Spinet Type Ferrite And Metal Composites: Preparation By Disproportionation Reaction Of Fe (Ⅱ) Preparation And Their Magnetic Properties

The Fe/Fe₃O₄composite materials have aroused much attention, due to theirexcellent magnetoelectric, magnetic transport, and high track propertie s. Andrecently, it was revealed that this composite exhibited excellent catalytic oxidationactivities toward organic molecules. Meanwhile, CoFe₂O₄/CoFe₂composite, whichhas similar structures with Fe/Fe3O₄, has also attached much attention in varieties offields such as catalyst and etc.. Several methods, such as hydrogenous reduction,oxidized by oxygen, ball milling, host-guest chemistry, etc., have been used tosynthesize the composite materials mentioned above. However, few reports havebeen focused on the pure chemical method. Hence, the objective of this dissertationis to synthesize spinel type ferrite and metal composites through the typicaldisproportionation reaction of Fe （II）. The detailed research work is as follows:In the second chapter, one-pot syntheses of composites of Fe/Fe3O₄andFe-Co/Co_1-xFe_xFe₂O₄have been carried out. And two main methods have beenconfirmed through study of different factors. On one hand, we have carried out theexperiment under concentrated KOH aqueous solution. On the other hand,hydrothermal reaction has taken place at relatively lower concentration baseenvironments. And the results reveal that the size of particles is in micro meter scalewhen the concentration of base are very high, and the sizes are ranged fromsub-micro meter to nano meter scale when the concentration is low. Through thestudy of Fe/Fe3O₄and Fe-Co/Co_1-xFe_xFe₂O₄composite obtained from highconcentration of base, we can find that the configurations of Fe-Co/Co_1-xFe_xFe₂O₄composite have been changed under different thermal treatment. The composite hasa face-centered cubic structure and body centered cubic lattice respectively for thesamples treated at300oC and500oC. And the study of magnetic properties reveals that the coercivity of composite increases with the concentration of Co. Themaximum value is2925.44Oe. When the concentration ratio of Co/Fe is0.3, thecomposite has the maximum saturated intensity of magnetization （94.69emu/g）.And as far as Fe/Fe3O₄composite is concerned, the sizes of α-Fe are between100nm and150nm, while the sizes of Fe3O₄are ranged from300nm to450nm. Andalso, the magnetic properties changed obviously under different thermal treatment.The sample treated at300oC exhibits the maximum saturated intensity ofmagnetization （108.4emu/g）, and the concentration of Fe is also the highest.Furthermore, the TEM characterization of Fe-Co/Co_1-xFe_xFe₂O₄obtained from thelow concentration of base reveals that the sizes of the particles change obviouslywith the concentration of KOH. As the concentration of KOH is0.1M, the size ofparticles is ca.100nm. Finally, we reaction mechanism under the base condition hasalso been discussed.In the third chapter, the change of magnetic properties of composites has beenachieved through introduction of transition metal elements based on thehydrothermal method mentioned in Chapter two. Meanwhile, the reduction of thecomposites has been carried out and FexCo1-x, Fe1-x-yCoxNiy, and Fe1-x-yCoxMnyalloyhave been obtained. And the structures and magnetic properties of these alloys havebeen studied. The magnetic properties of FexCo1-x/FeyNizCo1-y-zFe₂O₄andFe_xCo_1-x/Fe_yMn_zCo_1-y-zFe₂O₄composites have been studied as well. As forFexCo1-x/FeyNizCo1-y-zFe₂O₄composite, the saturated intensity of magnetization andcoercivity increase at first and then decrease with the concentration ratio of Ni/Fe,when the concentration ratio of Co/Fe is0.1and0.3. The maximum value ofsaturated intensity of magnetization is ca.98.49emu/g. And the maximum value ofcoercivity is430Oe, when the concentration of Co is0.3. It’s suggested that bettermagnetic properties can be realized with longer doping time. When it comes toFe_xCo_1-x/Fe_yMn_zCo_1-y-zFe₂O₄composite, the