中文摘要：

利用非均相沉淀-H2还原方法制得了平均粒径为20-30nm的Co／SiO2纳米复合颗粒。探讨了非均相沉淀-H2还原法的还原温度和SiO2壳层对Co／SiO2纳米复合颗粒尺寸和组织的影响。实验结果表明，在复合颗粒中，非晶SiO2壳层对纳米Co颗粒成功地进行了包覆。纳米尺度的fcc结构芯核Co可以在室温存在，但颗粒尺寸大于某一临界尺寸时，芯核Co将由fcc向hcp相转变。通过试验得出芯核Co由fcc向hcp相转变的临界尺寸，该试验结果和理论数据相吻合。并证明，还原过程中fcc结构Co的出现对应于一个临界温度，当还原温度低于该临界温度时，不能得到fcc结构的Co。

英文摘要：

Nanocomposite Co/SiO2 particles that average size is 20- 30nm 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 fee structure and the fee Co structure can not be obtained if the reducing temperature is lower than the critical temperature.