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Combustion synthesis and dielectric properties of B4C/Al2O3/CNTs composite powders Donghai Ding1,* Jiyuan Luo1 1

, Bing Bai1, Guoqing Xiao1, Xing Chen1, Kaidi Li1, Xiaochuan Chong1, and

College of Materials Science and Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China

Received: 15 July 2020

ABSTRACT

Accepted: 9 September 2020

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, aAl2O3, and residual CNTs. The better crystallinity B4C particles had a grain size about 0.5–1.0 lm 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 e and dielectric loss tand have a growing tendency with the increase of the CNTs. The dielectric real part (e0 ) and the loss tangent (tand) 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 e0 and tand increased with the increase of the CS-2, while the impedance matching ratio decreased.

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Springer Science+Business

Media, LLC, part of Springer Nature 2020

1 Introduction Microwave absorbing materials can dissipate the incident electromagnetic wave (EMW) and convert microwave into heat energy by magnetic or dielectric loss [1], and have received extensive attention over the last decades due to their excellent performance in the radar stealth technology. The stealth technology have imposed requirements on microwave absorbing materials such as thin thickness, wide effect

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https://doi.org/10.1007/s10854-020-04471-8

absorption bandwidth, low density, and strong absorption capacity [2]. Some new equipment such as hypersonic vehicles need absorbing materials which can work in harsh condition, for instance, high temperature and oxidation atmosphere. In recent years, carbon-based composites have attracted considerable attention as EMW absorbing materials. As we know, carbon materials have high electrical conductivity and strong reflection to the EMW. Therefore, it is necessary to improve their impedance matching

J Mater Sci: Mater Electron

property when they are used as microwave absorbing materials. However, the carbon materials can be oxidized at 370 °C, and the oxidation rate is significantly increased at 500 °C. Carbon nanotubes (CNTs) are one of the most important carbon materials, which can be used as a high-efficient microwave absorbers due to their special properti