Silica-Coated Iron Microflakes (Fe/SiO2)-Based Elastomeric Composites as Thin Microwave Absorber

Abstract

Thin flexible microwave absorbers are highlighted as current research focus not only for lightweight but also for their easy applicability on the surface of complex geometries. In order to achieve it, we prepared iron microflakes of planar size in the range of 5–15 $\mu \text{m}$ with the thickness of 1–2 $\mu \text{m}$ , and thereafter, silica coating has been provided on surface of flakes by utilizing modified Stobers method to improve the oxidation resistance. The silica coating on surface of iron microfalkes has been established through different techniques, namely, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Rubber-based composites are prepared at different Fe at SiO2 loading fractions [40–70 parts per hundred (PHR)] in nitrile butadiene rubber (NBR) and their electromagnetic properties are investigated. The 70 PHR Fe at SiO2/NBR composite showed more than 90% microwave absorption [reflection loss (RL) > 10 dB] over 10.5–16.5 GHz at absorber thickness of ~1.2 mm and also showed tunable RL of more than 10 dB with variation of thickness from 1 to 2.0 mm within 4–18 GHz. Furthermore, Fe at SiO2 microflakes exhibited better microwave-absorption performance in comparison to uncoated Fe microflakes in the rubber composite, which may be due to improved impedance matching.