Magnetic properties of iron nitride-silica nanocomposite materials prepared by high-energy ball milling

Powder mixtures of (FexN)y and (SiO2)1-y, with x between 3 and 4 and y equal to 0.2 or 0.6, were ball-milled for 4, 8, 16, 32, and 64 h. X-ray diffraction, thermal analysis, and magnetization measurements allowed an investigation of structural and magnetic properties to be carried out. The samples consist of nanostructured Fe3N and Fe4N particles in a SiO2 matrix. As the milling time increases, the Fe4N phase is eliminated from the particles in favor of Fe3N. Coercive fields as high as 270 and 84 Oe are obtained for (FexN)0.2(SiO2)0.8 at 5 and 300 K, respectively. This higher coercive field, upon cooling, indicates the presence of small superparamagnetic particles. The coercive field also increases with milling time, which is due to the reduced particle size and induced stain. The saturation magnetization decreases with increased milling time as a consequence of an increase in the superparamagnetic fraction and increased strain. Hard and soft magnetic properties are observed for y = 0.2 and y = 0.6 samples, respectively.     

Nanostructure cathode materials prepared by high-energy ball milling method

We prepare Li₂MnO₃ and LiNi_0.5Mn_0.3Co_0.2O₂ as nanostructure cathode materials using a high-energy ball milling method with bulk-type electrodes. The nanostructure electrodes prepared by the ball milling exhibit much smaller particle sizes in diameter than those of bulk-type electrodes. The 1st charge–discharge capacitance and efficiency of the nanostructure cathode materials are superior to those of the bulk-type electrodes.     

Microstructure and electrical properties of ZnO-based varistors prepared by high-energy ball milling

ZnO-based varistor ceramics were prepared at sintering temperatures ranging from 900 °C to 1,300 °C, by subjecting the mixed oxide powders to high-energy ball milling (HEBM) for 0, 5, 10 and 20 h, respectively. Varistor ceramics prepared by HEBM featured denser body, better electrical properties sintered at low-temperature than at traditional high-temperature. The high density is due to the refinement of the crystalline grains, the enhanced stored energy in the powders coming from lattice distortion and defects as well as the promotion of liquid-phase sintering. Good electrical properties is attributed to proper microstructure formed at low-temperature and improved grain boundary characteristics resulting from HEBM. With increasing sintering temperatures, the electrical properties and density became worse due to the decrease in amount of Bi-rich phase. Temperature increased up to 1,200 °C or above, the Bi-rich phase vanished and the ceramics exhibited very low nonlinear coefficient.     

高能球磨制备钛酸锶铋陶瓷及其介电弛豫研究

采用高能球磨和固相烧结法制备了一系列Sr1-1.5xBixTiO3(SBT)陶瓷.采用XRD和SEM分析了样品的相结构和显微结构.结果表明,高能球磨过后的粉末为具有钙钛矿结构的SBT固溶体,且SBT陶瓷的固溶度有所提高.其介电性能结果表明,SBT的介电常数温度特性具有明显的弛豫现象,并且随Bi含量的增加,相转变温度向高温移动,相变弥散及弛豫程度增强,并对SBT陶瓷的弛豫机制进行了探讨.     

Microstructural characterization of amorphous and nanocrystalline boron nitride prepared by high-energy ball milling

Microstructural parameters like crystallite size, lattice strain, stacking faults and dislocation density were evaluated from the X-ray diffraction data of boron nitride (BN) powder milled in a high-energy vibrational ball mill for different length of time (2-120 h), using different model based approaches like Scherrer analysis, integral breadth method, Williamson-Hall technique and modified Rietveld technique. From diffraction line-broadening analysis of the successive patterns of BN with varying milling time, it was observed that overall line broadening was an operative cause for crystallite size reduction at lower milling time (∼5 h), whereas lattice strains were the prominent cause of line broadening at higher milling times (>19 h). For intermediate milling time (7-19 h), both crystallite size and lattice strain influence the profile broadening although their relative contribution vary with milling time. Microstructural information showed that after long time milling (>19 h) BN becomes mixture of nanocrystalline and amorphous BN. The accumulations of defects cause this crystalline to amorphous transition. It has been found that twin fault (β′) and deformation fault (α) significantly contributed to BN powder as synthesized by a high-energy ball-milling technique. Present study consider only three ball-milled (0, 2 and 3 h) BN powder for faults calculation because fault effected reflections (1 0 1, 1 0 2, 1 0 3) disappear with milling time (>3 h). The morphology and particle size of the BN powders before and after ball milling were also observed in a field emission scanning electron microscope (FESEM).     

