烧结钕铁硼制备快淬带性能的研究

采用单辊急冷法熔融NdFeB烧结磁体(工业产品)制取快淬永磁合金.合金薄带具有很高的矫顽力,剩磁比达到0.5以上.合金带经过适当的热处理,可消除制备冷速过高时退磁曲线及磁性能的缺陷.随着烧结磁体磁性能等级提高,其快淬合金的剩磁和最大磁能积均提高,内禀矫顽力下降.由N50烧结磁体制备的快淬合金的较佳性能为:Br=0.84T、Hci=959kA/m、(BH)max=112 kJ/m3.X射线衍射分析表明快淬合金以Nd2Fe14B相晶粒为主,只有少量杂相.     

添加元素对稀土粘结磁体退磁曲线方形度的影响

采用快淬法制备镨基(Nd,Pr)10.5(Fe,Co)83.5-xMxB6(M=Zr,Nb,Ti)系列粘结磁体,研究添加Zr、Nb和Ti等元素对快淬合金显微结构和磁性能的影响.(Nd,Pr)10.5(Fe,Co)83.5B6合金中适量添加Zr、Nb和Ti元素能有效细化合金晶粒,获得细小、均匀的晶粒,平均晶粒尺寸为50～70 nm.添加Zr、Nb和Ti元素的粘结磁体,由于晶粒细化和非磁性相对磁畴畴壁钉扎的共同作用,Hk/Hcj值大幅度增加,退磁曲线方形度得到明显改善,磁性能也显著提高.在Zr、Nb和Ti3种元素中,Zr对细化晶粒和提高磁性能的效果最好.含1％Zr(原子分数)的(Nd,Pr)10.5(Fe,Co)82.5Zr1B6合金薄带晶粒细小、均匀,平均尺寸约为60 nm,其粘结磁体退磁曲线方形度最好,Hk/Hcj值达到了39.9％,剩磁Br为0.675 T,内禀矫顽力Hci为616 kA/m,最大磁能积(BH)m为77 kJ/m3.     

Ti添加对快淬Pr基永磁合金磁性能与显微结构的影响

采用快淬法制备了Pr基(Nd,Pr)10.5Fe81.5-xTixCo2B6(x=0.0,1.0,2.0,3.0,4.0,5.0)系列粘结磁体,研究了添加Ti元素对快淬合金显微结构和磁性能的影响。Ti元素能有效细化合金的晶粒,添加3at%Ti的合金,晶粒细化到约70nm,且大小均匀;添加量超过3at%,晶粒进一步细化,但均匀性变差。含Ti3at%的(Nd,Pr)10.5Fe78.5Ti3Co2B6合金,粘结磁体磁性能达到最佳值,Br=0.655T,Hci=681kA/m,(BH)m=68kJ/m3。Ti元素低于3at%,合金晶粒粗大,磁性能较低;超过3at%后,富Ti的晶间相加厚,晶粒间的交换作用和剩磁增强效应减弱,且晶粒大小不均匀,合金的内禀矫顽力虽然增加,但剩磁Br和最大磁能积(BH)m降低。     

Nb元素对纳米晶（Nd，Pr）FeB／α-Fe复合永磁合金显微结构与磁性能的影响

添加Nb元素会使(Nd,Pr)FeB/α-Fe纳米晶复合永磁合金的平均晶粒尺寸显著减小.用AFM观察快淬(Nd,Pr)10.5Fe81.5-xNbxCo2B6(x(at%,下同)=0.0,0.5,1.0,1.5,2.0,2.5,3.0)合金条带自由表面的显微结构,晶粒平均直径从不含Nb的(Nd,Pr)10.5Fe81.5Co2B6合金的175 nm减小到含2 at%Nb的(Nd,Pr)10.5Fe79.5Nb2Co2B6合金的68 nm,晶粒平均直径细化了61%;当Nb超过2 at%后,Nb含量的增加对晶粒的细化作用明显减弱,含3 at%Nb的合金平均晶粒直径为63 nm,比含2 at%Nb仅细化了7.3%.含2 at%Nb的(Nd,Pr)10.5Fe79.5Nb2Co2B6合金,粘结磁体磁性能达到最佳值,Bτ=0.665 T,Hci=748 kA·m-1,(BH)m=73 kJ·m-3.Nb元素含量在2 at%Nb以下时,合金晶粒粗大,磁性能较低;超过2 at%后,富集在晶界处的富Nb晶间相加厚,晶粒间的交换作用和剩磁增强效应减弱,合金的内禀矫顽力虽然增加,但剩磁Bτ和最大磁能积(BH)m降低.     

