ZnO varistor ceramics doped with Bi2O3, Sb2O3, CO2O3, Cr2O3, and MnO2 were prepared separately by two high-energy ball milling processes： oxide-doped and varistor ceramic powder. A comparison in the electrical and mi...ZnO varistor ceramics doped with Bi2O3, Sb2O3, CO2O3, Cr2O3, and MnO2 were prepared separately by two high-energy ball milling processes： oxide-doped and varistor ceramic powder. A comparison in the electrical and microstructural properties of the samples obtained by both methods was made. The best results on these characteristics were achieved through the high-energy ball milling varistor ceramic powder route, obtaining a nonlinear coefficient of 57 and a breakdown field of 617 V/mm at a sintering temperature of 1000 ℃ for 3 h. The samples synthesized by this technique show not only high density value, 95% of the theoretical density, but also a homogeneous microstructure, which compete with those obtained by the high-energy ball milling oxide-doped powder route. With the advantage that the high-energy ball milling varistor ceramic powder route can refine grain, increase the driving force of sintering, accelerate the sintering process, and reduce the sintering temperature.展开更多
Bimodal-grained Ti containing coarse and fine grains was fabricated by high-energy ball milling and spark plasma sintering (SPS). The microstructure and mechanical properties of the compacts sintered by Ti powders bal...Bimodal-grained Ti containing coarse and fine grains was fabricated by high-energy ball milling and spark plasma sintering (SPS). The microstructure and mechanical properties of the compacts sintered by Ti powders ball-milled for different time were studied. Experimental results indicated that when the ball-milling time increased, the microstructure of sintered Ti was firstly changed from coarse-grained to bimodal-grained structure, subsequently transformed to a homogeneous fine-grained structure. Compared with coarse-grained Ti and fine-grained Ti, bimodal-grained Ti exhibited balanced strength and ductility. The sample sintered from Ti powders ball-milled for 10 h consisting of 65.3% (volume fraction) fine-grained region (average grain size 1 μm) and 34.7% coarse-grained region (grain size > 5 μm) exhibited a compress strength of 1028 MPa as well as a plastic strain to failure of 22%.展开更多
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, le...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.展开更多
The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing ...The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.展开更多
The mathematical models are developed to evaluate the ultimate tensile strength( UTS) and hardness of CNTs / Al2024 composites fabricated by high-energy ball milling. The effects of the preparation variables which are...The mathematical models are developed to evaluate the ultimate tensile strength( UTS) and hardness of CNTs / Al2024 composites fabricated by high-energy ball milling. The effects of the preparation variables which are milling time,rotational speed,mass fraction of CNTs and ball to powder ratio on UST and hardness of CNTs / Al2024 composites are investigated. Based on the central composite design( CCD),a quadratic model is developed to correlate the fabrication variables to the UST and hardness. From the analysis of variance( ANOVA),the most influential factor on each experimental design response is identified. The optimum conditions for preparing CNTs / Al2024 composites are found as follows: 1. 53 h milling time,900 r / min rotational speed,mass fraction of CNTs 2. 87% and Ball to powder ratio 25 ∶ 1. The predicted maximum UST and hardness are 273.30 MPa and 261.36 HV,respectively. And the experimental values are 283.25 MPa and256.8 HV,respectively. It is indicated that the predicted UST and hardness after process optimization are found to agree satisfactory with the experimental values.展开更多
In this paper, the milling parameters of high energy ball mill (Fritsch Pulverisette 7) like vial geometry, number and size of balls and speed of the mill were modelled and discussed. Simulations through discrete elem...In this paper, the milling parameters of high energy ball mill (Fritsch Pulverisette 7) like vial geometry, number and size of balls and speed of the mill were modelled and discussed. Simulations through discrete element method (DEM) provide correlation between the milling parameters. A mathematical model is used to improve and develop this process. The results show that the loss of powder mass can remarkably improve the performance of milling. The balls made of stainless-steel have a positive effect on the milling efficiency. The simulation shows that the high ball milling velocities can contribute to faster particle size reduction.展开更多
A TiAl alloy was fabricated by high-energy ball milling and subsequent reactive sintering from the mixed powders of Ti and Al. High-energy ball milling produced a kind of particular composite powders with an extremely...A TiAl alloy was fabricated by high-energy ball milling and subsequent reactive sintering from the mixed powders of Ti and Al. High-energy ball milling produced a kind of particular composite powders with an extremely fine altemative Ti and Al lamella structure. The composite powders not only possessed good consolidation and densification characteristics, but also resulted in the augment of nucleation rate of α and γ titanium aluminides during solid-phase reactive sintering After a series of processing, pressing, degassing, extrusion, and sintering, the resultant TiAl alloy presented high relative density and refined grain sizes of （α2 ＋ γ） lamella and γ phases. The compressive yield strength of the sintered TiAl reached 600 MPa at 800℃.展开更多
