Magnetic Nanomaterials Coated By Boron Nitride

Due to its unique structure,the core/shell nanomaterials have merited the advantages of each component material and are widely used in the fields of catalysis,biomedicine,batteries and bionics.However,the research on the inorganic-inorganic core/shell nanomaterials with magnetic nanoparticles as the core and BN as the shell isn’t mature enough till now.Therefore,the BN coated magnetic nanoparticles(Fe_xNi_1-x/BN,FeCo/BN)was systematically studied and analyzed in this thesis.Firstly,Fe_xNi_1-x-x and FeCo precursors were prepared by liquid-phase reduction method,and then the precursors were calcined under high temperature in a vacuum tube furnace to obtain nanoalloy.The as-synthesized Fe_xNi_1-x-x and FeCo samples were characterized by XRD、TG-DTA、SEM and VSM techniques.The results show that the Fe_xNi_1-x-x alloy was typical face-centered cubic structure（fcc）with narrow and sharp diffraction peaks,and none of impurity peaks were observed,indicating that the purity of the sample is high.With the increase of Fe（NO₃）₃·9H₂O,the characteristic peaks of FeNi gradually shift towards the left,which means that the lattice constant becomes large,because the atomic radius of Fe（1.27?）is larger than the atomic radius of Ni（1.24?）.In addition,with increase of Fe content,the saturation magnetization Ms and the coercive force Hc of the sample increase simultaneously,the initial oxidation temperature and the exothermic peak（oxidation peak）intensity of the alloy also gradually increases.FeCo nanoalloy exhibited a body-centered cubic structure（bcc）,the average particle sizes are around 300 nm with serious partical agglomeration.The reaction temperature and heat preservation time have obviously influenced the crystal structure,magnetic properties and micro-structure of the alloy.With the increase of preservation time and annealing temperature,the crystal structure of the sample is gradually being improved,the morphology becomes more and more regular,and the surface becomes more and more smooth.The magnetic nano core/shell particles(Fe_xNi_1-x/BN、FeCo/BN)coated with boron nitride have been prepared by annealing the mixture of alloy precursors and H₃BO₃powders with flowing ammonia.Ammonia not only serves as a reducing gas,but also participates in the reaction to promote the formation of BN.The shell BN limits the growth of the core to a certain degree,and also improves the dispersion of the core,which increases the antioxidant capacity of the core by 2.3 times.Compared with the pure alloy,the Ms of the core/shell nanoparticles decreased,while the Hc increased obviously.In addition,we have synthesized hexagonal boron nitride materials using M·2B（C₃N₆H₆·2H₃BO₃）as precursor under NH₃ atmosphere.SEM、HRTEM and TG-DTA results show that the samples exhibited flake-like or block structure with the interplanar spacings of 0.336 nm and performed a strong thermal stability under air temperature of no more than 850℃.