| As a kind of magnetism materials, the development of Ba-Fe-O ferrite attracts many people's notice, ferrite magnetic materials occupy important status in magnetism study and development for excellent magnetism performance and cheap price, and bring broad interest to investigator. Ba-Fe-O ferrites had been applied extensively in mircrowave and millimeterwave device, high density magnetic recording and medical cure field etc. For example, they were made of coats of latent aeroplane and scout without people, airplane obtain aim of conceal themselves by absorbed microwave. In order to bring to applied value mostly from Ba-Fe-O, The task is arduous for improving cocercive, optimizing magnetic performance, studying form mechanism and controling adulteration element state. Our present study work was significant in advanced Ba-Fe-O ferrites and enrich magentism theory.Ba-Fe-O ferrites have three kinds structure:spinel type, magnetoplumbite type(M type) structure and garnet type structure. Spinel ferrite was a kind of soft magnetic material, it widely used high density magnetic recording materials, microwave devices (MW) and magnetic fluid etc. The chemical formula of structure was AB2O4, belong to facecenter cubic structure, many tetrahedral and octahedral interspaces in crystal cells, these interspaces offer changes for improving magnetism performance of ferrite, also created conditions for adulteration and substitution of metal ionic, so many kinds of spinel ferrites have appeared, their performancs were excellent. As a forevermagetic material of M type Ba-Fe-O ferrites was hard magnetic material, widely used in magnetic recording, engine motor and absorbing electromagnetic wave materials etc. It possess many characteristic, such as wide hysteresis curve, high coercivity, single axial magnetic crystal anisotropy, excellent spin magenitsm performance, high stability of chemistry, high curie temperature, high remanence and high quality to price ratio etc.In recently years, some synthesis technologies improve gradually, some reports of structures and phase changes for synthesis process about adulterating elements and adopted different methods appeared a large number, mechanical alloy method was used abroadly as a synthesis magnetic nanometer material mode, because the reaction of mechanical alloy was complex, so different structure phase changes were happened for different material ratios and milling energies. So high performance precursor nanometer powders were perpared by ball milling. Glycin nitrate method also called self-combustion high temperature synthesis, was arise in recently twenty-thirty years, it is a kind of new technologies. The performances of samples which were prepared by this method were stable and sizes distributed uniformity, at the same time the grain of producation for combustion synthesis was small and relative surface was large, the reaction character was high, so high performance ferrites could be prepared by this method.Ba-Fe-O ferrites was synthesized in mechanical alloy method, BaxFe3_xO4 with spinel structure was fabricated by ball milling BaCO3 andα-Fe2C>3 powders for the first time. The result of study show that, theα-(Fe,Ba)2O3 solid solubility body was formed in the milling process firstly, the Ba content in theα-(Fe,Ba)2O3 increased with increasing milling time, when the Ba content exceeded a limited solubility, theα-(Fe,Ba)2O3 transformed into a high density phase of BaxFe3_xO4 with spinel structure, in which the Fe2+was substituted Ba2+occupied an octahedral site. The composition of production was Ba0.23Fe2.77O4, the saturation magnetization was 53.3emu/g and coercivity was 113.7Oe.The research work for preparation, characteristic and magnetism performance of M type barium hexaferrite (M-BaFe12O19) were developed in general sinter method, mechanical alloy method and Glycin nitrate method. Then, the form mechanism of M-BaFe12O19 which were prepared in different methods was studied by sintering curve. The study result show in the process of preparing M-BaFe12O19 with a-Fe2O3 and BaCO3 as raw and processed materials in general sinter method, fistly the a-Fe2O3 reacted with BaCO3 to form Orthorhombic BaFe2O4 middle phase, then the BaFe2O4 reacted with a-Fe2O3 to form M-BaFe12O19 in a sintering temperature ranging from 770 to 920℃. However, in mechanical alloy method, the a-Fe2O3 reacted with BaCO3 to form BaxFe3-xO4 with spinel structure, while the M-BaFe12O19 was obtained by annealing the BaxFe3-xO4 at 700-1000℃. In the glycin-nitrate procedure, the precursor powders containing a-Fe2O3, Fe3O4 and BaFe2O4 were fabricated by self-propagating reaction firstly, and then the single M-BaFe12O19 was produced by sintering the precursor powders at 1000℃. The form temperature of M-BaFe12O19 which was sintered for precursor powders of BaxFe3-xO4 with spinel structure was lowest. We find that saturation magnetization and the coercivity of the M-BaFe12O19 which was fabricated by mechanical alloy method were 47.24 emu/g and 5086.34 Oe, respectively, which were much larger than those of the M-BaFe12O19 produced by other two procedures. The cause was Ba ion occupied octahedral 2a site, it was independent of grain sizes and purity.M-BaFe12O19 was prepared by Al3+, Dy3+and La3+substituted in Glycin-nitrate method, at the same time we study the law and mechanism which were influenced of adulteration element. The result show that, single phase M-BaFe12O19 was prepared at 900℃when fuel and oxide ratio was 1.5:1. Therefor all of adulterations were done in this proportion. Al3+substituted Fe3+in the process of Al adulterated M-BaFe12O19, it marked BaAlxFe12-xO19. XRD results indicate that the diffraction angle moved toward high angle direction when x of BaAlxFe12-xO19 increases from 0 to 4, the cause was the radius of Al3+is smaller than radius of Fe3+. The calculation result indicate adulteration influence crystal lattice a greatly, the value of a dropped from 5.887 A to 5.189 A, the change trend of crystal lattice c was same. Otherwise the FWHM (full width at half maximum) increases when adulteration quantity of AI increase, namely crystal grain size decreased when adulteration quantity of Al increased. This result account for growth speed of crystal grains was slower because of Al adulteration. The coercive force increased from 4012 Oe to 13738 Oe along with changes of crystal lattice constant and crystal grain size, it almost equal to the coercive of Nd-Fe-B. But when x up to 5, the other impurity phases appeared, the sample was made of M-BaAlxFe12-xO19, a-Fe2O3 and BaAl2O4 the coercive force declines to 8430 Oe. It indicate solid solubility of Al in BaAlxFe12-xO19 was limited. Because Al lock-in 2b and 12k site of M-BaAlxFe12-xO19 firstly, substituted Fe3+of this site, cause to decrease of magnetism Fe3+ion number, so the saturation magnetization reduces monotonously along with adulteration quantity of Al increases. When Ba was substituted by Dy, the crystal quality of BaxDy1-xFe12O19 sintered at 900℃was not good, Coercive forces did not increased for the sample of BaxDy1-xFe12O19. it decreased a little on the contrary, that was different from literature report, the cause might be different preparation method. M-BaxLa1-xFe12O19, was prepared when Ba was substituted by La, x changes from 1 to 5 range, The changes of coercive forces was not obvious, but the saturation magnetization reduces from 60.4 emu/g when x equal to 0 to 38.6 emu/g when x equal to 0.5. M-Bao.5La0.5AlFe12O19 was prepared when La and Al together adulterate, coercive foerce was 8740 Oe higher than 6679 Oe of BaAIFe11O19, the saturation magnetization was 26.7 emu/g. The anterior result show:the coercive force improvement of M-BaFe12O19come from substituting Fe3+, the method of substituted Ba2+was secondary.
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