The structural evolution of Fe-doped TiO2 by high-energy ball milling was investigated by X-ray diffraction and Mǒssbauer spectroscopy, The results show that the original anatase-TiO2 transforms to srilankite-type an...The structural evolution of Fe-doped TiO2 by high-energy ball milling was investigated by X-ray diffraction and Mǒssbauer spectroscopy, The results show that the original anatase-TiO2 transforms to srilankite-type and rutile-type during ball milling. Iron atoms are preferable to dissolve in rutile-TiO2 and there are two relative doublets appearing in Mǒssbauer spectra. A doublet is found in the condition of Fe atoms dissolved in srilankite TiO2 lattice. Mǒssbauer spectra show that the composition distribution is nonuniform in TiO2 during the mechanical alloying with Fe atoms rich at the interface or surface of TiO2 crystalline.展开更多
Using electrolytic manganese dioxide and Li 2CO 3 as starting materials, the precursor of LiMn 2O 4 as cathode materials for lithium ion batteries was obtained by high energy ball milling. The LiMn 2O 4 powder was syn...Using electrolytic manganese dioxide and Li 2CO 3 as starting materials, the precursor of LiMn 2O 4 as cathode materials for lithium ion batteries was obtained by high energy ball milling. The LiMn 2O 4 powder was synthesized by calcinating the as milling powder at 750 ℃ for 24 h. X ray diffraction, SEM, cyclic voltammograms and charge discharge were carried out to investigate the property of LiMn 2O 4 cathode materials. Results show that the synthesized material, which is of standard spinel structure, possesses high reversibility of electrochemistry. The capacity in EC DMC(1∶1)+1 mol/L LiPF 6 electrolyte during first discharge is determined to be 125 mA·h/g.[展开更多
We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With a...We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With an increasing milling time, this particle size of mixture is gradually reduced, thus, we have mostly an amorphous phase. The BIT ceramics were duly obtained by sintering the synthesized powders at temperatures ranging from 850°C to 1000°C. The BIT ceramics sintered at 1020°C for 1 h, exhibiting a density with 7.52 g/cm3 of a crystaline phase and a dielectric of K = 288.11 (100 Hz), as well as a dielectric loss of 0.05 (100 kHz). The High-energy ball milling process is a promising way to prepare BIT ceramics. After the preparation of the BIT, we doped it with the Multi-Walled Carbon Nanotubes which are properly obtained by a chemical vapour deposition (CVD), using nickel as a catalyst, as well as using acetilene at 720°C, and then proceeded with the dielectric and optical measurements.展开更多
The effects of ball milling time and Ni content on the dehydrogenation performance of MgH2/Ni composite weresystematically investigated.The structural evolution of ball milled MgH2+x%Ni(x=0,2,4,8,20,30,mass fraction)s...The effects of ball milling time and Ni content on the dehydrogenation performance of MgH2/Ni composite weresystematically investigated.The structural evolution of ball milled MgH2+x%Ni(x=0,2,4,8,20,30,mass fraction)samples duringmechanical milling process and dehydrogenation properties were investigated by a series of experimental techniques.The resultsshow that the desorption kinetics is independent of particle size,grain size and defects as the temperature is above380oC.Thedesorption kinetics is improved by prolonged milling time due to refined and uniformly distributed Ni.The formation of Mg2Ni afterdehydrogenation is proposed to explain the degradation of hydrogen storage properties of MgH2during de-/hydrogenation cyclingprocess.The desorption activation energy of MgH2decreases with the increase of Ni content due to the catalytic effect of Ni.It isfound Ni favors the nucleation of magnesium phase and accelerates the recombination of hydrogen atoms.展开更多
Nanocrystalline calcium titanate(CT)ceramic has been synthesized by a combination of solid-state reaction and high-energy ball milling.This nano-ceramic is characterized by X-ray diffraction(XRD),dielectric study and ...Nanocrystalline calcium titanate(CT)ceramic has been synthesized by a combination of solid-state reaction and high-energy ball milling.This nano-ceramic is characterized by X-ray diffraction(XRD),dielectric study and impedance spectroscopy.The XRD pattern shows single phase ceramic of orthorhombic symmetry.The frequency-dependent dielectric study shows that the dielectric constant is maximized at low frequencies and decreases with an increase in frequency.Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon.A significant shift in impedance loss peaks toward the higher-frequency side indicates conduction in the material favoring the long-range motion of mobile charge carriers.The grain conduction effect is observed from the complex impedance spectrum by the appearance of one semicircular arc in Nyquist plot.It is also observed that the resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance(NTCR).Various thermistor parameters have been calculated by fitting with Steinhart-Hart equation.The modulus plots represent the presence of temperature-dependent electrical relaxation phenomenon with the material.The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated.The activation energy has been calculated from an Arrhenius plot of DC conductivity and relaxation frequency.展开更多
