A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study.The obtained alloy shows finer grains,higher strength,and a negligible tension-compressi...A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study.The obtained alloy shows finer grains,higher strength,and a negligible tension-compression yield asymmetry,compared with that prepared via room-temperature rotary swaging.Transmission electron microscopy investigations showed that at the initial stage,multiple twins,mostly tension twins,were activated and intersected with each other,thereby refining the coarse grains into a fine lamellar structure.Then,two types of nanoscale subgrains were generated with increasing swaging strain.The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries.This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress.The second type of nanoscale subgrain was formed within the twin lamellae.The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays.Finally,randomly oriented nanograins were obtained via dynamic recrystallization,under the combined function of deformation heat and increased stored energy.Compared with room-temperature rotary swaging,cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging.展开更多
Artificial synapses utilizing spike signals are essential elements of new generation brain-inspired computers.In this paper,we realize light-stimulated adaptive artificial synapse based on nanocrystalline zinc oxide f...Artificial synapses utilizing spike signals are essential elements of new generation brain-inspired computers.In this paper,we realize light-stimulated adaptive artificial synapse based on nanocrystalline zinc oxide film.The artificial synapse photoconductivity shows spike-type signal response,long and short-term memory(LTM and STM),STM-to-LTM transition and paired-pulse facilitation.It is also retaining the memory of previous exposures and demonstrates spike-frequency adaptation properties.A way to implement neurons with synaptic depression,tonic excitation,and delayed accelerating types of response under the influence of repetitive light signals is discussed.The developed artificial synapse is able to become a key element of neuromorphic chips and neuromorphic sensorics systems.展开更多
A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering (SPS) at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of ...A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering (SPS) at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.展开更多
The structure and electrochemical properties of nanocrystalline LaNi_5-type alloys were studied. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materia...The structure and electrochemical properties of nanocrystalline LaNi_5-type alloys were studied. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the partial substitution of Ni by Al or Mn in LaNi_(5-x)M_x alloy leads to an increase in discharge capacity. The alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi_5 material. For example, in the nanocrystalline LaNi_(3.75)Mn_(0.75)Al_(0.25)Co_(0.25) powder, discharge capacity up to 258 mAh·g^(-1) was measured (at 40 mA·g^(-1) discharge current). Furthermore, the effect of the graphite coating on the structure of some nanocrystalline alloys and the electrodes characteristics were investigated. The mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials. The combination of a nanocrystalline LaNi_5-type hydride electrodes and a nickel positive electrode to form a Ni-MH battery, was successful.展开更多
High-temperature AC magnetic properties for (Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9 alloy annealed at various temperatures have been investigated using an impedance analyzer. Annealing temperature Ta has obvious effects on h...High-temperature AC magnetic properties for (Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9 alloy annealed at various temperatures have been investigated using an impedance analyzer. Annealing temperature Ta has obvious effects on high-temperature AC magnetic properties of the alloy. The Hopkinson peak appears only in the amorphous alloy when Ta≤703K. As Ta increases above 733K, the real part of the complex initial permeability μi′descends gradually, μi′decreases more slowly with temperature in the high temperature range. The high-temperature (about 750K) AC initial permeability for the alloy annealed at Ta= 763K has been found to maintain a stable high value of 950 up to a frequency of- 1 × 10^5Hz. Partial substitution of Co for Fe in the F73.5Cu1Nb3Si13.5B9 alloy leads to an increase of around 110K of the Curie temperature of the amorphous phase, much higher than Ge-containing Finemet alloy.展开更多
A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5...A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1). after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).展开更多
Classical molecular dynamics(MD)simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium(Mg)of varying grain size levels.The mean grain size of the sample is varied from 6.4...Classical molecular dynamics(MD)simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium(Mg)of varying grain size levels.The mean grain size of the sample is varied from 6.4 nm to 45 nm,with each sample containing about 43 million atoms in the modeling system.The deformation nanomechanics reveals two distinct deformation mechanisms.For larger grain-sized samples,dislocation dominated deformation is observed while,in smaller grain-sized samples,grain boundary-based mechanisms such as grain boundary sliding,grain boundary rotation are observed.The transition of normal and inverse Hall-Petch relation occurs at around lOnm.Dislocation density quantification shows that the dislocation density in the sample drastically reduces with decreasing grain size.Elastic modulus of nanocrystalline Mg with mean grain size above 20 nm remains comparable to that of the coarse-grained polycrystalline bulk,followed by a rapid reduction below that grain size.The present work reveals the nanomechanics of nanocrystalline Mg,facilitating the design and development of Mg-based nanostructured alloys with superior mechanical properties.展开更多
