Etude du rôle de la microstructure sur les propriétés électromagnétiques du fer ex-carbonyle

Abstract
Thermal decomposition of pentacarbonyl iron is known to produce spherical micronic iron particles. By this process, special microstructure, called "onion skin structure", is obtained. We try to correlate this structure with powder composition especially with the impurities (such as carbon, nitrogen and oxygen) which have been introduced during the elaboration process. Then, the influence of this onion skin structure on the electromagnetic properties of iron carbonyl powder has been investigated. Thermal annealings have been carried out at various temperatures under different atmospheres (hydrogen, argon) and the induced effects on microstructure and impurities contents have been studied. 300°C annealing in flowing H₂ resulted in a sensible growth of cristallites, as shown by XRD and MET studies, and 450°C annealing in a complete disappearance of the onion skin structure. Concerning microwaves properties, annealed samples exhibited a lower resonance frequency and a lower intrinsic permeability, deduced from effective medium approximation. These samples were compared to non carbonyl iron powders so as to explain this behaviour.