Microstructural characterization of Mg-SiC nanocomposite synthesized by high energy ball milling

High-energy ball milling is successfully used to produce magnesium matrix nanocomposites reinforced with SiC nanoparticles. Changes in morphology and microstructural features of the milled powders were characterized in order to highlight advantages of the mechanical milling process and evaluate the role of the SiC nanoparticles. It was observed that with increasing volume fraction of SiC nanoparticles, a finer nanocomposite powder with more uniform particle size distribution is obtained. A homogeneous distribution of SiC nanoparticles, even up to 10% volume fraction, in magnesium matrix after 25?h milling was confirmed by elemental mapping and TEM results. The analysis of the XRD patterns accompanied by dark-field TEM images revealed that magnesium crystallites refine to fine nanocrystalline sizes after the mechanical milling. The results showed that the crystallite size of the magnesium matrix reduced with increasing SiC nanoparticle content in addition to the induced lattice strain.     

Structural evolution in nano-crystalline Cu synthesized by high energy ball milling

Nano-crystalline copper with a mean crystallite size of 27 nm was synthesized through solid state reduction of Cu₂O by graphite using high energy planetary ball mill. The structural and morphological changes during mechanical milling were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mean crystallite size and residual strain were determined by XRD peak broadening using the Williamson–Hall approximation. It was found that the reaction is completed in a manner like a nucleation and growth process. Although the crystallite size and internal strain changes in Cu₂O were regular during mechanical milling, there was an irregularity in both parameters in Cu particles. This irregularity was probably due to the progressive formation of copper during milling.     

The nanostructure evolution of Ag powder synthesized by high energy ball milling

In this paper, nanostructured silver with an average crystallite size of 28 nm and internal strain of 0.44% was synthesized by mechanochemical reduction of Ag₂O using graphite in a high energy planetary ball mill. XRD, SEM and TEM techniques were used to characterize the structural evolution and morphological changes of products. The results showed that the reaction is progressed by a nucleation and growth mechanism process. Although the changes of crystallite size and internal strain in Ag₂O were regular during the milling, there was an irregularity in the aforementioned parameters of Ag particles. This irregularity was probably owing to the progressive generation of silver during the milling.     

Synthesis of the CaAl2O4 nanoceramic compound using high-energy ball milling with subsequent annealing

Monocalcium aluminate, CaAl₂O₄, is the main constituent of calcium alumina cements which have found wide applications in refractory industries. In the present work, CaAl₂O₄ nanoceramic compound was produced by high-energy ball milling of the oxide powders followed by annealing. The phase evolution and microstructural changes of the powders during the process were investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that no CaAl₂O₄ was formed during ball milling even after 100 h. By subsequent annealing, the nucleation and growth of CaAl₂O₄ took place at 1000 °C after 2 h. Depending on milling time, the amount of CaAl₂O₄ increased with increasing annealing temperature. The CaAl₂O₄ single phase was obtained by milling the sample for 100 h and subsequently annealing at 1200 °C for 2 h. The quantitative phase analysis was used to measure CaAl₂O₄ phases in these processes. The average particle diameter of the sample milled for 100 h and annealed at 1200 °C was found to be less than 100 nm as measured by transmission electron microscopy.     

Microstructural evolution during high energy ball milling of Fe2O3-SiO2 powders

The reaction of a 25 mol% Fe₂O₃-SiO₂ (hematite-amorphous silica) powder mixture during high energy ball milling in both closed and open containers has been studied by x-ray diffraction and Mössbauer spectroscopy. After around 21 h of milling, the α-Fe₂O₃ powders with an average particle size of 15 nm have formed and no reaction between α-Fe₂O₃ and SiO₂ is found in the two types of milling containers. This demonstrates that the high energy mechanical milling technique is able to prepare a dispersion of ultrafine α-Fe₂O₃ particles. After extended milling in the open container all iron atoms are found in a hematite phase. In the closed container the hematite phase transforms into an iron-rich spinel phase and some of the iron atoms react with the amorphous SiO₂, forming a new Fe(II)-containing silicate compound.     

Fe3O4/聚苯胺纳米复合材料高能球磨法制备及其性能研究

以Fe3O4粉体及导电聚苯胺为原料,用高能球磨法制备Fe3O4／聚苯胺纳米复合材料,用Moessbauer谱、XRD、FTIR、VSM等方法对样品进行表征。结果表明随着球磨时间的增加,Fe3O4的粒径迅速减小到纳米量级;Fe3O4表面与聚苯胺作用生成了某种顺磁性物质;同时有少量的α—Fe3O4生成;复合物中Fe3O4颗粒A、B晶位中Fe的含量发生了明显的变化。复合物的电磁性能也明显发生了改变。     

Electrical and magnetic properties of nanocrystalline BiFeO3 prepared by high energy ball milling and microwave sintering

A new synthesis route with high energy ball milling and microwave sintering is used to obtain nanocrystalline BiFeO3 with improved dielectric and magnetic properties. Electrical and magnetic properties are compared with a conventionally sintered microcrystalline BiFeO3. It is found that the dielectric constant is increased more than one order of magnitude, electrical resistivity by six orders of magnitude and remnant polarization value is increased by 4-5 times for nanocrystalline BiFeO3 in comparison to conventionally sintered microcrystalline BiFeO3. Nanocrystalline BiFeO3 is seen to have ferromagnetic behavior whereas microcrystalline BiFeO3 is known to be antiferromagnetic.     