In this study, nanostructured Fe powders were synthesized following 10 hours of high-energy ball milling with a superimposed dielectric barrier discharge plasma （DBDP）. The mean size of the milled powder was approxi...In this study, nanostructured Fe powders were synthesized following 10 hours of high-energy ball milling with a superimposed dielectric barrier discharge plasma （DBDP）. The mean size of the milled powder was approximately 100 nm with an average grain size of 16.2 nm. The influence of DBDP on the underlying grain refinement mechanisms during ball milling was investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and BET methods. Our results show that the Fe particles displayed an extraordinary plasticity during the early milling stages under the action of DBDP, and that the plastic deformation experienced by the Fe particles during this stage was more severe than that present in normal milling. A high concentration of spherical Fe particles, approximately 50-100 nm in diameter, was documented via TEM. We propose that these spherical particles were generated via high temperature disintegration as a result of DBDP electron bombardment during ball milling. Our results suggest that it may be possible to significantly refine metallic powders during milling via the superimposition of DBDP.展开更多
High silicon content Al-Si composites with a composition of Al-40 wt% Si were fabricated via a highenergy ball milling method. The microstructure evolution of Al-40 wt% Si milled powders and sintered composites has be...High silicon content Al-Si composites with a composition of Al-40 wt% Si were fabricated via a highenergy ball milling method. The microstructure evolution of Al-40 wt% Si milled powders and sintered composites has been thoroughly studied by scanning electron microscopy, X-ray diffraction, energydispersive spectrometry and high-resolution transmission electron microscopy. The mechanism of ball milling Al-40 wt% Si powders has been disclosed in detail: fracture mechanism dominating in the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. It has been found that the average particle sizes of mixed Al-Si powders can be refined to the nanoscale, and the crystallite sizes of Al and Si have been reduced to 10nm and 62nm upon milling for 2h–50h, respectively. The finally formed Al-Si interfaces after ball milling for 50h are wellcohesive. A dense and homogenous Al-40 wt% Si composite have been achieved by solid-state sintering at550?C. The results thus provide an effective support for producing bulk nanostructured Al-Si composites.展开更多
Al-xV alloys(x=2 at.%,5 at.%,10 at.%)with nanocrystalline structure and high solid solubility of V were produced in powder form by high-energy ball milling(HEBM).The alloy powders were consolidated by spark plasma sin...Al-xV alloys(x=2 at.%,5 at.%,10 at.%)with nanocrystalline structure and high solid solubility of V were produced in powder form by high-energy ball milling(HEBM).The alloy powders were consolidated by spark plasma sintering(SPS)employing a wide range of temperatures ranging from 200 to 400°C.The microstructure and solid solubility of V in Al were investigated using X-ray diffraction analysis,scanning electron microscope and transmission electron microscope.The microstructure was influenced by the SPS temperature and V content of the alloy.The alloys exhibited high solid solubility of V–six orders of magnitude higher than that in equilibrium state and grain size<50 nm at all the SPS temperatures.The formation of Al3V intermetallic was detected at 400℃.Formation of a V-lean phase and bimodal grain size was observed during SPS,which increased with the increase in SPS temperature.The hardness and elastic modulus,measured using nanoindentation,were significantly higher than commercial alloys.For example,Al-V alloy produced by SPS at 200℃ exhibited a hardness of 5.21 GPa along with elastic modulus of 96.21 GPa.The evolution of the microstructure and hardness with SPS temperatures has been discussed.展开更多
In this paper, TiAl alloy powders were prepared successfully by high-energy ball milling and diffusion reaction in vacuum at low temperature. The titanium powder, aluminum powder, and titanium hydride powder were used...In this paper, TiAl alloy powders were prepared successfully by high-energy ball milling and diffusion reaction in vacuum at low temperature. The titanium powder, aluminum powder, and titanium hydride powder were used as raw materials. The samples were characterized by scanning electron microscopy（SEM）, X-ray diffraction（XRD）, field-emission scanning electron microscopy（FESEM）, and differential thermal analysis（DTA）. The results show that the alloy powders with the main intermetallic compounds of TiAl are obtained using Ti-Al powders and TiH2-Al powders after heated for 2 h at 500 ℃,3 h at 600 ℃,and 3 h at 750 ℃,respectively.The average grain sizes of alloy powder are about 45 and20 μm with irregular shape, respectively. The prepared TiAl alloy powders are relatively pure, and the average quality content of oxygen in the alloy powders is0.33 wt%. The forming process of alloy powder contains both the diffusion reaction of Ti and Al,which gives priority to the diffusion reaction of aluminum.展开更多
