Effect of filler particle size on electric energy density of epoxy-aluminum nanocomposites

The size effect of filler particles on the dielectric properties and maximum electric energy density of epoxy-aluminum composites are evaluated. Aluminum particles encapsulated with aluminum oxide layers are used as the fillers to enhance the dielectric constant of the composite and also to maintain the breakdown strength. Experiments were conducted to evaluate the dielectric constant, dissipation factor, breakdown voltage and maximum electric energy density of the composites as a function of filler loading. Dielectric property measurements demonstrated that, for composites containing 70 nm (average particle size) aluminum the dielectric constant is increased by a factor of 7 at 18 wt% filler loading as compared with that of pure epoxy matrix. Even if there is a reduction in breakdown strength, the addition of nanoparticles resulted in potential gain in electric energy density. To analyze the size effect of filler particles on the performance of the composites, samples with a different filler size of 40 nm (APS) were prepared and dielectric properties were evaluated. It is observed that the enhancement in dielectric constant is 6 times that of pure epoxy at a lower filler concentration of 14 wt% for 40 nm (APS) filler samples. The improvement in maximum energy density is 4 times at 18 wt% filler loading and 3.5 times at 14 wt% filler loading for 70 nm (APS) and 40 nm (APS) composites respectively. Material characteristics were analyzed using Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermogravimetric (TGA) techniques.