Microstructure and morphology of Mo-based Tm2O3 composites synthesized by ball milling and sintering

Mo-based Tm₂O₃ composites used as neutron absorbers were synthesized by ball milling, cold isostatic pressing and sintering. The size of Mo grain was decreased rapidly in the initial stage and then kept a constant in the later stage. After ball milling for 96 h, the size of Mo grain was up to approximately 8 nm. Ball milling induced Tm₂O₃ to be first fined, nano-crystallized, then transformed to amorphization, and finally dissolved into Mo crystal. The supersaturated nanocrystalline solid solution of Mo (Tm, O) was formed after 96 h of ball milling. Sintering caused Tm and O atoms precipitated from Mo crystal and then formed Tm₂O₃ precipitates that uniformly distributed in the Mo matrix. After sintered for 12–24 h at 1400–1600 °C, only diffraction peaks of Tm₂O₃ and Mo could be observed in the XRD spectrums, which indicated that there was not a chemical reaction between Tm₂O₃ and Mo. The microhardness of sintered bulks increased with increasing ball-milling time, sintering temperature and time, and the chemical content of Tm₂O₃ in the powder mixtures. The evolutionary mechanism of the microstructural characteristics during ball milling and subsequent sintering was discussed.     

Synthesis of the porous spinel Co-Al2O4 powder produced by ball milling and annealing

Ball milling (BM) of elemental Co and Al was conducted for 30 h (h). This process has altered the original morphologies of both elemental Co and Al powders. Spherical Al powder particles has changed into a smooth pancake-shape while the original irregular-shaped Co agglomerates became disintegrated ultrafine particles. BM of the Co20 wt.% Al powder mixture after 30 h yielded thin irregular-shaped particles. XRD analysis revealed a partial structural transformation after BM and further structural change upon annealing the powder at 600 °C, as confirmed by the SEM images. The formation of the cubic spinel superstructure with lattice parameter a = 8.066 Å (ZnAl₂O₄ prototype) and Fd-3 m # 227 space group was realized. By means of LEO 1525 field-emission scanning electron microscope (FE-SEM), a fibrous mesoporous structure was revealed on the milled powder after annealing the Co-Al mixture at 600 °C. The EDS analysis confirmed a minor N impurity on the annealed powder.     

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     

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.     

高能球磨时间和退火温度对制备TiNi合金粉的影响

为获得高能球磨时间和退火温度对TiNi机械合金粉特性的影响机制,采用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、差示扫描量热法(DSC)等分析方法对TiNi合金粉进行了研究。结果表明,机械合金的相成分随着在氩气保护气氛中的球磨时间和退火温度的不同而发生变化。球磨22h的产物是非晶态TiNi合金、Ti的固溶体、Ni的固溶体,球磨27h的产物是非晶态TiNi合金粉和Ni固溶体相,球磨30h发生了明显的固相反应,生成了TiNi、Ni3Ti、Ti3Ni4等物相;在650℃/5h和1000℃/5h下的退火产物都是Ni3Ti、Ti2Ni、TiNi2、TiNi和TiC,但在上述2个退火温度下TiNi并不是主要物相,其中在650℃退火时TiNi的含量明显更低。     

Spark plasma sintered Sm(2)Co(17)-FeCo nanocomposite permanent magnets synthesized by high energy ball milling

Nanocomposite Sm(2)Co(17)-5?wt% FeCo magnets were synthesized by high energy ball milling followed by consolidation into bulk shape by the spark plasma sintering technique. The evolution of magnetic properties was systematically investigated in milled powders as well as in spark plasma sintered samples. A high energy product of 10.2?MGOe and the other magnetic properties of M(s) = 107?emu?g(-1), M(r) = 59?emu?g(-1), M(r)/M(s) = 0.55 and H(c) = 6.4?kOe were achieved in a 5?h milled and spark plasma sintered Sm(2)Co(17)-5?wt% FeCo nanocomposite magnet. The spark plasma sintering was carried out at 700?°C for 5?min with a pressure of 70?MPa. The nanocomposite showed a higher Curie temperature of 955?°C for the Sm(2)Co(17) phase in comparison to its bulk Curie temperature for the Sm(2)Co(17) phase (920?°C). This higher Curie temperature can improve the performance of the magnet at higher temperatures.     

