球磨法制备(Gd0.9Dy0.1)5Si4粉末及分析

采用行星式球磨机进行磁制冷材料（Gd0.9Dy0.1)5Si4的纳米粉末制备，在一定的球磨条件下，一定范围内颗粒粒度与球磨时间成正比，并最终制备出纳米级颗粒，但在此过程中，磁性材料的磁性完全消失，估计是由于材料的晶体结构转变为非晶状态和应力共同作用所致。     

Preparation of MgTiO3 Ceramics by High Energy Ball Milling

1 IntroductionMgTiO3ceramic is widely usedin manufacturing ce-ramic capacitors with a super thermal stability,due toitssmall dielectricloss and dielectric constant .However ,thesinteringtemperature of pure MgTiO3ceramicis as highas1 400-1 470 ℃even withfluxingagents .Inaddition,thesinteringrangeis much narrower withthe addition of flux-ing agents ,which makes it difficult to sinter[1].High-energy ball milling is an effective grindingmeans whichinduces a series of physicochemical changesto t…     

Microscopic evidence of destroying the order of magnetic sequence in CuO2 chain by Zn, Ni, Co Doping in Sr14Cu24O41 compound

The Zn2＋, Ni2＋ and Co3＋ doped Sr14Cu24041 compounds were synthesized by standard solid state method. X-ray diffraction results show that the changes in lattice parameters are very small. Selected area electron diffraction patterns （EDPs） show that the diffraction spots corresponding to the CuO2 chain substructure are extended to streaks along a＊ and b＊ directions for all the samples, while the diffraction spots produced merely by the Cu203 ladder substructure are still very sharp. This means that the periodicities of chains in a＊ and b＊ directions are partially destroyed upon doping ofZn, Ni and Co due to that the initial phase of each chain becomes a random variable. The temperature dependence of magnetic properties was measured for every sample. And the number of dimers in CuO2 chain per formula unit （f.u.） and dimer coupling constant are obtained by fitting the temperature dependence of the magnetic susceptibility. It is found that the degree of initial phase disorder is related to the order degree of magnetic sequence in CuO2 chain. For the un-doped sample, the decoupling of dimers is weak, the magnetic sequence is slightly destroyed, and the streaks in EDP are also very weak, which implies the degree of initial phase disorder in CuO2 chain is very low. When Zn2~ and Ni2＋ ions are doped, the number of dimers per f.u. decreases, and the intensity of diffraction streaks increases in comparison with the corresponding spots. Furthermore, when the high spin magnetic ions Co3＋ are doped, the number of holes in Sr14Cu24041 decreases, the magnetic sequence is destroyed very seriously, and the spots in EDP are extended to streaks almost completely. The phenomenon that the diffraction spots ofCuO2 chain extend to streaks in EDP appears as evidence that the magnetic sequence in the CuO2 chain is destroyed by doping of Zn, Ni, Co.     

高能振动球磨作用对纳米Al2O3相变温度的影响

为了探讨球磨作用对纳米A l2O3颗粒相变温度的影响,利用高能振动球磨机分别对纳米A l2O3进行不同时间的球磨,并将球磨作用后的A l2O3粉末在不同温度下进行退火处理。采用XRD、TEM、FT-IR及DTA等方法测定处理前后A l2O3粉末的结构、物相组成及相变温度。结果表明:随着球磨时间的增长,A l2O3的相变温度降低,当球磨时间达50 h时,-γA l2O3到θ-A l2O3相变以及-θA l2O3到-αA l2O3相变的温度均降低了100℃左右;球磨作用促进了A l2O3的晶化,同时可以造成纳米氧化铝的晶格缺陷,是导致相变温度降低的主要原因。     

反应高能球磨制备纳米WC/MgO复合粉末

将WO3、C和Mg粉末按摩尔比为1∶1∶3混合,在室温下用高能球磨法对其进行球磨,经XRD、SEM和TEM分析表明,在球磨到4.7 h时,WO3、石墨和镁之间发生氧化还原反应直接生成了WC和MgO粉末,之后随球磨时间的延长,粉末不断细化.球磨50 h后,得到WC晶粒度和颗粒度分别约为25 nm和100 nm的WC/MgO复合粉末.实验结果和热动力学分析表明,WC/MgO的合成是一个自蔓延反应过程,此反应可以在很短的时间内完成.     

