Temperature-dependent electromagnetic shielding properties of SiCf/BN/SiC composites fabricated by chemical vapor infiltration process

The SiCf/SiC composites with BN interphase were prepared by chemical vapor infiltration (CVI) process for electromagnetic interference (EMI) shielding applications at the temperatures from 25 degrees C to 700 degrees C in X band. The results reveal that the flexural strength of CVI-SiCf/BN/SiC composites can be up to 289 MPa, which shows an excellent mechanical property. Owing to the excess carbon and thermal excitation of SiC materials, both the complex permittivities and electrical conductivities of the composites increase with the increasing temperatures. Consequently, the composites show poor microwave absorption properties at various temperatures due to the impedance mismatch between the composites and free space. However, the absorption, reflection and total shielding effectiveness of the composites are improved from 9.0 dB, 4.5 dB and 13.5 dBe13.5 dB, 9.0 dB and 22.0 dB as the temperature increases to 700 degrees C. The mechanisms for the evolutions of complex permittivities and EMI shielding properties with the rising temperatures are also proposed. (C) 2017 Elsevier B.V. All rights reserved.