| Nanoseparation is attracting more and more interest as an important and effective complementary process to synthesis optimization for providing strictly monodisperse nanoparticles(NPs) for investigations of their size- or shape-dependent properties. Here we used differential centrifugation, centrifugal methods of changing the density and permittivities of the dispersion medium to separate ?-Al2O3 NPs. Disperse fine uniform equiaxed ?-Al2O3 NPs are essential for sintering Al2O3 nanocrystalline ceramics, which may be the fundamental strategy to overcome the brittleness of Al2O3 ceramics, but dispersed equiaxed ?-Al2O3 NPs smaller than 15 nm are extremely difficult to prepare. Dispersed equiaxed ?-Al2O3 NPs obtained by removing the Fe matrix in the ?-Al2O3-NPs-embedded nanocomposites through acid corrosion, have a quite wide size distribution from 2 nm to 1 um. According using the above three methods to explore the separation properties of different particle sizes and size distributions of ?-Al2O3 NPs, superfine, disperse, equiaxed ?-Al2O3 NPs with an average particle size of 3.7 nm and size distribution of 2.1 ~ 5.5 nm were obtained. The results of this work not only provide an experimental basis and theoretical guidance for further separation of NPs, but also lay a foundation for sintering Al2O3 nanocrystalline ceramics.According the theory of centrifugal sedimentation of NPs, the differential centrifugation was applied to separate ?-Al2O3 NPs(2 nm~1 ?m). By selecting the appropriate speed and time, ?-Al2O3 NPs with average particle sizes of 745.0 nm, 345.5 nm, 273.8 nm, 92.5 nm, 40.2 nm, 14.7 nm, 11.2 nm, 8.2 nm and 6.1 nm and size distributions of 482.1~1573.2 nm, 200.7~969.1 nm, 122.4~863.5 nm, 45.6~237.2 nm, 16.5~98.7 nm, 5.41~38.2 nm, 3.5~25.6 nm, 2.7~15.8 nm and 2.1~12.2 nm were obtained. Comparisons of the particle size distributions and the histogram fitting curves of the respective fractions, results show that the differential centrifugation can both separate micron grade ?-Al2O3 NPs and ?-Al2O3 NPs smaller than 30 nm, but when the sizes of the particles are less than 30 nm, the size distribution ranges overlap seriously and separation precision is not high.Density is another key factor to influence the descent velocity of NPs. Therefore, in order to separate the ?-Al2O3 particles smaller than 30 nm, our research group introduce density as an important parameter to control the descent velocity of the particles. ?-Al2O3 NPs with average particle sizes of 20.98 nm, 14.01 nm, 10.07 nm and 6.1 nm and size distributions of 12.38~32.83 nm, 6.25~24.24 nm, 4.32~21.1 nm and 2.94~11.3 nm were separated. Compared with differential centrifugation, the results show that this method has high separation precision for ?-Al2O3 NPs smaller than 30 nm.?-Al2O3 NPs with an average particle size of 6 nm and size distribution of 2~12 nm are the best results for differential centrifugation, and centrifugal method of changing the density of dispersion medium. Through adding n-hexane into ?-Al2O3 NPs solutions to change the permittivities of mixture solutions, ?-Al2O3 NPs in this size range have been further subdivided. The idea has been used to separate ?-Al2O3 NPs and obtain ?-Al2O3 NPs with more narrow size distributions and smaller average particle sizes. Research shows that through optimizing the parameters, ?-Al2O3 NPs with average particle sizes of 5.92 nm, 5.21 nm, 4.36 nm and 3.65 nm and size distributions of 3.42~9.66 nm, 3.09~7.81 nm, 2.80~6.36 nm and 2.05~5.52 were obtained. |
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