Li Shuai 1, 2, Xie Pengyuan 1, 2, Jia Yujun 1, 2
(1. Institute of Carbon Matrix Composites, Henan Academy of Sciences, Zhengzhou 450046, Henan, China; 2. School of Materials
Science and Engineering, Henan University of Science and Technology, Luoyang, 471023, Henan, China)
Extended abstract:
[Background and purposes] With the development of radar detection technology, electromagnetic wave absorbing materials have become important for defence stealth and civil electromagnetic protection. Ceramic-based absorbing materials are ideal candidates for hypersonic vehicles and high-temperature environments, due to their high-temperature resistance, oxidation resistance, and strong mechanical properties. However, traditional absorbing ceramics often suffer from narrow absorption bandwidth and large matching thickness. As a highly conductive ceramic, ZrC exhibits high dielectric loss, but when used alone, it is prone to impedance mismatch, leading to strong surface reflection. Yttria-stabilized zirconia (YSZ) has low dielectric loss and high thermochemical stability, thus being able to serve as a matrix material to adjust electromagnetic parameters of the composite. This study was aimed to prepare ZrC-YSZ composite ceramics by using pressureless sintering, focusing on the effects of ZrC content and sintering temperature on microstructure, dielectric properties and microwave absorption performance, in order to achieve broadband and efficient absorption at low thickness.
[Methods] ZrC powder and YSZ powder were used as raw materials. Different mass fractions of ZrC (10%, 20%, 30%) were ball-milled, dried and sieved. The mixtures were then pressureless-sintered at 1400 ℃ and 1500 ℃ for 2 h to prepare ZrC-YSZ composite ceramics. Phase composition and microstructure were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex permittivity and reflection loss (RL) of the composite ceramics were measured using a vector network analyzer in the frequency range of 8–18 GHz. The effective absorption bandwidth (EAB, RL≤−10 dB) and minimum reflection loss (RLmin) at different thicknesses were calculated based on transmission line theory.
[Results] In this work, ZrC-YSZ composite ceramics with different ZrC contents were prepared by pressureless sintering, and the evolution of their dielectric properties as a function of sintering temperature was investigated. The complex permittivity increased with increasing ZrC content. At a ZrC content of 30 wt.%, the composite ceramics exhibited excellent broadband EMW absorption. At a thickness of only 1.5 mm, the samples sintered at 1400 and 1500 ℃ achieved EAB of 9.55 and 8.6 GHz, respectively, in the 8–18 GHz range. This superior absorption performance is attributed to the synergistic coupling effect among conductive loss, interfacial polarization relaxation, and impedance matching optimization induced by high porosity.
[Conclusions] By adjusting the content of ZrC (30 wt.%) and sintering temperature (1400–1500 ℃), ZrC-YSZ composite ceramics were successfully prepared by using pressureless sintering. The composite ceramics achieve broadband (EAB≥8.6 GHz) and high-intensity (RLmin≤−43.3 dB) electromagnetic wave absorption at a low thickness of 1.5 mm. Among them, the sample sintered at 1500 ℃ exhibits higher loss in the X-band. It is demonstrated that ZrC-YSZ composite ceramics are promising lightweight thin-layered absorbing materials for broadband stealth applications in high-temperature environments.
Key words: composite ceramics; pressureless sintering; electromagnetic wave absorption; conductive network; interfacial polarization