 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 sensitiz er. The optimum experimental conditions were presented. A single laser pulse can initiate an explosive reaction provided that the total Fe(C O)(5)-O-2 pressure exceeds 5 kPa and the O-2-Fe(CO)(5) partial pressur e ratio is greater than or equal to 1. The reaction results in the com plete disappearance of iron carbonyl and the energy consumption is ver y low compared with the conventional chemical process. The maximum qua ntum efficiency is ca. 10(2), suggesting that the explosive reaction m ay proceed according to a chain reaction mechanism. The relationships between the total pressure and the quantum efficiency and laser fluenc e threshold were both derived. IR, XRD, TEM and XPS were used to chara cterize the powders. The experimental results showed that the powders consisted of both crystalline gamma-Fe2O3 and amorphous Fe2O3. The for mer phase is 50-100 nm in diameter while the latter is 5-12 nm in diam eter. This is the first time that crystalline gamma-Fe2O3 prepared in this way has been found to be present as regular polyhedra and not sph erical particles.