Sub-micron sized Al2TiO5 powders prepared by high-energy ball milling

High energy ball milling to obtain ultrafine aluminium titanate particles has been investigated. Tempered steel has been selected as material for the containers and balls because the desirable properties of aluminium titanate are not degraded by small amounts of Fe₂O₃. The starting powders have been milled during different periods (1–60 h) and the evolution of the morphology and crystallinity of the treated powders as well as the extent of contamination from the milling media have been characterised. Different experimental techniques, X-ray diffraction, BET-analysis, chemical analysis, scanning electron microscopy and low and high resolution transmission electron microscopy have been used. High energy ball milling has been proved to be an efficient route to obtain submicron sized (50–100 nm) aluminium titanate powders, but further milling of the powders is accompanied by contamination from the milling media and the formation of hard agglomerates.     

Synthesis of Cu-W nanocomposite by high-energy ball milling

The Cu-W bulk nanocomposites of different compositions were successfully synthesized by high-energy ball milling of elemental powders. The nanocrystalline nature of the Cu-W composite powder is confirmed by X-ray diffraction analysis, transmission electron microscopy, and atomic force microscopy. The Cu-W nanocomposite powder could be sintered at 300-400 degrees C below the sintering temperature of the un-milled Cu-W powders. The Cu-W nanocomposites showed superior densification and hardness than that of un-milled Cu-W composites. The nanocomposites also have three times higher hardness to resistivity ratio in comparison to Oxygen free high conductivity copper.     

用高能球磨法制备的细晶Al-50Si合金的组织与性能

用高能球磨工艺制备Al-50Si合金粉末,将粉末经冷压、烧结、热压等工艺制备出Al-50Si合金块体材料,对球磨粉末和块体样品进行了显微组织观察、EDS分析和XRD分析,测定了块体样品的密度、硬度和热扩散系数.结果表明:高能球磨后Al-50Si合金粉末的硅粒子明显细化,其尺寸分布为1-15μm;在烧结过程中块体样品的硅粒子长大,其尺寸增大到5-30μm;Al-50Si合金块体材料具有较高的密度和硬度,其室温热扩散系数为55mm2·s-1.     

铁/聚氯乙烯高能球磨的穆斯堡尔谱研究

用高能球磨法制备了铁 /聚氯乙烯 (PVC)纳米复合材料。穆斯堡尔谱学 (MS)用来测量复合材料中铁化合物的组分和铁的价态 ,结果表明复合材料中存在二价铁 (FeCl2 ·H2 O)、三价铁 ,还有界面谱垒加在原有的铁的六线谱上     

机械球磨和烧结制备CoSb3的工艺研究

针对skutterudite材料制备工艺中熔融法和固相反应法合成周期长、工序多的不足,尝试将机械合金化法应用于skutterudite材料制备中.探讨了CoSb3的机械合金化和烧结制备工艺,研究表明,Co、Sb粉末的机械合金化在球磨10 h后开始,球磨40h后已全部合金化,得到CoSb,和CoSb2相混合物.合金化过程中CoSb3相先于CoSb2相形成.采用球磨10 h-700℃烧结2 h的工艺可得到单相CoSb3,制备工序简单,所需时间大大缩短.     