The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan,sorbitol and nanocrystalline cellulose.The morphology of the resulting nanocomposite ...The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan,sorbitol and nanocrystalline cellulose.The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose.The average pore diameter,bulk density,porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques.Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films.Control xylan films had average pore diameter,bulk density,porosity and tortuosity factor of 0.1730 μm,0.6165 g/ml,53.0161% and 1.258,respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 μm,bulk density of 1.1513 g/ml,porosity of 22.8906% and tortuosity factor of 2.005.Oxygen transmission rate tests demonstrated that films prepared with xylan,sorbitol and 5%,10%,25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387,1.0933,0.8986 and 0.1799 cm^3×μm/m^2×d×k Pa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm^3×μm/m^2×d×k Pa.These properties suggested these nanocomposite films have promising barrier properties.展开更多
Chemical solution deposited CdSe particulate film possess nanocrystalline structure and exhibit quantum size effects. By changing the temperature of chemical deposition and subsequent annealing, CdSe particulate films...Chemical solution deposited CdSe particulate film possess nanocrystalline structure and exhibit quantum size effects. By changing the temperature of chemical deposition and subsequent annealing, CdSe particulate films with different particle sizes can be obtained.展开更多
Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7-xZrxB6.0 (x=0-3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnet...Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7-xZrxB6.0 (x=0-3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnetometer (VSM) revealed that Zr addition was significantly effective in improving the magnetic properties at room temperature. The intrinsic coercivity Hci of the optimally processed ribbons increased monotonically with increasing Zr content, from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. Unlike the coercivity, the remanence polarization Jr increased first with Zr addition, from 0.898 T up to 1.041 T at x=1.5, and then decreased with further Zr addition. The maximum energy product (BH)max behaved similarly, increasing from 103.1 kJ/m3 to a maximum of 175.2 kJ/m3 at x=1.5. Microstruc- ture studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM) had shown a significant microstructure refinement with Zr addition. The absolute values of temperature coefficients of induction and coercivity were significantly increased with increasing Zr content, indicating that Zr was detrimental to thermal stability of the melt-spun Nd2Fe14B-type material.展开更多
Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method.According to the configurations during demagnetization pr...Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method.According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed.For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries.However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucle-ated domain.For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.展开更多
Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition (PECVD) at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, st...Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition (PECVD) at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS), respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V (vs SCE).展开更多
In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by...In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by which nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 (wt pct) composite powders with mean grain size of 25 nm were prepared in 32 min, and the quantity of the powders for a batch was as much as 800 grams. The as-prepared powders were analyzed and characterized by chemical analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results show that high energy ball milling with variable rotation rates and repeatious circulation could be used to produce nanocrystalline WC-Co powder composites with high efficiency. The compositions of the powders meet its specifications with low impurity content. The mean grain size decreases, lattice distortion and system energy increase with increasing the milling time. The morphology of nanocrystalline WC-Co particles displays dominantiy sphere shape and their particle sizes are all lower than 80 nm. The eutectic temperature of the nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 composites is about 1280℃.展开更多
