Correlation between the microstructure and the electromagnetic properties of carbonyl iron filled polymer composites

Electromagnetic properties of polymer composites based on different types of carbonyl iron (CI) are investigated in the frequency range from 1 MHz to 10 GHz. A significant difference in the high frequency permeability of composites filled with primary and processed CI powders is revealed, although the chemical composition and particle size distribution of these powders show small difference. Composites based on processed CI exhibit two regions of magnetic dispersion and higher absolute values of permeability and permittivity in the radio-frequency (RF) band. The observed differences are attributed to the microstructure of particles; namely, these differences depend on whether or not the particles are characterized by “onionlike” multilayered morphology. Electron microscopy and X-ray diffraction analyses show structural changes in the processed CI, which are responsible for the variety of electromagnetic properties of the composites.