| With the coming of information technology era, microwave is widely used not only in the military field, but also attracts more and more attention in the civilian uses. The electromagnetic wave has gradually penetrated into every aspect of our life. Therefore, the preparation of high performance microwave absorption materials has become a hot spot in the research field. Currently, the new absorbing agents is committed to "thin", "light", "width", "strong" for further development. Preliminary experiment shows that micro-Fe4N has a good microwave-absorbing ability. However, the nanoscale fe4N didn’t meet the requirement. Based on the mature preparation technology of carbon/iron compounds composites in our lab, the iron nitride of different microstructure were successfully synthesized.Using weak electrolyte K.3[Fe(CN)6] and strong electrolyte FeCl3 as an iron source, put it into a sealed reactor and carry out with a hydrothermal method, respectively. We explored the relationship between the morphology of the products and experimental process under different duration time of the reaction (12h-60h), the concentration of different materials (0.02mol/L-0.2mol/), different medium pH and post-processing time (Oh-air-cooled) and analysized the regulation between microstructure and the properties. It was found that the concentration has great influence on the morphology of dendritic a-Fe2O3. As the increasing of the concentration, the crystalline grain become bigger and the secondary structure become less obvious. The best concentration for the hydrothermal synthesis of K.3[Fe(CN)6] is O.lmol/L. However, the post-processing time has less impact on the size of dendritic products. As for the flake products, pH has a great influence on the morphology of the products. Spherical samples will be obtained under a low pH and flake samples will be obtained under a high pH. Other experimental conditions has a weak impact on the products.The preparation of iron nitride is based on the a-Fe2O3 synthesized in the previous work. The dendritic product was obtained through the nitriding process under the atmosphere of pure NH3. We explored the relationship between the experimental parameters and the properties of the products under different nitriding process duration(3h-9h), different reaction temperature (450℃-540℃), different nitrogen potential(0.4-1.2). The morphology and structure of the sample were characterized by field emission scanning electron microscopy and high revolution transmission electron microscopy. The phase composition was analyzed by X-ray diffraction. Magnetic properties were obtained by vibrating sample magnetometer and the electromagnetic parameters was measured by vector network analyzer. The microwave absorption ability of the two kinds of iron nitride is discussed in this work. The results show that the nitrogen potential and nitriding duration has the greatest impact on the products. It’s tend to generate pure y-Fe4N when the nitrogen potential is below 1 and tend to generate Fe3N when the nitrogen potential is over 1. The longer the nitriding duration time, the more thoroughly the reaction goes on. As to dendritic samples, it appears more irregular and curb in microstructure.as to flake samples, it appears thinner in the surface texture. This work also confirmed that the iron nitride in different microstructure has different microwave absorbing ability. The dendritic y-Fe4N has good performance in high frequent electromagnetic wave between 7GHz to 18GHz. when the matched thickness is 2mm, the Fe and y-Fe4N composites has the highest absorption intensity in 5GHz.The absorption peak is about-9.5dB. With the match thickness increasing, the absorption peak moves to lower frequency, the bandwidth become thinner but the absorption intensity is stronger. The maximum absorption peak is-12dB at 3GHz with the thickness of 3mm.the flake y-Fe4N has a certain microwave absorption ability in the low frequency bandwidth between 2GHz to 6GHz but performed not as good as dendritic y-Fe4N. |
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