| With the development of modern industry and stealth technology, the investigation and application of microwave absorption materials look increasingly important because of reducing radar cross section (RCS) and preventing TV ghosting, and microwave leakage from various electric devices and so on. This means that the microwave absorbing materials should have the characteristics of "thin, light, broad, strong", high temperature resistance, corrosion resistance and the weatherability. So traditional materials (e.g. magnetic metal powders and ferrite) can not satisfied with above demands. Because of the huge surface area and special capability, nanometer materials become new absorbing materials, specially magnetic nanometer absorbers. However, nano-magnetic metals and their oxides have high density and are easily oxided. Then the metal-alloys are very interesting investigation as absorbers. In this paper, Fe3Al intermetallic is used as absorber to study its microwave absorbing characteristics first.Fe3Al intermetallic has high magnetic permeability and definite electric conductivity with low density, high temperature oxidation resistance and excellent corrosion resistance compared with magnetic metal materials. All of these properties make iron aluminum intermetallic ideal candidates for application in microwave absorber. The electro-magnetic property of materials has a crucial effect on its absorbability. Therefore, in this paper at first Fe3Al intermetallic powder is prepared and its surface is modified by coupling agents; Its electric and magnetic properties are studied; The electro-magnetic parameters(ε',ε",μ',μ") of Fe3Al intermetallic powders and R (dB) ~f (GHz) cures are tested, then themicrowave absorbability of "Fe3Al absorber + epoxy resin" coating in both centimeter(2~18Ghz) and millimeter bands (26~40GHz) will been investigated. Finally the absorbing mechanism of nano-Fe3Al powder will be discussed. Above studies provide the firmly theoretical foundation for the practical application of it. The following works have been developed.Nano-Fe3Al powders were prepared by mechanical alloying technology. The structural evolution of Fe-Al elemental during mechanical alloying process under the protection of argon atmosphere and low temperature annealing process, and the Fe3Al particle shape, average particle sizes and the size distribution, and the total amount percent of nano-particle have been investigated by means of XRD, TEM, SEM, DSC, LSA and EDS. The results show that disordered a-Fe solid solution formed during milling. The reduction of crystal size and the increase of microstrain exist simultaneity, and the microstrain increasedwith the increasing of milling time. The disorder a-Fe solid solution milled for 20h translates to order DO3 structure through Al atom order rearrangement and removing of APS domains during annealing at 750°C for 1h..With increasing of milling time at the same annealing temperature, the deformation, hardening and lattice deformation change more seriously, and then the more rapidly diffusing rates between Fe and Al atom leads to high ordered degree of Fe3Al alloy. After 100h milling time, nonspherical shape of Fe3Al particles becomes spherical-like. The total amount percent of nano-particles reaches 80.45%. Most of them are several ten nanometer particles and average size is 95nm. The particle size distribution shows Gaussian distribution. Ultrafine Fe3Al magnetic particles attract each other to form the aggregates of loose structure in different sizes varying from 400 nm to several micrometer.The kinds and contents of Coupling agents play very important roles on increasing the dispersivity and compatibility between ultrafine Fe3Al powder and polymer matrix. The single molecular layer saturated absorptions of HSt(1.24%,) , A-172( 1.8%) , aluminate (EAX1.92%) and PHY (0.05%)prepared by ourselves on Fe3Al powder surface were determined by TG. By means of IR spectrums and SEM the reaction mechanism is that the chemical reaction between powder surface and coupling agents takes plac...
|
PDF Full Text Request