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nanocrystalline La2Mo2O9 and Its Characterization

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Journal of Rare Earths 2004年第Z2期22卷 102-106页

作者： Li Qin Xia Tian Li Jiayan Liu Xiangdong Ma Xianfeng Meng Jian Cao Xueqiang Key Laboratory of Rare Earth Chemistry and Physics Changchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China Key Laboratory of Rare Earth Chemistry and PhysicsChangchun Institute of Applied ChemistryChinese Academy of Sciences.Changchun 130022China

In this work, both the thermal expansion and electrical conductivity of nanocrystalline La2Mo2O9 were studied.The nanocrystalline powder of La2Mo2O9 was obtained by sol-gel method, and with the help of SHP (superhigh pressure)up to 4.5 × 104 atm at 700 ℃ for a short time, and the nanocrystalline powder was densified without obvious particle size growth. The electrical conductivity of nanocrystalline La2Mo2O9 was one orderof magnitude lower than that of the microcrystalline sample at the same temperature. Owing to the phase transition, the microcrystalline La2Mo2O9 has an abrupt increase of thermal expansion with a peak value of 48 × 10-6 K-1 at 556 ℃. For the nanocrystalline material, the peak value increases to 112 × 10-6 K-1 at 520 ℃. On the other hand, above 600 ℃ the significant growth of particle size of the nanocrystalline La2Mo2O9 was observed, accompanying by a tremendous increase of thermal expansion with a peak value of third higher than that of La2Mo2O9.

关键词： nanocrystalline electrical conductivity lanthanum molybdate superhigh pressure rare earths

Structure and magnetic properties of nanocrystalline dysprosium powders

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Rare Metals 2020年第1期39卷 28-35页

作者： Hong-Jian Li Qiong Wu Ming Yue Yu-Qing Li Rong-Chun Zhu Jing-Ming Liang Jiu-Xing Zhang College of Materials Science and Engineering Key Laboratory of Advanced Functional MaterialsMinistry of Education of ChinaBeijing University of TechnologyBeijing100124China

In this current study,nanocrystalline Dy powders were prepared by melt-spinning and subsequent highenergy ball-milling.The effect of ball-milling time on the structure and magnetic properties of the powders was studied.The crystal structure and microstructure of the melt-spun ribbons and ball-milled powders were observed by X-ray diffraction(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Magnetic measurement of all samples was performed with vibrating sample magnetometer(VSM).XRD results indicate that the average crystal grain size of the powders decreases from 90.09 nm of the ribbons to 10.42 nm of the4-h ball-milled powders.Further TEM observation shows that the grains are fine and uniform.The Neel temperature(TN)decreases from 182 K of the ribbons to 172 K of the powders,while the Curie temperature(TC)increases from100 to 130 K,demonstrating that the grain size has substantial influence on the magnetic transition process.Moreover,at 60 K,as the ball-milling time increases,the coercivity of the powders increases first,peaking at 0.48 T for 2-h milling,then drops again,while the remanence of the powders decreases monotonic ally.As a result,the powders milled for 2 h exhibit an optimal maximum energy product of 64.0 kJ·m-3,demonstrating the good potential of these powders as a permanent magnet at low temperatures.

关键词： Dysprosium nanocrystalline Low temperature Magnetic properties

Dislocation-mediated creep process in nanocrystalline Cu

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Chinese Physics B 2013年第3期22卷 457-465页

作者：穆君伟孙世成江忠浩连建设蒋青 Key Laboratory of Automobile Materials Department of Materials Science and EngineeringJilin University

nanocrystalline Cu with average grain sizes ranging from ～ 24.4 to 131.3 nm were prepared by the electric brushplating technique.Nanoindentation tests were performed within a wide strain rate range,and the creep process of nanocrystalline Cu during the holding period and its relationship to dislocation and twin structures were examined.It was demonstrated that creep strain and creep strain rate are considerably significant for smaller grain sizes and higher loading strain rates,and are far higher than those predicted by the models of Cobble creep and grain boundary sliding.The analysis based on the calculations and experiments reveals that the significant creep deformation arises from the rapid absorption of high density dislocations stored in the loading regime.Our experiments imply that stored dislocations during loading are highly unstable and dislocation activity can proceed and lead to significant post-loading plasticity.