Yttria-reinforced copper matrix composites were prepared by dry ball milling （DBM） and wet ball milling （WBM）, respectively, followed by spark plasma sintering （SPS）. It is to determine which milling process is ...Yttria-reinforced copper matrix composites were prepared by dry ball milling （DBM） and wet ball milling （WBM）, respectively, followed by spark plasma sintering （SPS）. It is to determine which milling process is better for fabricating Cu-Y2O3 composites. It is found that Cu-Y2O3 composites synthesized by DBM exhibit better densification, mechanical and electrical properties than those by WBM. Less agglomeration of reinforcements in the bulk composites by DBM is responsible for the better perfor- mances. To further understand the reason of less agglomeration of Y2O3 in the bulks by DBM, morphologies of prepared powders were investigated and analyzed. Higher ball＇s impact energy and the formation of copper oxide on the matrix surface during DBM process contribute to small matrix particles, which is beneficial for less agglomeration.展开更多
LiBH_(4) has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity,which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversio...LiBH_(4) has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity,which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversion via anodic oxidation reaction of direct borohydride fuel cells(DBFCs).However,the realization of practical hydrogen applications heavily depends on the effective synthesis of high-purity LiBH_(4) and recycling of the spent fuels(LiBO_(2)·xH_(2)O).The present work demonstrates a convenient and high-efficiency solvent-free strategy for regenerating LiBH_(4) with a maximum yield close to 80%,by retrieving its by-products with MgH_(2) as a reducing agent under ambient conditions.Besides,the hydrogen released from the regeneration course can completely compensate the demand for consumed MgH_(2).The isotopic tracer method reveals that the hydrogen stored in LiBH_(4) comes from both MgH_(2) and coordinated water bound to LiBO_(2).Here,the expensive MgH_(2) can be substituted with the readily available and cost-effective MgH_(2)-Mg mixtures to simplify the regeneration route.Notably,LiBH_(4) catalyzed by CoCl_(2) can stably supply hydrogen to proton exchange membrane fuel cell(PEMFC),thus powering a portable prototype vehicle.By combining hydrogen storage,production and utilization in a closed cycle,this work offers new insights into deploying boron-based hydrides for energy applications.展开更多
Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw...Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.展开更多
The amorphous boron powders with high activity were prepared by the high-energy ball milling-combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology a...The amorphous boron powders with high activity were prepared by the high-energy ball milling-combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology and reactivity of amorphous boron powder were studied. The results show that the crystallinity of amorphous nano-boron powder is only 22.5%, and its purity reaches 92.86%. The high-energy ball milling can significantly refine boron powder particle sizes, whose average particle sizes are smaller than 50 nm, and specific surface areas are of up to 70.03 m2/g. When the transmission electron beam irradiates the samples, they rapidly melt. It can be seen that the monomer amorphous boron size is less than 30 nm from the specimen melting traces, which indicates that the samples have high reactivity.展开更多
基金Project (BK2011243) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject (EIPE11204) supported by the State Key Laboratory of Electrical Insulation and Power Equipment,China+4 种基金Project (KF201104) supported by the State Key Laboratory of New Ceramic and Fine Processing,ChinaProject (KFJJ201105) supported by the Opening Project of State Key Laboratory of Electronic Thin Films and Integrated Devices,ChinaProject (2011-22) supported by State Key Laboratory of Inorganic Synthesis and Preparative Chemistry,ChinaProject (10KJD430002) supported by the Universities Natural Science Research Project of Jiangsu Province,ChinaProject (11JDG084) supported by the Research Foundation of Jiangsu University,China
文摘ZnO varistor ceramics doped with Bi2O3, Sb2O3, CO2O3, Cr2O3, and MnO2 were prepared separately by two high-energy ball milling processes： oxide-doped and varistor ceramic powder. A comparison in the electrical and microstructural properties of the samples obtained by both methods was made. The best results on these characteristics were achieved through the high-energy ball milling varistor ceramic powder route, obtaining a nonlinear coefficient of 57 and a breakdown field of 617 V/mm at a sintering temperature of 1000 ℃ for 3 h. The samples synthesized by this technique show not only high density value, 95% of the theoretical density, but also a homogeneous microstructure, which compete with those obtained by the high-energy ball milling oxide-doped powder route. With the advantage that the high-energy ball milling varistor ceramic powder route can refine grain, increase the driving force of sintering, accelerate the sintering process, and reduce the sintering temperature.
