Preparation, Mechanism And Liquid Transformation Of Products In The Presence Of EDTA

Because of the wide application of nanosized iron oxides in many aspects, such as catalysis, antisepsis, pigments and magnetic recording materials, at the same time, Fe₂O₃ and FeOOH are also components of corrosion products of steel. Nanosizedα- Fe₂O₃ can be prepared from Fe(â…¢) ion and Fe(â…¡) ion. On one hand, the nanosizedα- Fe₂O₃ prepared from Fe(â…¢) ion is of good quality, but the cost is high; on the other hand, the nanosizedα-Fe₂O₃ prepared from Fe(â…¡) ion costs lowly but is poor in uniformity . Therefore,the way to explore the best-quality iron oxides with low cost and being suitable for the industrialized production has been attracting much attention.This article described the preparation of nanosized iron oxides, using FeSO₄ as the raw material by catalytic oxidation of Fe(OH)₂ suspension in the presence of trace EDTA, and investigated the formation conditions of different kinds of nanosized iron oxides. Subsequently, we have a primary discuss on liquid phase transformation of products and transformation mechanisms. This research can provide some data for the preparation of iron oxides using FeSO₄ as the raw material, and can also benefits the investigation of corrosion mechanisms,soilchemistry,geochemistry chemistry and so on.The main results of the thesis are as follows:1.γ-FeOOH were prepared, using FeSO₄ as the raw material by air oxidation of Fe(OH)₂ under irradiation by visible light in the presence of trace EDTA. Many factors were discussed such as concentration,temperation,precipitant and lighe. The result revealed that :when pH=8.6,and FeSO₄ concentration≤0.2M, the low crystallization ofγ-FeOOH will be obtained. Along with the increase of concentration, the crystallization degree ofγ-FeOOH is improved, and theα-FeOOH phase emerges. If the concentration of FeSO₄ continue to increase, the product is a single product ofα-FeOOH, and the reaction time will be increased; When the reaction temperature is within the scope of 14-20℃, the products are surelyγ-FeOOH, and with the rise of temperature, the crystallization degree of the productγ-FeOOH gradually decreased; Using the ammonia as precipitation, near Raft-γ-FeOOH will be obtained 2. Using the low crystallineγ-FeOOH as the precursor product, in the presence of trace Fe(â…¡), the various factors'affection on theγ-FeOOH catalyst's transformation intoα-Fe₂O₃ were discussed. In the presence of trace Fe(â…¡) and near-neutral conditions, low crystallineγ-FeOOH can be quickly converted into 30 nmα-Fe₂O₃ uniform spherical particles when the system is heated to the boiling temperature at rate in the scope of 5 to 7.4℃·min^-1; And compared with static water bath aging, the boiling reflux easily lead to the liquid phase's transformation from low crystalline FeOOH intoα-Fe₂O₃.3. Liquid phase transformation situation ofγ-FeOOH in higher degree of crystallization has been investigated. The results show that: relatively rapid warming (12.2℃·min^-1) is beneficial to get higher axial ratio and less branches pure phaseα-FeOOH; At the same time the reaction time can also affect the morphology of product, the appropriate reaction time is helpful to get relatively higher axial ratio and less branchesα-FeOOH; Using precipitation of ammonia can get less branches and larger sizeα-FeOOH than using precipitation of NaOH in the transformation formγ-FeOOH toα-FeOOH.4. Liquid phase transformation of precursor productγ-FeOOH in different crystallization and catalytic conversion mechanism have been discussed under the condition of coexistence of EDTA and visible light. By tracking the change of Fe (â…¢)-t, t-pH in the liquid phase transformation process with different crystallizationγ-FeOOH and products at different time, it is found that the liquid phase transformation process ofγ-FeOOH is actually a process of dissolution and recrystallization. The lower degree of crystallization ofγ-FeOOH the faster it dissolved in the process of boiling reflux, and the more easily achieving the critical concentration ofα-Fe₂O₃. Moreover, along with the reaction, theα-FeOOH andα-Fe₂O₃ nucleate at the same time andα-FeOOH gradually transformed intoα-Fe₂O₃; Theγ-FeOOH of high degree crystallinity dissolved slowly in the process of boiling reflux, and a small number of Fe³⁺ can reach nucleating saturation concentration ofα-FeOOH, thus get theα-FeOOH products. Adding Fe(â…¡) to solution can makeγ-FeOOH dissolve faster, and benefit transformation toα-Fe₂O₃.