The In-situ Preparation Of Magnetic Nanocomposite Materials And Their Electromagnetic Properties

With the development of information technology, microwave absorbing materials with band width, thickness, high absorption ability, light quality have attracted much attention.Nanomaterials, in particular magnetic metal nanomaterials are increasingly becoming the central of attention in the preparation of microwave absorbing materials for their unique physical performance in optical, electricity, and magnetic. However, it's difficult to match the requirements of high performance microwave absorbing material due to the agglomerate caused by small size effect and magnetic, which is the disadvantage for microwave absorbing properties and room temperature stability. Thus, their applications are limited. Herein, we made use of different dispersion medium to control the size of magnetic metal nanoparticals by in-situ composite method, moreover supplying other mechanism of loss. The results are showing in the follow:The Ni-C composite material was prepared through high-temperature reduction nitridation process of the precursor by mixing Ni(NO3)2·6H2O and sucrose according to a certain proportion.The results show that Ni nanoparticles uniformly distribute in the carbon matrix and the size decreases with the increase in carbon content due to the inhibition of carbon in the growth and agglomeration of Ni nanoparticles in high-temperature reduction nitridation process. Furthermore,the magnetic and electromagnetic performance was investigated. It was found that the radio of Ni to C has the great influence on Ni nanoparticles size, magnetic and electromagnetic absorbing properties. The nano Ni-C composite materials with good electromagnetic absorbing properties can be obtain by optimizing the ratio of Ni to C. For example, sample N5 with a thickness of 4mm has a reflection loss of-39.98 d B under a frequency of 4.16 GHz, which implies that N5 is a promising electromagnetic wave absorption material.Considering that the good conductivity of both carbon and Ni is against to achieve impedance matching, as a typical microwave transparent material, SiO2 was introduced to investagate the magnetic and electromagnetic absorbing properties of composite materials. As one of kind of insulation materials, SiO2 makes contributions to transmission channel of microwave in composite materials. The results show that SiO2 in proper proportions can afford to further dispersion and the controllable size of Ni nanoparticles. However, excess SiO2 will reduce the ratio of effective microwave absorbing agents and even cause bad influence on electromagnetic absorbing properties of composite materials. The sample, S-0.3, with a thickness of 5 mm has a reflection loss of-32.3 d B under a frequency of 14.16 GHz, meaning 99% electromagnetic wave is absorbed.The precursor Ni-SiO2 composite materials were prepared by a liquid-phase reduction process. Then a series of Ni3N-SiO2 composite materials with different nitridation degrees and Ni/Ni3N-SiO2 composite materials with different ratios of Ni to Ni3 N were prepared through a high-temperature nitridation process of the precursor and high-temperature decomposition process of the Ni3N-Si O2 composite materials under different temperature and nitridation time. The pure phase Ni3 N was shown to be a typical dielectric loss material without the static and dynamic magnetic loss. In addition, the dynamic dielectric of Ni3 N has a great relationship. With the nitridation degree completely, the dielectric property of Ni3 N is enhanced. Ni/Ni3 N composite materials were found showing better electromagnetic absorbing properties than pure Ni or Ni3 N through the appropriate optimization.