【作者】 张春祥；

【导师】 杨绪杰；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2010， 博士

【摘要】 本文面向热塑性高分子感应加热应用来开展微纳米磁性粒子的制备与表征,对制备过程、结构控制、磁性能以及在热塑性高分子材料中的发热与传热行为等进行了研究,主要内容包括以下几个方面：以无机硝酸盐为原料,采用两种软化学法（乙二胺四乙酸络合法和硬脂酸法）在相对较低的温度下分别制备了系列超细镍锌尖晶石铁氧体(Ni_1-X0ZnxFe2O4,系统研究了Zn对晶体结构以及磁学性质的影响。对不同方法制备镍锌铁氧体的反应历程进行了探讨。结果表明硬脂酸法制备纯相的产物所需的处理温度较高（900℃）,团聚程度较重；乙二胺四乙酸络合法制备的产物结构疏松,粒子分散均匀,对系列产物的磁性能研究发现,热处理温度、时间、取代离子浓度等制备条件对比饱和磁化强度、矫顽力、剩磁和居里温度等有较大的影响,适当调整制备条件能够降低粉体粒径、优化物相组成、改善磁学性能,使磁性粒子的居里温度能够满足热塑性高分子熔融加工所需的窗口温度。系列产物的频谱研究表明,Ni₁-xZn_xFe₂O₄铁氧体的致密化程度与晶粒的大小能够影响存储磁能和磁损耗的大小,提高热处理温度以及增加锌离子取代浓度有助于在较低的磁场频率中,获得较高的存储磁能和较大的磁损耗,满足感应加热的应用需求。采用乙二胺四乙酸络合法和硬脂酸法合成了系列Y型六角晶系铁氧体粉末(Ba₂Co_2-xZn_xFe₁₂O₂₂),系统研究了焙烧温度、初始溶液pH值、取代离子浓度等工艺参数对产物微结构与磁性能的影响,并探讨了六角晶系铁氧体的反应历程。结果表明通过乙二胺四乙酸络合法制备了形貌均匀、尺寸分布较窄的六角片状粉体,目标产物是通过多步反应实现的,络合物的条件稳定常数对于最终产物的结构组成具有较大影响。锌离子对钴离子的取代只是引起晶胞的膨胀,没有改变铁氧体的晶型结构。居里温度满足T_c=352.66-146.28x的线性关系。磁导率的实部和虚部随着取代量的增加均有所提高,共振频率则不断下降。在1～10MHz范围内磁损耗随着焙烧温度和取代量的增加快速增加。用硬脂酸法制备的目标产物颗粒较小但尺寸分布较宽,BaCO₃对于中间相（у-Fe₂O₃）具有稳定作用。与乙二胺四乙酸络合法制备的同组分产物相比,具有较小的比饱和磁化强度和较大的矫顽力,不利于弱交变磁场中的感应发热应用。采用液相还原法制备了系列形貌可控、粒度分布均匀的超细镍粉,系统研究了溶剂体系、反应溶液的pH值、镍盐初始浓度、反应温度以及表面活性剂的种类和浓度等工艺条件对粒径、形貌和磁性能的影响。结果表明,长链结构的表面活性剂具有调控粒径、形貌和团聚程度以及改善镍粉热稳定性的作用；所制粒径为50～900nm镍粉均表现出明显的铁磁性,比饱和磁化强度均低于体相金属材料,且随着粒径的减小而下降,可能与粒子不同的比表面导致有关；随着粒径的增加,复数磁导率的实部和虚部均出现增大,磁损耗峰具有向低频移动的趋势。从实现热塑性树脂基复合材料熔融加热的均匀性、居里温度控制的智能性以及加热的快速性等角度出发,基于磁场理论,计算了交变磁场中磁滞损耗、涡流损耗、趋肤效应以及热量传递等相关参数,并考察其与高分子基体中感应发热的关系。结果表明镍锌铁氧体、Y型六角晶系铁氧体和镍粉三类磁性粒子在饱和磁场中的磁滞损耗密度大小与材料的组分与粒径存在依赖性；镍锌铁氧体和Y型六角铁氧体在1～10MHz频率范围内的涡流损耗和趋肤效应可以忽略,而镍粉的粒径必须控制在1.1μm以内,才能避免影响；加热速率与粒子的体积分数、磁场频率、磁滞损耗密度以及材料的热力学参数相关,在1.5MHz、150 Oe交变磁场中体积分数为10%的Ni_0.7Zn_0.3Fe₂O₄、Ba₂Co_1.5Zn_0.5Fe₁2O₂₂和Ni三类粒子在PEEK基体中的理论升温速率分别为69.3、17.0和8.6℃／s。采用溶液浸渍法制备了三类磁性粒子/PPESK复合材料薄层,考察了磁性粒子/PPESK复合材料的磁滞发热行为。结果表明磁场强度对于复合材料体系的最终温度和加热速率是关键因素之一,足够的磁场强度才能满足材料的居里温度智能控制和具有实际应用价值的加热速率。体积分数为10%的Ni_0.7Zn_0.3Fe₂O₄、Ba₂Co_1.5Zn_0.5Fe₁₂O₂₂和150nmNi三类粒子在PPESK基体中初始加热速率可达9.7、6.2和5.5℃／s,最终温度为394、266和329℃,具有良好的感应发热效果。更多还原

