Microwave Absorbing Performance of Electroless Co-Ni-P Alloy Coating on Fly Ash Hollow Microspheres

A novel lightweight microwave absorbing powder material with core-shell structure was prepared by conducting electromagnetic modification of fly-ash cenospheres(5 μm scale) via electroless plating of Co-Ni-P.The effects of electroless plating parameters on the morphology,composition and microwave absorbing performance of Co-Ni-P alloy coating were investigated by using a scanning electron microscope,an energy dispersive spectrometer and a microwave vector network analyzer.Results show that the coating on the surface of cenosphere particles consists of stacked Co-Ni-P spheres with a size of 0.5～1.0 μm.The coating was even in terms of thickness,but its composition was much different from that of the plating bath.Besides,the coated hollow microspheres were magnetic loss dielectric media and possessed strong soft ferromagnetic properties.The coating obtained from the plating bath with a Co2+/Ni2+ mass ratio of 3∶1 had a Co/Ni mass ratio of 1.34 and the best microwave absorbing performance.When the concentration of hypophosphite in the plating bath was increased to 50 g/L,resultant coating had increased content of amorphous phase and turned into two-phase soft magnetic material,showing enhanced microwave absorbing ability.Namely,it had a lowest reflectivity of-31.5 dB,and its frequency range corresponding to a reflectivity below-10.0 dB was as much as 4.5 GHz(8.2～12.7 GHz).