【作者】 刘昭成；

【导师】 郑雅杰；

【作者基本信息】 中南大学 ， 有色金属冶金， 2011， 博士

【摘要】 本文首次以硫铁矿烧渣为原料,采用水热法制备了云母氧化铁(MIO),开展了云母氧化铁的形成机理及其表面改性和防腐性能研究。硫铁矿烧渣经硫酸酸浸后,以氨水为沉淀剂,在中性条件下采用水热法制得了云母氧化铁。在反应温度为230℃,n(Fe2+)/n(Fe3+)为0.07～0.1,总铁浓度为1.25mo1.L-’,氧化铁红晶种量为5g.L-1及反应时间为30 min的适宜工艺条件下制得云母氧化铁。所得的云母氧化铁为规则的正六边形单晶a-Fe203片状体,粒径约为0.5μm,径厚比为5左右；云母氧化铁中Fe203含量为98.54%,其产品质量达到涂料用云母氧化铁颜料国际标准(ISO 10601-2007)要求。中性条件下,系统研究了Fe2+、Al3+的作用下云母氧化铁的形成机理。Fe2+催化了Fe(OH)3胶体的溶解,促进了α-Fe2O3晶体的生长。随着Fe2+浓度的增加氧化铁粒径逐渐增大,形成的氧化铁粒子为立方体,这是由于SO42-在氧化铁晶体{012}晶面上的吸附所致。A13+存在下,随着Al3+浓度的增加所得氧化铁晶胞参数a和c呈线性减少,其形貌为小片状体,这归功于A13+在氧化铁晶体(0001)晶面的吸附,抑制了氧化铁晶体在z轴方向的生长。模拟硫铁矿烧渣酸浸液制备云母氧化铁实验表明,云母氧化铁的形成归功于A13+在氧化铁晶体(0001)晶面的吸附和SO42-在{012}晶面的吸附而导致受限生长,云母氧化铁形成过程主要以溶解-再结晶机理为主,同时存在固相转化机理。高碱性介质下,以硫铁矿烧渣酸浸液为原料,采用水热法制得云母氧化铁。NaOH浓度对云母氧化铁的制备起决定性作用,随着NaOH浓度的增加,氧化铁形貌由球形体变为片状体,其粒径逐渐增加。云母氧化铁适宜的制备工艺条件为：NaOH浓度≥7.0mol.L-1,总铁浓度为0.94～2.2mo1.L-1,反应温度≥200℃,反应时间为0.5h,搅拌速度为200r.min-1及不需加氧化铁红晶种。该条件下所得云母氧化铁颜色为钢灰色,粒子为均匀大小的片状体,粒径和径厚比分别为7μm、7.0；云母氧化铁中Fe203含量达99.34%,达到涂料用云母氧化铁颜料国际标准(ISO 10601-2007)要求。高碱介质下研究了Al、Si对云母氧化铁晶体生长的影响。研究表明,Al存在下云母氧化铁片状体厚度变薄,且随着Al含量的增加,云母氧化铁粒子粒径逐渐减小,Al以[Al(OH)4]-形式吸附在氧化铁晶体(0001)晶面上；Si存在下阻碍了Fe(OH)3胶体向Fe203相转化,并随着Si含量的增加阻碍作用越强。基于α-Fe203晶体的结晶形态系统地构建了云母氧化铁晶体生长条件,探讨出高碱介质下云母氧化铁的形成归功于OH-在α-Fe203晶体(0001)晶面上的强烈吸附,降低了(0001)面的晶面能,抑制了α-Fe203晶体沿z轴方向的生长,使(0001)面显露。系统研究了云母氧化铁表面改性对亲油性和亲水性的影响。当硬脂酸钠用量为5.0%,球料比为8：1,球磨时间为2h时,云母氧化铁的亲油化度为43.5%,云母氧化铁由亲水性变为亲油性；当KH550用量为1.5%,球料比为8：1,球磨时间为1h时,改性云母氧化铁的初始浊度和静置60min后的浊度均达到最大值,其亲水分散性良好。IR和TG-DSC分析表明,硬脂酸钠改性的云母氧化铁,其表面-OH与硬脂酸发生了脂化反应,云母氧化铁表面带上-CH2-基团,表现出亲油憎水性；云母氧化铁经KH550改性,其表面-OH基团与KH550水解生成的硅醇成氢键结合,并脱水形成Si-O-Fe键。偶联剂高分子链通过空间位阻作用使云母氧化铁在水性介质中稳定分散。XRD和TEM分析表明改性后云母氧化铁晶型和形貌没发生改变。借助电化学阻抗谱技术及涂层附着力分析研究了环氧MIO涂层的防腐性能,比较了不同形貌粒径的氧化铁环氧涂层的防腐性能。开路电位测量结果表明,MIO用量为50%的环氧涂层在3.5%NaCl溶液中浸泡72h后开路电位最高,其防腐性能最佳。电化学阻抗谱实验表明,MIO含量为50%的环氧涂层浸泡32d后涂层电阻最大,为3.5×106Ω·cm2,达到有机涂层阻抗值>1.0×106Ω.cm2要求,具有较好的防腐性能。Machu实验和沸水浸泡实验表明,MIO含量为40%和50%的环氧涂层表面未出现起皮和鼓泡现象,具有较好的涂层附着力。不同粒径MIO环氧涂层和球形氧化铁环氧涂层在3.5%NaCl溶液浸泡10d后,粒径为7.0μm的MIO环氧涂层高频段的阻抗为6.1 0×106Ω·cm2,粒径为1.0μm的MIO环氧涂层高频段的阻抗为1.89×105Ω.cm2,环氧球形氧化铁涂层高频段阻抗为1.01×105Ω.cm2,其防腐性能依次降低。Machu实验和沸水浸泡实验表明, MIO环氧涂层的附着力强于球形氧化铁环氧涂层的附着力。更多还原

【Abstract】 In this dissertation, micaceous iron oxide (MIO) particles have been prepared from pyrite cinders by hydrothermal process for the first time. Its formation mechanism, surface modification and corrosion resistance are investigated.MIO particles were prepared from sulphuric acid leaching solution of pyrite cinders using ammonia as a precipitant by hydrothermal process in neutral condition. MIO particles can be successfully prepared when the optimal parameters of reaction temperature, n(Fe2+)/n(Fe3+), total iron concentration, the amount of red iron oxide seed, and reaction time are set to be 230℃,0.07～0.1,1.25 mol·L-1,5 g·L-1 and 30 min, respectively. As-synthesized MIO particles show regularα-Fe2O3 hexagonal flakes which are about 0.5μm in diameter