Hierarchically Structured Fe3O4 Nanoparticles for High-Performance Magnetorheological Fluids with Long-Term Stability

Abstract The magnetic Fe3O4 nanoparticles were produced by chemical precipitation from ferric chloride (FeCl3) and ferrous chloride (FeCl2) in an alkaline medium (ammonia hydroxide). The magnetic particle suspension was stabilized with citric acid. Hierarchically structured Fe3O4 (HS-Fe3O4) particles of submicrometer size were successfully produced from citric acid-capped Fe3O4 solution by using a simple electrospray (ES) process and applied for magnetorheolgical (MR) fluids. Submicrometer-sized spherical HS-Fe3O4 particles were formed by evaporation of the solvent and agglomeration of capped Fe3O4 particles during the ES process. With formation of hierarchically structured particles, the density of HS-Fe3O4 particles (ρ = 3.32 g/cm3) was noticeably decreased from that of the capped Fe3O4 (ρ = 4.29 g/cm3) without use of light materials, while the saturation magnetization was comparable t…