氧化铝高能球磨时机械力化学效应研究

研究了氧化铝在高能球磨过程中机械力化学效应的变化.机械力化学效应因子随球磨时间的变化可分为三个阶段:第一阶段主要是晶粒尺寸减小和显微应变增加同时进行;第二阶段主要是有效温度系数的增加;第三阶段主要是点阵膨胀至饱和.用溶解法比较了球磨前后氧化铝的活性,发现经球磨后,氧化铝在盐酸中的溶解活化能由18 kJ/mol降至4 kJ/mol,表面活化层增厚.     

Fast diffusion in nanocrystalline ceramics prepared by ball milling

Nanocrystalline materials can show enhanced diffusivity compared to their microcrystalline counterparts due to the large fraction of atoms or ions located in interfacial regions. In the case of ceramics, resulting properties with potential applications are, e.g., fast ionic conductivity, high mechanical creep rate and increased catalytic activity. Different nanocrystalline ceramic materials were prepared by high-energy ball milling of coarse grained source materials. The samples were characterized by XRD, TEM, BET method and IR spectroscopy. These measurements show that the primary crystallites form larger agglomerates with internal interfaces and that the reduction of the crystallite size is accompanied by a structural degradation of the surface zone. An example is the partial amorphization observed for LiBO₂ by IR spectroscopy. The diffusivity and ion conductivity in these materials was studied by NMR relaxation, NMR line shape and impedance spectroscopies. It was possible to discriminate between highly mobile ions in the interfacial regions and immobile ions in the grains. In general diffusion in the nanocrystalline systems was found to be fast compared to that in the corresponding microcrystalline source materials.     

Fast amorphization and crystallization in Al-Fe binary system by high-energy ball milling

Large amount of amorphous phase of Al-Fe binary system was obtained by MA of elemental powders using a high-energy ball mill at milling intensity of 150G (G is the gravitational acceleration). XRD, HRTEM and DSC were used to analyze the process of amorphization and crystallization. The time required achieving almost complete amorphous state is only 4.2 ks for Al-25 at.%Fe system and 3 ks for Al-30 at.%Fe system, respectively. The time of amorphous formation is very shorter than that of previous reports on Al-Fe binary system. Further milling causes rapid crystallization of the amorphous phase. By analysis of S(Q), the presence of a strong Al-Fe chemical short-range order in the amorphous matrix is suggested. Moreover, the superstructure of these Al-Fe clusters in the amorphous matrix is similar to the solid structure of Al₅Fe₂, and the clusters transform into the nucleus of Al₅Fe₂ intermetallic compound under the action of milling energy.     

Anisotropic mullitization in CuO-doped oxide mixture activated by high-energy ball milling

Mullite phase formation and grain growth, in a CuO-doped Al₂O₃ and silica mixture, has been investigated. The oxide mixture was activated with both stainless steel and tungsten carbide milling media. The milled powders demonstrated a much lower mullite formation temperature when compared to the conventional solid-state reaction process. Anisotropic grain growth was observed in the powders milled with stainless steel media, while well-shaped mullite whiskers were produced in the WC milled samples. The lowered mullitization temperature together with the anisotropic grain growth behavior was attributed to the refined microstructure of the powders as a result of the high-energy ball milling process.     

高能球磨锐钛矿型TiO2晶型转变的研究

应用机械力化学原理，研究高能行星磨粉磨锐钛矿型TiO2引起晶型转变的过程，采用XRD、SEM、TEM、FT－IR技术对粉体进行表征，探讨了机械力化学引起晶型转变的机制。研究发现：在一定操作参数（行星磨公转转速300r/min)条件下，粉磨初期（5h)为无定形形成期，颗粒出现团聚现象，晶粒尺寸减小，晶格畸变，转变为无定形，并形成金红石型TiO2晶核；粉磨中期（5－15h)为晶粒长大期，金红石型TiO2晶粒长大；粉磨后期（15h以后）为动态平衡期，晶粒长大与粉磨引起的晶粒减小处于动态平衡，研究表明；行星磨粉磨锐钛矿型TiO2可使晶型转变为金红石型TiO2，团聚的二次颗粒尺寸为1μm左右，并由颗粒尺寸为20－40nm团聚组成。     

