The Research On Preparation Technology Of CoFe₂O₄Nanoparticles Via Microwave-assisted Ball Milling

As a spinel efrirte material, CoFe2O₄exhibits excellent magnetic properties includingmoderate saturation magnetization, strong anisotropy and high coercivity at room temperature,as well as good chemical stability, however, its preparation process tend to be complicated,easy to introduce impurities, and the performance of the ifnal product is diiffcult to guarantee.The research on the inlfuence of microwave to the preparation of cobalt ferrite was carired outby milling COC₂O₄·4H₂0,2CoCO₃·3Co（OH）₂·H₂O and Co₂O₃in aqueous solution using smallmilling balls. The impact of mateiral of grinding ball, ratio of grinding media to mateiral andraw material on the preparation process of microwave-assisted ball milled for cobalt ferritepowder and the products’ performance have been studied. The results were listed as follows:1.Researches showed that:Ellipsoidal cobalt cobalt particles were directly synthesized atlow temperature of <100°C in60h，without the need of calcination, via microwave-assistedaqueous ball milling technique using COC₂O₄·4H₂0as raw material and small iron balls asmilling balls, and the average particle size of cobalt ferrite powder is40.07nm, and themagnetic saturation intensity is52.05emu/g. However, only only a part of the CoFe₂O₄andaccompanied by a large amount of residual CoC₂O₄were obtained when COC₂O₄·4H₂0milledwithout microwave assistance for60h. Pure CoFe₂O₄pHase was also obtained bymicrowave-assisted aqueous ball milling technology using CoC₂O₄.4H₂O and Fe powder asraw materials and small stainless steel balls as milling balls in40h，and the average particlesize of cobalt ferrite powder is33.68nm, and the magnetic saturation intensity is82.09emu/g.The reaction was much faster than the milling process with COC₂O₄·4H₂O as raw mateiral andsmall iron balls as milling balls. This is because COC₂O₄·4H₂0and Fe sources could be mixedifilly when Fe powders were used, which increased the contacting area and accelerated thereaction.2.Fiulher studied on the inlfuence of different ball material ratio on cobalt ferritepreparation process and the property of products Intermediate products.lt turned out that:generated after12h of microwave-assisted ball mill aqueous solution, With stoichiometricratio2CoCO₃·3Co（OH）₂·H₂O+Fe powder （20g） as raw materials, Small stainless steel （1000g）as girnding balls, Pure CoFe₂O₄was obtained when the milling time last to48hours, theaverage particle size of cobalt ferrite powder is30.26nm，and the magnetic saturationintensity is62.07emu/g. How ever, the products were the mixture of CoFe₂O₄and CO₃CO4when2CoCO₃·3Co（OH）₂·H₂O+Fe milled without microwave for80h. The products were alsothe mixture of CoFe₂O₄and CO₃CO4when2CoCO₃.3Co（C）H)2.H₂O+Fe powder （30g） via 50h’s microwave-assisted aqueous ball milling using Small stainless steel balls （1000g） asgirnding balls.Finally has carried on the study of preparation of nano cobalt ferrite powders by usesmall ball as grinding balls, the stoichiometric ratio of Co₂O₃and Fe powder mixture as rawmaterials. Analyzed the preparation process and the prod’ucts performance of CoFe₂O₄prepared imder the same technology condition but the raw mateiral is different. It turned outthat: Pure CoFe₂O₄was obtained when Co₂O₃ball milled with microwave assistance for48husing Small stainless steel balls. However, the Crystal structure CoFe₂O₄is imperfect, theaverage particle size of cobalt ferrite powder is34.37nm，and the magnetic saturationintensity is33.75emu/g. From the compairng we can ifnd that, we can get pure cobalt ferriteefstest by use Co₂O₃+Fe as raw materials and the CoFe₂O₄with the most perfect crystalstructure and excellent magnetic property prepared by use CoC₂O₄·4H₂O+Fe as raw materials.