Alnico合金添加量对Nd-Fe-B薄带磁体的微结构和磁性能的影响

在Nd_2Fe_(14)B合金中添加具有调幅分解能力的Alnico合金,采用熔体快淬法在40m/s的快淬速度下制备出名义成分为Nd_2Fe_(14)B+x%Alnico(x=0,3,5)的薄带磁体,探究多元复合添加Alnico合金组成元素对薄带磁体的微结构和磁性能的影响。试验结果表明:在薄带磁体中形成了由硬磁性相Nd2Fe14B、软磁性相Fe7Co3、弱磁性或非磁性相Al_3Ni和Al_(13)Co_4以及部分非晶相组成的合金体系,在x=3时获得了最佳的综合磁性能:Hc=665kA/m,Br=0.58T,Br/Bs=0.60。     

混合合金法添加Ga对Nd—Dy—Fe—Co—B烧结磁体的磁性和微观结构的影响

对用混合合金法制备的Nd7.69Dy6.62Fe64.33Co14.83B6.53/Ga烧结磁体的磁性和微观结构进行了研究。结果表明：添加0.5%（质量分数）的Ga后;磁体的iHc由1232kA/m升高到1819kA/m,在200℃放置0.5h后的磁通不可逆损失由33.3%下降到5%以下,当Ga的添加量达到1.0%左右时,Ga的作用达到最大值,微观结构分析表明,不添加Ga磁体的晶粒边界,尤其是晶界角隅处多呈现弯曲和凹凸不平的形状,添加Ga磁体的晶粒边界则呈现平滑和近似直线的形状,烧结过程中Ga原子置换Nd2Fe14B相中Fe原子形成Nd2Fe14-xGaxB相,与此同时,被置换的Fe原子进入液相与富和Nd相、富B相反应形成新的Nd2Fe14B（或Nd2Fe14-xGaxB）相,这是导致磁体的磁性和微观结构发生变化的主要原因。     

动态晶化对纳米晶交换耦合Nd2Fe14B/α-Fe磁性能和显微组织的影响

为改善纳米晶交换耦合Nd2Fe14B/α-Fe永磁合金微结构以提高磁性能，用熔体快淬和动态晶化热处理的方法制备了纳米晶交换耦合Nd2Fe14B/α-Fe永磁体，采用XRD和TEM等方法系统研究了动态晶化热处理对Nd10.5（FeCoZr）83.4B6.1永磁体磁性能和显微组织的影响。结果表明：与传统晶化相比，动态晶化可以在相同的晶化温度下缩短晶化时间，同时能细化晶粒，增强晶粒间磁交换耦合作用，提高磁性能。Nd10.5（FeCoZr）83．4B6.1合金快淬薄带经700℃，10min动态晶化热处理后，制得的粘结磁体获得最佳磁性能，剩磁Br=0．685T，内禀矫顽力Hcj=732kA／m，磁感矫顽力Hcb=429kA／m，最大磁能积（BH）m=75kJ／m^3。     

Nd_2Fe_(14)B/Fe_3B基纳米复合磁体的热磁行为

研究了快淬方法制备的Nd4 Fe80 B16和Nd4 Fe76Co3 Hf0 5Ga0 5二种合金的磁性和热行为。发现添加Hf和Ga能有效地降低Nd2 Fe14 B/Fe3 B复合磁体的晶化速度。矫顽力 (iHc)随后时效处理的不同仅有轻微的变化 ,这表明iHc 对晶粒尺度和交换耦合是磁不敏感参量。实验所观察的Mr 和Hc 随晶粒的增大变化不大 ,这与在临界晶粒尺寸 (dc)附近所做的数字计算理论不一致。本文对在各向同性纳米复合材料中的剩磁和矫顽力与晶粒尺寸的关系进行了分析。     

Cu/Ti复合添加对Nd2Fe14B/α-Fe纳米双相磁体磁性能和相分解的影响

用熔体快淬法制备了高性能纳米双相耦合Nd2Fe14B/α-Fe磁体，研究了Cu/Ti复合添加对Nd2Fe14B/α-Fe纳米双相磁体磁性能和相分解的影响，实验结果表明，Cu和Ti复合添加可提高快淬带的晶化温度，并且改变α－Fe相析出方式，α－Fe直接从TbCu7结构的亚稳相分解中析出，而不是从非晶相中析出，这有利于形成α－Fe相晶粒细小且均匀分布的微结构，其最优磁性能为Hc=384kA/m(4.8kOe),σ＝110Am^2/kg(110emu/g),(BH)max=120kJ/m^3(15MGOe)。     

