The Formation And Liquid-phase Conversion Of Nano-iron Oxide With Additive

Because of the unique physical and chemical properties of the nano-iron oxides, they are widely used in the fields of building materials, paint, catalysts, functional ceramics, glass, art paints, medicine, advanced grinding materials, magnetic recording materials and so on. Therefore how to improve the process, reduce cost, and improve the quality of the products are the goals of research. The known research has shown that: additives have some effect on the formation and transformation of the iron oxides. But the type and the adding amount of additives, light, magnetic field and other factors on the influence of formation and conversion of iron oxides as well as the mechanism haven't to be in depth investigated up to now.The thesis used Fe(â…¡) as raw material, added complexing agents or surfactants, to synthesize nano-iron oxide by the method of air oxidation. The influnce of additives on the particle size and dispersion of Fe₃O₄ as well as different forms of FeOOH was discussed in this thesis. And the conditions such as visible light, the dropwise modes of alkali, the magnetic field and so on were also investigated. Furthermore we explored the external magnetic field on the liquid-phase conversion of FeOOH intoα-Fe₂O₃,arriving at the purpose of making it fast. The study will be able to offer new date for using Fe (â…¡) salt as raw materials to produce nano-iron oxide, and provide a new technics way for the process of nano-α-Fe₂O₃ production, so as to enhance its applicability.The research of this thesis included:(1) We used FeSO₄ as raw materials, NaOH as the precipitating agent, with room light and the initial pH = 11.00, to produce Fe₃O₄ by air oxidation. At the same time we observed the agents such as citric acid, tartaric acid, glutamic acid, and surfactant agent (sodium dodecyl sulfate) on the effect of size and dispersion of Fe₃O₄.We found that adding the right amount of such complexing agents separately all could reduce particle size of Fe₃O₄.And adding surfactant sodium dodecyl sulfate could reduce particle size of Fe₃O₄ all,while improve its dispersibility and stability.(2) We control the initial pH = 8.60, to prepare FeOOH by air oxidation of Fe(OH)₂, studying ethylenediamine, glutamic acid, citric acid and oxalic acid and other complexing agents, as well as the factors of visible light, magnetic field, the dropwise modes of alkali on the impact of products. The results showed that: room light, for glutamic acid, ethylenediamine, oxalic acid, citric acid, when a certain amount of which was added, it generated pureγ-FeOOH phase, however excessive or too small compared toα-FeOOH andγ -FeOOH mixed phase, and without complexing agent for the pureα-FeOOH phase. We also found that with the existence of complexing agents such as ethylene diamine, citric acid, and oxalic acid, visible light influenced the system. With the room light compared to darkroom adding ethylenediamine generatedγ-FeOOH easily; adding citric acid or oxalic acid made the products ofγ-FeOOH crystallized badly, and the light system with glutamic acid had no effect. By studying its mechanism, we reckoned that:For the glutamic acid because of its adsorption on the green rust GR(â…¡) surface, so that its crystallization became badly, and speeded up the GR(â…¡) to dissolve. For adding complexing agent such as citric acid, oxalic acid or ethylenediamine, not only generated intermediate green rust GR(â…¡) crystal weakened, also the complex of complexing agent with the Fe²⁺ can absorb some visible light to generate strong oxidizing free radicals, improving the oxidative capacity of air oxidation process and oxidizing Fe²⁺ to Fe³⁺ rapidly, and that the rapid oxidation generatedγ-FeOOH. Different dropwise modes of alkali also had an impact on the products phase, normal-dripping was easy to formγ-FeOOH, anti-dripping or dropping simultaneously to generateγ-FeOOH andα-FeOOH mixed phase. External magnetic field under the same conditions could promote formation ofα-FeOOH.(3) Using the preparedγ-FeOOH as precursor for the study of boiling liquid-phase conversion. The results showed that: the magnetic field could accelerate the boiling liquid-phase conversion ofγ-FeOOH toα-Fe₂O₃. By analyzing the intermediate sample, we found that the role of external magnetic field could speed up the dissolution ofγ-FeOOH and make solution Fe³⁺ concentration achieveα-Fe₂O₃ nucleation saturation concentration in a relatively short time. Besides in the role of the external magnetic field, we investigated the precursor ofγ-FeOOH crystallization, initial pH of returning fluid, heating rate, catalyst effects of Fe²⁺.We concluded that low degree of crystallization ofγ-FeOOH, pH near neutral, quick heating rate , and the addition of moderate catalyst Fe²⁺(β=0.01,P=[Fe(â…¡)]/[Fe(â…¢)]) speeded up the conversion ofγ-FeOOH toα-Fe₂O₃.Under the best conditions, we got the products of sphericalα-Fe₂O₃ particles about size 20-30nm.