Preparation of nanophase M-type ferrite and its laser-attenuated characteristics

Abstract

By citrate sol-gel auto-combustion method, the nanophase M-type planar hexagonal ferrite is prepared. The transmission electron microscopy (TEM), X-ray diffraction (XRD) and thermal analysis are used to study the grain size, phase composition, microstructure and crystallization process. The results show that the nanophase M-type Sr-ferrite prepared by this method is single, and its grain size is smaller than 100 nm. Moreover, most of the grains present hexagonal sheet shape. Tests are carried out for its attenuation to 1.06 m laser. It is found that the extinction capability of the nanophase M-type Sr-ferrite smoke is good, and its mass extinction coefficient is 1.628 m 2 /g.In recent years, with the latest development in radar and microwave communication technology, the new and efficient electromagnetic wave absorbing materials have become a focus and attracted more interests around the world [1][2][3][4] . The hexagonal ferrite, a main radar absorbing material, has been widely used at home and abroad [5][6][7][8][9][10][11] because of its strong absorbing ability, broad-band absorbency and low-cost preparation. But the bigger particle size and specific gravity by traditional preparation methods can't fulfill the strategic requirements of future applications for radar absorbing materials. Therefore, preparation and application of nanophase hexagonal ferrite are turning into the research focuses now [12][13][14] .In this paper, the nanophase M-type planar hexagonal Sr-ferrite is prepared by means of citrate sol-gel auto-combustion method. Its performance, including grain size, phase composition, microstructure and crystallization process, is characterized. Moreover, as a new smoke material, its attenuation performance to 1.06 m laser is tested in a 20 m 3 smoke chamber.The nanophase M-type SrFe 12 O 19 is synthesized by citrate sol-gel auto-combustion process as follows. Analytically pure strontium nitrate, iron nitrate and citric acid are selected as raw materials. Firstly, strontium nitrate and iron nitrate in stoichiometric proportion are added to proper amount water solution of citric acid. With stirring, the mixed system in water bath is heated at 80 o C till the insoluble matters are dissolved completely. Secondly, adjust pH to about 7 using ammonia and keep on stirring for 2 h at 80 o C in water bath. Then the mixed solution is moved into the oven where it is dried in 130 o C till dark brown brittle xerogel is formed. As soon as the xerogel is ignited at a certain condition, the combustion can spread out rapidly and stably, as far as the xerogel is burned away to make fluffy powder. Then the powder is moved into the muffle furnace where it is presintered for 2 h at 450 o C and is sintered for 4 h at 900 o C. Lastly, after natural cooling, the brown-red Sr-ferrite powder is gained.In this paper, main complex reactions are:*