Investigation of Dielectric and Thermal Properties of Mineral Oil‐Based Fe ₃ O ₄ ‐Coated SiO ₂ Core‐Shell Nanofluids

ABSTRACT This study investigates the dielectric and thermal properties of transformer oil‐based nanofluids incorporating Fe 3 O 4 ‐coated SiO 2 core–shell nanoparticles as nanofillers. The nanoparticles were synthesised with varying shell thicknesses, and two samples underwent surface treatment. Fourier transform infrared spectroscopy was used to characterise the nanoparticles. The spectra for unmodified and modified nanoparticles detected Fe‐O bond, Si‐O‐Si bond and oleic acid existence. The nanofluids were prepared using a two‐step method: nanoparticles were first prepared at concentrations of 0.04, 0.07 and 0.10 g/L, and then mixed with the base oil and dispersed using ultrasonication. AC breakdown strength was measured for samples at these concentrations to determine the optimum concentration for each type of nanoparticle. The optimum concentration, which provided the best performance for AC breakdown voltage across all nanoparticle types, was found to be 0.07 g/L. Thermal conductivity testing was then conducted at this optimum concentration. The addition of nanofillers resulted in increased AC breakdown strength and thermal conductivity. Particle size and zeta size measurements were carried out to assess the dispersion behaviour of the nanofluid samples. The physical discussion examined potential reasons for improvements in AC breakdown voltage and thermal conductivity. Trapping and de‐trapping processes, shell thickness and surface modifications were analysed in relation to improved dielectric performance. Ballistic phonon transport and Brownian motion mechanisms were employed to explain the observed enhancements in thermal conductivity. These findings indicate the potential for developing a new class of liquid dielectrics suitable for use in power transformers.