Abstract: Microwave absorbing properties of the carbonyl iron particles filled epoxy-silicone resin coatings showed visible degression when the coatings were heat treated at 300°C with different time. The complex permittivity and permeability of the coatings before and after heat treatment were measured. After heat treatment at 300°C, the real part of permittivity of the coatings increased with increasing treatment time and showed frequency dependence dielectric response. The complex permeability showed remarkable variation while the resonance frequency of the coatings heat treated at 300°C shifted from 7 to 12 GHz. The electromagnetic results indicated that microwave absorbing properties of the coatings showed more dependent on the complex permeability. The results showed that the difference of the electromagnetic and microwave absorbing properties before and after heat treatment was mainly attributed to the crystalline state transition of carbonyl iron particles.

Key words: Microwave absorption, Dielectric properties, Magnetic properties, Heat treatment