高性能Sm2Fe17Nx磁粉制备关键技术研究

采用粉末冶金工艺制备了Sm2Fe17Nx永磁粉末,研究了工艺参数对Sm2Fe17合金的显微组织及Sm2Fe17Nx粉末磁特性的影响。结果表明,铸态合金的均匀化、粉末的氮化以及粉碎过程是获得高性能磁粉的关键因素。采用最佳工艺条件制备的磁粉的磁特性为：4πMr=1．24T．iHc=756kA／m,(BH)max=220kJ／m^3。     

还原扩散法制备稀土永磁Sm2Fe17Nx的研究

研究了还原扩散法(R/D)制备Sm2Fe17合金及通过气-固相反应法生成Sm2Fe17Nx(x≈3)化合物的整个工艺过程,并通过XRD和SEM等分析测试手段对还原扩散过程和机理作了理论分析和实验研究,通过VSM分析了Sm2Fe17Nx磁粉的磁滞回线.     

Sm2Fe17Nx永磁材料的研究进展

综述了目前Sm2Fe17Nx化合物及Sm2Fe17Nx磁粉的制备方法，以及Sm2Fe17Nx化合物渗氮过程的条件选择．并进一步指出了Sm2Fe17Nx磁粉的发展现状和趋势。     

HDDR处理的Sm2Fe16.5Ti0.5合金的结构与氮化

采用HDDR及氮化工艺制备了Sm2Fe16.5Ti0.5Ny粉末.铸态Sm2Fe16.5Ti0.5合金存在择优取向,Sm2(Fe,Ti)17主相的214衍射峰增强.均匀化退火后,只有约0.6%的α-Fe(Ti)相与主相Sm2(Fe,Ti)17共存.经不同循环的HDDR工艺处理后,物相组成不发生变化,但α-Fe(Ti)相含量增加.HDDR工艺有助于获得细晶结构,提高磁粉的矫顽力.HDDR处理的合金的氮化由初期的Sm-Fe-Ti合金与氮快速反应阶段及后期氮在合金中的均匀化扩散阶段组成.随着氮化时间的延长,富铁相含量增加.氮化物中Sm2(Fe,Ti)17Ny主相的晶格膨胀行为由HDDR与氮化工艺共同决定.在500℃氮化2h后,796kA/m最大外场下得到的最大矫顽力为164.9kA/m,氮化12h时后得到最大剩磁45.7Am2/kg.     

HDDR处理的Sm2Fe16Ti1Nx化合物高能球磨的研究

在用HDDR法制备Sm2Fe16Ti1Nx氮化物过程中,研究了高能球磨对氮化物粉末的形貌、物相结构及磁性能的影响.发现高能球磨Sm2Fe16Ti1Nx氮化物使粉末颗粒细化的过程可描述为大粉末颗粒→压延成层片状→断裂成短棒状及球形颗粒→压延成层片状→断裂成球形小颗粒,并在球磨一定时间后使粉末中的Sm2(FeTi)17Nx主相完全非晶化,α-Fe含量增高且没有非晶化.球磨后粉末的矫顽力随着球磨时间的延长而降低,而剩磁在球磨短时间时降低,再延长球磨时间又增高,在球磨较长时间到Sm2(FeTi)17Nx主相完全非晶化后又使剩磁降低,最高磁场下的磁化强度值则随着球磨时间的延长而增加.手研磨后粉末的矫顽力随研磨时间的延长而逐渐升高而剩磁及最高场下磁化强度值变化不大.     

磁场下球磨处理各向异性纳米级Sm2Co17磁粉的制备与分析

2∶17型SmCo稀土永磁合金以良好的温度特性和较高的磁性能已成为不可或缺的高温永磁器件,通过球磨工艺,利用有机试剂庚烷和油酸对2∶17型Sm(CobalFe0.07Cu0.088Zr0.025)7.5磁粉表面包覆预处理,并在磁场强度为1.5T的外磁场下,对该磁粉进行细磨0.5～20h,制备得到厚度为20～100nm、具有各向异性能的纳米级磁片,其对应的磁性能(BH)m为127.36kJ/m3。     

