Preparation And Properties Of Micron Plate Barium Ferrite

In order to prepare Ba Fe₁2O₁9 with particle size in micron range（the radial size is bigger than 5μm）, and with excellent saturation magnetization（Ms）, in this article four methods, chemical co-precipitation method, chemical twice co-precipitation method, sol-gel combustion method and sol-gel co-precipitation method, were used to synthesize hexagoal Ba Fe₁2O₁9 plate particles. The uniform design and optimization experiment was applied in chemical co-precipitation method,, sol-gel combustion method and sol-gel co-precipitation method, and with the aid of DPS software, the dependence of magnetic performances of Ba Fe₁2O₁9 on preparation conditions was studied based on the regression equation established between magnetization（Ms） and experimental factors. Meanwhile, by using XRD、IR、TG/DTA、SEM/EDS, the synthesis process of Ba Fe₁2O₁9 prepared by sol-gel co-precipitation method was investigated.The results show that the uniform design can be applied in preparation of Ba Fe₁2O₁9 by chemical co-precipitation method. Through regression analysis of the experimental result by uniform design, the regression equation was built between the experimental index（Ms） and the synthetic reaction temperature（X1）, mixing time（X2）, holding time（X3） and drop acceleration（X4）. Ms=52.4954+1.7545X4-0.0682X42. According to the regression equation, X4 has a significant impact on Ms, and the impact level of these factors on Ms was revealed as follow: X4>X1≈X2≈X3. At the same time, the optimal combination of these factors for experimental index Ms was identified. Under the optimal combination of these factors for Ms tested through the experiments, and the prepared hexagonal plate Ba Fe₁2O₁9 was proved to be pure phase with radial size, radius-thickness ratio, saturation magnetization（Ms）, coercive force（Hc） being 0.35⁰.65μm, 4⁷, 64.13emu/g, 1546 Oe respectively.By the single factor alternate method, the chemical twice co-precipitation method were used to synthesize the hexagonal plate Ba Fe₁2O₁9 with radial size, radius-thickness ratio, saturation magnetization（Ms）, coercive force（Hc） being 0.7¹.4μm, 10¹5, 65.48emu/g and 1958 Oe. The main synthesis conditions, including metal salt mixed solutions, adding ways of precipitating agent, baking and heating mode, bake temperature, bake time, have influences on the phase composition, particle shape and size and magnetic properties of the prepared Ba Fe₁2O₁9. Using the anti dripping mode impure phase can be avoided to form and the pure hexagonal plate Ba Fe₁2O₁9 was prepared with high crystalline, large radial size and ratio of diameter to thickness so that the Ms value of the prepared Ba Fe₁2O₁9 is relatively large. Through the pre-baking of precursor the generation of impurity phase α-Fe2O3 can be avoided, and the purity and crystalline of Ba Fe₁2O₁9 can be improved and the radial size and diameter to thickness ratio can be increased, all of which lead to a increase of Ms. An increase of baking temperature can also bring about the disappearance of impure phases in the prepared Ba Fe₁2O₁9 disappears, improvement of crystalline and increase of radial size and radius-thickness ratio, and the Ms is eventually raised. Whether the baking time is too long or too short can cause a decrease in crystallinity, radial size and diameter to thickness ratio of the prepared Ba Fe₁2O₁9, leading to the decrease of Ms.Uniform design can be applied to prepare Ba Fe₁2O₁9 with sol-gel combustion method. Through the regression analysis, the regression equation established between the experimental index（Ms） and synthesis factors, including mole ratio of iron to barium（X1）, mole ratio of citric acid to total metal ion（X2）, p H value of reaction solutions（X3）, pre-baking temperature（X4）, pre-baking time（X5）, baking temperature（X6） and baking time（X7）. Ms=24.5891- 0.0310X6-0.0002X42 + 0.0034X1X4 + 0.0058X1X6 + 0.4292X1X7 + 0.0116X3X4- 0.0034X3X6-0.1540X3X7. According to the regression equation, there are interactions between X1 and X4, X1 and X6, X1 and X7, X3 and X4, X3 and X6, X3 and X7, and these interactions and factor X4 and X6 have significant impact on the Ms, the impact order of these factors was shown as follow: X1>X7>X4>X6>X3>X5≈X2. An optimal combination level of these factors on the experimental index（Ms） was identified. Experimental results indicate that the pure hexagonal plate Ba Fe₁2O₁9 was prepared with the radial size, radius-thickness ratio, saturation magnetization（Ms）, coercive force（Hc） being 1.0².8μm, 5⁹, 65.68emu/g and 4278OeThe uniform design can be applied to prepare Ba Fe₁2O₁9 by sol/gel-co precipitation method, Through the regression analysis, the regression equation established between the index Ms and synthesis factors, including the mole ratio of barium to iron（X1）, reaction temperature（X2）, p H value（X3）, holding time（X4）, the dropping rate（X5）. Ms =-129.6533 + 28.0438X1 + 9.7522X3- 1.3715X12- 0.4536X32 + 0.0546X42- 0.1166X1X4. According to the regression equation, the interaction exists between X1 and X4, and factor X1, X3, X4 and the interaction between X1 and X4 have significant impact on the Ms, the impact of these factors on Ms follows the following order: X1>X4>X3>X5≈ X2. The optimal combination level of these factors for experimental index Ms was identified. Through the testing experiment, the pure hexagonal plate Ba Fe₁2O₁9 with radial size, radius-thickness ratio, saturation magnetization（Ms） and coercive force（Hc） being 5.4⁷.8μm, 7¹4, 66.01emu/g and 1941 Oe.was prepared under the conditions of the optimal combination level. The formation process of sol/gel-co precipitation can be described as followl: precursor（plate Ba Fe₁2O₁9 coated by low crystalline state Ba CO3、α-Fe2O3、amorphous state Fe OOH） ????? ®?--,,2OHOHα-Fe2O3 + Ba CO3® Ba Fe₁2O₁9). Compared with the twice co-precipitation method, the difference of raw materials（Ba Fe₁2O₁9） make precursor prepared by the sol/gel-co precipitation method showed relatively good coating layer, which results in the prepared Ba Fe₁2O₁9 showed high crystallization and large radial size and high Ms value.