关键词： nanocrystalline creep dislocation nanoindentation

Revealing the atomistic deformation mechanisms of face-centered cubic nanocrystalline metals with atomic-scale mechanical microscopy: A review

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Journal of Materials Science & Technology 2018年第11期34卷 2027-2034页

作者： Duohui Li Xinyu Shu Deli Kong Hao Zhou Yanhui Chen Institute of Microstructure and Properties of Advanced Materials Beijing University of Technology

nanocrystalline metals have many functional and structural applications due to their excellent mechanical properties compared to their coarse-grained counterparts. The atomic-scale understanding of the deformation mechanisms of nanocrystalline metals is important for designing new materials, novel structures and applications. The review presents recent developments in the methods and techniques for in situ deformation mechanism investigations on face-centered-cubic nanocrystalline metals. In the first part,we will briefly introduce some important techniques that have been used for investigating the deformation behaviors of nanomaterials. Then, the size effects and the plasticity behaviors in nanocrystalline metals are discussed as a basis for comparison with the plasticity in bulk materials. In the last part, we show the atomic-scale and time-resolved dynamic deformation processes of nanocrystalline metals using our in-lab developed deformation device.

关键词： In situ atomic-scale nanocrystalline Deformation mechanisms Size effect

Genesis of nanocrystalline Ho_2O_3 via thermal decomposition of holmium acetate: Structure evolution and electrical conductivity properties

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Journal of Rare Earths 2019年第2期37卷 185-192页

作者： Bahaa M.Abu-Zied Abdullah M.Asiri Center of Excellence for Advanced Materials Research (CEAMR) King Abdulaziz University Chemistry Department Faculty of Science King Abdulaziz University Chemistry Department Faculty of Science Assiut University

This study focuses on the preparation of nanostructured holmium oxide via the decomposition of holmium acetate precursor utilizing the non-isothermal strategy. Thermogravimetric analysis(TGA) was used to follow up the various thermal events involved in the decomposition process. Dehydration completes approximately at 150℃, which is followed by the decomposition of the anhydrous acetate leading to the formation of holmium oxide. Based on the TGA results the acetate precursor was heated non-isothermally at the temperature range of 150 e700℃. The obtained solids were characterized using powder X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR), field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). It is found that nanocrystalline Ho_2 O_3 starts to form at 500℃ and presents the only phase detected at the 500 e700℃ range. The electrical conductivity of the solids that form at the temperature range of 300 e700℃ was investigated. The obtained values were correlated with the observed structural modifications accompanying the heat treatment. The electrical conductivity of the Ho_2 O_3 samples prepared at 500, 600 and 700℃ reaches the values of 1.92 × 10^(-7), 1.61 × 10^(-7) and 8.33 × 10^(-8) Ω^(-1)cm^(-1) at a measuring temperature of 500℃, respectively. These values are potentially advantageous for high-resistivity devices.

关键词： nanocrystalline Ho2O3 Thermal decomposition Ho2O3 Holmium oxide Rare earth oxides Nanomaterials

Effect of stress state on deformation and fracture of nanocrystalline copper:Molecular dynamics simulation

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Chinese Physics B 2014年第9期23卷 488-495页

作者：张亮吕程 Kiet Tieu 裴林清赵星 School of Mechanical Materials and Mechatronic EngineeringUniversity of Wollongong

