Soft magnetic composite particles of reduced iron coated with poly(p-xylylene) via chemical vapor deposition polymerization

Soft magnetic composite particles of reduced iron coated with ultrathin films of poly(p-xylylene) (PPX) were prepared via chemical vapor deposition (CVD) polymerization. The structure, morphology, magnetic properties, and chemical stability of PPX encapsulated reduced iron particles were studied. It can be confirmed from FTIR spectrum that the polymer covered outside the reduced iron particles is PPX. The thickness of PPX film is averagely 100 nm according to the results of transmission electron microscopy (TEM). The mean diameter of the composite particles is about 6.0 μm. The resistance to thermooxidation of the composite particles is much higher than that of the reduced iron particles due to the protection of PPX ultrathin film outside the iron powder. After being encapsulated with PPX ultrathin film, the resistance to acidic corrosion of the reduced iron particles is obviously improved. Although the saturation magnetization (Bs) of the composite particles is reduced from 1.42 T to 1.33 T after the coating process, their coercive force (Hc) decreases from 10.6 kA/m to 6.02 kA/m, which is advantageous for the application of soft magnetic particles in MR fluid.