From Polymer‐Continuous to Particle‐Continuous: Coupled Acoustic–Dielectric Behavior of Al ₂ O ₃ /Epoxy Composites for Gas Insulated Switchgear Applications

Al ₂ O ₃ /epoxy resin acoustic composite materials for potential applications in extra‐high voltage insulation were prepared with epoxy resin as the matrix and Al ₂ O ₃ as the filler. The effects of the Al ₂ O ₃ content on the sound propagation characteristics and dielectric properties of the composites were investigated. Composites containing 0, 20, 40, and 60 wt.% Al ₂ O ₃ were characterized by scanning electron microscopy (SEM), density/porosity measurements, 0.5 MHz pulse–echo ultrasonic testing, and dielectric spectroscopy. SEM observations reveal a transition from a polymer‐continuous epoxy matrix at low filler loadings to a particle‐dominated Al ₂ O ₃ framework at 60 wt.%, with isolated pores confined within the ceramic network. With increasing Al ₂ O ₃ content, the longitudinal wave velocity and acoustic impedance increase, whereas the 0.5 MHz attenuation coefficient decreases, indicating improved acoustic transmission in the highly filled composites. Dielectric measurements show that the real permittivity increases and the dielectric loss (tan δ ) decreases with filler loading; moreover, the loss peak in the 60 wt.% composite becomes broader and shifts slightly to higher temperature, suggesting more constrained polarization processes. These results indicate that a particle‐continuous Al ₂ O ₃ /epoxy architecture can simultaneously provide favorable acoustic and dielectric performance for gas insulated switchgear (GIS) basin‐insulator applications.