The Effect of Sr-CoFe₂O₄ Nanoparticles with Different Particles Sized as Additives in CIP-Based Magnetorheological Fluid

This study investigated the effect of adding strontium (Sr)-doped cobalt ferrite (CoFe₂O₄) nanoparticles in carbonyl iron particle (CIP)-based magnetorheological fluids (MRFs). Sr-CoFe₂O₄ nanoparticles were fabricated at different particle sizes using co-precipitation at calcination temperatures of 300 and 400 °C. Field emission scanning electron microscopy (FESEM) was used to evaluate the morphology of the Sr-CoFe₂O₄ nanoparticles, which were found to be spherical. The average grain sizes were 71-91 nm and 118-157 nm for nanoparticles that had been calcinated at 300 and 400 °C, respectively. As such, higher calcination temperatures were found to produce larger-sized Sr-CoFe₂O₄ nanoparticles. To investigate the rheological effects that Sr-CoFe₂O₄ nanoparticles have on CIP-based MRF, three MRF samples were prepared: (1) CIP-based MRF without nanoparticle additives (CIP-based MRF), (2) CIP-based MRF with Sr-CoFe₂O₄ nanoparticles calcinated at 300 °C (MRF CIP+Sr-CoFe₂O₄-T300), and (3) CIP-based MRF with Sr-CoFe₂O₄ nanoparticles calcinated at 400 °C (MRF CIP+Sr-CoFe₂O₄-T400). The rheological properties of these MRF samples were then observed at room temperature using a rheometer with a parallel plate at a gap of 1 mm. Dispersion stability tests were also performed to determine the sedimentation ratio of the three CIP-based MRF samples.