Preparation And Properties Of Nano-coated Microwave Absorbing Materials

CoAl2O4(Co) and Ni/α-Fe2O3 nanocomposite powders were prepared by changing conditions of coating process. The phase constitution, particles morphologies, size distributions, microstructure and the binding energy of the elements of these different kinds of nanocomposite powders and the structure characteristics of the aggregates have been studied by means of X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) in details. The magnetic characteristics and electromagnetic (EM) properties of the nanocomposite powders were measured by Vibrating sample magnetism (VSM), network vector analyzer. The physical mechanism of the good EM absorption properties in these nanocomposite powders was discussed.The result reveals CoAl2O4(Co) nanocapsules were successfully prepared by arc discharge. HRTEM studies revealed the particles have a distinct shell/core structure, the size of the nanocapsules ranges from 10 to 90 nm and the thickness of shell is in 3-10nm. Based on X-ray photoelectron spectroscopy investigation, the core of the as-prepared nanocapsules is Co, while the shell is mainly composed of CoAl2O4 and a small amount of Al2O3. Co(OH)2,,Co2O3. The results of microwave absorbing capability indicated that the maximum reflection loss of CoAl2O4(Co) nanocapsules reached -21.1dB with 2.5mm and the absorption is less than-lOdB in the range of 5.01-17.87GHz.Ni/α-Fe2O3 nanocomposite powders were successfully prepared by chemical plating, the size of which is 2-5μm and the thickness is in 4-8nm. It is approved that the core isα-Fe2O3 and the shell is Ni measured by XRD and XPS photoelectron spectrum.Magnetism research shows that the saturation magnetization decreases of nanocapsules and the coercive force increases of nanocomposite powders, compared with pure bulk Fe2O3. The reflection loss R(dB) of the Ni/α-Fe2O3 nanocomposite powders/ paraffin wax composite materials were simulated by experimental date. The reflection loss R(dB) of the nanocapsules/paraffin wax composite materials 4 mm in thickness reaches to-16.8dB at 6.82GHz, and EM absorption properties (RL<-10dB) in the 3.97-18GHz range. Although the saturation magnetization of Ni/α-Fe2O3 is lower, this special shell/core structure, ferromagnetic Ni shell and shape anisotropy is an important factor to the appearance of high performance absorbing property.