基金Project(51104066)supported by the National Natural Science Foundation of ChinaProjects(2015A010105011,2015A020214008)supported by Science and Technology Program of Guangdong Province,ChinaProject(201505040925029)supported by Science and Technology Research Program of Guangzhou,China
文摘Bimodal-grained Ti containing coarse and fine grains was fabricated by high-energy ball milling and spark plasma sintering (SPS). The microstructure and mechanical properties of the compacts sintered by Ti powders ball-milled for different time were studied. Experimental results indicated that when the ball-milling time increased, the microstructure of sintered Ti was firstly changed from coarse-grained to bimodal-grained structure, subsequently transformed to a homogeneous fine-grained structure. Compared with coarse-grained Ti and fine-grained Ti, bimodal-grained Ti exhibited balanced strength and ductility. The sample sintered from Ti powders ball-milled for 10 h consisting of 65.3% (volume fraction) fine-grained region (average grain size 1 μm) and 34.7% coarse-grained region (grain size > 5 μm) exhibited a compress strength of 1028 MPa as well as a plastic strain to failure of 22%.
文摘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.
基金Project supported by National Natural Science Foundation of China (50471045) Shanghai Nano-Technology PromotionCenter (0452nm026)
文摘The microstructure, electrical properties and density of ZnO-based varistor ceramics with different Er2O3 content prepared by high-energy ball milling （HEBM） and sintered at 800℃ were investigated. With increasing Er2O3 content, the ZnO grain size decreases due to the Er-rich phases inhibiting grain growth ; and nonlinear coefficient （ α ） decreases because of the decrease of barrier height （φB） The breakdown voltage （Eb） and density increase, whereas leakage current （IL） decreases with increasing Er2O3 content. The barrier height （φB）, donor concentration （Nd）, density of interface states （Ns） decrease and barrier width （ω） increases with increasing Er2O3 content due to acceptor effect of Er2O3 in varistor ceramics.
基金Sponsored by the Program for Innovative Research Team in University of Yunnan Province and Major Projects of Yunnan Province(Grant No.2014FC001)
文摘The mathematical models are developed to evaluate the ultimate tensile strength( UTS) and hardness of CNTs / Al2024 composites fabricated by high-energy ball milling. The effects of the preparation variables which are milling time,rotational speed,mass fraction of CNTs and ball to powder ratio on UST and hardness of CNTs / Al2024 composites are investigated. Based on the central composite design( CCD),a quadratic model is developed to correlate the fabrication variables to the UST and hardness. From the analysis of variance( ANOVA),the most influential factor on each experimental design response is identified. The optimum conditions for preparing CNTs / Al2024 composites are found as follows: 1. 53 h milling time,900 r / min rotational speed,mass fraction of CNTs 2. 87% and Ball to powder ratio 25 ∶ 1. The predicted maximum UST and hardness are 273.30 MPa and 261.36 HV,respectively. And the experimental values are 283.25 MPa and256.8 HV,respectively. It is indicated that the predicted UST and hardness after process optimization are found to agree satisfactory with the experimental values.
文摘In this paper, the milling parameters of high energy ball mill (Fritsch Pulverisette 7) like vial geometry, number and size of balls and speed of the mill were modelled and discussed. Simulations through discrete element method (DEM) provide correlation between the milling parameters. A mathematical model is used to improve and develop this process. The results show that the loss of powder mass can remarkably improve the performance of milling. The balls made of stainless-steel have a positive effect on the milling efficiency. The simulation shows that the high ball milling velocities can contribute to faster particle size reduction.
基金This project was financially supported by the National Natural Science Foundation of China (No. 59875015)the Natural Science Foundation of South China University of Technology (No. E5305293).
文摘A TiAl alloy was fabricated by high-energy ball milling and subsequent reactive sintering from the mixed powders of Ti and Al. High-energy ball milling produced a kind of particular composite powders with an extremely fine altemative Ti and Al lamella structure. The composite powders not only possessed good consolidation and densification characteristics, but also resulted in the augment of nucleation rate of α and γ titanium aluminides during solid-phase reactive sintering After a series of processing, pressing, degassing, extrusion, and sintering, the resultant TiAl alloy presented high relative density and refined grain sizes of （α2 ＋ γ） lamella and γ phases. The compressive yield strength of the sintered TiAl reached 600 MPa at 800℃.