A number of studies have been reported on the use of nanocrystalline plasma electrolytic nitrocarburising technology for surface hardening of stainless steels for higher corrosion resistance resulted from this techniq...A number of studies have been reported on the use of nanocrystalline plasma electrolytic nitrocarburising technology for surface hardening of stainless steels for higher corrosion resistance resulted from this technique. However, very few studies have focused on the optimization of the nanocrystalline plasma electrolytic nitrocarburising process parameters. In this study, a design of experiment (DOE) technique, the Taguchi method, has been used to optimize the nanocrystalline plasma electrolytic nitrocarburising not only for surface hardening but also for the corrosion protection of 316L austenitic stainless steel by controlling the coating processes factors. The experimental design consisted of four factors (Urea concentration, electrical conductivity of electrolyte, voltage and duration of process), each containing three levels. Potentiodynamic polarization measurements were carried out to determine the corrosion resistance of the coated samples. The results were analyzed with related software. An analysis of the mean of signal-to-noise (S/N) ratio indicated that the corrosion resistance of nanocrystalline plasma electrolytic nitrocarburised 316L stainless steel was influenced significantly by the levels in the Taguchi orthogonal array. The optimized coating parameters for corrosion resistance are 1150 g/L for urea concentration, 360 mS/cm for electrical conductivity of electrolyte, 260 V for applied voltage, 6 min for treatment time. The percentage of contribution for each factor was determined by the analysis of variance (ANOVA). The results showed that the applied voltage is the most significant factor affecting the corrosion resistance of the coatings.展开更多
A new type of dye-sensitized nanocrystalline solid state photovoltaic cell based on the wide band gap n-TiO2/p-CuI heterojunction was fabricated. Tetra-carboxyphenyl porphyrine (TPP-(COOH)(4)), squarylium cyanine deri...A new type of dye-sensitized nanocrystalline solid state photovoltaic cell based on the wide band gap n-TiO2/p-CuI heterojunction was fabricated. Tetra-carboxyphenyl porphyrine (TPP-(COOH)(4)), squarylium cyanine derivative (SQ-(CH2),(SO3Py+)-Py-.) and ruthenium bipyridyl complex (RuL2(NCS)(2)) were used as photosensitizers. Larger photocurrents and photovoltages were shown in the cell sensitized by ruthenium bipyridyl complex and can be further increased by intercalation of a TiO2 thin underlayer.展开更多
CO2 reforming of methane (CDRM) was carried out over MgO supported Ni catalysts with various Ni loadings. The preparation of MgO supported Ni catalysts via surfactant-assisted precipitation method led to the formati...CO2 reforming of methane (CDRM) was carried out over MgO supported Ni catalysts with various Ni loadings. The preparation of MgO supported Ni catalysts via surfactant-assisted precipitation method led to the formation of a nanocrystalline carrier for nickel catalysts. The synthesized samples were characterized by XRD, N2 adsorption-desorption, H2 chemisorption, TPR, TPO and SEM techniques. It was found that the high catalytic activity and stability of the prepared catalysts could be attributable to high dispersion of reduced Ni species and basicity of support surface. In addition, the effect of feed ratio, nickel loading and GHSV on the catalytic performance of CDRM over the catalysts were investigated.展开更多
Nd 12.3 Fe 81.7 x Ga x B 6.0 (x = 0-1.8) ribbons were prepared by melt spinning at 22 m/s and subsequent annealing treatment. The influences of Ga addition and annealing conditions on the magnetic properties and mic...Nd 12.3 Fe 81.7 x Ga x B 6.0 (x = 0-1.8) ribbons were prepared by melt spinning at 22 m/s and subsequent annealing treatment. The influences of Ga addition and annealing conditions on the magnetic properties and microstructure of the nanocrystalline alloys were systematically investigated. After being annealed at 620℃ for 20 min, the J r and H ci increased from 0.85 T and 582.6 kA/m for Ga-free sample to 0.97 T and 734.6 kA/m for the x = 0.9 sample, respectively. The (BH) max for the x = 0.9 sample increased by about 40% from 96.3 to 135.5 kJ/m 3 compared with that of the Ga-free one. The significant improvement of magnetic properties originated from the refinement of grains in the samples by introducing Ga, which led to a stronger exchange coupling between the neighboring grains in comparison with that in Ga-free samples. The microstructure and magnetic properties of the samples depended strongly on annealing parameters, while the sensitivity of micro-structure to annealing conditions could be significantly suppressed by the addition of Ga element.展开更多
Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling (cryomilling) method. The morphology, microstructure, size distr...Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling (cryomilling) method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy (SEM), laser scattering for particle size analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM). After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr2O3 phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.展开更多
The microwave magnetic properties of the ball milled FeCo panicles were investigated as functions of ball milling time ( t ) using microwave electromagnetic parameters analysis techniques. The results show that the ...The microwave magnetic properties of the ball milled FeCo panicles were investigated as functions of ball milling time ( t ) using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability ( ui ) of the ball- milled panicles is much bigger than that of raw powders. ui strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni ' s model of non-uniform exchange resonance modes. The present microwave permeabilhy behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.展开更多
基金Xin Chen,Chuming Liu,Yingchun Wan and Zhiyong Chen acknowledge National Natural Science Foundation of China(Grant number 51574291 and 51874367).
