Microstructure of pre-sintered permanent magnetic strontium ferrite powder

The microstructure and characteristics of pre-sintered strontium ferrite powder were investigated by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The present study shows that the pre-sintered strontium ferrite powder is provided with a certain particle size distribution, which results in high-density magnets. The strontium ferrite particle has a laminar hexagonal structure with a size similar to ferrite single domain. Ferric oxide phase due to an incomplete solid phase reaction in the first sintering is discovered, which will deteriorate the magnetic properties of ferrite magnet. In addition, the waste ferrite magnets with needle shape arranging along C axis in good order into the powders are found, which have no negative effects on finished product quality.

Research progress of permanent ferrite magnet materials

Permanent ferrite magnet materials are extensively employed due to their exceptional magnetic properties and cost-effectiveness.The fast development in electromobile and household appliance industries contributes to a new progress in permanent ferrite materials.This paper reviews the deveolpement and progress of permanent ferrite magnet industry in recent years.The emergence of new raw material,the advancement of perparation methods and manufacturing techniques,and the potential applications of permanent ferrite materials are introduced and discussed.Specifically,nanocrystallization plays a crucial role in achieving high performance at a low cost and reducing reliance on rare earth resources,and therefore it could be a promising development trendency.

TEM observation of sintered permanent magnetic strontium ferrite

Sintered permanent magnetic strontium ferrites were studied using transmission electron microscopy to investigate the microstructure morphology and its correlation with the magnetic properties. The present study shows that the microstructure of sintered permanent magnetic strontium ferrites is an important parameter in determining their magnetic properties. The microstructure morphology in low-performance ferrite magnet is obviously different from high-performance one. The magnetic properties of sintered permanent strontium ferrite depend strongly on the orientation degree of strong magnetic crystals. The presence of ferric oxide phase in ferrite magnet can deteriorate the magnetic properties. Moreover, proper quantities of crystal defects are beneficial to high coercive force due to the fixing of magnetic domain.

Synthesis and characterization of La doped M-type hexagonal barium ferrite fine powders

The hexagonal BaLa x Fe 12- x O 19 fine powders with M type structure were synthesized by sol gel method. The pH of the solution, the molar ratio of nitrate to citric acid and the calcination temperature were investigated to clarify the forming conditions of the ferrites. The crystal structure, grain size, form and magnetic properties were studied by means of XRD, SEM and vibrating sample magnetometer. It is concluded that at pH of 7.0 or so, molar ratio of nitrate to citric acid of 1/3 and calcination temperature of 850 ℃(1 h), 1 000 ℃, M type BaLa x Fe 12- x O 19 fine powders with a particle size of less than 300 nm was obtained. [

Magnetic properties of M-type strontium ferrites with different heat treatment conditions

The effects of heat treatment conditions on the magnetic properties and microstructure of M-type strontium ferrite according to calcination temperature were analyzed.Strontium ferrite Sr0.06Ca0.52La0.52Fe11.68Co0.22O19magnetic powder was prepared by a standard ceramic process.During experiments,the calcination temperature was varied from 1180 to 1260℃,and sintering temperature was fixed.While the M-phase(SrFe12O19)existed with hematite(Fe2 O3)in the powder calcined at below 1220℃,the pure M-phase was observed in the powder calcined at over1240℃.With an increase in the calcination temperature,the magnetization of the calcined powder increases,meanwhile,the coercivity decreases.The magnetization is improved by decreasing the lattice constant c and activating the Fe3+-OFe3+superexchange interaction,and the coercivity decreases by the large particle sizes due to the grain growth.

Development of high-performance dry-pressed anisotropic permanent ferrite for La-Ca-Sr-Co system

In this work,the BMS-12 pre-sintered material was used as the basic material,and the optimal secondary additive addition amount was found by the wet pressing process.Then,the anisotropic ferrite material was prepared by dry-pres sing method,and the effects of camphor adhesives,calcium stearate lubricant and powder particle size on the magnetic properties were studied.The experimental results show that the appropriate addition amount of camphor adhesive and calcium stearate lubricant is 0.6 wt%and 0.8 wt%,respectively.High remanence and coercivity can be obtained for particle size of 0.85-1.00μm.Superior dry-pressed magnet ferrite was prepared with typical properties of magnetic induction intensity of Br=421 mT,induction coercivity of Hcb=296 kA·m-1,intrinsic coercivity of Hcj=369 kA·m-1 and maximum energy product of(BH)max=33.3 kJ·m-3,which have reached the level of TDK corporation product of FB5 D.This shows that the dry-pressed magnet of La-Ca-Sr-Co system has higher remanence and intrinsic coercivity than the traditional wetpressed Sr-ferrite.