【Abstract】 In this dissertation, a series of magnetic particles suiting for induction heating application of thermoplastic polymers were prepared and characterized. The preparation process, crystal structure control, magnetic properties, heating and heat transfer behavior in thermoplastic polymer were studied. The main research results are as follows:A series of ultrafine spinel ferrites (Ni_1-xZn_xFe₂O₄) were synthesized at relatively low temperature by two soft chemical methods （EDTA complexing method and stearic acid method） using nitrates as raw materials. The effects of Zn content on the crystal structure and magnetic properties were studied. The reaction mechanism of different methods was preliminary discussed. The results indicated the pure phase products could be obtained at 900℃by stearic acid method and severe aggregations existed. The products obtained by EDTA conplexing method had high dispersible and loose structure. The study on the magnetic properties found the process conditions such as calcination temperature, time and the content of Zn ion had a large impact on the magnetization, coercivity, remanence and Curie temperature. The particles could ensure the induction heating of thermoplastic polymer by properly adjusting particles size, composition and magnetic properties. The magnetic spectra showed the capacity of magnetic energy storage and loss were related to the densification and grain growth of Ni_1-xZn_xFe₂O₄. The increasing energy loss and storage suited for the induction heating at moderate frequency could be achieved by increasing the calcination temperature and the content of Zn ion.A series of Y type hexaferrite (Ba2Co_2-xZn_xFe₁2O₂2) powders were prepared by EDTA complexing method and stearic acid method. The effects of calcination temperature, initial pH, ion concentration on the microstructure and magnetic properties were systemically investigated. The reaction process was discussed in detail. The results showed the products via EDTA method had uniform hexagonal shape and narrow particle size distribution, which were obtained by multi-step reactions. The structure and composition of products had a large dependence on the conditional stability constant of complexes precursor. The substitution of Co²⁺by Zn²⁺could not change the crystal structure except for expanding the lattice. The Curie temperature of products has a linear relation:Τ_c=352.66-146.28x. With increasing substitution, the real and imaginary parts of complex permeability increase and the resonance frequency decrease. The increasing calcination temperature and substitution could improve the loss in 1～10MHz frequency. The products obtained by stearic acid method were small in particle size and broad in distribution. The existence of BaCO₃ had good stabilization on the transition phase y-Fe2CO₃. Compared with EDTA method, products with the same composition had smaller magnetization and larger coercivity, which was not suitable for the induction heating under low alternating magnetic fields.Ultrafine nickel powders with controllable morphology and size were prepared by reducing nickel salts solution. The effects of the solvent ratio, pH value, Ni²⁺ concentration, temperature, different surfactants and concentration on the structure and magnetic properties are systemically studied. The results show the surfactants with chain structure can improve the thermal stability of products and control particles growth and aggregation. The obtained 50-900nm nickel powders showed evident ferromagnetism. The saturation magnetization was below the corresponding bulk counterpart and decreased with smaller size due to the different surface area. With increasing particle size, the real and imaginary parts of complex permeability increase and the loss peak shifts to lower frequency.Based on the magnetic field interaction theories, the parameters including hysteresis, eddy current loss, skin effect and heat transfer were preliminarily calculated to understand the uniform, Curie temperature control and quick induction heating process in thermoplastic polymer. The results indicated the dependence of hysteresis energy density of Ni-Zn ferrites, Y type hexaferrites and nickel powders on the composition and particles size in saturation fields. The impacts of eddy current loss, skin effect on the induction heating may neglect in 1～10MHz when Ni-Zn ferrites, Y type hexaferrites and< 1.1μm nickel powders are as susceptors. The heating rate is associated with the volume fraction, frequency, hysteresis energy density and the thermal properties. Under 1.5MHz frequency,150Oe alternating field, the heating rates of 10%volume fraction of Ni_0.7Zn（0.3）Fe₂O₄, Ba₂Co_1.5Zn_0.5Fe₁₂O₂₂and 150nm nickel in PEEK polymer are theoretically 69.3,17.0and 8.6℃/s.Three kinds of magnetic particles/PPESK composites layers were produced by solution impregnation process and their hysteresis heating behaviors were investigated. The results showed the field strength had a large impact on the finial temperature and heating rate of composites. Enough field strength is necessary to Curie temperature control and quick heating rate in the practical application. The experiment heating rates of 10% volume fraction of Ni_0.7Zn_0.3Fe₂O₄, Ba₂Co_1.5Zn_0.5Fe₁2 and 150nm nickel in PPESK matrix are 9.7,6.2 and 5.5℃/s, which shows good induction heating characteristics.更多还原