Synthesis Of Nano/micrometer Composite Materials And Study On Microwave Absorbing

At present, with the development of science and technology, the traditional absorbing materials,which were composeed of only one kind of materials, can't meet the demand any longer.Therefore, much attraction has been devoted to the composite materials, which many possess better absorbing properties.In this paper, we report the synthesis of ZnO nanoparticles on hollow glass microspheres(HGMS)by the simplify controlled doubled-jet precipitation method in an ethanol-water solution. SEM photos show that the ZnO coatings on hollow glass microsphere comprise numerous one-dimensional nanorods with their c-axes pointing toward the center of hollow glass microsphere.The diameter and length of these nanorods are in the ranges of 100-200nm and 1μm, respectively. The as-synthesized HGMS/ZnO composites have been determined by X-ray diffraction technology to demonstrate the formation of wurtite ZnO nanocrystals. The PL spectra of HGMS/ZnO contain a strong UV band peak at 392nm and a very weak broad green band centered 530nm. The UV emission is originated from excitonic recombination corresponding to the near-band-edge emission of ZnO. The luminescence emission peak located 530nm corresponds to the transition from the shallow level of oxygen vacancy to the shallow level of zinc vacancy. The triethanolamine appears to play a dual role, that is, in the generation of ZnO and in the modification of the surface of HGMS for the coating.The HGMS/ZnO exhibited excellent wave absorbing properties at the testing frequency range from 4GHz to 18GHz, the reflectivity was below 5dB at the frequency range from 16.1 GHz to 18 GHz and the lowest reflectivity was～11.9 dB at 18GHz.Heterogencous nucleation processing is applied in coating zinc hydroxide on flaky graphite(FG)using a buffered PH solution as the precipitation reagent. When PH value is 5.4,SEM micrographs showed the best coating . Flaky graphite coated with Zinc oxide (FG/ZnO) exhibit good absorption performances in the low frequency, which is better than FG, because the piezoelectric character of ZnO is a factor of damaging the entered energy of microwave and reducing the reflectivity. It is noted that the R.L. of FG/ZnO less than～5dB begins from 5.9GHz to 9.3GHz. The grinding flaky graphite coated with zinc oxide (GFG/ZnO) exhibit good absorption ability in the range of 4-18GHz. The bandwidth in the frequency is 1.2 GHz(6.2-7.4GHz) and 2.8GHz(13.6-16.4GHz) for the high frequenc, the maximum absorption is～25.9dB and～25.2dB, respectively.