Preparation and properties of cenospheres-barium ferrite composites

The composites of fly ash cenospheres coated with barium ferrite particle were successfully prepared by sol-gel auto-combustion method.The morphology,crystal structure,magnetic properties,electromagnetic properties and microwave absorbing behavior of the samples were characterized by scanning electron microscope(SEM),X-ray diffraction(XRD),vibrating sample magnetometer(VSM) and vector network analyzer.The results showed that continuous and uniform coating layer of barium ferrite is formed on the surface of fly ash cenospheres.In addition,it is found that the crystal phases of barium ferrite appears after the as-burnt powders of precursor gel was calcined at 850℃ for 2 h.Furthermore,the samples exhibit better dielectric loss and magnetic loss properties within the frequency range from 2 GHz to 18 GHz.The maximum reflection loss of the composite material reaches –15.44 dB at 8.4 GHz with a thickness of 3.0 mm,the bandwidth for –12 dB is 4.2 GHz.