| M-type hexagonal strontium ferrite (SrFe12O19) is a kind of permanent magnetic material. It has been widely used today due to its high Curie temperature, great coercivity and favorable performance/price ratio. However, permanent magnetic properties of the SrFe12O19is not able to meet the needs of the society today, therefore, it is necessary to improve its magnetic properties.The magnetic properties can only be promoted by enhancing the coercivity due to the limit of the low saturation magnetization and remanent magnetization of SrFe12O19. To improve the coercivity, high magnetocrystalline anisotropy, single domain structure or the introduction of shape anisotropy is needed. The one-dimensional linear nanomaterial has unique advantages on obtaining the single domain structure and improving the shape anisotropy, because of its small size, large aspect ratio and other properties. Therefore, the study of linear magnetic nano-materials is essential.Electrospinning method was adopted in this paper. High performance permanent magnet SrFe12O19nanofibers were prepared by improving the electrospinning equipment, adjusting the parameters of electrospinning process and doping the rare earth ions. The microstructure, morphology and magnetic properties of SrFe12O19and SrDyxFe12-xO19nanofibers were investigated. The main contents and results of this study are as follows:1. The preparation of SrFe12O19nanofibers by the vertical electrospping equipment:1) The effect of sintering conditions on SrFe12O19nanofibers was studied. Heating rate and holding time should be the right, in order to ensure that the prepared samples possess good crystallinity and fiber morphology.2) When Fe3+/Sr2+=10.6, the SrFe12O19nanofibers with pure phase were obtained. The SrFe12O19nanofibers with an average diameter about85nm were obtained after sintering at800℃for1h. The average grain size is of about43nm, which is close to the single domain critical size. The optimum magnetic properties is of Hc=6853Oe, Ms=59.0emu/g,(BH)max=1.06MG-Oe.2. The preparation of SrFe12O19nanofibers by the horizontal electrospping equipment:1) The preparation of SrFe12O19nanofibers by the improving equipment with an adding water bath:a. When the volume ratio of solvent in the precursor solution DMF:H2O=1and2, the rises of the bath temperature is conducive to the formation of SrFe12O19phase and the improvement of magnetism, b. When the solvent volume ratio DMF:H2O=3, due to the addition of the ultrasound, the conductivity of the solution is improved, and then the magnetic properties of the sample is improved; When the spinning needle of steel is exchanged by a plastic needle, it can effectively weaken the discharge phenomenon between the needle and the water bath, and stabilize the spinning process. Therefore, the SrFe12O19nanofibers with a better morphology and magnetic properties were prepared, c. When the solvent volume ratio DMF:H2O=3, and the molar ratio of Fe3+/Sr2+was of12, the pure phase SrFe12O19nanofibers were prepared.2) Without water bath, the SrFe12O19nanofibers were prepared after the precursor solution preheated. When the preheating time is of30min, the optimal magnetic properties is obtained:Hc=6905Oe, Ms=62.2emu/g,(BH)max=1.00MG-Oe.3. Using the horizontal electrospinning equipment, SrDyxFe12-xO19(x=0-0.1) nanofibers were successfully prepared with a incorporation of rare earth element Dy; Under the conditions of no preheating the precursor solution and the sintering temperature of800℃, better fiber morphology is obtained.4. The incorporation of rare earth element Dy improved the coercivity value of the permanent magnet SrFe12O19:When the sintering temperature is of900℃, the SrDyxFe12-xO19nanofibers are prepared, at x=0.1, Hc=7092Oe (Ms=56.7emu/g); When the sintering temperature is of800℃, at x=0.08, Hc=7155Oe (Ms=52.9emu/g). |
PDF Full Text Request