文摘The structural evolution of Fe-doped TiO2 by high-energy ball milling was investigated by X-ray diffraction and Mǒssbauer spectroscopy, The results show that the original anatase-TiO2 transforms to srilankite-type and rutile-type during ball milling. Iron atoms are preferable to dissolve in rutile-TiO2 and there are two relative doublets appearing in Mǒssbauer spectra. A doublet is found in the condition of Fe atoms dissolved in srilankite TiO2 lattice. Mǒssbauer spectra show that the composition distribution is nonuniform in TiO2 during the mechanical alloying with Fe atoms rich at the interface or surface of TiO2 crystalline.
基金Project supported by the State Key Laboratory for Powder Metallurgy of CSUT
文摘Using electrolytic manganese dioxide and Li 2CO 3 as starting materials, the precursor of LiMn 2O 4 as cathode materials for lithium ion batteries was obtained by high energy ball milling. The LiMn 2O 4 powder was synthesized by calcinating the as milling powder at 750 ℃ for 24 h. X ray diffraction, SEM, cyclic voltammograms and charge discharge were carried out to investigate the property of LiMn 2O 4 cathode materials. Results show that the synthesized material, which is of standard spinel structure, possesses high reversibility of electrochemistry. The capacity in EC DMC(1∶1)+1 mol/L LiPF 6 electrolyte during first discharge is determined to be 125 mA·h/g.[
基金We would like to thank to the institution below:UFC,LOCEM,UECE,CNPq,CAPES,FUNCAP,G.D.Saraiva acknowledges the support from MCT/CNPqEdital 14/2010(process 476569/2010-9)FUNCAP/Edital 02/2010(process 10293648-0)+1 种基金 FUNCAP/Edital 05/2009(process 186.01.00/09)The other authors acknowledge CNPq and FUNCAP for partial financial support.
文摘We prepared the Nano-sized bismuth titanate Bi4Ti3O12 (BIT) powders, through a high-energy ball milling process from their oxides Bi2O3 and TiO2. This BIT phase can be formed after a milling process for 40 min. With an increasing milling time, this particle size of mixture is gradually reduced, thus, we have mostly an amorphous phase. The BIT ceramics were duly obtained by sintering the synthesized powders at temperatures ranging from 850°C to 1000°C. The BIT ceramics sintered at 1020°C for 1 h, exhibiting a density with 7.52 g/cm3 of a crystaline phase and a dielectric of K = 288.11 (100 Hz), as well as a dielectric loss of 0.05 (100 kHz). The High-energy ball milling process is a promising way to prepare BIT ceramics. After the preparation of the BIT, we doped it with the Multi-Walled Carbon Nanotubes which are properly obtained by a chemical vapour deposition (CVD), using nickel as a catalyst, as well as using acetilene at 720°C, and then proceeded with the dielectric and optical measurements.
基金Project(95-QZ-2014) supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject supported by the Defense Industrial Technology Development Program,ChinaProject(B08040) supported by the 111 Program,China
文摘The effects of ball milling time and Ni content on the dehydrogenation performance of MgH2/Ni composite weresystematically investigated.The structural evolution of ball milled MgH2+x%Ni(x=0,2,4,8,20,30,mass fraction)samples duringmechanical milling process and dehydrogenation properties were investigated by a series of experimental techniques.The resultsshow that the desorption kinetics is independent of particle size,grain size and defects as the temperature is above380oC.Thedesorption kinetics is improved by prolonged milling time due to refined and uniformly distributed Ni.The formation of Mg2Ni afterdehydrogenation is proposed to explain the degradation of hydrogen storage properties of MgH2during de-/hydrogenation cyclingprocess.The desorption activation energy of MgH2decreases with the increase of Ni content due to the catalytic effect of Ni.It isfound Ni favors the nucleation of magnesium phase and accelerates the recombination of hydrogen atoms.
文摘Nanocrystalline calcium titanate(CT)ceramic has been synthesized by a combination of solid-state reaction and high-energy ball milling.This nano-ceramic is characterized by X-ray diffraction(XRD),dielectric study and impedance spectroscopy.The XRD pattern shows single phase ceramic of orthorhombic symmetry.The frequency-dependent dielectric study shows that the dielectric constant is maximized at low frequencies and decreases with an increase in frequency.Impedance spectroscopy analyses reveal a non-Debye type relaxation phenomenon.A significant shift in impedance loss peaks toward the higher-frequency side indicates conduction in the material favoring the long-range motion of mobile charge carriers.The grain conduction effect is observed from the complex impedance spectrum by the appearance of one semicircular arc in Nyquist plot.It is also observed that the resistance decreases with an increase in temperature showing a negative temperature coefficient of resistance(NTCR).Various thermistor parameters have been calculated by fitting with Steinhart-Hart equation.The modulus plots represent the presence of temperature-dependent electrical relaxation phenomenon with the material.The frequency-dependent AC conductivity at different temperatures indicates that the conduction process is thermally activated.The activation energy has been calculated from an Arrhenius plot of DC conductivity and relaxation frequency.