新型定子聚磁式铁氧体永磁磁通切换电机研究

磁通切换电机作为一种无刷电机,其定转子采用双凸极结构,转子仅由硅钢片叠压而成,定子内置有集中绕组和永磁体,运行时只需一组功率开关器件和二极管即可实现电机的控制,因此,具有结构简单、控制方便、可靠性高等优点,广泛应用于风机泵类等高速负载。该文提出一种铁氧体永磁单相磁通切换电机结构,并对该电机的基本结构和工作原理进行深入分析。根据电机性能目标,对其进行电磁设计,确定电机几何尺寸参数,并提出消除该电机起动死区的转子分段结构方案。与一台尺寸相同的电励磁单相磁通切换电机进行全面对比,验证所提电机在静态性能和瞬态性能上的优势。最后制作样机,并对所提出电机进行实验测试。

高性能La-Co共替代M型永磁铁氧体的磁各向异性增强机理研究进展

自20世纪末以来,La-Co共替代的M型铁氧体备受关注,已成为高性能永磁铁氧体的基础材料.Co2+的未淬灭轨道矩被认为是增强铁氧体单轴各向异性的原因,但其微观作用机理尚未完全解释清楚.为了满足铁氧体材料日益增长的性能需求,理解其磁各向异性增强机理至关重要,并寻求从根源上的提升、低成本和高效的方法,以制定开发高性能产品的指导原则.本文综述了一系列研究工作,旨在确定Co离子在晶格中的取代位置,这是增强磁各向异性的关键.这些研究为进一步提高永磁铁氧体的磁性能提供了重要的材料设计参考.

轻稀土镧取代M型钡铁氧体超微粉末的合成与表征

利用溶胶 凝胶自蔓延高温合成法制备了稀土镧掺杂钡铁氧体BaLaxFe12 -xO19超微粉末。讨论了起始溶液pH值、柠檬酸配比、煅烧温度等对粉末性能参数的影响。用X射线衍射仪、扫描电子显微镜和振动样品磁强计等对粉末的结构、形貌和磁学性能进行了研究。

纳米BaFe_(12)O_(19)永磁铁氧体的制备、结构和磁性的研究

In this paper, the nanometer permanent magnetic BaFe12O19 powder was synthesized by a novel method of independent nucleation and crystallization steps and subsequent heat treatment,during the synthesis, Ba(NO3)2, Fe(NO3)2 and NH4HCO3·NH2COONH4 were used as starting materials. The effect of crystallization process and heat treatment conditions on the particle size, microstructure and magnetic properties of powder was studied by using XRD, TEM and vibration sample magnetometometer techniques.XRD results showed that the hematite, α Fe2O3, was the main phase in the powder at heat treatment temperatures below 650℃ and its amount in the powder was decreased with increasing temperature and small amount of α Fe2O3 was still remained after being heated at 900℃ for 8hrs. BaFe12O19 was formed about 650℃ and its amount increased in the powder as temperature raised and the higher temperature was needed to attain considerable amount of BaFe12O19 and ideal nanometer BaFe12O19 particle in the powder. The temperature between 40℃～60℃ in the crystallization process was favor to the formation of good BaFe12O19 crystal and to the good magnetic properties of the powder. TEM showed that the particle size in the powder increased with the enhancement of the temperature and the powder crystallized at 40℃ and heated at 800℃ for 8hrs afterwards had a very homogenous particle size distribution, and that the powder heated at 900℃ for 8hrs with the same crystalline condition as the former had a typical hexagonal shape and a chain aggregation. Specific saturation and residential magnetizations and coercive force of the powder increased monotonically with the increase of temperature, and reached 39.86A·m2·kg-1, 23.96A·m2·kg-1, 480kA·m-1 at 900℃, respectively.

