Preparation and characterization of SiO_2 encapsulated Ni nanoparticles

SiO2 encapsulated Ni core-shell structure composite nanoparticles were prepared by the sol-gel method using TEOS and Ni nanoparticles as the main raw materials. The crystal structure,morphology,constituent elements and magnetic properties of the products were investigated by means of X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM),corresponding electron diffraction(SAED),X-ray energy dispersive spectrometry(EDS) and the vibrating sample magnetometer(VSM). The results show that SiO2 encapsulated Ni nanoparticles with clear core-shell structure,the core of the particles is face centered cubic structure Ni,and the shell of the particles is noncrystal silica and it prevents the nanoparticles from agglomerating. The particles are scattered homogeneously in spherical or ellipsoidal shapes,The dimeter of the particles ranges from 20 to 80 nm,with an averaged value about 30 nm,and the thickness of the shells is about 4-6 nm. After coating the saturation magnetization and remnant magnetism decreases,while the coercivity increases.