CoFe2O4磁性液体冰冻前后的磁性

 介绍了Massart法制备CoFe2O4磁性液体的方法。用X射线衍射仪、透射电子显微镜测量CoFe2O4微粒的结构、粒径，表明微粒粒径呈对数正态分布，平均粒径为12.76nm，平均晶粒粒径为11.15nm。利用振动样品磁强计，在室温下测量CoFe2O4微粒的磁化曲线和体积分数为1%、1.2%、1.5%的磁性液体冰冻前后的磁化曲线。结果表明，磁性液体饱和磁化强度明显小于等量磁性微粒的饱和磁化强度?准VMps，冰冻后磁性液体的饱和磁化强度大于冰冻前磁性液体的饱和磁化强度。其原因是，磁性液体中存在块状、链状、环状团聚体，其中块状和环状团聚体导致饱和磁化强度降低；在磁性液体冰冻过程中，由于水分子的作用环状团聚体破裂成链，使压缩参数?酌变大，导致冰冻后磁性液体饱和磁化强度增大。

CoFe2O4 Ferrofluids' Magnetization Before and After Frozen

The preparation of CoFe2O4 ferrofluids by Massart's method is discussed in this paper. The structure and the shape of CoFe2O4 nanoparticles are characterized by X-ray diffraction and transmission electron microscopy, respectively, and the results show that the particles' size follows a logarithmic normal distribution, with the average diameter of 12.76nm and the crystal particle's average diameter is 11.15nm. The magnetization curve of CoFe2O4 particles is determined at room temperature by VSM, with the saturation magnetization of CoFe2O4 particles of 217.50kA/m. The magnetization curves of ferrofluids with volume fractions of 1%, 1.2% and 1.5% are determined at room temperature by VSM. It is found that the saturation magnetization of ferrofluids is significantly less than particle's saturation magnetization fVMps, because of bulk aggregations, chain-like aggregations and ring-like aggregations in ferrofluids at the same time. The bulk aggregations and the ring-like aggregations reduce the saturation magnetization of ferrorluids. The saturation magnetization of ferrofluids after frozen is greater than that before frozen, as the ring-like aggregations are broken by H2O molecule's interaction during the frozen process, which increases the parameter γ and the saturation magnetization of ferrofluids after frozen.