Aspects of annealing and particle morphology on the microwave absorption characteristics of carbonyl iron powders

In this study, carbonyl iron powder (CIP) with an average particle size of 3–4 µm made by the thermal decomposition of iron pentacarbonyl Fe(CO)₅ was subjected to annealing in an oxidizing environment at 200–400 °C and CIP was ball-milled to transform from spherical to flake morphology. The particle morphology, oxidation state, dielectric, magnetic, and electromagnetic wave absorption characteristics were investigated. The results revealed that for the as-made CIP complex permittivity, permeability, attenuation, impedance matching, and reflection loss consistently increased from 60 to 80% weight addition in wax, whereas for the flake morphology, the subject characteristics were compromised. For the annealed CIP samples, the complex permittivity increased with increasing temperature causing enhanced polarization loss, whereas the complex permeability decreased with oxide formation. Significant improvements in impedance matching and microwave absorption performance were achieved for samples annealed at 200 and 250 °C. The as-made CIP exhibited an effective absorption bandwidth (EAB) of 6.4 GHz with a thickness of 1.5 mm, demonstrating a minimum reflection loss (RLmin) of − 32 dB. For the CIP sample annealed at 200 °C, the EAB (RL < − 10 dB) is 8.32 GHz at a thickness of 1.5 mm, whereas the 250 °C-annealed CIP presents an EAB (RL < − 10 dB) 7.94 GHz at thickness of 1.5 mm. This study presents advancements in the field of microwave absorption for practical stealth applications to reduce the radar cross-section to a thin thickness and ultrawide absorption bandwidth.