Properties of cobalt nanofiber-based magnetorheological fluids

Co nanofibers were synthesized by a surfactant-assisted solvothermal method. They were characterized by XRD, EDS, SEM, TEM and SQUID. The results indicated that the obtained products were hexagonal close-packed cobalt nanofibers with high purity. They presented large length to diameter ratio, and a high saturation magnetization of 142 emu g(-1). Two magnetorheological (MR) fluids were prepared by the Co nanofibers and carbonyl iron particles with 12% particles volume fraction, respectively. Their magnetorheological properties and sedimentation stability were tested and compared. The results indicated that the Co nanofiber-based MR fluid presented higher yield stress than the carbonyl iron particles-based one at low field levels (0-150 kA m(-1)). The strong chains or column structure caused by the specific morphology and high magnetization of the Co nanofibers is responsible for their significant MR properties. In 15 days setting, the Co nanofibers-based MR fluid presented little sedimentation, while the sedimentation ratio of the carbonyl iron particles-based MR fluid was 50%. The Co nanofibers are ideal candidates to prepare MR fluids with good sedimentation stability as well as good magnetorheological properties.