Rare Earth Doped Pani Modified Strontium Ferrite Microwave Absorption

Ferrites are a sort of traditional electromagnetic wave absorbing materials , but they have the problems of high-density and narrow-bandwidth as for the aspect of microwave absorption. So the modification of the ferrite absorbing materials is still a hot topic at present. As for those problems above, M-type hexagonal strontium ferrite was modified by doping and compounding to improve their microwave absorbing properties. Rare-earth elements have the peculiar electromagnetic structure and function. Thus , electromagnetic parameters can be tailored and the microwave absorbing properties can be improved as for the ferrites by doping rare-earth elements. However, the related researches are rarely reported on microwave absorbing properties in the range of 2-18GHz and M type strontium ferrites by doping La and Ce. The doped polyaniline (PAn) is a sort of microwave absorbing material with low-density and great electrical loss. Therefore, the way that the ferrites in which magnetic loss is main are compounded with PAn is an effective approach to improve the microwave absorbing properties. At present, the research on strontium ferrite/PAn microwave absorbing composite materials is deficient.The ultrafme powder samples of Sr_0.7La_0.3-xCe_xFe_11.7Zn_0.3O₁₉ ferrite were prepared by sol-gel method. The conducting PAn was prepared by chemical oxidation of doping hydrochloric acid, and the composite materials of different polymerization mass ratio strontium ferrite/PAn were synthesized in stiu chemical polymerization. The structure, morphology and the formation process of samples were analyzed by XRD, FTIR, DSC-TGA and SEM. Room temperature conductivity of samples was measured by cylindrical method. Electromagnetic parameters were measured by microwave vector network analyzer (AV3620). The reflection coefficient and electromagnetic loss were calculated according to the measured datas and the microwave electromagnetic loss mechanisms of the modified systems were discussed. XRD analyzing showed that all the Sr_0.7La_0.3-xCe_xFe_11.7Zn_0.3O₁₉ samples were magnetoplumbite hexagonal ferrites with a small amount ofα-Fe₂O₃ impurity phase. SEM analyzing also showed that the morphology of Sr_0.7La_0.15Ce_0.15Fe_11.7Zn_0.3O₁₉ particles with hexagonal flaky structure was irregular. The particles' size is about 100 nm. The composites were characterized by XRD, FTIR, SEM. Results showed that the surface of strontium ferrite was covered by PAn.The results of the conductivity measurement showed that the Sr_0.7La_0.3-xCe_xFe_11.7Zn_0.3O₁₉ samples stayed at the realm of semiconductor, but its conductivity is low. While the Sr_0.7La_0.15Ce_0.15Fe_11.7Zn_0.3O₁₉/PAn composites stayed at the realm of semiconductor, whose conductivity was increasing firstly and then reducing with more polymerization.The results of electromagnetic parameters and microwave absorption showed that, the best effect of microwave absorption was the sample of x=0.15. When the thickness of sample is 3.0mm, the absorbing peak is 12.3dB and the effective bandwidth above 10dB reaches 2GHz. The composites have better microwave absorbing properties.When the thickness is 3.2mm, the absorbing peak of HCl-PAn is 32dB at 10.1GHz and the effective bandwidth above lOdB reaches 3.3GHz. When the relative content of doping strontium ferrite is 40%, the composite have the best effect of microwave absorption. When the thickness is 2.6mm, the absorbing peak is close to 40dB at a higher frequency over 12.4GHz, and the effective bandwidth above 10dB was expected to be 5.5GHz.The theoretical analyzing showed that the microwave power loss of Sr_0.7La_0.3-xCe_xFe_11.7Zn_0.3O₁₉ derived from magnetic loss and dielectric loss. The microwave power loss of HCl-PAn derived from electrical loss and the microwave absorption of composites originated from electrical loss and magnetic loss. The Sr_0.7La_0.15Ce_0.15Fe_11.7Zn_0.3O₁₉/PAn composites have the features of strong loss, wide bandwidth and light mass and can be used as microwave absorbing materials.