基金supported by the National Natural Science Foundation of China (No.51177008)Natural Science Fundation of Fujian Province(No. 2012J01228)+1 种基金the Program for New Century Excellent Talents in Fujian Province University (No. NCETFJ–Z80136)Fujian Provincial Department of Science & Technology (Nos. 2011J01324 and JK2010030)
文摘In this study, nanostructured Fe powders were synthesized following 10 hours of high-energy ball milling with a superimposed dielectric barrier discharge plasma （DBDP）. The mean size of the milled powder was approximately 100 nm with an average grain size of 16.2 nm. The influence of DBDP on the underlying grain refinement mechanisms during ball milling was investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray diffraction （XRD） and BET methods. Our results show that the Fe particles displayed an extraordinary plasticity during the early milling stages under the action of DBDP, and that the plastic deformation experienced by the Fe particles during this stage was more severe than that present in normal milling. A high concentration of spherical Fe particles, approximately 50-100 nm in diameter, was documented via TEM. We propose that these spherical particles were generated via high temperature disintegration as a result of DBDP electron bombardment during ball milling. Our results suggest that it may be possible to significantly refine metallic powders during milling via the superimposition of DBDP.
基金financially supported by the National Natural Science Foundation of China (No.51571148)the National Key Research and Development Program of China (No.2017YFE0302600 and No.2017YFB0701801)the Thousand Talents Program for Distinguished Young Scholars of China
文摘High silicon content Al-Si composites with a composition of Al-40 wt% Si were fabricated via a highenergy ball milling method. The microstructure evolution of Al-40 wt% Si milled powders and sintered composites has been thoroughly studied by scanning electron microscopy, X-ray diffraction, energydispersive spectrometry and high-resolution transmission electron microscopy. The mechanism of ball milling Al-40 wt% Si powders has been disclosed in detail: fracture mechanism dominating in the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. It has been found that the average particle sizes of mixed Al-Si powders can be refined to the nanoscale, and the crystallite sizes of Al and Si have been reduced to 10nm and 62nm upon milling for 2h–50h, respectively. The finally formed Al-Si interfaces after ball milling for 50h are wellcohesive. A dense and homogenous Al-40 wt% Si composite have been achieved by solid-state sintering at550?C. The results thus provide an effective support for producing bulk nanostructured Al-Si composites.
基金the financial support received from the National Science Foundation(Nos.NSF-CMMI 1760204 and 2131440)under the direction of Dr.Alexis Lewissupported by the State of North Carolina and the National Science Foundation(No.ECCS-1542015)support from the National Science Foundation(DMR1726294)。
文摘Al-xV alloys(x=2 at.%,5 at.%,10 at.%)with nanocrystalline structure and high solid solubility of V were produced in powder form by high-energy ball milling(HEBM).The alloy powders were consolidated by spark plasma sintering(SPS)employing a wide range of temperatures ranging from 200 to 400°C.The microstructure and solid solubility of V in Al were investigated using X-ray diffraction analysis,scanning electron microscope and transmission electron microscope.The microstructure was influenced by the SPS temperature and V content of the alloy.The alloys exhibited high solid solubility of V–six orders of magnitude higher than that in equilibrium state and grain size<50 nm at all the SPS temperatures.The formation of Al3V intermetallic was detected at 400℃.Formation of a V-lean phase and bimodal grain size was observed during SPS,which increased with the increase in SPS temperature.The hardness and elastic modulus,measured using nanoindentation,were significantly higher than commercial alloys.For example,Al-V alloy produced by SPS at 200℃ exhibited a hardness of 5.21 GPa along with elastic modulus of 96.21 GPa.The evolution of the microstructure and hardness with SPS temperatures has been discussed.
