Research On Preparation Of Cenospheres Coated With Barium Ferrite

Cenospheres coated with barium ferrite were synthesized by sol-gel method. The composition of samples was identified by means of X-ray diffractometer (XRD). Magnetic properties were measured by vibrating sample magnetometer (VSM).The combustion behavior and crystallization process of the gel were studied by means of differential thermal analysis-thermalgravimetric analysis (DTA-TG).Scan electron microscope (SEM),transmission electron microscope (TEM)and atomic force microscope (AFM) were used to examine the morphology .Some important results are concluded.Based on experimental study, the effect of the composition of the solution, the different kinds of intermediate, the pH value of starting precursor solution, the concentration of solution, the temperature of water area, the amount of complexing agent, the adding of dispersion and the condition in heat treatment of the gel on crystal phase, particle size, morphology and magnetic properties of BaFe12O19 ultrafine powders were investigated to clarify the optimum forming conditions. There are two key steps in the process of preparing BaFe12O19:controlling the pH value of starting solution at 7.0 or so and preprocessing the gel into γ-Fe2O3 before calcining were two key steps which can prevent the formation of α-Fe2O3 intermediate, thus the pure BaFe12O19 can be obtained at lower calcining temperature.In order to cleanout gas and organic compound which adhered to the cenospheres, it was necessary to wash and seperate cenospheres before the process of coating barium ferrite. There are two ways to improve the thickness of coatings, One way is coating more times; the other way is adding some ultrafine BaFe12O19 powders to the starting precursor solution.In contrast with BaFe12O19, the saturation magnetization, residual magnetization and coercive force of barium ferrite doped with rare earth are almost ten times improved. At the same time, the area of magnetic loop was greatly improved. The saturation magnetization of cenospheres coated with doped barium ferrite have little changes, whereas the residual magnetization, coercive force and the area of magnetic loop are improved.