文摘A bulk nanocrystalline AZ31B Mg alloy with extraordinarily high strength was prepared via cryogenic rotary swaging in this study.The obtained alloy shows finer grains,higher strength,and a negligible tension-compression yield asymmetry,compared with that prepared via room-temperature rotary swaging.Transmission electron microscopy investigations showed that at the initial stage,multiple twins,mostly tension twins,were activated and intersected with each other,thereby refining the coarse grains into a fine lamellar structure.Then,two types of nanoscale subgrains were generated with increasing swaging strain.The first type of nanoscale subgrain contained twin boundaries and low-angle grain boundaries.This type of subgrain appeared at the twin-twin intersections and was mainly driven by high local stress.The second type of nanoscale subgrain was formed within the twin lamellae.The boundaries of this type of subgrain did not contain twin boundaries and were transformed from massive dislocation arrays.Finally,randomly oriented nanograins were obtained via dynamic recrystallization,under the combined function of deformation heat and increased stored energy.Compared with room-temperature rotary swaging,cryogenic rotary swaging exhibits a slower grain refinement process but a remarkably enhanced grain refinement effect after the same five-pass swaging.
基金supported by the Ministry of Science and Higher Education of the Russian Federation (Grant№075-15-2020-801)by Non-commercial Foundation for support of Science and Education 《INTELLECT》.
文摘Artificial synapses utilizing spike signals are essential elements of new generation brain-inspired computers.In this paper,we realize light-stimulated adaptive artificial synapse based on nanocrystalline zinc oxide film.The artificial synapse photoconductivity shows spike-type signal response,long and short-term memory(LTM and STM),STM-to-LTM transition and paired-pulse facilitation.It is also retaining the memory of previous exposures and demonstrates spike-frequency adaptation properties.A way to implement neurons with synaptic depression,tonic excitation,and delayed accelerating types of response under the influence of repetitive light signals is discussed.The developed artificial synapse is able to become a key element of neuromorphic chips and neuromorphic sensorics systems.
文摘A 92WC-8Co powder mixture with 33 nm WC grains was prepared by strengthening ball milling and was then sintered by spark plasma sintering (SPS) at 1000-1200℃ for 5-18 rain under 10-25 kN, respectively. Movement of the position of low punch shown shrinkage of the sintered body began above 800℃. The shrinkage slowly rose as the temperature rose from 800 to 1000℃ and then quickly rose at above 1000℃ and then gradually rose at above 1150℃. The densities of the samples increased with an increase in sintering temperature, rapidly below 1100℃, and then gradually above 1100℃. WC grains grow gradually with increasing sintering temperature. The powder was sintered to near full density at 1100℃ for 5 rain under 10 kN. The best result of the sample with 275 nm WC grains and no pores was obtained at 1150℃ under 10 kN for 5 rain. The research found the graphite die had a function of carburization, which could compensate the sintered body for the lack of carbon, and had the normal microstructure.
