Silicone-encapsulated carbonyl iron filler for corrosion-resistant electromagnetic shielding

Carbonyl iron (CI) powder (CIP) is highly considered for use as a microwave absorber because of the high activity as well as the high magnetic permeability and saturation magnetization; yet, CIP is vulnerable to corrosion and aging in harsh conditions, such as salty and humid (e.g. ocean) or acidic environments, which limit the spectrum of its applications. The coatings can efficiently solve this problem. This study presents a novel simple approach for enhancing the electromagnetic wave absorption ability and the corrosion resistance of CI, which involves PDMS (polydimethylsiloxane) coating on the surface of CI particles using glycine (G) as a grafting agent. The properties of the resultant composite powder (G-CI/PDMS), such as thermal stability, corrosion resistance, hydrophobicity, and electromagnetic absorption, were determined. The thermal stability, hydrophobicity, and corrosion resistance of the G-CI/PDMS were enhanced, compared to CIP, ascribed to the barrier effect of PDMS. The electromagnetic parameters were reduced, but its electromagnetic wave absorption capacity was improved at specific frequencies and absorber thicknesses due to impedance matching. The polarization curves showed that the corrosion potential of the G-CI/PDMS was shifted to the positive direction and the corrosion current decreased by two orders of magnitude, compared to CIP.