不同稀土元素掺杂M型钡铁氧体超微粉末的磁性研究

利用溶胶 凝胶自蔓延高温合成法制备了 4种稀土元素 (La、Nd、Sm、Gd)掺杂钡铁氧体超微粉末。就稀土元素的种类、稀土掺杂量、合成工艺条件对钡铁氧体磁学性能的影响进行了较系统的研究。

热处理温度对BaFe_(12)O_(19)粉体微结构和磁性的影响

以 Ba(NO3 ) 2 、Fe(NO3 ) 2 和 NH4HCO3 ·NH2 COONH4为反应原料 ,采用成核 /晶化隔离法和后续热处理工艺过程 ,制备了平均粒径 5 0 nm的永磁铁氧体 Ba Fe12 O19粉体 .用 X射线衍射、透射电子显微镜及磁测量手段分析研究了粉体的微观结构与磁性能 .结果表明 ,热处理温度决定粉体的相组成、微观结构和磁性 .当热处理温度升高到 65 0℃时 ,粉体中出现 Ba Fe12 O19永磁相 ,随着热处理温度进一步升高 ,磁性 Ba Fe12 O19结晶进一步完善 ,晶粒长大 ,形成六角形片状粉体 ,粉体的比饱和磁化强度 σs、比剩余磁化强度 σr和矫顽力 Hc增大 .经过 90 0℃热处理后的粉体 ,矫顽力可达到 480 k A/m.

各向异性的粘结钕铁硼/铁氧体永磁复合材料的磁性能

采用高性能的各向异性ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ磁粉和铁氧体磁粉与塑料复合，制成了各向异性粘结ＮｄＦｅＢ／铁氧体复合永磁材料，研究了它们的磁性能。结果表明，随ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ含量增加，各向异性的塑料粘结ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ／铁氧体复合永磁材料磁性能ｂＨｃ和密度几乎是线性增大，而ｊＨｃ，（ＢＨ）ｍａｘ和Ｂｒ开始都增大，当达到一定值后基本保持不变，出现一平台，随后又继续增大，但ｊＨｃ与Ｂｒ和（ＢＨ）ｍａｘ的平台值所对应的铁氧体／ＨＤＤＲ－Ｎｄ－Ｆｅ－Ｂ的比例却不一样。这是由于这两种不同磁性能的磁粉混合后颗粒之间的相互作用随着混合比例也会发生变化所致。同时环氧树脂种类也对ＨＤＤＲ－ＮｄＦｅＢ／铁氧体的磁性能有显著影响。

我国永磁行业的发展现状

回顾评述我国磁性材料行业的发展历程与现状。我国是稀土资源大国 ,也是永磁材料和稀土永磁材料的生产大国。从建国至今 5 0余年的时间 ,我国的永磁行业取得了巨大成就 ,成为世界永磁材料的制造中心和永磁材料的消耗大国。但我国的永磁行业仍然面临技术、市场、规模和专利许可等方面的问题和不足。

稀土Dy掺杂SrFe_(12)O_(19)永磁铁氧体的结构与性能

研究了掺杂稀土Dy对锶铁氧体制备工艺、结构与性能的影响关系。研究表明,取向磁场对铁氧体磁性能的影响十分显著:随着取向磁场强度的增加,锶铁氧体晶粒发生的晶面择优取向度也增大,剩磁Br、最大磁能积(BH)max和矫顽力Hc均有上升趋势。烧结温度的影响则较复杂:随着烧结温度的增加,剩磁Br和最大磁能积(BH)max均有上升趋势,而矫顽力Hc则呈下降之势。通过在Y30牌号SrFe12O19预烧料基础上掺杂0.2%Dy2O3,经700kA/m磁场、4414N/cm2压力湿法成型的样品在1230℃温度下烧结1h后的磁性能达到了Br=398mT、Hcj=254kA/m和(BH)max=29.1kJ/m3,它与不掺杂Dy2O3的样品相比分别提高了12mT、31kA/m和0.7kJ/m3。

