The effects of reducing temperature and SiO₂ coating layer on nanocomposite Co/SiO₂ particles size and phase structure

Nanocomposite Co/SiO₂ particles that average size is 20-30 nm were obtained by heterogenous precipitation-H2 reducing method. The effects of the reducing temperature and content of surrounding SiO₂ on size and phase structure of the nanocomposite Co/SiO₂ particles have been investigated. Experimental results showed that the Co nanoparticles were coated effectively by the coating layer SiO₂. The core Co of nanosize with face centered cubic (fcc) can be remained in the room temperature. However, if the size of particles is larger than a critical size, the core Co transform from face centered cubic (fcc) to hexagonal closed packed (hcp) structure. By the experiments, the critical size of the core Co from face centered cubic (fcc) to hexagonal closed packed (hcp) structure has been obtained. This result is accordant with that of the reference. Furthermore, the experimental result proved there is a critical temperature for the formation of Co with fcc structure and the fcc Co structure can not be obtained if the reducing temperature is lower than the critical temperature.