Abstract: Fe₃O₄ nanoparticles were treated by surfactant to prepare stable well-dispersed nano-sized Fe₃O₄ magnetic fluid on ball-grinding.3 kinds of surfactants of GD-01,GD-02， and GD-03 were selected and effects of pH,grinding time,and dosage of surfactant on dispersivity of magnetic fluid were studied.Fe3O4 nanoparticles in magnetic fluid were characterized by infrared-ray spectrum (FT-IR) and high resolution transmission electron microscopy (HRTEM). Results showed the optimum pH of GD-02 was 4.5 and 2.5 of GD-01 and GD-03,the optimum grinding time was 5 h,and the optimum surfactant was GD-02 with optimum dosage of about 0.5 g.Under the optimum conditions,stable double-electric layer adsorption structure was formed on nanoparticle′s surface to prevent agglomeration,and the prepared nano-sized Fe₃O₄ magnetic fluid was stable and well-dispersed.

Key words: nano-sized Fe₃O₄, magnetic fluids, surfactant, dispersivity