The Preparation And Characterization Of Magnetic Nano Carbon Powders

Magnetic nano material is a new material appeared in the 1980's. Due to the effect of the nano materials not only small size effect, quantum size effect, surface effect and macroscopic quantum tunnel effect, but the magnetic function such as magnetic recording, magnetic separation, wave adsorbing and so on. Therefore,as a new material,magnetic nano-carbon powders occupy an important position in the field of electronic,information, agriculture, aerospace, chemistry and biomedical etc, and have been one of the hotspots in the current research field on materials.At present, there are several methods to prepare magnetic particles such as precipitation method, hydrothermal method, micro-emulsion and reverse micro-emulsion method, sol-gel method, chemical vapor deposition method and evaporation condensation method and so on. In all these methods, due to its advantages of mild reaction conditions, not high demand of the equipment technology, good system chemical homogeneity, high purity of prepared product, uniform distribution of particle size and narrow size distribution, sol-gel method has became the primary means in preparing nano-magnetic material at home and abroad.In this paper, The magnetic nano carbon powders were prepared by sol-gel method, in which the coal tar pitch was first oxidized into aqua-mesophase pitch (AMP) by mixtures of concentrated sulfuric acid and nitric acid, and then the AMP was dissolved in aqueous solution of ammonia hydroxide to form the carbonaceous hydrogel, in which various ferric salt solution was added to form composite Fe/C gel. then, the Fe/C gel directly exchanged with ethanol to remove water and dried at room temperature. After carbonization at certain temperatures, the magnetic nano carbon powders were obtained. The research includes that using hot pumping filtration to replace the previous cold method to improve the process conditions in AMP preparation. Moreover, the influence of stirring velocity on the yields and properties of AMP were studied. The various composite Fe/C gels were gotten by add different ferrous salt using the sol-gel method, the Fe/C gel was dried at room temperature and carbonized at different temperatures to get the magnetic nano carbon powders. The AMP, the primary magnetic nano-carbon powders and their heat-treated products with different Fe content were characterized by FT-IR, TG, XRD, TEM, M-H loops and wave absorbing performance test.The results show that the reactions such as nitration, oxidation and sulfonation mainly happened during the reactions of coal tar pitch with mixing acids. The yield of AMP and the efficiency have been greatly increased because of using the hot pumping filtration. The particle size of magnetic nano carbon powders prepared by ferric chloride and ferric sulfate is 5nm.There is a turbostratic carbon structure in all the magnetic nano carbon powders, and the Fe element exists as the form ofγ-Fe₂O₃ in the powders treatment at low temperature. In high temperature treated powders the Fe element exists as form of a-Fe,rhombic Fe₂O₃,γ-Fe₂O₃ and Fe₃C. The pyrolysis process of original magnetic nano-carbon powders can be divided into five stages, including removal of ethanol and water, pre-pyrolysis, heavy pyrolysis, construction of carbon structure and decomposition of Fe(OH)₃, rearrangement of carbon structure with deoxidization of Fe₂O₃. The magnetic nano-carbon powders belong to the soft magnetic materials and have a good property of magnetic response, The saturation magnetization became larger with the Fe content increased. The coercivity is basically the same of magnetic nano carbon powders with different Fe content. The prepared magnetic nano carbon powders with low Fe content have a better reflective properties of microwaves than the powders that with high Fe content during the frequency of 8-18GZ. Choose five different organic materials to prepare coated magnetic nano carbon powders, it was made by the tartartic acid and, but the particle size is large.