Phase evolution and microstructure characteristics of Mo-based Tb2O3-Dy2O3 composites synthesized by ball milling and sintering

Mo-based Tb₂O₃-Dy₂O₃ composites used as neutron absorbers in nuclear power reactor were synthesized by powder metallurgy. The comparative studies of Mo-based Tb₂O₃ and Mo-based Dy₂O₃ composites were carried out to deeply understand the phase evolution and microstructure characteristics of Mo-based Tb₂O₃-Dy₂O₃ composites. Ball milling induced terbium oxide and dysprosium oxide in the powder mixtures to be first fined, nano-crystallized, amorphized and finally dissolved into Mo matrix to form the supersaturated nanocrystalline solid solution that was driven by mechanical work, not by negative heat of mixing. Mo lattice parameter increased with increasing ball-milling time, opposite for Mo grain size. A phase transformation of Dy₂O₃ crystal from cubic to monoclinic and then to amorphous was observed during ball milling. The microhardness of sintered bulks was first increased and then decreased with increasing sintering time. The maximum value was obtained at the bulks sintered for 8?h. The microhardness and bulk density were increased with increasing sintering temperature before 1600?°C. The mechanism of ball milling and sintering was also discussed.     

高能球磨法制备Bi12SiO20粉体

以Bi2O3和SiO2为原料，采用高能球磨法制备了硅酸铋（Bi12SiO20）粉体。通过x射线衍射和扫描电子显微镜分析了合成粉体的相结构和形貌，研究了球磨时间对产物相组成的影响；使用红外光谱分析和拉曼散射光谱对球磨得到的样品进行了分析。结果显示：球磨8h后出现了Bi12SiO20的晶相结构；随着球磨时间的延长促进了Bi12SiO20的形成，从而提供了一种可以商业化大规模生产Bi12SiO20压电粉体的方法。     

纳米Mg2 Ni-Ni非晶合金的球磨制备和电极性能

球磨Mg2Ni合金粉和Ni粉制得纳米Mg2Ni-Ni非晶合金。用XRD和SEM分析表征了球磨过程中的相和结构的变化。模拟电池测试结果表明,Mg2Ni/Ni复合粉的首次放电容量随球磨时间的延长有明显提高。当球磨150h形成了纳米Mg2Ni-Ni非晶合金,其放电容量和电极循环性能得到明显改善。     

Mechanical alloying of immiscible Pb-Al binary system by high energy ball milling

In the present work, mechanical alloying has been applied to the Pb-Al immiscible binary system by using the method of high energy ball milling. The microstructural features of the milled powder, such as grain size, lattice constant and morphology of phases have been studied by X-ray diffraction, analytical transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, energy dispersive spectroscopy was used to analysis chemical composition of phases presented after milling. Differential Scanning Calorimetry measurement was also made on the milled Pb-Al powder. The results show that homogenous blending of Pb and Al can be easily achieved by high energy ball milling in spite of their mutual immiscibility and large difference in density. The obtained alloy exhibits nanocrystalline microstructure. Further more, the experiment result implies the formation of supersaturated solid solution in immiscible Pb-Al system by high energy ball milling.     

Mechanical behavior of bulk nanocrystalline copper alloys produced by high energy ball milling

Copper alloys with different amounts of zinc were synthesized via high energy ball milling at liquid nitrogen and room temperature. Bulk samples were produced in situ by controlling the milling temperature. It is shown that temperature plays an important role in formation of artifact-free consolidated samples via its effect on defect formation and annihilation during the milling process. The mechanical behavior of Cu–Zn nanocrystalline alloys was examined using Vickers microhardness and tensile tests. The nanostructure of the alloys was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness results of processed alloys vary as a function of the alloying elements. Considering typical low ductility of nanocrystalline materials, the improved ductility with the high strength observed in these alloys suggests that they are artifact-free and may have several deformation mechanisms, which may include dislocation activity and nano-twinning.     

Microstructure and magnetic properties of nano-sized Ba-Al ferrite particles by high energy ball milling

The magnetic nano-structured Ba-Al ferrite powders were prepared by high energy ball milling under the conditions of various rotation rates and milling times. The micro structure was characterized by SEM, XRD and TEM, and the magnetic properties were obtained by VSM. As the rotation rate and milling time increased, the size of nano-sized particles gradually decreased. The high energy ball milling for 5 h without relation to the rotation rate drastically reduced the coercivity as a consequence of the formation of nano-sized particle with the amorphous structure. However, the coercivity gradually decreased with increasing the milling time, resulting from the decrease of particle size with maintaining the crystal structure.