基金financially supported by the National Natural Science Foundation of China (No. 51274039)the Guangdong Foundation of Research (No. 2011A090200091)
文摘In this paper, TiAl alloy powders were prepared successfully by high-energy ball milling and diffusion reaction in vacuum at low temperature. The titanium powder, aluminum powder, and titanium hydride powder were used as raw materials. The samples were characterized by scanning electron microscopy（SEM）, X-ray diffraction（XRD）, field-emission scanning electron microscopy（FESEM）, and differential thermal analysis（DTA）. The results show that the alloy powders with the main intermetallic compounds of TiAl are obtained using Ti-Al powders and TiH2-Al powders after heated for 2 h at 500 ℃,3 h at 600 ℃,and 3 h at 750 ℃,respectively.The average grain sizes of alloy powder are about 45 and20 μm with irregular shape, respectively. The prepared TiAl alloy powders are relatively pure, and the average quality content of oxygen in the alloy powders is0.33 wt%. The forming process of alloy powder contains both the diffusion reaction of Ti and Al,which gives priority to the diffusion reaction of aluminum.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0301400)the Organization Department of Jiangxi Province(No. 2012215)+1 种基金the Education Department of Jiangxi Province (No. KJLD13041)the Outstanding Doctoral Dissertation Project Fund of JXUST (No. YB2017011)
文摘Yttria-reinforced copper matrix composites were prepared by dry ball milling （DBM） and wet ball milling （WBM）, respectively, followed by spark plasma sintering （SPS）. It is to determine which milling process is better for fabricating Cu-Y2O3 composites. It is found that Cu-Y2O3 composites synthesized by DBM exhibit better densification, mechanical and electrical properties than those by WBM. Less agglomeration of reinforcements in the bulk composites by DBM is responsible for the better perfor- mances. To further understand the reason of less agglomeration of Y2O3 in the bulks by DBM, morphologies of prepared powders were investigated and analyzed. Higher ball＇s impact energy and the formation of copper oxide on the matrix surface during DBM process contribute to small matrix particles, which is beneficial for less agglomeration.
基金This work was financially supported by the National Natural Science Foundation of China Projects(Nos.51771075)the National Key R&D Program of China(No.2018YFB1502101)+2 种基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.NSFC51621001)by the Project Supported by Nat-ural Science Foundation of Guangdong Province of China(2016A030312011)Shao acknowledges support from Macao Science and Technology Development Fund(FDCT)(Project No.:0062/2018/A2 and 0019/2019/AGJ).
文摘LiBH_(4) has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity,which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversion via anodic oxidation reaction of direct borohydride fuel cells(DBFCs).However,the realization of practical hydrogen applications heavily depends on the effective synthesis of high-purity LiBH_(4) and recycling of the spent fuels(LiBO_(2)·xH_(2)O).The present work demonstrates a convenient and high-efficiency solvent-free strategy for regenerating LiBH_(4) with a maximum yield close to 80%,by retrieving its by-products with MgH_(2) as a reducing agent under ambient conditions.Besides,the hydrogen released from the regeneration course can completely compensate the demand for consumed MgH_(2).The isotopic tracer method reveals that the hydrogen stored in LiBH_(4) comes from both MgH_(2) and coordinated water bound to LiBO_(2).Here,the expensive MgH_(2) can be substituted with the readily available and cost-effective MgH_(2)-Mg mixtures to simplify the regeneration route.Notably,LiBH_(4) catalyzed by CoCl_(2) can stably supply hydrogen to proton exchange membrane fuel cell(PEMFC),thus powering a portable prototype vehicle.By combining hydrogen storage,production and utilization in a closed cycle,this work offers new insights into deploying boron-based hydrides for energy applications.
基金the National Natural Science Foundation of China (Grant No.10774040) and the joint Chinese-Russian Project for their financial supports
文摘Strontium doped perovskite-type Nd0.7Sr0.3MnO3 ceramics were synthesized completely by high-energy ball milling raw oxides of Nd2O3, SrCO3 and MnO2. The optimal ball milling time and mass ratio of milling balls to raw materials are 4 h and 10：1, respectively. The grain size of as-milled Nd0.7Sr0.3MnO3 ceramics ranges from 51 to 93 nm, and the fine particles contain two phases of crystalline phase and amorphous phase. For the Nd0.7r0.3MnO3 synthesized by ball milling and sequent heat treatment, a remarkable colossal electroresistance （CER） effect is observed and the CER ratio reaches 900% at Curie temperature Tc when the load voltage increases from 0.1 to 0.8 V.
基金Project(51002025)supported by the National Natural Science Foundation of China
文摘The amorphous boron powders with high activity were prepared by the high-energy ball milling-combustion synthesis method. The effects of the milling rate and milling time on the crystallinity, microscopic morphology and reactivity of amorphous boron powder were studied. The results show that the crystallinity of amorphous nano-boron powder is only 22.5%, and its purity reaches 92.86%. The high-energy ball milling can significantly refine boron powder particle sizes, whose average particle sizes are smaller than 50 nm, and specific surface areas are of up to 70.03 m2/g. When the transmission electron beam irradiates the samples, they rapidly melt. It can be seen that the monomer amorphous boron size is less than 30 nm from the specimen melting traces, which indicates that the samples have high reactivity.
