【作者】 刘建兴；

【导师】 薛向欣；

【作者基本信息】 东北大学 ， 钢铁冶金， 2019， 博士

【摘要】 铁氧体是一类具有优异磁性能的铁氧化物,在过去的50年中,铁氧体材料得到了广泛的研究和应用。在钢材生产过程中会产生大量的铁鳞和酸洗废液,其经过处理后可获得含铁量极高的氧化铁红。但是由于氧化铁红原料本身具有粒径分布不均匀,形貌复杂等特点,严重影响了以其为原料制备铁氧体的磁性能,同时也限制了铁氧体的应用,并且铁氧体材料的磁性能往往与它们的粒径大小、原子占有率和形貌密切相关。因此,材料科学家们正致力于开发简单而有效的方法来制造尺寸和形貌可控的铁氧体材料,从而达到调控其磁性能的目的。本文结合材料制备过程中“自上而下”和“自下而上”方法的特点,先探索了对氧化铁红原料进行纳米化或非晶化处理,然后利用处理后的原料作为反应物前驱体探索性的制备一些不同粒径和形貌铁氧化物(SrFe12O19、CoFe2O4、NiFe2O4、γ-Fe2O3和α-Fe2O3)。利用X-射线衍射(XRD)、场发射扫描电镜(FE-SEM)、透射电镜(TEM)、傅里叶红外光谱(FTIR)、X-射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis)和振动样品磁强计(VSM)等表征测试手段对制备的铁氧化物晶体结构、粒径、形貌和磁性能进行了表征,具体的研究内容和结果如下:(1)在高能球磨过程中,行星式球磨机的自转与公转转速比对球磨过程有重要的影响。在熔盐法制备SrFe12O19过程中,研究了 Fe2O3与SrCO3摩尔比、焙烧温度及熔盐类型对SrFe12O19磁性能的影响。研究结果表明:当Fe2O3与SrCO3摩尔比为5.3时,能合成单相的SrFe12O19并表现出较好的磁性能;SrFe12O19的矫顽力随着合成温度的升高呈现出先增大后减小的趋势;熔盐类型对制备SrFe12O19的晶体结构、原子占有率、粒径分布、形貌及磁性能产生了重要的影响,样品的饱和磁化强度实测值(Ms(obv))和通过原子占有率计算得到值(Ms(XRD))表现出基本一致趋势;且在NaCl-KCl共熔盐中制备的SrFe12O19样品获得相对比较高的矫顽力(Hc=4043 Oe)。(2)采用水热法制备CoFe2O4中,研究了不同含铁前驱体、pH、反应时间及添加无机离子对CoFe2O4生成及磁性能的影响;在熔盐合成法中,主要研究了不同熔盐类型对CoFe2O4生成及磁性能的影响。研究结果表明:采用水热法时,随着pH的升高,有利于CoFe2O4的形成;以氧化铁红直接作为反应原料时,反应速度较慢,难以形成单相的CoFe2O4;以经KOH活化后的氧化铁红为原料时,CoFe2O4样品矫顽力随着pH升高出现增大的趋势,在pH=10的条件下,添加无机离子对CoFe2O4的矫顽力产生了一定的影响。不同的熔盐类型对CoFe2O4的晶体结构、原子占有率、粒径分布、形貌及磁性能产生了重要的影响,在NaCl-NaF熔盐中合成的CoFe2O4样品表现出最大的饱和磁化强度,其数值为63.28 emu/g。(3)采用水热法合成NiFe2O4中,研究了pH和添加无机离子对NiFe2O4生成及磁性能的影响;在熔盐合成法中,主要研究了不同熔盐的类型对NiFe2O4生成及磁性能的影响。研究表明:在水热法中,pH和添加无机离子对NiFe2O4的磁性能影响比较小,制备的NiFe2O4样品展现出较低的矫顽力和饱和磁化强度。不同的熔盐类型对NiFe2O4的晶体结构、原子占有率、粒径分布、形貌及磁性能产生了重要的影响,对比不同熔盐条件下制备的NiFe2O4样品的矫顽力和饱和磁化强度,发现矫顽力值与饱和磁化强度呈现出负相关的趋势,这与Stoner-Wohlfarth理论相一致。(4)以NaOH熔盐处理氧化铁红,经过水解后再进行热处理制备出了γ-Fe2O3。研究表明:利用XRD、X-射线光电子能谱(XPS)和UV-vis漫反射光谱对获得的样品进行表征分析,判定获得的产物为γ-Fe2O3;α-Fe2O3和NaOH反应形成NaFeO2中间相,利用FTIR光谱对水解后的产物进行表征,发现水解产物中存在着具有尖晶石结构(FeO4)的特征振动峰,其符合γ-Fe2O3的晶体结构的特征。此过程突破了传统以γ-FeOOH和Fe3O4为前驱体来制备γ-Fe2O3的方法。(5)以氧化铁红为原料,采用非晶化处理和再结晶的方法制备出了不同形貌的α-Fe2O3纳米粒子。研究表明:采用水热再结晶时,不同的阴离子(OH-、Cl-、SO42-、NO3-、CH3COO-)对制备α-Fe2O3形貌、禁带宽度和磁性能产生了影响。由Fe(OH)3转变为α-Fe2O3过程中,首先是发生纳米颗粒的聚合,随着反应时间的延长,聚合的块体开始结晶形成具有特定形貌的产物,最后通过奥斯特瓦尔德熟化机理再进一步生长成具有结晶性良好的产物。在煅烧法中,添加不同的无机离子(KCl、K2SO4、KNO3、KBr)制备得到了粒径小于50 nm的α-Fe2O3纳米粒子,添加不同的无机离子对α-Fe2O3样品的禁带宽度影响较小,但是对磁性能影响比较大。更多还原