3%C-Cu机械球磨复合粉末的烧结

为了给后续的致密化工序（如热挤压）提供较高质量的烧结坯,用扫描电镜和光学显微镜分析了3%C-Cu机械球磨复合粉末所制备烧结坯的显微组织,并研究了工艺参数对其相对致密度的影响规律。结果表明,烧结温度对未机械球磨混合粉烧结行为的影响很大,而机械球磨复合粉对烧结温度不敏感。真空热压烧结可以明显地促进致密化过程。提高烧结温度、延长烧结保温时间或增加热压压强,均有助于提高烧结坯的相对致密度。在相同条件下,烧结坯的相对致密度随着复合粉末机械球磨时间的延长而降低。     

Phase transformation of nano-grained W(Co, C) composite powder and its phase constitute

1 INTRODUCTION Nano-grained WC-Co cemented carbides with high toughness and high hardness have drawn extensive attention of hard metal industry[1?2]. There are two key processes for the fabrication of this high performance alloy[3?4]. One is the preparation of nanometer WC-Co composite powders, the other is the effective control of grain growth during sintering. At present, great technical breakthrough has been achieved in the preparation of nanometer powders. The typical methods of na…     

Sm、La掺杂TiAl结构和性能的第一性原理计算

为研究稀土元素掺杂对Ti-Al系金属室温延性的影响,基于密度泛函理论第一性原理,应用广义梯度近似(GGA)和局域密度近似(LDA)平面波超软赝势法,建立稀土元素Sm、La掺杂Ti Al晶胞模型,运用Castep计算分析Sm、La两种稀土元素掺杂的Ti Al结构,对本征Ti Al和掺杂Ti Al的结构及力学性质进行分析.结果表明:稀土元素Sm掺入Ti Al后,Ti Al的共价性增强、成键方向性增加、硬度提高、离子性下降、延性降低;稀土元素La掺入Ti Al后,Ti Al的共价性下降、成键方向性减弱、硬度下降、离子性增强、延性提高.稀土元素掺杂金属间化合物,可改善其力学性能.     

Laser-induced phase transformation in chalcogenide glasses investigated by micro-Raman spectrometer

A 488 nm continuous wave （CW） laser was employed in Raman spectrometer to both induce and characterize phase transformation in chalcogenide glasses. Laser-induced Raman inactive changes, structural evolution, and crystallization were observed at laser-irradiated region in GeS2-Sb2S3 glasses. The composition dependence of laser-induced phase transformation was discussed in terms of thermal stability and microstructural modification. It is strongly suggested from these results that fabrication of passive and active chalcogenide glass waveguides, such as refractive index change and nonlinear optical crystal line, is controllable by selecting appropriate glass composition, and convenient by using common CW lasers.     

Mg2FeH6储氢材料的反应机械合金化合成及其放氢性能

以Mg和Fe元素粉末为原料，在双行星式球磨机的氢气气氛中反应球磨，合成Mg2FeH6储氢材料。探讨分别采用Mg和Fe原料配比为化学计量（2：1）和非化学计量（3：1）直接反应球磨，以及采用将Mg和Fe混合粉末在氩气气氛中预磨20h后再通氢反应等球磨方式。研究结果表明：Mg和Fe以非化学计量比（3：1）在氢气气氛中直接球磨所得样品，Mg2FeH6的合成产率最高，达到83．7％；DSC和TGA测试显示样品实际放氢量为2．91％，Mg和Fe以化学计量比（2：1）直接反应球磨得到的Mg2FeH6具有最低的起始放氢温度204．4℃。     

Microstructure and electrical properties of Y2O3-doped ZnO-based varistor ceramics prepared by high-energy ball milling

Y2O3-doped ZnO-based varistor ceramics were prepared using high-energy ball milling （HEBM） and low-temperature sin- tering technique, with voltage-gradient of 1934-2197 V/mm, non-linear coefficients of 20.8-21.8, leakage currents of 0.59-1.04 μA, and densities of 5.46-5.57 g/cm3. With increasing Y2O3 content, the voltage-gradient increases because of the decrease of ZnO grain size; the non-linear coefficient and the leakage current improve but the density decreases because of more porosity; the donor con- centration and density of interface states decrease, whereas the barrier height and width increase because of the acceptor effect of Y2O3 in varistor ceramics.