Sm3(Fe,Ti)29Nx/α-Fe双相纳米磁性材料的微结构与磁性能

研究了熔体快淬工艺及添加元素Ti对Sm-Fe合金相的形成及结构的影响,成功制备了Sm3(Fe,Ti)29Nx/α-Fe双相纳米耦合永磁材料.研究发现,快淬薄带由Sm3(Fe,Ti)29和α-Fe两相组成,晶化前在纳米晶周围存在部分非晶相,晶化后的晶粒间晶界平直光滑、且晶粒间结合紧密没有界面相,为晶粒间直接接触耦合.对甩带后的样品采用750℃保温10min的晶化退火得到的颗粒比较细小且均匀.氮化磁粉磁滞回线的第二象限没有出现明显的台阶,表现为单相永磁材料的特点,说明硬磁相Sm3(Fe,Ti)29Nx与软磁相α-Fe晶粒之间的交换耦合作用已形成.     

Sm2Fe17和Sm10.5Fe88.5Zr1.0的氮化行为

通过真空电弧炉制备了Sm2Fe17和Sm10.5Fe88．5Zr1．0母合金，铸态Sm2Fe17先经均匀化处理后再氮化．而Sm10.5Fe88．5Zr1．0则不经均匀化退火而直接在高纯氮气中氮化。运用扫描电子显微镜和X射线衍射技术对其氮化行为进行了研究。薄片扩散实验表明氮在Sm2Fe17中的扩散要比在Sm10.5Fe88．5Zr1．0中的扩散快。运用Fick第二定律通过理论计算得出直径为20μm的Sm2Fe17合金和Sm10.5Fe88．5Zr1.0合金球形粉末粒子，实现充分氮化的时间为10h和16h。实际粉末实现完全氮化的时间要比理论计算的时间少。这和粒径分布、颗粒表面状态、氮化过程产生的微裂纹以及实际条件和理想条件的差异有关。对于直径为20μm的粉末，氮化时间为6h时氮化已基本完成，氮化时间过长．Sm2Fe17Nx会发生分解。     

合金元素对Sm2Fe17Nx微观结构和性能的影响

综述了合金元素的添加对Sm2Fe17Nx稀土永磁材料的微观结构以及性能的影响.介绍了取代元素的分类,从理论和研究现状等方面分析和总结了合金元素对Sm2Fe17Nx稀土永磁材料的热稳定性、磁性能以及工艺性能的影响规律,并对今后Sm2Fe17Nx稀土永磁材料的研究和开发提出了建议.     

粘结Sm0.88 Dy0.12 Fe2合金的制备工艺与性能研究

采用树脂粘结法制备了Sm0．88Dy0.12Fe2合金样品,研究了粘结剂的含量、模压压力、磁粉粒度对样品密度、磁致伸缩性能、电阻率和抗压强度的影响规律。结果表明3个制备工艺参数对粘结Sm0．88Dy0.12Fe2合金的磁致伸缩性能具有较大影响,而对样品的电阻率的影响不十分明显。同时粘结剂的含量和模压压力对粘结Sm0．88Dy0.12Fe2合金样品的抗压强度具有一定影响。     

脉冲磁场退火对纳米晶复合Nd8.5Fe77Co5Zr2.7Ga0.6B6.2永磁合金磁性能的影响

对快淬Nd8.5Fe77Co5Zr2.7Ga0.6B6.2合金,采用脉冲磁场下热处理的方法制备纳米晶复合永磁材料,研究脉冲磁退火对合金的晶化过程、相组成、交换耦合作用以及磁性能的影响,结果表明,同常规退火相比,脉冲磁退火降低了合金的最佳退火温度,改善了合金的微结构,从而增强了软、硬磁性晶粒间的交换耦合作用,明显提高了合金的磁性能,经670℃脉冲磁退火后合金具有最佳的磁性能,即iHc=586kA/m,Jr=1.01T,(BH)max=138kJ/m3,最大磁能积比常规退火工艺条件下提高了15%。     

