Preparation of low-density superparamagnetic microspheres by coating glass microballoons with magnetite nanoparticles

A novel low-density (0.4-0.5 g/cm3) hollow composite material with the superparamagnetic character has been synthesized by coating glass microballoons (GMBs) with magnetite (Fe3O4) nanoparticles via chemical deposition process. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersion X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). A uniform and continuous Fe3O4-coating with thickness ca. 400-500 nm was obtained under the given conditions. The size of Fe3O4 particles of the coating was below 25 nm. The magnetization of the Fe3O4-coated GMBs can be controlled by changing the GMB content and the reaction temperature. These low-density magnetic microspheres are expected to have many advantages in applications such as microwave absorbing materials and catalysts.