| With the development of electronic equipments, their generated electromagneticwave not only influences the normal use of the euquipments, but also endangers people’shealth. Meanwhile, electromagnetic wave technology, such as detecting, guidauce,interferce et. al., has been used in modern warfare to influence the outcome of warfare. Tomeet demands of the civil and military needs, the microwave absorption materials havebeen forcus on more and more attention. In our work, to design microwavce absorptionmaterials with strong absorption and wide absorption bandwidth, we chose cobalt metal asobject to investigate electromagnetic response and microwave absorption in GHz range,and the mechanism were also discussed in this paper. Our work mainly includes the parts asfollows:(1) The flower-like cobalt particles, composed by face-centered-cubic structure (fcc)and hexagonal-close-packing structure (hcp), were successfully synthesized by liquidreduction method. The effect of concentration of CoSO4, reaction temperature and dosageof N2H4·H2O on morphology, crystal structure were studied in this part. The magnetizationof fcc-cobalt flower-like particles were higher than that of fcc-cobalt flower-like particles,and covervity of fcc-cobalt flower-like particles were lower than that of hcp-cobaltflower-like particles. It has been shown that flower-like hcp-cobalt particles and fcc-cobaltparticles indicates different electromagnetic response spectrums. The reflection loss offcc-cobalt particles were larger than that of hcp-cobalt particles. The hcp-cobalt particlesexhibited the maxmium reflection loss was-17.97dB at18GHz with a matching layerthickness of1.5mm, corresponding to a maxium bandwidth of3.95GHz. The fcc-cobaltparticles possessed a maximum reflection loss of-54.90dB corresponding to a matchinglayer thickness of1.5mm, and the maximum bandwidth was5.26GHz in the microwaverange of1~18GHz;(2) The spherical cobalt particles, mainly assembled by fcc-cobalt structure, weresynthesized through liquid reduction method. The calculated maximum reflection loss ofspherical cobalt particles was-13.82dB with a matching layer thickness of2mm in themicrowave range of1~18GHz. The sphercial cobalt particles were ball-milling treatment,and effect of ball-milling time on reflection loss were disscussed. It has been indicated that the maximum reflection loss value increased with ball-milling time increasing. The12h-ball-milling cobalt particles indicated the maximum reflection loss reached-45.00dBwith a matching layer thickness of2mm. The effect of heat treatment at350oC onball-milling cobalt particles were also investigated. The heat treatment at350oC couldenhanced the maximum effective bandwidth of ball-milling cobalt particles. The maximumeffective bandwidth of8h-ball-milling coablt particles with heat treatment at350oCreached7.10GHz;(3) The sword-like cobalt particles, composed by fcc-cobalt and hcp-cobalt, wereprepared by liquid reductuion method. The effect of reaction temperature, concentration ofNaOH and complex ratio on the morphology was studied. The maximum reflection loss ofsword-like cobalt particles was-59.18dB at13.89GHz with a matching thickness of1.4mm. The effect of heat treatment on reflection loss of cobalt particles were studied. Theeffect of mixing ratio of spherical and sword-like cobalt particles on reflection loss ofcobalt particles was investigated in microwave range of1~18GHz. It has been shown thatthe reflection loss of cobalt particles increaseed with mixing ratio of spherical andsword-like cobalt particles increasing;(4) The calculated results showed that the fcc-cobalt particles could effectivelyenhance the reflection loss and widen the effective bandwidth through comparing themicrowave absorption properties of cobalt particles with different morphologies and crystalstructures, and the cobalt particles wtih spatial extentive morphologies, such as flower-likeand sword-like cobalt particles possess strong reflection loss. |
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