NiFe_2O_4/T-ZnO_w复合材料的制备及磁性能

采用化学镀法在四角氧化锌晶须(T-ZnO_W)表面包覆NiFe_2O_4镀层,制备了NiFe_2O_4/T-ZnO_W复合材料。利用X射线衍射仪、扫描电镜、能谱分析仪、振动样品磁强计对镀覆前后T-ZnOw的结构、形貌等进行了表征。结果表明,化学镀覆后,在T-ZnO_W表面包覆了致密的尖晶石型NiFe_2O_4镀层,T-ZnO_W针尖部位生成的镀层厚度比根部薄。NiFe_2O_4/T-ZnO_W复合材料具有软磁特性。随着退火温度的升高,复合材料的饱和磁化强度和矫顽力逐渐升高,在800℃达到最高。     

绝缘包覆工艺对Fe78Si9B13非晶磁粉芯磁性能影响研究

实验以气流破碎的Fe78Si9B13非晶粉末为原料制备磁粉芯。采用扫描电镜和B-H分析仪研究了绝缘包覆工艺过程中添加钝化剂以及粘结剂和绝缘剂的添加量对磁粉芯磁性能的影响。结果表明添加钝化剂可以有效地提高磁粉芯的频率特性,降低磁损耗,增大品质因数;增加绝缘剂的添加量可以降低磁粉芯的涡流损耗,但过多的绝缘剂又会降低其磁导率;最佳的粘结剂添加量为3.5%。     

Nanocrystallization kinetics of amorphous Fe81B13.5Si3.5C2 magnetic ribbons

The kinetics of the nanocrystallization of amorphous Fe₈₁B_13.5Si_3.5C₂ ribbon is studied. The changes in the microstructures and magnetic properties of ribbons annealed at 425 and 495 °C for 0.5-10 h were investigated using an X-ray diffractometer (XRD), Mössbauer spectroscopy (MS), differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM). The changes in the surface morphology were observed by a changed atomic force microscope (AFM). The XRD patterns and the Mössbauer spectrums show the formation of nanocrystallites of α-Fe(Si), Fe-B, Fe₃C and Fe₃Si of different grain sizes when annealed at different temperatures. The nanocrystallization kinetics of the Fe₈₁B_13.5Si_3.5C₂ ribbon are described by an Avrami growth curve with an exponent values of 1.34 and 1.01 for the isothermal annealing at 425 and 495 °C, respectively. AFM topography pictures and surface image show that the density of the microstructure and the size of the grain increase as higher annealing temperatures are used.     

Crystal structure and magnetic properties of Cu4NiSi2S7

The structure of the compound Cu₄NiSi₂S₇ has been determined. It crystallizes in a new, monoclinic distorted sphalerite superlattice with the parameters: $\text{a}\text{= 11.551}\text{A}\text{?}$, $\text{b}\text{= 5.313}\text{A}\text{?}$, $\text{c}\text{= 8.165}\text{A}\text{?}$, β = 98.72°, $\text{V}\text{= 495.2}\text{A}\text{?}{}^3$, Z = 2, space group C2. The analogous compound Cu₄NiGe₂S₇ is isotypic. At a Neél temperature T_N = 20.2 K, Cu₄NiSi₂S₇ becomes antiferromagnetic. The magnetic moment of the paramagnetic phase is 2.6μ_B.     

Microstructure and magnetic properties of plasma-sprayed Fe73.5Cu1Nb3Si13.5B9 coatings

Amorphous and nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ coatings were formed by plasma-spraying micron-sized powders onto H62 brass substrates and aluminum pipes. The coatings are about 0.2-0.3 mm in thickness with fully dense and low porosity. The microstructure of the coatings is classified into two regions, namely, a full amorphous phase region and homogeneous dispersion of α-Fe nanoscale particles with a scale of 30-70 nm. The hardness of the amorphous and nanocrystalline coatings is about 960 HV_100g. Coercivity (Hc), saturation induction (B₈₀₀), and initial relative permeability (μ_i) of the coatings are 144 A/m, 0.27 T, 249, respectively, under 800 A/m direct current (DC) magnetic field. The magnetic shielding performance is good under DC magnetic field and its magnetic shielding effectiveness (SE) is 10-12 dB at coating thickness of 0.45 mm under static magnetic field of 2-40 Oe. The SE increases by increasing the coating thickness when the magnetic field frequencies are 50, 100 and 200 Hz with an intensity of 0.85 Oe. The results indicate that the amorphous and nanocrystalline alloy coatings can be good for some magnetic shielding applications.     