saturated intensity of magnetizationincrease at first and then decrease with the concentration ratio of Mn/Fe, when the concentration ratio of Co/Fe is0.1. The maximum value of saturated intensity ofmagnetization is ca.92emu/g. And the coercivity increases with the concentrationratio of Mn/Fe, the maximum value is180Oe, when ratio of Mn/Fe reach0.12.When the ratio of Co/Fe is0.3, saturated intensity of magnetization changes little atfirst and then decreases, while the coercivity decreases at first and then increases alittle. Through the reduction of Fe-Co/Fe3-xCoxO₄、FexCo1-x/FeyNizCo1-y-zFe₂O₄andFe_xCo_1-x/Fe_yMn_zCo_1-y-zFe₂O₄composites, the alloys of Fe-Co, Fe-Co-N, andFe-Co-Mn, with different compositions and concentrations, can be obtained. Andtheir magnetic properties have been studied as well. The sizes of samples, whichwere heated at500oC, are ca.500nm, while the sizes of samples heated at1000oCare ca.200nm. As for Fe-Co alloy, the saturated intensity of magnetization of thesamples heated at1000oC is twice of those heated at500oC. The value is302.92emu/g，and the suggested formula is Co0.412Fe0.588. And during the synthesis processof Fe-Co-Ni and Fe-Co-Mn, as the temperature raises, the alloys are inclined to bepure. As the ferrite decreases, saturated intensity of magnetization increases whilecoercivity decreases.In the fourth chapter, we exploit new Fe （II） to carry out hydrothermaldisproportionation reaction in order to synthesize Fe_xNi_1-x/Ni_yFe_2-yFe₃O₄composite.During this process, PEG-20000as dispersant is introduced. Meanwhile, NiMnLaferrite has been also synthesized through introduction of the same dispersant. Andthe corresponding morphology and performance are compared. Through usingFeSO₄and PEG-20000, we have synthesized Fe_xNi_1-x/Ni_yFe_2-yFe₃O₄nanoparticleswith the size at10-20nm. Compared with FeCl2system without dispersant, thisreaction can take place without Co ions. The saturated intensity of magnetizationincreases slowly at first and then decrease rapidly with the concentration ratio ofNi/Fe. The maximum value of saturated intensity of magnetization is ca.82.5emu/g,and the minimum value is31.4emu/g. And the coercivity exhibits no obviouschange rules, the maximum value of coercivity is121Oe （Ni/Fe is1:1,1:2）, while the minimum value is77Oe （Ni/Fe is1:4,1:6）. Furthermore, the properties ofFe_xNi_1-x/Ni_yFe_2-yFe₃O₄and NiMnLa ferrite are studied and compared, whichsuggests that the different composites in the composites play important roles for thefinal properties. Through TEM characterization, we find that the sizes of these twosamples are similar although the synthesis methods are different. It’s suggests thatPEG-20000plays an important role in the dispersion of particles. And thecomparison of magnetic properties reveals that the saturated intensity ofmagnetization of Fe_xNi_1-x/Ni_yFe_2-yFe₃O₄is higher than that of NiMnLa ferrite.In the fifth chapter, the synthesis and magnetic properties of diluted magneticsemiconductors have been studied. Sol-gel method has been used to co-doped Co-Fewith ZnO nanocrystals. The research system in this chapter is ZnO: Co_0.02Fe_0.02andZnO：Co_0.02Fe0.04, the structures and magnetic properties of which have been studiedby XRD and SQUID. Through sol-gel method, ZnO nanoparticles doped with Fe-Cohave been obtained. And the structures and morphology have been characterized.XRD spectra suggest that there is no oxidation state of Fe ions. And TEMcharacterization reveals that the particles are even, with the size of10nm. Thesuperparamagnetic properties of particles have been also been studied. And it’ssuggested that the nanoparticles exhibit superparamagnetic characteristic.Meanwhile, the effects of the amount of Fe ions on the magnetic properties ofparticles are studied as well. The results reveal that the magnetic properties are notmerely due to the metal oxide, but also owing to the super-exchange interactionbetween delocalized carriers and free valence electrons.