ROLE OF THE MICROSTRUCTURE ON ELECTROMAGNETIC PROPERTIES OF IRON EX-CARBONYL

Thermal decomposition of pentacarbonyl iron is known to produce spheri cal 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 (suc h as carbon, nitrogen and oxygen) which have been introduced during th e elaboration process. Then, the influence of this onion skin structur e on the electromagnetic properties of iron carbonyl powder has been i nvestigated. Thermal annealings have been carried out at various tempe ratures under different atmospheres (hydrogen,argon) and the induced e ffects on microstructure and impurities contents have been studied. 30 0-degrees-C annealing in flowing H-2 resulted in a sensible growth of cristallites, as shown by XRD and MET studies, and 450-degrees-C annea ling in a complete disappearance of the onion skin structure. Concerni ng microwaves properties,annealed samples exhibited a lower resonance frequency and a lower intrinsic permeability, deduced from effective m edium approximation. These samples were compared to non carbonyl iron powders so as to explain this behaviour.