Preparation And Microwave Absorbing Properties Of Nanocomposite Coatings Containing Surface Modified Nanopowder Within Epoxy Resin

Microwave absorbing materials, as a kind of functional material, can effectively absorb or attenuate the incident electromagnetic wave by converting the electromagnetic energy into heat energy or making the electromagnetic wave disappear by interference. Presently, the most widely used and studied traditional microwave absorbers are metal and ferrite powders with shortcomings of large area density and narrow absorption band. Hence, developing new type of light weight microwave absorber has become one hotspot in the research and development (R&D) of microwave absorbing materials. Carbon nanotubes (CNTs) is a promising microwave absorber thanks to its own characteristics, such as hollow, light, adjustable conductivity, high mechanical properties and chemical stability. Fly ash cenospheres with outstanding properties of light, hollow, low density, fine granularity, high intensity, good heat endurance and high wear resistance are spherical particles expelled from electricity factory. After surface metallization modified, they may partly replace metal and ferrite absorber and become a new light microwave absorber.In this paper, new types of light absorbers were successfully prepared by electroless plating Ni-Co-P alloy films on CNTs and Ni-Co-P, Co-P and Ni-P alloy films on fly ash cenospheres after the pretreatment of sensitization and activation by SnCl₂ and PdCl₂. XRD was adopted to show the phase composing of samples, SEM was utilized to observe the surface appearance of samples, TEM was applied to show the samples' microstructure and morphology, EDS was employed to characterize the element composing and content of samples, metallographic microgragh analytical method was utilized to show the polished inlaid samples' sectional morphology. The mechanisms of electroless plating Ni-Co-P films on CNTs and growth of the alloy films on fly ash cenospheres were also discussed. Nanocomposite microwave absorbing coatings were prepared by using prepared Ni-Co-P/CNT and Ni-Co-P , Co-P , Ni-P/fly ash cenospheres composite powders as absorbers, choosing epoxy resin as film forming resin and adding some proper solvent, curing agent and auxiliary agents. Coating samples were obtained by painting the dope on plastic board. The dependences of reflectivity and frequency (R-F) of coating samples were measured to characterize the microwave absorbing properties of each samples on microwave attenuation test system within the band of 8¹8GHz. The results indicated that uniform, integrated and high quality of alloy films could be obtained by electroless plating after the pretreatment of sensitization and activation by SnCl₂ and PdCl₂. The depositing films were amorphous, after heat-treated in H₂ at 450℃ for lh, crystalloid phase Ni₃P and α-Co appeared. Nanocomposite microwave absorbing coatings using Ni-Co-P/CNT andNi-Co^ Co-? > Ni-P/fly ash cenospheres composite powders as absorbers had better microwave absorbing properties and the highest reflectivity could reach to 18.7dB. Minishing absorber granularity, increasing the content of absorbers, adjusting the layer numbers to obtain optimal coating thickness, choosing proper resin and solvent could help us to enhance the microwave reflectivity of coating samples.