Synthesis and microwave shielding properties of carbon - coated cobalt ferrite / epoxy nanocomposite / Nur Amirah Athirah Binti Zaini

Faculty of Industrial Sciences and Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2024

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An increase in the electromagnetic wave pollution generated from wireless telecommunication devices as well as natural electromagnetic waves have called for the development of suitable shielding materials. The synergistic effect of composite materials had demonstrated favorable shielding performance against electromagnetic wave pollution. In this regard, carbon-coated CoFe2O4/epoxy composites were prepared by the facile hydrothermal method, in which epoxy was used as the matrix and the carboncoated CoFe2O4 as the filler with different composition of carbon coating ratio at 1:1 (Sample 1), 2:1 (Sample 2), 3:1 (Sample 3) and 4:1 (Sample 4). The structural, morphological, microstructural and chemical interaction of carbon-coated CoFe2O4 were characterized and studied by using specific techniques and instrument respectively. The crystallographic properties from the analysis confirmed the formation of CoFe2O4 with a crystallite size of ~13 nm. The amorphous carbon coating over the CoFe2O4 nanosphere was further validated by its morphological properties that showed the carbon coating was uniformly dispersed over the CoFe2O4 nanosphere particles. For the thickness of its morphology, a thin layer of carbon coating for sample 4 with ratio of 4:1 was found to be the thickest at ~3.8 nm. The electromagnetic parameters were evaluated by the vector network analyzer based on the measured S-parameter in the frequency range of 8.2 to 12.4 GHz, X-band region and is adequate for radar applications. Sample 4 was also found to achieve the highest total SE of ~ -17 dB at ~10 GHz with 2 mm. The presence of carbon enhanced the shielding properties. Sample 4 was further studied for its electromagnetic properties at different compositions of filler. The 20% filler showed the best magnitude at ~-36 dB at 10.1 GHz compared to the others. The shielding effectiveness of the sample could be tuned as high as possible by adding the conductive polymer as the property modifier. These studies conclude that the carbon-coated CoFe2O4/epoxy composites can serve as a good candidate for shielding from electromagnetic wave pollution at a certain point of carbon coating and filler composition.