Preparation and Microwave Properties of Silica Coated Ni–Fe–Mo Flakes Composites

Fabrication of silica coated permalloy-like flaky particles and microwave properties of uncoated and coated particles dispersed in a polymer matrix are presented. The silica layer is successfully obtained through the Stöber process and its thickness is about 50 nm. Permeability and permittivity measurements are carried out using an APC7 coaxial line. It is demonstrated that composites with an insulating layer exhibit the same permeability levels as the ones filled with uncoated permalloy-like flakes but lower permittivity levels which improves its impedance matching and thus enhances its microwave absorbing properties. Calculated reflection loss of 1 mm composite layer shows that peak frequencies are shifted to higher frequencies while their intensities are slightly increased when composites are filled with coated flaky particles (-4.26 dB at 1.89 GHz for the uncoated flakes and -4.53 dB at 2.57 GHz for the coated ones at the same volume content of 21%). Composites filled with higher volume contents are expected to be promising candidates as absorbing materials above the GHz range.