稳恒磁场下水热法制备钡铁氧体

Hydrothermal Synthesis of Ba-ferrite in Steady Magnetic Field

利用XRD,SEM,TEM和振动样品磁强计(VSM)等检测手段对不同磁场强度下水热法制备的钡铁氧体粉末进行了分析.实验结果表明,无磁场下,150℃时得到的产物为BaFe2O4颗粒,而180℃时产物为片状BaFe12O19.施加磁场后,150和180℃下水热反应产物都为棒状BaFe12O19.随着磁感应强度的增加,水热反应产物中棒状BaFe12O19的比例呈增加趋势.当磁感应强度达到10 T时,可获得直径100 nm以内长度数十微米的纳米棒状单晶BaFe12O19.不同磁感应强度下获得的水热反应产物粒径都很小,并呈现超顺磁性.热力学计算结果表明,施加磁场使水热反应的磁吉布斯自由能为负值,因而从热力学角度影响了水热反应进行的方向,使水热反应有利于生成更高磁化率的产物.

Using XRD,SEM,TEM and VSM methods,the shape,micro structure and magnetic property of the barium ferrite powder prepared by hydrothermal synthesized in different magnetic fields were discussed.BaFe2O4 powder was prepared at the reaction temperature of 150 ℃ without magnetic field.The powder is composed of BaFe12O19 with sheet shape at the reactive temperature of 180 ℃.With the imposed magnetic field,the powder is composed of rod-like BaFe12O19 at the reactive temperature of both 150 and 180 ℃.With the increase of magnetic flux density,the proportion of rod-like BaFe12O19 also increased.When the magnetic flux density reached 10 T,the single-crystal BaFe12O19 with the diameter less than 100 nm and length of tens of microns were obtained.The products obtained by hydrothermal reaction under different magnetic flux are all small size and showed paramagnetic property.Thermodynamic calculation results show that with the application of magnetic field,the magnetic Gibbs free energy of hydrothermal reaction reached-103 kJ/mol.So it changed the hydrothermal reaction in the thermodynamic aspect,which made the hydrothermal reaction turn to generate the product with higher susceptibility.