文摘The structure and electrochemical properties of nanocrystalline LaNi_5-type alloys were studied. These materials were prepared by mechanical alloying (MA) followed by annealing. The properties of hydrogen host materials can be modified substantially by alloying to obtain the desired storage characteristics. It was found that the partial substitution of Ni by Al or Mn in LaNi_(5-x)M_x alloy leads to an increase in discharge capacity. The alloying elements such as Al, Mn and Co greatly improved the cycle life of LaNi_5 material. For example, in the nanocrystalline LaNi_(3.75)Mn_(0.75)Al_(0.25)Co_(0.25) powder, discharge capacity up to 258 mAh·g^(-1) was measured (at 40 mA·g^(-1) discharge current). Furthermore, the effect of the graphite coating on the structure of some nanocrystalline alloys and the electrodes characteristics were investigated. The mechanical coating with graphite effectively reduced the degradation rate of the studied electrode materials. The combination of a nanocrystalline LaNi_5-type hydride electrodes and a nickel positive electrode to form a Ni-MH battery, was successful.
基金supported by the National Natural Science Foundation of China(No.50471094).
文摘High-temperature AC magnetic properties for (Fe0.5Co0.5)73.5Cu1Nb3Si13.5B9 alloy annealed at various temperatures have been investigated using an impedance analyzer. Annealing temperature Ta has obvious effects on high-temperature AC magnetic properties of the alloy. The Hopkinson peak appears only in the amorphous alloy when Ta≤703K. As Ta increases above 733K, the real part of the complex initial permeability μi′descends gradually, μi′decreases more slowly with temperature in the high temperature range. The high-temperature (about 750K) AC initial permeability for the alloy annealed at Ta= 763K has been found to maintain a stable high value of 950 up to a frequency of- 1 × 10^5Hz. Partial substitution of Co for Fe in the F73.5Cu1Nb3Si13.5B9 alloy leads to an increase of around 110K of the Curie temperature of the amorphous phase, much higher than Ge-containing Finemet alloy.
文摘A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1). after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).
基金This work was performed under the auspices of startup funds from the San Diego State University(SDSU)the support of the US National Science of Foundation,Division of Materials Research,under Award No.1900876.
文摘Classical molecular dynamics(MD)simulation method is employed to study the uniaxial tensile deformation of nanocrystalline magnesium(Mg)of varying grain size levels.The mean grain size of the sample is varied from 6.4 nm to 45 nm,with each sample containing about 43 million atoms in the modeling system.The deformation nanomechanics reveals two distinct deformation mechanisms.For larger grain-sized samples,dislocation dominated deformation is observed while,in smaller grain-sized samples,grain boundary-based mechanisms such as grain boundary sliding,grain boundary rotation are observed.The transition of normal and inverse Hall-Petch relation occurs at around lOnm.Dislocation density quantification shows that the dislocation density in the sample drastically reduces with decreasing grain size.Elastic modulus of nanocrystalline Mg with mean grain size above 20 nm remains comparable to that of the coarse-grained polycrystalline bulk,followed by a rapid reduction below that grain size.The present work reveals the nanomechanics of nanocrystalline Mg,facilitating the design and development of Mg-based nanostructured alloys with superior mechanical properties.
基金the member companies of IPST at the Georgia Institute of Technology and the IPST Fellowship
文摘The goal of this work is to produce nanocomposite film with low oxygen permeability by casting an aqueous solution containing xylan,sorbitol and nanocrystalline cellulose.The morphology of the resulting nanocomposite films was examined by scanning electron microscopy and atomic force microscopy which showed that control films containing xylan and sorbitol had a more open structure as compared to xylan-sorbitol films containing sulfonated nanocrystalline cellulose.The average pore diameter,bulk density,porosity and tortuosity factor measurements of control xylan films and nanocomposite xylan films were examined by mercury intrusion porosimetry techniques.Xylan films reinforced with nanocrystalline cellulose were denser and exhibited higher tortuosity factor than the control xylan films.Control xylan films had average pore diameter,bulk density,porosity and tortuosity factor of 0.1730 μm,0.6165 g/ml,53.0161% and 1.258,respectively as compared to xylan films reinforced with 50% nanocrystalline cellulose with average pore diameter of 0.0581 μm,bulk density of 1.1513 g/ml,porosity of 22.8906% and tortuosity factor of 2.005.Oxygen transmission rate tests demonstrated that films prepared with xylan,sorbitol and 5%,10%,25% and 50% sulfonated nanocrystalline cellulose exhibited a significantly reduced oxygen permeability of 1.1387,1.0933,0.8986 and 0.1799 cm^3×μm/m^2×d×k Pa respectively with respect to films prepared solely from xylan and sorbitol with a oxygen permeability of 189.1665 cm^3×μm/m^2×d×k Pa.These properties suggested these nanocomposite films have promising barrier properties.