and with a diameter-to-thickness ratio of 5.0. Besides, the content of Fe2O3 of the prepared MIO is 98.54% and its quality meets the requirements of MIO pigments for paints (ISO 10601-2007).The formation mechanism of MIO has been investigated under the presence of Fe2+ and Al3+ in neutral conditions. Fe2+ could accelerate the dissolution of Fe(OH)3 gels and promote the growth ofα-Fe2O3 crystals. The formedα-Fe2O3 particles are cube in shape, and its particle size increased gradually with higher Fe2+ concentration. The cubic morphology ofα-Fe2O3 particles is attributed to the SO42- adsorption on {012} planes ofα-Fe2O3 crystal. In the presence of Al3+, the cell parameters ofα-Fe2O3 (a and c) decrease linearly with the increasing of Al3+ concentration. And the formedα-Fe2O3 particles are platelet-type, which is attributed to the adsorption of Al3+ ions onto (0001) planes, retarding the crystal growth along z axis. The preparation of MIO from simulated pyrite cinders lixivium, demonstrates that the formation of MIO is ascribed to Al3+ ions adsorption on (0001) planes and SO42-adsorption on {012} planes, which induces growth restriction forα-Fe2O3 crystals. The MIO formation process is dominated by dissolution re-precipitation, though solid-state transformation also happens. MIO particles were also prepared from pyrite cinders lixivium by hydrothermal process in highly concentrated alkaline medium. The concentration of NaOH has played a crucial role in the morphologies of MIO particles. The morphology ofα-Fe2O3 changes from spheres into flakes, and its particle size increases with the increasing of NaOH concentration. The optimal conditions for MIO preparation are concluded as follows:CNaOH(?)7.0 mol·L-1; CFe(Ⅲ)=0.94～2.2 mol·L-1; T(?)200℃; t= 0.5～1.0 h; stirring rate should be 200r·min-1 and there is no need to add red iron oxide seeds. As-prepared MIO particles are quite uniform with flake shape of metallic gray color, the mean particle size and aspect ratio of which are～7.0μm and～7.0, respectively. Furthermore, the content of Fe2O3 in the prepared MIO is 99.34%, and its quality fulfills the standards of MIO pigments for paints (ISO 10601-2007).Effects of Al and Si on MIO crystals growth in highly concentrated alkaline medium have been investigated. The thickness of MIO decreases in the presence of Al and its particle size gradually reduces with the increasing Al content. Al in this system is in the form of [Al(OH)4]-, which is adsorbed on the (0001) planes ofα-Fe2O3 crystals. Si inhibits the phase transformation of Fe(OH)3 gels into Fe2O3 and the inhibition becomes stronger when the content of Si is increased.Based on the crystal habit ofα-Fe2O3, the crystal growth system of MIO was established. It comes to the conclusion that the formation of MIO is due to strong adsorption of OH- on the (0001) planes