Role of micro- and nano-cobalt ferrite as an additive in enhancing the viscous behaviour of magnetorheological grease

The incorporation of micro- and nanosized additives offers a significant potential solution to improve the viscous behavior which can minimize energy consumption and surpass pumpability demonstrated by magnetorheological grease (MRG). The role of the additives utilized, on the other hand, has piqued the interest of researchers. Therefore, cobalt-ferrite (CoFe2O4) in micro- (M) and nanosized (N) as an additive incorporated in this study to reduce the initial off-state viscosity and simultaneously maintain the resultant shear and yield stress of MRG during on-state conditions. To analyze the viscous behavior effect of MRG types, the samples underwent rheological tests in different parameters. Then, MRG was dried to elucidate the morphological changes. The results showed that micro-sized additives recorded the lowest off-state viscosity with 43.2 % of reduction, followed by nano-CoFe2O4 (26 %) and pure grease. It is due to M has shortened and disentangled the fibrous structures of grease thickener whilst N has filled in the voids among the thickener which contributed to the discharged of base oil thus reduced the viscosity of MRGs. Meanwhile, at on-state conditions, M1 and N1 exhibited enhanced performances of yield and shear stress as compared to pure MRG, O attributed to the improved magnetic attraction among particles in the grease medium. These findings are beneficial for MRG to be employed in MR devices for various purposes.