The Process And Mechanism Of Spherical Iron Nano-powder Prepared By Hydrogen Reduction Of Calcium Ferrites

Iron nano-powder has widely applied in magnetic materials,catalysis and biomedical field for its higher saturation magnetization,superior chemical activity and biocompatibility.However,obvious aggregation and coarsening may happen during the reduction process.In this thesis,a novel method has been exploited to prepare spherical iron nano-powder by hydrogen reduction of calcium ferrites.The size,morphology and purity of iron nano-powder were tested by scanning electron microscope and X-ray diffraction.The process,mechanism and properties of precursor and iron nano-powder were studied systematically.Its major contents are as follows:1.The phase transformation during the process of the calcination of CaO and Fe₂O₃ at different mass ratio was studied.The optimum calcination temperature at the mass ratio of CaO/Fe₂O₃ at 7:20,7:10 and 7:3 are 1100oC,1300oC and 1300oC,respectively.And CaFe₂O₄,Ca₂Fe₂O₅ and Ca₂Fe₂O₅&CaO precursors are successfully obtained.2.The influence of calcium ferrites precursors and reduction temperature on the size and morphology of iron-powder were discussed.It’s shown that:With the increases of the mass ratio of Fe₂O₃ in precursor,result in the increases of the reduction temperature of precursor and size of iron-powder,meanwhile the morphology of iron-powder transferred from regular spherical into irregular bulk.Spherical iron nano-powder with better sphericity and crystalline state is successfully prepared by Ca₂Fe₂O₅&CaO precursor.And the reduction process of calcium ferrites is completed through a continuous transformation of Ca-Fe-O ternary phases.3.With the increases of reduction temperature,the average size,saturation magnetization value and dispersion of iron nano-powder increases,while the coercivity decreases.The average size,saturation magnetization value and coercivity of iron nano-powder were 21 nm,95.9 emu/g and 4.2 Oe,respectively,when reduced at 850oC.When the reduction temperature increases to 950oC,The average size and saturation magnetization value of iron nano-powder increases to 34 nm,144.5 emu/g,respectively,while the coercivity decreases to 1.7 Oe.