Structural evolution of B2-NiAl synthesized by high-energy ball milling

Structural evolution during the synthesis of B2–NiAl intermetallic compound by mechanical alloying of equiatomic elemental mixtures was studied by Rietveld analysis, DSC and HTXRD. The lattice parameter, crystallite size, microstrain, amount of phase and ordering of the B2 phase were monitored as a function of milling time. Formation of the B2–NiAl phase shows a sigmoidal behavior, which suggests that Johnson–Mehl–Avrami nucleation and interface-controlled growth are the responsible mechanisms in the transformation. Almost complete transformation (~ 97 mol%) was obtained after 25 h of milling. A specific phase transformation sequence during milling was not absolutely determined, however, the sequence Ni + Al → NiAl₃ → Ni₂Al₃ → B2–NiAl was identified by HTXRD. This sequence was confirmed by DSC. The transformation temperature of the B2–NiAl phase and the presence of additional intermetallic compounds show a direct dependence on the Ni–Al layer spacing. Using a production-scale Simoloyer horizontal Attritor Mill, the presence of Ni₂Al₃ phase was observed prior to the full synthesis of B2-NiAl.     

Synthesis of BF–PT perovskite powders by high-energy ball milling

0.7BiFeO₃–0.3PbTiO₃ (BF–PT) powders were synthesized from a mixture of the oxides Bi₂O₃, Fe₂O₃, PbO and TiO₂ using a Fritsch P4™ vario-planetary ball milling system. The perovskite structure of the BF–PT powder can be obtained well and the crystallite size of the powders was greatly reduced to 20–35 nm after milling for 8 h. The pre-calcined course shows a rhombohedral–tetragonal phase transition with the increasing temperature and shows the structure transition near the Curie temperature T_c.     

机械合金化法制备N型Skutterudite热电材料研究

研究了采用机械合金化加热压烧结工艺制备n型Skutterudite热电材料的工艺路线.采用了XRD、DTA等测试方法分析了试样的成分,研究了NixCo1-xSb3系材料采用机械合金化加热压烧结的基本工艺路线.研究表明Ni含量在0.2以下的NixCo1-xSb3系材料在球磨10h之后进行2h热压烧结后,试样基本上转化为CoSb3相,并且已经有大量的Ni被置换入CoSb3的晶格之中,形成(NixCo1-x)Sb3材料.     

高能球磨Mg-Zr-Ni合金组织演变

为了改善Mg-Ni合金的电化学性能,采用高能球磨技术合成了Mg-Zr-Ni储氢合金,通过改变球磨条件和添加合金元素Zr,利用XRD物相分析和电化学测量技术,研究了Mg-Ni合金的组织演变过程及其对电化学容量的影响.结果表明,高能球磨Mg-Ni和Mg-Zr-Ni合金都经历了非晶态向纳米晶态的转变过程,用少量Zr替代部分Mg后,促进了高能球磨Mg-Zr-Ni合金的非晶化和纳米晶化的过程.与非晶态Mg(Zr)Ni相比,纳米晶的Mg(Zr)Ni中氢更易放出,放电曲线主要呈现高电位放电特征,添加Zr后合金的放电容量有所下降.     

Production of nanocrystalline powders by high-energy ball milling: model and experiment

A model of high-energy ball milling of powders has been proposed. It is demonstrated that part of the energy is consumed for initiation of microstrains ε during milling and, hence, the process of the powder grinding is decelerated. An analytical expression has been deduced describing the size of nanocrystalline powder particles as a function of the milling time. The model and the experiment have been compared, using a powder of tungsten carbide (WC). The average size of the particles and the value of the microstrains in the ball-milled powder were determined by an x-ray method from broadening of diffraction reflections. The size of the particles was also evaluated using scanning electron microscopy and the sedimentation method.