【Abstract】 Ferrites are a large class of oxides with remarkable magnetic properties,which have been investigated and applied during the last～50 years.A large amount of iron scale and pickling waste liquid will be produced in the process of steel production.Iron oxide red with high iron content can be obtained by treating iron scale and pickling waste liquor.However,the ferrite red material itself has the characteristics of uneven particle size distribution and complex morphology,which seriously affects the magnetic properties of prepared ferrites and it also limits the application of ferrites.The magnetic properties of ferrite materials are often closely related to their particle size,cation occupation and morphology.Therefore,materials scientists are working on developing simple and effective ways to prepare ferrite materials with controllable size and morphology,and thus to adjust their magnetic properties.In this paper,according to the characteristics of the methods of "top-down" and"bottom-up" in the process of material preparation,the nanometer or amorphous treatment of iron oxide red raw materials was first explored by "top-down" method,and then some iron oxides(SrFe12O19,CoFe2O4,NiFe2O4,γ-Fe2O3 and α-Fe2O3)with controllable particle size and morphology were prepared by "bottom-up" method with using the treated raw materials as reactant precursor.The size,morphology,composition,and magnetic properties of these materials were characterized using the following complementary analytical techniques:X-ray power diffraction(XRD),field emission scanning electron microscopy(FE-SEM),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),UV-vis spectroscopy(UVvis),and vibrating sample magnetometer(VSM).The specific research contents and results are as follows:(1)In the process of high energy ball mill,the speed ratio of rotation to revolution have an important influence on the process of ball mill.The effects of molar ratio of Fe2O3/SrCO3,roasting temperature and molten salts type on the magnetic properties of SrFe12O19 were studied.The results show that SrFe12O19 can be synthesized with good magnetic properties,when the molar ratio of Fe2O3/SrCO3 is 5.3.The coercivity of SrFe12O19 firstly increased and then decreased with the increase of synthesis temperature.The type of molten salt has an important influence on the crystal structure,atom occupancy,particle size distribution,morphology and magnetic properties of SrFe12O19.The measured values of saturation magnetization(Ms(obv))and the calculated values(Ms(XRD))using atom occupancy of the samples showed a basically consistent trend.The SrFe12O19 sample prepared in NaCl-KCl eutectic molten salts obtained relatively good magnetic properties(Hc=4043 Oe).(2)The effects of different iron-containing precursors,pH,reaction time and the introduction of inorganic ions on the formation and magnetic properties of CoFe2O4 prepared by hydrothermal method.The effects of different molten salt types on the formation and magnetic properties of CoFe2O4 were studied with molten salt synthesis.The results showed that the formation of CoFe2O4 was propitious with the increase of pH.When iron oxide red was used as raw material,the reaction speed was slow and it was difficult to form singlephase CoFe2O4.When iron oxide red activated by KOH was used as raw material,the coercivity of CoFe2O4 samples tended to increase with the increase of pH.Under the condition of pH=10,the addition of inorganic ions has a certain impact on the coercivity of CoFe2O4.Different types of eutectic molten salts have important effects on the crystal structure,atom occupancy,particle size distribution,morphology and magnetic properties of CoFe2O4.CoFe2O4 sample synthesized in NaCl-NaF eutectic molten salts exhibits the maximum saturation magnetization,and the value is 63.28 emu/g.(3)The effects of pH and inorganic ions on the formation and magnetic properties of NiFe2O4 were studied with hydrothermal method.Also,the effects of different types of molten salt on the formation and magnetic properties of NiFe2O4 were studied.The results showed that in hydrothermal method,pH and inorganic ions had little effect on the magnetic properties of NiFe2O4,and the prepared NiFe2O4 samples showed low coercivity and saturation magnetization.Different types of molten salt have an important impact on the crystal structure,atom occupancy,particle size distribution,morphology and magnetic properties of prepared NiFe2O4.By comparing the coercivity and saturation magnetization strength of NiFe2O4 samples prepared under different molten salt conditions,it is found that the coercivity value is negatively correlated with the saturation magnetization strength,which is consistent with Stoner-Wohlfarth theory.(4)The y-Fe2O3 was prepared with iron oxide red by pre-treated with molten sodium hydrate,hydrolysis and subsequent heat treatment method.The results showed that the product was turned out to γ-Fe2O3 by XRD,XPS and UV-vis.The intermediate phase of NaFeO2 was formed,when the α-Fe2O3 reacted with NaOH.FTIR spectrum was used to characterize the hydrolyzed product,and it was found that the characteristic vibration peak of spinel structure(FeO4)existed in the hydrolyzed product,which was in line with the characteristic of y-Fe2O3 crystal structure.This process breaks through the traditional method of using y-FeOOH and Fe3O4 as precursors to prepare y-Fe2O3 by heat treatment method.(5)Nano-sized α-Fe2O3 particles with different morphologies were prepared by the amorphous and recrystallization processes using iron oxide red.The results showed that different anions(OH-,Cl-,SO42-,NO3-,CH3COO-)affected the morphology,band gap width and magnetic properties of the prepared α-Fe2O3.During the process of Fe(OH)3 transformation into α-Fe2O3,the polymerization of nanoparticles was occurred in the initial stage of crystallization reaction.With the extension of the reaction time,the polymerized bulk began to crystallize and form crystal structure with a specific morphology.Finally,through the Ostwald ripening mechanism,the polymerized bulk was further grown into fine crystalline products.In the calcination process,α-Fe2O3 nanoparticles with particle size less than 50nm were prepared by introducing different inorganic ions(KCl,K2SO4,KNO3,KBr).Different inorganic ions have less effect on the band gap of prepared α-Fe2O3 samples,but more effect on the magnetic properties.更多还原