X射线荧光光谱熔融法测定锶永磁铁氧体中各组分含量

本文使用自制标准样品,采用混合熔剂熔融样品,用X射线荧光光谱法(XRF)测定锶永磁铁氧体半成品中Fe、Sr、Si等元素的含量。熔融制样有效地消除了矿物效应,并降低了基体效应的影响。实验结果表明,本法准确度高,重现性好,平行测定11次相对标准偏差(RSD)可达到0.1%。该方法用于实际样品分析,其结果与传统化学分析方法结果相符。

不同溶胶组成对BaLa_(0.3)Fe_(11.7)O_(19)纳米粉末生成过程的影响

利用溶胶-凝胶自燃烧高温合成法制备了稀土 La 掺杂钡铁氧体 BaLa0.3Fe11.7O19 纳米粉末。用 X 射线衍射仪、振动样品磁强计和透射电镜对不同溶胶组成下合成的粉末的结构、磁学性能、粒度及形貌进行了研究。试验表明:用氨水调节溶液起始 pH 值以及加入适量的柠檬酸和乙二醇是合成结构纯净、性能优异的 BaLa0.3Fe11.7O19 纳米粉末的 2 个关键步骤。在溶液起始 pH 值呈弱酸性(7.0 左右)、柠檬酸/硝酸盐=3、煅烧温度为 850℃,保温 1 h 的条件下, 利用溶胶-凝胶自燃烧高温合成法可以制备出粒径为 36 nm 的磁铅石结构的 BaLa0.3Fe11.7O19 粉末,其磁学性能优异,比饱和磁化强度可达 65.54 A·m2/kg,矫顽力可达 433 kA/m。

粘结剂对锶铁氧体磁性能的影响

为了提高干压永磁铁氧体的产品性能,降低生产成本,减少樟脑对人身的危害和对环境的污染,试验采用聚合物粘结剂来替代樟脑作为干压永磁锶铁氧体的粘结剂。利用聚合物粘结成型工艺,得到了高的永磁性能:Br=388mT,HcB=215.7kA·m-1,(BH)max=27.1kJ·m-3,这已接近于向等级铁氧体磁粉(Y30BH)的湿压产品水平。研究了成型温度对永磁性能的影响,用X-ray衍射方法分析了锶铁氧体的相结构,用金相显微镜和扫描电子显微镜观察了锶铁氧体的微观组织与形貌。

M型永磁铁氧体的现状与进展

评述了 M型永磁铁氧体的现状与进展。讨论了 M型永磁铁氧体在工业生产中的关键技术问题 ,如预烧工艺、微粉加工、料浆在磁场成型时的取向。详细地调研了高性能锶铁氧体的化学成分、显微结构、宏观的和亚微观的磁性能。57Fe Mossbauer谱显示非化学计量的 M型永磁铁氧体性能与 4 f1与 4 f2 晶位谱线强度相关。La2 O3掺杂对稳定磁铅石结构和提高永磁体性能有益。La3+和 Zn2 +联合取代对 M型六角铁氧体晶粒取向度、质量密度、亚微米尺寸结构和饱和磁化强度有明显的作用 ,正像人们期望的那样 ,M型锶铁氧体的 Br和 (BH)

以炼钢烟尘为原料制备硬磁铁氧体恒磁瓷的研究

利用炼钢平炉尘为原料，通过晶型转化成功地制成了（ＢＨ）＿（ｍａｘ）为７．２８ｋＪ·ｍ￣（－３）的各向同性钡铁氧体（属于黑瓷系），其性能达到部颁标准。本研究采用Ｘ射线衍射，电子衍射和显微形貌分析的方法，论述并证明了钡、锶铁氧体在制备过程中各种因素的影响和作用，如：原料的晶体结构及其转化，掺杂物质种类和数量的控制等。制备之前，对粉尘的形貌、结构和组成进行了研究，同时也研究了最大磁能积和成型、球磨、预烧、第二次烧结以及添加物质的影响之间的关系。文中展示了用形貌相与反应产物的模拟相表示相应反应过程中的化学物理状态。并且，钡、锶铁氧体六角形结构与磁性能之间的关系也在本工作中进行了研究，开辟了一条全新的原料来源，对于治理环境污染具有重大的意义。