Pure carbon microwave absorbers from anion-exchange resin pyrolysis

A series of carbon materials [CF-x (where x denotes carbonization temperature)] have been prepared by pyrolysis of an anion-exchange resin at different temperatures (500–700 °C). X-ray diffraction and Raman spectroscopy suggest the presence of tiny crystalline domains in these materials, whose content is strongly determined by carbonization temperature. The microwave absorption of these materials is examined in the frequency range of 2–18 GHz, and it is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, CF-600 exhibits the best microwave absorbing ability with a maximum reflection loss of −20.6 dB at 16 GHz, and a bandwidth exceeding −10 dB in the range 13.5–18 GHz. It is concluded that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of CF-600. Furthermore, a reflection loss exceeding −10 dB can be obtained in the range of 7–18 GHz by manipulating the thickness from 2 to 3.5 mm, and the maximum can reach −37.0 dB at 10.8 GHz with a thickness of 2.8 mm. These materials may be used as light-weight and highly effective microwave absorbers over a wide frequency range.