文摘Chemical solution deposited CdSe particulate film possess nanocrystalline structure and exhibit quantum size effects. By changing the temperature of chemical deposition and subsequent annealing, CdSe particulate films with different particle sizes can be obtained.
文摘Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7-xZrxB6.0 (x=0-3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnetometer (VSM) revealed that Zr addition was significantly effective in improving the magnetic properties at room temperature. The intrinsic coercivity Hci of the optimally processed ribbons increased monotonically with increasing Zr content, from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. Unlike the coercivity, the remanence polarization Jr increased first with Zr addition, from 0.898 T up to 1.041 T at x=1.5, and then decreased with further Zr addition. The maximum energy product (BH)max behaved similarly, increasing from 103.1 kJ/m3 to a maximum of 175.2 kJ/m3 at x=1.5. Microstruc- ture studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM) had shown a significant microstructure refinement with Zr addition. The absolute values of temperature coefficients of induction and coercivity were significantly increased with increasing Zr content, indicating that Zr was detrimental to thermal stability of the melt-spun Nd2Fe14B-type material.
基金supported by the National Natural Science Foundation of China (10574156)
文摘Magnetization configurations were calculated under various magnetic fields for nanocrystalline Pr-Fe-B permanent magnets by micromagnetic finite element method.According to the configurations during demagnetization process, the mechanism of magnetization reversal was analyzed.For the Pr2Fe14B with 10 nm grains or its composite with 10vol.% α-Fe, the coercivity was determined by nucleation of reversed domain that took place at grain boundaries.However, for Pr2Fe14B with 30 nm grains, coercivity was controlled by pinning of the nucle-ated domain.For Pr2Fe14B/α-Fe with 30vol.% α-Fe, the demagnetization behavior was characterized by continuous reversal of α-Fe moment.
基金This work was supported by the National Natural Scmnce Foundation of China(Grant Nos.20276069,20476097)
文摘Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition (PECVD) at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS), respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V (vs SCE).
文摘In order to explore the high efficiency of fabricating nanocrystalline WC-Co composite powders, this paper presented a unique high energy ball milling process with variable rotation rate and repeatious circulation, by which nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 (wt pct) composite powders with mean grain size of 25 nm were prepared in 32 min, and the quantity of the powders for a batch was as much as 800 grams. The as-prepared powders were analyzed and characterized by chemical analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential thermal analysis (DTA). The results show that high energy ball milling with variable rotation rates and repeatious circulation could be used to produce nanocrystalline WC-Co powder composites with high efficiency. The compositions of the powders meet its specifications with low impurity content. The mean grain size decreases, lattice distortion and system energy increase with increasing the milling time. The morphology of nanocrystalline WC-Co particles displays dominantiy sphere shape and their particle sizes are all lower than 80 nm. The eutectic temperature of the nanocrystalline WC-10Co-0.8VC-0.2Cr3C2 composites is about 1280℃.
文摘A number of studies have been reported on the use of nanocrystalline plasma electrolytic nitrocarburising technology for surface hardening of stainless steels for higher corrosion resistance resulted from this technique. However, very few studies have focused on the optimization of the nanocrystalline plasma electrolytic nitrocarburising process parameters. In this study, a design of experiment (DOE) technique, the Taguchi method, has been used to optimize the nanocrystalline plasma electrolytic nitrocarburising not only for surface hardening but also for the corrosion protection of 316L austenitic stainless steel by controlling the coating processes factors. The experimental design consisted of four factors (Urea concentration, electrical conductivity of electrolyte, voltage and duration of process), each containing three levels. Potentiodynamic polarization measurements were carried out to determine the corrosion resistance of the coated samples. The results were analyzed with related software. An analysis of the mean of signal-to-noise (S/N) ratio indicated that the corrosion resistance of nanocrystalline plasma electrolytic nitrocarburised 316L stainless steel was influenced significantly by the levels in the Taguchi orthogonal array. The optimized coating parameters for corrosion resistance are 1150 g/L for urea concentration, 360 mS/cm for electrical conductivity of electrolyte, 260 V for applied voltage, 6 min for treatment time. The percentage of contribution for each factor was determined by the analysis of variance (ANOVA). The results showed that the applied voltage is the most significant factor affecting the corrosion resistance of the coatings.