ofα-Fe2O3 crystal, which reduces surface energy of (0001) planes and retards the crystal growth along z axis, leading to the exposure of (0001) planes.Effects of surface modification on the lipophilicity and hydrophilicity of MIO have been systematically studied. The lipophilic degree of MIO is 43.5% when the optimal modification conditions of sodium stearate, ball to powder and milling time were 5.0%,8:1 and 2 h, respectively. And the modified MIO changes from hydrophilic into hydrophobic. Under the optimal modification conditions of KH5501.5%, ball to powder ratio of 8:1,and milling time of 1h, the initial turbidity and turbidity after standing 60min for modified MIO are the largest, which shows an excellent hydrophilic dispersion. According to IR and TG-DSC analysis, when MIO is modified by sodium stearate, the surface hydroxyl groups of MIO are esterified with stearic acid and -CH2- groups are grafted on its surface, showing oil-water-repellent; when MIO is modified by KH550, the surface hydroxyl groups of MIO are held together with silanol groups from silane hydrolysis by hydrogen bond, and further form Si-O-Fe bond by dehydration. The formed polymer chains of silane coupling agents make MIO disperse well in aqueous media because of its steric hindrance. XRD and TEM analysis results show the crystalline phase and morphology of modified MIO have no change compared with that of unmodified MIO.Corrosion resistance of MIO epoxy coatings was investigated by electrochemical impedance spectra (EIS) and coating adhesion testing. And comparison of corrosion resistance of different morphology and particle size of iron oxide epoxy coatings was conducted. Open-circuit potential measurements show that epoxy coating with 50% MIO possesses the maximum open-circuit potential when they were immersed in 3.5% NaCl solution for 72 h, exhibiting the best corrosion resistant. EIS results show that the coating resistance are higher than 3.5×106Ω·cm2 when epoxy coating with 50% MIO immersed in 3.5% NaCl solution for 32d, which fulfills the requirements of coating impedance >106Ω·cm2 for common organic coatings, showing a better corrosion resistant. Machu test and boiling water immersion test indicate that no peeling and blistering of epoxy coating with amount of 40% and 50% MIO are observed, showing a fine coating adhesion. When epoxy coating with different particle size of MIO and spherical iron oxide immersed in 3.5% NaCl solution for 10 days, EIS results show the impedance at high frequency of 6.10×106Ω·cm2,1.89×105Ω·cm2 and 1.01×105Ω·cm2 for 7.0μm MIO,1.0μm MIO and spherical iron oxide, respectively. Their corrosion resistant decreased one by one. Machu test and boiling water immersion test indicate that the coating adhesion of MIO epoxy coatings is stronger than that of spherical iron oxide epoxy coatings.更多还原