The nano-sized carbon black (NCB) with particle sizes of 15, 25, 55 and 65 nm are added in epoxy matrix in order to investigate the impact of particle sizes on the microwave absorption properties of the nano composites. The NCB powders were characterized by X-ray diffraction and Scanning electron microscopy (SEM) for identification of impurity phases. The complex permittivity spectra were recorded for the composites in the frequency range of 8.2-12.4 GHz. The results revealed that the particle sizes had substantial impact on the electromagnetic properties. On decreasing the particle size, the complex permittivity increases first up to certain extent then decreases. Interestingly, the particle size dependent tangent loss of NCB/epoxy composites shows that 25 nm size is most suited for high loss characteristics, whereas, losses decreases with size < 25 nm, which is attributed to high surface area of the particles. In addition, NCB/epoxy composite with 25 nm particle size illustrated substantial EM absorption efficiency at a frequency of 9.5 GHz, with RL reaching −13.2 dB and reflection loss below −10 dB up to 2.5 GHz with thickness of 2.0 mm. The effect of particle sizes on the electromagnetic properties was also discussed.
Efforts to use microwaves in material processing are gradually increasing. However, the phenomenon associated with the processing is less understood. The conversion of electromagnetic energy into heat depends largely on the dielectric properties of the material being treated. Therefore, the fundamental knowledge of these properties is essential for processing of materials using microwaves. In this study, first the dielectric evolution of silicon carbide (SiC) infused epoxy nanocomposites prepared at room temperature with 0-0.3 wt% content of SiC was measured. Secondly, the dielectric properties of the prepared nanocomposites after heating for 10 min in microwaves at a power of 500 W were investigated in order to see the effect of microwave curing. The dielectric properties of all the samples were measured at the microwave frequency of 2.45 GHz using the advanced cavity perturbation method attached to a vector Network Analyzer (VNA). The results indicate that the dielectric properties of the resultant nanocomposites increase with the increase in SiC content as compared to the neat epoxy sample. However, the dielectric properties were found to be decrease after microwave curing signaling the maximum possible extent of curing. This indicates that reinforcement of SiC nanoparticles in epoxy makes them ideal candidates for efficient microwave curing of nanocomposites. Lastly, the determination of thermal properties also confirms the maximum possible extent of curing of epoxy using SiC as nanofillers.
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