Nd2Fe14B／Fe3B基纳米复合磁体的热磁行为

研究了快淬方法制备的Nd4Fe80B16和Nd4Fe76Co3Hf0.5Ga0.5二种合金的磁性和热行为。发现添加Hf和Ga能有效地降低Nd2Fe14B/Fe3B复合磁体的晶化速度。矫顽力（iHc)随后时效处理的不同仅有轻微的变化,这表明iHc对晶粒尺度和交换耦合是磁不敏感参量。实验所观察的Mr和Hc 随晶粒的增大变化不大,这与在临界晶粒尺寸（dc）随近所做的数字计算理论不一致。本文对在各向同性纳米复合材料中的剩磁和矫顽力与晶粒尺寸的关系进行了分析。     

Comparison of geometries and electronic structures of polyacetylene,polyborole, polycyclopentadiene,polypyrrole, polyfuran,polysilole, polyphosphole,polythiophene, polyselenophene and polytellurophene

Geometries of monomers through hexamers of cylopentadiene, pyrrole, furan, silole, phosphole, thiophene, selenophene and tellurophene, and monomers through nonamers of borole were optimized employing density functional theory with a slightly modified B3P86 hybrid functional. Bandgaps and bandwidths were obtained by extrapolating the appropriate energy levels of trimers through hexamers (hexamers through nonamers for borole) to infinity. Bandgaps increase with increasing π-donor strengths of the heteroatom. In general, second period heteroatoms lead to larger bandgaps than their higher period analogs. Polyborole is predicted to have a very small or no energy gap between the occupied and the unoccupied π-levels. Due to its electron deficient nature polyborole differs significantly from the other polymers. It has a quinoid structure and a large electron affinity. The bandgaps of heterocycles with weak donors (CH₂, SiH₂ and PH) are close to that of polyacetylene. For polyphosphole this is due to the pyramidal geometry at the phosphorous which prevents interaction of the phosphorus lone pair with the π-system. The bandgap of polypyrrole is the largest of all polymers studied. This can be attributed to the large π-donor strength of nitrogen. Polythiophene has the third largest bandgap. The valence bandwidths differ considerably for the various polymers since the avoided crossing between the flat HOMO — 1 band and the wide HOMO band occurs at different positions. The widths of the wide HOMO bands are similar for all systems studied. All of the polymers studied have strongly delecalized π-systems.     

The production,recovery, properties,and applications of americium and curium

Nuclear reactors produce mixtures of Am-241 and Am-242, and beta decay of plutonium produces radioactively pure Am-241. Curium is a product of intense neutron exposure of Pu-239. Separation and purification processes for americium and curium include ion exchange, precipitation, and both liquid-liquid and molten-salt extraction. This article reviews the principal production, recovery, and waste treatment processes and briefly discusses the chemical properties and uses of americium and curium.     

Microstructure,Mechanical Properties,and Corrosion Behavior of MoNbFeCrV,MoNbFeCrTi, and MoNbFeVTi High-Entropy Alloys

The development of high-entropy alloys(HEAs) has stimulated an ever-increasing interest from both academia and industries.In this work, three novel MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi HEAs containing low thermal neutron absorption cross section elements were prepared by vacuum arc melting. The microstructure, mechanical properties, and corrosion behaviors were investigated. A dominant body-centered cubic(BCC) phase was present in all these three HEAs. In addition,an ordered Laves phase was found to be another major phase in both MoNbFeCrV and MoNbFeCrTi alloys, whereas an ordered BCC(B2) phase was observed in the MoNbFeVTi alloy. The phase formation in these three alloys was discussed. It is found that the formation of the secondary phase in these alloys is mainly ascribed to the large atomic size difference and electronegativity difference. All the three HEAs show high hardness, high yield strength but limited plasticity. Moreover, the MoNbFeCrV, MoNbFeCrTi and MoNbFeVTi alloys exhibit excellent corrosion resistance in both deaerated 1 mol/L NaCl and 0.5 mol/L H _2 SO _4 solutions at room temperature. However, further composition adjustment and/or thermomechanical processing is required to enhance the mechanical properties of the three alloys.     

Electrical resistivities and phase transformations of lanthanum,cerium, praseodymium,and neodymium

The electrical resistivities of high purity lanthanum, cerium, praseodymium, and neodymium were investigated as a function of temperature over the range from room temperature to near the melting points of the metals. Transformation temperatures were observed in these metals which were confirmed by supplementary X-ray diffraction studies.     

敏感创新品牌——星球石墨设备的发展之路

民营企业要发展,靠的是什么？南通星球石墨设备有限公司在前十年里,年产值均未能超千万元,但进入新世纪之后,企业效益却突飞猛进,2005年、2006年销售额过亿元。回顾这几年来的道路,对市场的敏感、对产品的创新和对品牌的构建是星球公司发展过程中不可缺,步的因素。