Mechanical and dielectric properties of short carbon fiber reinforced Al₂O₃ composites with MgO additive

A series of short-carbon-fiber/Al₂O₃ composites with MgO as sintering additive were fabricated by pressureless sintering process. The effects of short carbon fiber (C_sf) content on the mechanical, dielectric and microwave absorbing properties of the composite were investigated. The results show that the addition of MgO enhances the density, hardness and the flexural strength of the alumina ceramic. However, these mechanical properties of the C_sf/Al₂O₃-MgO composite decrease with increasing C_sf content. Both the real and imaginary parts of the complex permittivity increase with increasing C _sf content in the frequency range of 8.2-12.4 GHz, which is attributed to the increasing electron polarization and associated polarization relaxation, respectively. When the C_sf content is 0.3 wt%, the reflection loss less than -10 dB and the minimum value of -27 dB are obtained with the coating thickness being 1.4 mm. The results indicate that the C _sf/Al₂O₃ with MgO is an excellent candidate for microwave absorbing material with favorable mechanical property.