Broadening of the magnetic entropy change in La0.75Ca0.15Sr0.10MnO3

A broad table-like entropy change (ΔS) at room temperature has been observed in the ferromagnetic compound La_0.75Ca_0.15Sr_0.10MnO₃, which is analyzed in the concept of Landau theory and with critical exponent analysis obtained from the magnetization measurements. The change in entropy in La_0.75Ca_0.15Sr_0.10MnO₃ is discussed in the light of magnetoelastic coupling between the magnetization and the lattice distortion. Application aspects of this unusual broad magnetocaloric effect with relative cooling power of 107 J kg⁻¹ in an applied magnetic field of 1.6 T with an operating temperature range of 93 K around the room temperature are also discussed.     

Hydrothermal synthesis and magnetic properties of Co0.2Cu0.03Fe2.77O4 nanoparticles

Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles with different morphologies have been synthesized directly via a simple hydrothermal method. The effects of pH value, precursor concentration, reaction temperature and surfactant on the particle size were discussed. X-ray diffraction analyses showed that the as-synthesized Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles possessed typical spinel structure. Scanning electron microscope images showed different morphologies of the particles, including truncated octahedron and octahedron. It was indicated that well-dispersed Co_0.2Cu_0.03Fe_2.77O₄ nanoparticles can be synthesized at pH values ranging from 11 to 13, and reaction temperature of 160 °C. The particle size decreased from 18 to 10 nm after the addition of sodium dodecyl sulphate at the pH value of 9. The magnetic measurement showed that the as-prepared Co-Cu spinel ferrite nanoparticles possessed hard magnetic property.     

Syntheses and magnetic properties of Eu3B2O6 and Sr3B2O6

Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions $\text{a}{}_{\mathrm{R}}\text{=6.697}\text{A}\text{?}$, α_R=85.17° for Eu₃B₂O₆, and $\text{a}{}_{\mathrm{R}}\text{=6.695}\text{A}\text{?}$, α_R=85.00° for Sr₃B₂O₆. The equivalent hexagonal lattice parameters are $\text{a}{}_{\mathrm{H}}\text{=9.069}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.542}\text{A}\text{?}$, and $\text{a}{}_{\mathrm{H}}\text{=9.046}\text{A}\text{?}$, $\text{c}{}_{\mathrm{H}}\text{=12.566}\text{A}\text{?}$ respectively. Eu₃B₂O₆ appears to be ferromagnetic below 7.5K.     

可磁分离Fe3O4/g-C3N4复合材料的制备及其性能

为了利用Fe₃O₄的磁响应性及石墨相C₃N₄（g-C₃N₄）优良的光催化活性,首先采用高温热聚合法,以尿素为前驱体制备g-C₃N₄,然后采用水热法合成了可磁分离Fe₃O₄/g-C₃N₄复合材料。利用TEM、XRD、TGA、BET和振动样品磁强计（VSM）等多种测试手段表征分析Fe₃O₄/g-C₃N₄复合材料的形貌、晶型结构、比表面积、成分、饱和磁化强度等。通过模拟太阳光下Fe₃O₄/g-C₃N₄复合材料光催化吸附降解亚甲基蓝（MB）的实验,评价了Fe₃O₄/g-C₃N₄复合材料的吸附性能及光催化性能。结果表明,可磁分离Fe₃O₄/g-C₃N₄复合材料具有较大的比表面积,约为71.89 m²/g;且具有较好的磁性,饱和磁化强度为18.79 emu/g,可实现复合材料的分离回收;光照240 min时,Fe₃O₄/g-C₃N₄复合材料对MB的去除率为56.54%。所制备的Fe₃O₄/g-C₃N₄复合材料具有优良的吸附性能、光催化活性和磁性,并可通过外加磁场进行分离与回收。