Synthesis And Microwave Absorbing Properties Of Nickel Zinc Ferrite Submicrospheres And Their Composites

Nickel zinc ferrite (Ni0.3Zn0.5Fe2O4, NZFO) submicrospheres are a kind of complex medium material, widely used in the field of electromagnetic wave absorption. They have many advantages such as strong absorption, no pollution, easy preparation, low cost, and so on. It is one of the hot issues that are researched at present. However, NZFO also has some shortcomings like high density and narrow absorbing band, which make the use of NZFO limited to a large extent.Therefore, it has become a primary problem that must be solved in this area to improve their density, absorbing band and other properties through the preparation of NZFO composite materials.In situ oxidation polymerization can effectively enhance and increase the comprehensive performance of NZFO by combining the NZFO and conducting polymer. The as obtained NZFO composites have both favorable dielectric loss and magnetic loss characteristics.In this paper, NZFO submicrospheres are prepared successfully by a sol-gel method, which have good dispersity, uniform particle size distribution and superparamagnetism. The effects of the morphology, structure and magnetism on the microwave absorbing properties of the materials are discussed. Then the NZFO submicrospheres are combined with polypyrrole (PPy), polyaniline(PANI) and epoxy resin, respectively. A new type of microwave absorbing composites with strong absorption, wide band, high chemical stability, low density and excellent electromagnetic performances are synthesized by controlling the doping ratio and optimizing the craft process. The effects of the morphology, structure, component, magnetism, electrical conductivity and doping ratio on the microwave absorbing properties of the composites are detailedly studied using fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis, thermogravimetric analysis(TGA), saturation magnetization (Ms) and conductivity, etc. The main research content is as follows:1. Superparamagnetic NZFO submicrospheres with good dispersivity and uniform particle size distribution are synthesized using sol-gel method. Through the analysis of reaction mixture composition, surface morphology and crystal structure in different reaction time, the formation mechanism of the submicrospheres were discussed. The result of magnetic measurement shows that the saturation intensity of NZFO is 86.3 emu·g-1. The sample of 35% volume fraction shows the minimum reflection loss (RL) of -50.2 dB.2. The Ni0.3Zn0.5Fe2O4@polypyrrole (NZFO@PPy) submicrocomposites with different shell thickness are prepared in water solution by in situ oxidation polymerization. The morphology,structure and chemical composition of the composite submicrospheres are studied through FT-IR,TEM and XRD, and the formation mechanism of the core-shell submicrospheres is discussed. The as received NZFO@ PPy composite submicrospheres show favorable dielectric loss properties because of the existence of the conducting PPy shell on the surface of NZFO. With the Py/NZFO ratio of 40, the volume fraction of 25% and the sample thickness of 2 mm, the minimum RL of the NZFO@PPy core-shell submicrospheres reaches -37.3 dB. The microwave-absorbing band width of RL < -10.0 dB is 3.9 GHz, which is much wider than that (1.7 GHz) of pure NZFO submicrospheres. What’s more, the density of the NZFO@PPy core-shell submicrospheres is decreased to a large extent.3. The superparamagnetic NZFO and the conducting PANI are compounded by in situ oxidation polymerization in water solution to prepare composites with different doping ratio. The morphology,structure and chemical composition of the composites are researched through FT-IR,TEM, and XRD, and the formation mechanism of the NZFO embedded PANI composites is discussed. The as received NZFO embedded PANI composites show good dielectric loss performance due to the existence of the conducting PANI. With the NZFO/ANI ratio of 100:3, the volume fraction of 45%, the minimum RL of NZFO embedded PANI composites reaches -46.5 dB.The microwave-absorbing band width of RL < -10.0 dB is 2.8 GHz, which is much wider than that(1.7 GHz) of pure NZFO submicrospheres. What’s more, the density of the NZFO embedded PANI composites is decreased to a large extent.4. The superparamagnetic NZFO submicrospheres are dispersed uniformly in the epoxy resin carrier with a spinner after surface treatment, and the composites are prepared into films by spreading. The results of magnetic measurement show that the maximum saturation intensity of the NZFO embedded UV-cured epoxy resin composite films is 75.0 emu·cm-3 at room temperature,which makes the composite show excellent magnetic properties. The composite film of 15 wt %NZFO doping ratio shows the minimum RL of -31.5 dB, showing favorable microwave-absorbing performance. The density of the NZFO embedded UV-cured epoxy resin composite films is decreased to a large extent, and the films show good thermostability and mechanical properties.