Dielectric spectroscopy on alumina-epoxy composites towards the quantification of filler-particulate microstructure effects

Cylindrical ingots of epoxy resin composites containing alumina of various microstructure particulates were prepared and their dielectric properties were investigated by the parallel capacitance method in the frequency range 20 Hz - 1 MHz, as a function of depth below the surface. Nano-porous (90 Å), or non-porous alumina particulates, with sizes varying from 63 to 200 μm, were mixed as composite fillers at various contents (up to 5% wt). Sample-wafers were extracted from the cylindrical ingots to investigate the porosity induced effects on particulate mixing, dispersibility, precipitation, and relate filler concentration to the electrical response observed at various depths. According to the experimental results, the nano-pore induced effects dominate and reduce the effective relative dielectric constant compared to the non-porous alumina, while the dissipation factor values remain unaffected. Finally, the presence of nano-pores in the alumina particulates induces particle stratification effects and the filler particles with increased pore concentrations become stratified within the upper layer of the molded material.