Spherical glassy carbon/AlN microwave attenuating composite ceramics with high thermal conductivity and strong attenuation

High density spherical glassy carbon/aluminum nitride (GC/AlN) microwave-attenuating composite ceramics were fabricated using hot-press sintering. The effects of GC content on sintering, mechanical, thermal, electrical, dielectric, and attenuating properties were systematically investigated. Addition of GC inhibited densification and AlN grain-growth. Strength decreased monotonically with GC content up to 12 wt%, whereas the toughness increased and then decreased. The spherical morphology of GC gives the composite higher thermal conductivity and conductivity percolation-threshold compared with AlN-based composites containing non-spherical second phases. Enhanced conduction loss, polarization loss and mini-capacitor effect result in a consistently increasing dielectric constant and loss, and an increasing and then decreasing reflection loss (RL). The 6 wt% sample exhibited an RL_min of −22.21 dB and a high thermal conductivity of 70.58 W·m⁻¹ K⁻¹. This work provides a novel strategy for preparing microwave-attenuating composite with combined high thermal conductivity and strong attenuation using spherical GC attenuating agent.