Inclusion of octahedron-shaped ZnFe2O4 nanoparticles in combination with carbon dots into carbonyl iron based magnetorheological suspension as additive

Octahedron-shaped nanoparticles of ZnFe2O4 and functionalized superparamagnetic nanoparticles of carbon (CNP) were synthesized and used as additives to prepare carbonyl-iron magnetorheological (CI-MR) fluids with improved shear stress and sedimentation rate. Single phase spinel ZnFe2O4 nanoparticles with cubic structure was prepared with hydrothermal route. Appearance of two absorption bands correspond to T-band at ∼471.77 and O-band at 556.19 cm−1 in FTIR spectra confirmed spinel phase formation. HRTEM micrographs indicated the average size of 12 nm and range of 5-15 nm for octahedron-shaped particles. Heating the as-synthesized ZnFe2O4 nanoparticles at 650 °C resulted in the lattice fringes with strong spotty ring in SAED patterns, indicating the good crystallinity of the as-synthesized nanopowders. Such heated nanoparticles showed an increase in the saturation magnetization from ∼ 21-52 emu/g and decrease in the coercivity from 80 to 35 Oe in the VSM analysis. Additionally, HRTEM image of the superparamagnetic nanoparticles of carbon (CNP) exhibited irregular shaped particles with the average size of 5 nm. Raman revealed the presence of D and G bands associated with the vibration of sp2-bonded carbon and the presence of defects. As prepared CNPs and heated-ZnFe2O4 nanopowder were introduced into the CI-MR suspension as additives. The rheological characteristics of the samples were investigated by employing various magnetic field strengths and temperatures. It was shown that the inclusion of nanoparticles in the free space of micron-sized CI particles results in strengthened chain-like structure formation as the yield shear stress of CI-based MR suspension with 1 vol% (CNPs-ZnFe2O4) additive is increased up to ∼12% at 500 mT at 25 °C. On the other hand, the sedimentation rate becomes slower up to ∼18% due to the increment of friction force in the presence of nanoparticles additive.