文摘A new type of dye-sensitized nanocrystalline solid state photovoltaic cell based on the wide band gap n-TiO2/p-CuI heterojunction was fabricated. Tetra-carboxyphenyl porphyrine (TPP-(COOH)(4)), squarylium cyanine derivative (SQ-(CH2),(SO3Py+)-Py-.) and ruthenium bipyridyl complex (RuL2(NCS)(2)) were used as photosensitizers. Larger photocurrents and photovoltages were shown in the cell sensitized by ruthenium bipyridyl complex and can be further increased by intercalation of a TiO2 thin underlayer.
文摘CO2 reforming of methane (CDRM) was carried out over MgO supported Ni catalysts with various Ni loadings. The preparation of MgO supported Ni catalysts via surfactant-assisted precipitation method led to the formation of a nanocrystalline carrier for nickel catalysts. The synthesized samples were characterized by XRD, N2 adsorption-desorption, H2 chemisorption, TPR, TPO and SEM techniques. It was found that the high catalytic activity and stability of the prepared catalysts could be attributable to high dispersion of reduced Ni species and basicity of support surface. In addition, the effect of feed ratio, nickel loading and GHSV on the catalytic performance of CDRM over the catalysts were investigated.
文摘Nd 12.3 Fe 81.7 x Ga x B 6.0 (x = 0-1.8) ribbons were prepared by melt spinning at 22 m/s and subsequent annealing treatment. The influences of Ga addition and annealing conditions on the magnetic properties and microstructure of the nanocrystalline alloys were systematically investigated. After being annealed at 620℃ for 20 min, the J r and H ci increased from 0.85 T and 582.6 kA/m for Ga-free sample to 0.97 T and 734.6 kA/m for the x = 0.9 sample, respectively. The (BH) max for the x = 0.9 sample increased by about 40% from 96.3 to 135.5 kJ/m 3 compared with that of the Ga-free one. The significant improvement of magnetic properties originated from the refinement of grains in the samples by introducing Ga, which led to a stronger exchange coupling between the neighboring grains in comparison with that in Ga-free samples. The microstructure and magnetic properties of the samples depended strongly on annealing parameters, while the sensitivity of micro-structure to annealing conditions could be significantly suppressed by the addition of Ga element.
基金supported by the National High-Tech Research and Development Program of China (No.2002AA331080)
文摘Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling (cryomilling) method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy (SEM), laser scattering for particle size analysis, X-ray diffraction (XRD), and transmission electron microscopy (TEM). After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr2O3 phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.
基金Funded by the 863 High Technology Research Project ( No.2001AA339020 and 2002AA305302) fromthe Ministry of Scienceand Technology of China , and the Excellent Young Teachers Pro-gramof MOE(2002[350]) ,China
文摘The microwave magnetic properties of the ball milled FeCo panicles were investigated as functions of ball milling time ( t ) using microwave electromagnetic parameters analysis techniques. The results show that the imaginary part of intrinsic dynamic permeability ( ui ) of the ball- milled panicles is much bigger than that of raw powders. ui strongly depends on t and exhibits several slightly damped ferromagnetic resonances. These phenomena are in qualitative agreement with the formation of the corresponding microstructure or the Aharoni ' s model of non-uniform exchange resonance modes. The present microwave permeabilhy behavior indicates that nanocrystalline materials with the same grain size may exhibit different properties that depend upon the microstructure, which provides a possibility for manufacturing high performance microwave absorber.