Combustion synthesis and dielectric properties of B4C/Al2O3/CNTs composite powders

To develop a novel high-temperature microwave absorber, B4C/Al2O3/CNTs composite powders were prepared by a combustion synthesis method. The experiment results show that the products are mainly composed by B4C, α-Al2O3, and residual CNTs. The better crystallinity B4C particles had a grain size about 0.5–1.0 μm and embedded in the Al2O3 matrix, while the CNTs cracked and dispersed in the composite powders. The results of combustion synthesis process illustrated that as CNTs increase, the product zone decreased, and the combustion temperature (Tc), the adiabatic combustion temperature (Tad), and the combustion wave velocity (VC) decreased. The dielectric permittivity of prepared composite powders has been determined in the X band. The results show that the dielectric real part ε´ and dielectric loss tanδ have a growing tendency with the increase of the CNTs. The dielectric real part (ε′) and the loss tangent (tanδ) reached the highest, when the molar excess coefficient of CNTs was 0.2 (CS-2). The different mass ratios of CS-2 and paraffin binder were combined to test their dielectric properties. The results show that both ε′ and tanδ increased with the increase of the CS-2, while the impedance matching ratio decreased.