| Spinel ferrite magnetic materials characterized by high dielectric properties and small eddy current loss have much larger resistance than metal and alloy magnetic material,which are widely used in many fields like electronic devices,ferromagnetism delete material sorting equipment,fighter stealth coating and biomedical materials.Current methods for preparing spinel ferrite powders majorly include self-combustion,hydrothermal,sol-gel method,co-precipitation,high-energy ball milling and mixing ball milling.However,their shortcomings,such as harsh reaction conditions,environmental pollution,low efficiency,incomplete reaction or poor magnetic properties,have been the main limitation of the industrial production.Therefore,it has important theoretical and practical significance to develop a new industrial way with highly efficient,energy-saving,environmental protection,easy to produce the high-performance ferrite*In this paper,a new method--microwave-assisted ball milling was developed for the preparation of spinel ferrite nanopowders.By introducing the microwave into milling process,this process is characterized by the combination function of microwave electromagnetic and mechanical milling force field to powders.A series of nickel ferrite,magnesium ferrite,manganese ferrite nickel zinc ferrite and Mn-Zn ferrite nano ferrite powders were successfully prepared by the self-developed design and manufacturing device which has obtained the national invention patent(Patent No.201 110 004 753).Then detailed investigations were took on the specific experimental techniques and their related response mechanisms were discussed.Firstly,we prepared a series of units and dual nano ferrite powder by using our methods,and then discussed some special phenomena arising in the process:(1)By taking nickel carbonate and iron as raw materials,the spinel nickel ferrite nanopowders could be obtained after 40h.Fitting the XRD diffraction peaks of products by voigt,the calculated average particle size of the powder particles obtained by hall calculating method is 22.59nm.Besides,the emerge of Fe(OH)2 ·Ni(CO3).2Ni(OH)2 ·2H2O as intermediates was different to the other report in the last decades.(2)By taking manganese dioxide and iron as raw materials,we could obtain the spinel manganese nanopowders with average size 15.95nm and saturation magnetization 70emu/g after 35h.During the process,manganese dioxidefirstly turned into manganese tetroxide with tetragonal lattice,then become the cubic lattice with the increase of milling time.At last,the changed material react with iron and transformed into manganese ferrite nanopowders.(3)The magnesium ferrite nanopowders were prepared by microwave-assisted ball milling after 60h with basic magnesium carbonate and iron as raw material.The saturation magnetization of magnesium ferrite obtained by this method could reach 40.56emu/g.(4)We also got a perfect polymorph of Ni0.5Zn0.5Fe2O4 with the nickel oxide,zinc oxide and iron powder as raw materials,whose saturation magnetization even could reach 40.56emu/g.It is noted that the MnxZn1-xFe2O4 have the performance of microwave scattering loss and dual microwave scattering loss peak.The influence of pretreatment of ball milling and microwave radiation,microwave power and other process parameters on the efficiency of microwave assisted milling was investigated during the preparation of Ni0.5Zn0.5Fe2O4 powders.The results have shown that the formation time of Ni-Zn ferrites are 18h,32h,60h,100h when the power are 1200W,1000W,600W and 300W,respectively.The subsequent treatment showed that the microwave-assisted ball milling have the direction adjustment function to the tetrahedral sits and octahedral sits of nickel and zinc ions,the particle size and saturation magnetization in the Ni-Zn ferrite.Finally,the reaction mechanism and the coupling function of microwave and ball milling during the preparation of ferrites were discussed.The mechanism included:the inter-diffusion and reactions of raw materials with peeling and crushing between balls;(2)with the combining effect of microwave and milling,a highly oxidizing OH radicals which improved the microwave absorption and conductivity of solution. |
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