|Alternative Title||Melting of iron nanoparticles embedded in silica
|Place of Conferral||兰州
|Other Abstract||In this work, to expand the above slim range of materials, the melting behavior of Fe nanoparticles embedded in SiO2 prepared by using mechanical milling are investigated. Effects of factors in sample preparation on the size, isolation and thermal stability of Fe nanoparticles are systematically studied. On this basis, the size-dependent melting of Fe is successfully traced. In addition, preliminary efforts are carried out on the synthesis and melting behaviors of Cu and Ag nanoparticles embedded in SiO2.
(i) By direct milling of Fe and SiO2 powders, Fe nanoparticles were obtained which were in principle single crystals with a narrow size distribution and are dispersedly embedded in the SiO2 matrix.
(ii) For the milling at 250 rpm, for samples with different Fe-SiO2 volume ratios, the particle size of Fe decreases gradually with extending milling time and finally becomes saturated at around 14 h. With the Fe-SiO2 volume ratio increasing from 1:7 to 6:4, the final particle size of Fe decreased from around 16 nm to 9 nm. For a same Fe content (Fe-SiO2 volume ratio 2:8) milled for 16 h, when the rotational speed increased from 100 rpm to 300 rpm, the size of Fe nanoparticles decreased from about 33 nm to 13 nm. However, for the 2:8 sample milled at 200 rpm for 16 h, when the milling was extended to 50 h, the particle size of Fe further decreased from 22 nm to 14 nm, indicating that the milling process needed a longer time to become complete if the rotational speed was less than 200 rpm.
(iii) Results from thermal analyses showed that good isolation of Fe nanoparticles may be obtained by increasing the volume ratio of SiO2 and by extending milling time until the size of Fe nanoparticles became saturated. For Fe nanoparticles with a diameter of about 15 nm, the melting point depression is 30 oC in comparison with bulk Fe, in accordance with our recent theoretical calculations.|
丁鹏. 氧化硅包覆铁纳米颗粒的熔化[D]. 兰州. 兰州大学,2013.
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