| is one kind of important inorganic pigment. It is widely used in the biomedical engineering, catalysis and fine ceramics, plastic products, coating, magnetic materials, electronics and other fields because of its high physical and chemical stability, high catalytic ability, its fine sunlight resistance, climate resistance,ultraviolet proof ability, high hiding power and non-toxic etc. The methods of production of pigment level a-Fe2O3 are nitric acid method and mixed acid method at current moment, but during these processes there are NOx produced and a large number of the wastewater which could pollute the environment. Therefore, it is important for researching on the production method which can obtain iron oxide red with good pigment performance, low cost and non-pollution.In this paper, pure phaseδ-FeOOH was synthesized with ferrous sulfate as raw materials and hydrogen peroxide as the oxidant. Ultrafine iron oxide red was prepared withδ-FeOOH as the seed by using two kinds of methods. The product was characterized by a variety of testing methods, discussing the influence of preparation conditions on the reaction products and measuring the performance ofα-Fe2O3 with different preparation methods. The main research contents and results are summarized as follows:(1)δ-FeOOH was synthesized with FeSO4 and NaOH as raw materials and H2O2 as the oxidant, and the influence of preparation conditions on the reaction products was discussed. The results indicated:concentration of FeSO4 no more than 0.9mol/L, mass fraction of H2O2 more than 20%, stirring speed for 500r/min at initial pH 8.6, pureδ-FeOOH can be prepared.(2)Ultrafine iron oxide red was prepared withδ-FeOOH as the seed by using two kinds of methods. Firstly,δ-FeOOH via catalytic phase transformation changed intoα-Fe2O3 nucleation, and through two-step oxidation got uniform sphericalα-Fe2O3 particles. Product color is dimer than iron red by nitric acid method. Secondly, crystallized very completely pseudocubeα-Fe2O3 particles with diameter of 90-100nm was prepared byδ-FeOOH seed through direct air oxidation, and product color was more bright than nitric acid method product.(3)We studied on preparation process ofα-Fe2O3 byδ-FeOOH seed via transformation and two-step oxidation, and determined the best reaction conditions:adjusting initial pH=9, β=0.05, adding water to dilute 700ml, boiling half an hour, the seed concentration for 0.04 mol/L, air flow for 100L/h, and constant temperature above 90℃air oxidation ten hours. Diameter of product at 90℃and 100℃respectively was 60nm and 90nm.(4)The mechanism of preparation process ofδ-FeOOH as seed was discussed. In weak alkali conditions, Fe2+ catalyzesδ-FeOOH seed phase transformation into a-Fe2O3 nucleation. Because the reaction process takes off protons, iron constantly dissolves and generates Fe2+. Air oxidates Fe2+ to generateα-FeOOH, and then a-FeOOH through dissolution-reprecipitation generatesα-Fe2O3 growing on nuclei. Two-step oxidation process releases H+ which continues to dissolve iron, and makes reactions to cycle.(5)This research shows that it is feasible thatδ-FeOOH is used as seed to preparate pure ultrafine iron oxide red. Product accords with national pigment oxide red standards, and this method has many advantages, such as low production cost, non-environmental pollution. So it can completely replace nitric acid method of industrial production. |
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