Deformation in a microcomponent is often constrained by surrounding joined material making the component under mixed loading and multiple stress states. In this study, molecular dynamics （MD） simulation are conducted to probe the effect of stress states on the deformation and fracture of nanocrystalline Cu. Tensile strain is applied on a Cu single crystal, bicrystal and polycrystal respectively, under two different tension boundary conditions. Simulations are first conducted on the bicrystal and polycrystal models without lattice imperfection. The results reveal that, compared with the performance of simulation models under free boundary condition, the transverse stress caused by the constrained boundary condition leads to a much higher tensile stress and can severely limit the plastic deformation, which in return promotes cleavage fracture in the model. Simulations are then performed on Cu single crystal and polycrystal with an initial crack. Under constrained boundary condition, the crack tip propagates rapidly in the single crystal in a cleavage manner while the crack becomes blunting and extends along the grain boundaries in the polycrystal. Under free boundary condition, massive dislocation activities dominate the deformation mechanisms and the crack plays a little role in both single crystals and polycrystals.

关键词： molecular dynamics nanocrystalline stress state deformation mechanism

THERMAL　STABILITY　OF　THE　MECHANICALLY　ALLOYED　Al－10Ti　nanocrystalline　ALLOY　DURING　CONSOLIDATION　PROCESS

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中国有色金属学会会刊：英文版 1995年第4期5卷 127-132页

作者： Liang, Guoxian Li, Zhichao Wang, Erde Harbin Inst of Technology Harbin China

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关键词： nanocrystalline Al-10Ti alloy consolidation process thermal stability

Synthesis of Mesoporous, nanocrystalline Lanthanum Phosphate in the Presence of Citric Acid and Stearic Acid

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Journal of Rare Earths 2007年第6期25卷 684-691页

作者： Li-Ngee Ho Hiroyasu Nishiguchi Katsutoshi Nagaoka Yusaku Takita Department of Applied Chemistry Oita University Dannoharu 700 Oita 870-1192 Japan

Lanthanum phosphate was prepared in the presence of citric acid and stearic acid under methanolic conditions at pH 4.5 and pH 7, respectively. The samples obtained were intensively characterized using X-ray diffraction, nitrogen adsorption-desorption isotherm study, transmission electron microscopy （TEM）, thermal gravimetric and differential thermal analysis, and Fourier transform infrared （FTIR） analysis . The as-synthesized samples prepared at pH 4.5 showed lamellar mesostruroned form with high crystallinity. Results showed that the pore size and pore volume changed when the materials were prepared under different pH conditions. Morphology of the samples was observed by using TEM, which showed that the samples possessed relatively small particles closely packed together. The as-synthesized samples were investigated using FTIR, and the mesopore formation mechanism was discussed.

关键词： mesoporous lanthanum phosphate citric acid stearic acid nanocrystalline rare earths

Bulk nanocrystalline Al prepared by cryomilling

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Journal of University of Science and Technology Beijing 2007年第6期14卷 523-528页

作者： Junsheng Cheng Hua Cui Hanbin Chen Bin Yang Jianzhong Fan Jishan Zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China Materials Science and Engineering School University of Science and Technology Beijing Beijing 100083 China Beijing General Research Institute for Nonferrous Metals Beijing 100088 China

Bulk nanocrystalline Al was fabricated by mechanically milling at cryogenic temperature （cryomilling） and then by hot pressing in vacuum. By using X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）, the microstructure evolution of the material during cryomilling and consolidation was investigated. With increasing the milling time, the grain size decreased sharply and reduced to 42 nm when cryomilled for 12 h. The grains had grown up, and the columnar grain was formed under the hot pressing and extrusion compared with the cryomilled powders. The grain size of as-extruded specimen was approximately 300-500 nm. The reason of high thermal stability of this bulk was attributed primarily to the Zener pinning from the grain boundary of the AlN arising from cryomilling and the solute drag of the impurity. Tensile tests show that the strength of nanocrystalline Al is enhanced with decreasing grain size. The ultimate tensile strength and tensile elongation were 173 MPa and 17.5%, respectively. It appears that the measured high strength in the cryomilled Al is related to a grain-size effect, dispersion strengthening, and dislocation strengthening.

关键词： nanocrystalline Al cryomilling thermal stability strengthening mechanism