In this paper, the capacity titration technique （CT technique） was developed on basis of the RPG （ratio of potentio-charge capacity to galvano-charge capacity） method to continuously determine the solid diffusion ...In this paper, the capacity titration technique （CT technique） was developed on basis of the RPG （ratio of potentio-charge capacity to galvano-charge capacity） method to continuously determine the solid diffusion coefficient D of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs. q （value of ratio of the potentio-charge capacity to the galvano-charge capacity） were given in different range of q. By the CT technique,the Li^＋ solid diffusion coefficients D within LiMn2O4 at different voltages were determined. The results showed that the values of D varied from 3.447×10^-9 cm^2/s to 7.60×10^-11 cm^2/s in the voltage range of charge from 3.3V to 4.3V as a function of voltage with “W” shape.展开更多
The stable and crystalline phase of pure nano- structured CeO2 was directly synthesized by flame-assisted spray pyrolysis and solid state diffusion route. Different characterization techniques, including X-ray diffrac...The stable and crystalline phase of pure nano- structured CeO2 was directly synthesized by flame-assisted spray pyrolysis and solid state diffusion route. Different characterization techniques, including X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Fourier trans- form infrared spectroscopy （FTIR）, ultraviolet-visible （UV- Vis）, and thermo gravimetric analysis （TGA） were employed to examine the structural, morphological, optical, and thermal properties of the final product. Similarly, the comparative carbon dioxide （CO2）-sensing response of as-synthesized CeO2 nanoparticles by both routes was also reported. The CeO2 nanoparticles synthesized by solid state diffusion method exhibit good sensitivity （3.38 %） at room temperature, low operating temperature （398 K）, fast response time （32 s）, and recovery time （36 s） along with good stability.展开更多
This work studies the impact of the carbon diffusion on the growth kinetics of austenite and the solute segregation,by utilizing the phase-field(PF)method to simulate the solidification of a Fe-C binary alloy.It is re...This work studies the impact of the carbon diffusion on the growth kinetics of austenite and the solute segregation,by utilizing the phase-field(PF)method to simulate the solidification of a Fe-C binary alloy.It is revealed that increasing the ratio of the carbon diffusion coefficient in solid to that in liquid is advantageous in reducing the solute segregation,and a novel microsegregation model is developed based on the quantitative analysis of the results from PF simulations.The simplified one-dimensional diffusion simulation is employed to analyse the quantitative relationship between the parameters of the proposed microsegregation model and the properties of materials.The universality and reliability of the new microsegregation model are then validated by comparing with the experimental data of various alloy systems.These findings contribute to our comprehension of the fundamental theory of solidification and also provide a potential and promising approach to controlling the solidification microstructure.展开更多
The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480...The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time （8, 16, and 24h）. The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test （in 3.0% NaCl solution, temperature is （28±1）℃, and time is 96h）. Optical microscopy （OM） and EDS （energy dispersive spectrum） composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones （especially the samples treated for 24h at 480℃）, was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase （WP-zone） of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.展开更多
A theoretical prediction of ion conductivity for solid state HfO2 is carried out in analogy to ZrO2 based on the density functional calculation. Geometric and electronic structures of pure bulks exhibit similarity for...A theoretical prediction of ion conductivity for solid state HfO2 is carried out in analogy to ZrO2 based on the density functional calculation. Geometric and electronic structures of pure bulks exhibit similarity for the two materials. Negative formation enthalpy and negative vacancy formation energy are found for YSH （yttria-stabilized hafnia） and YSZ （yttria- stabilized zirconia）, suggesting the stability of both materials. Low activation energies （below 0.7 eV） of diffusion are found in both materials, and YSH＇s is a little higher than that of YSZ. In addition, for both HfO2 and ZrO2, the supercells with native oxygen vacancies are also studied. The so-called defect states are observed in the supercells with neutral and ＋1 charge native vacancy but not in the ＋2 charge one. It can give an explanation to the relatively lower activation energies of yttria-doped oxides and ＋2 charge vacancy supercells. A brief discussion is presented to explain the different YSH ion conductivities in the experiment and obtained by us, and we attribute this to the different ion vibrations at different temperatures.展开更多
Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and...Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 k J/mol, respectively.展开更多
BaGdB9O16：Eu^3＋ and Ba（Gd,Ln）B9O16：Eu^3＋（Ln=La, Y） phosphors were synthesized by solid state diffusion method. The X-ray diffraction, scanning electron microscopy（SEM） and photoluminescence properties were i...BaGdB9O16：Eu^3＋ and Ba（Gd,Ln）B9O16：Eu^3＋（Ln=La, Y） phosphors were synthesized by solid state diffusion method. The X-ray diffraction, scanning electron microscopy（SEM） and photoluminescence properties were investigated. The as-synthesized BaGdB9O16：Eu^3＋ and Ba（Gd,Ln）B9O16：Eu^3＋（Ln=La, Y） phosphors showed strong red emission under ultraviolet light excitation. By partially substituting Gd^3＋ by La^3＋ and Y^3＋ ions in the host BaGdB9O16：Eu^3＋ materials, the maximum emission intensity was observed for the optimum composition of BaGd0.91La0.8B9O16Eu0.01 phosphor. The experimental results indicated that the Eu doped BaGdB9O16 and Ba（Gd,Ln）B9O16（Ln=La, Y） phosphors were promising red phosphors, which might find potential applications in near-UV excited LED lighting as well as display devices. Comparison of as-synthesized phosphors with standard phosphor used in CFL（compact fluorescent lamp） was also done. Energy transfer mechanism of Gd^3＋ to Eu^3＋ was also discussed in this paper.展开更多
The adsorption of methane onto five dry coal samples was measured at 298 K over the pressure range from 0 to 3.5 MPa using a volumetric method.The isotherm data were fitted to the Langmuir and the Freundlich equations...The adsorption of methane onto five dry coal samples was measured at 298 K over the pressure range from 0 to 3.5 MPa using a volumetric method.The isotherm data were fitted to the Langmuir and the Freundlich equations.The kinetic data were fitted to a pseudo second order equation,the linear driving force equation(LDF),and an intra-particle diffusion model.These results showed that higher methane adsorption is correlated with larger micro-pore volumes and specific surface areas.The adsorption was related to the narrow micro-pore size distribution when the previous two parameters are large.The kinetics study showed that the kinetics of methane adsorption onto these five dry coal samples followed a pseudo second order model very well.Methane adsorption rates are controlled by intra-particle diffusion.The faster the intra-particle diffusion,the faster the methane adsorption rate will be.展开更多
The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments ...The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments have predicted that the shielding ice formed on the hydrate surface after initial dissociation of the hydrate plays an important role in the self-preservation effect. We propose ice-shielding models of gas hydrates to investigate the dissociation rates quantitatively, including the self-preservation process, at temperatures below the ice-melting point and at atmospheric pressure. Three general models are constructed for two temperature ranges The rate-determining process for the lower temperature range is hydrate dissociation, and those for the higher range are gas diffusion through ice or hydrate layers, which depend on the thickness of the shielding-ice layer. Our models suggest that the extent of self-preservation depends on temperature, original hydrate size, and vip substances, which can explain the experimental results.展开更多
The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma(flux ~ 3.71 × 1021 D/m2·s, energy ~ 25 eV, and fluenc...The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma(flux ~ 3.71 × 1021 D/m2·s, energy ~ 25 eV, and fluence up to 1.3 × 1026D/m2)are studied. The results show that the total amount of deuterium released from W–2%Y2O3 is 5.23 × 1020 D/m2(2.5 K/min),about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra(TDS) at different heating rates(2.5 K/min–20 K/min) reveal that both W and W–2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV(grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV(vacancy) in W and 1.73 eV(vacancy) in W–2%Y2O3.展开更多
In order to predict the actual quantity of non-bulk GaAs layers after long-time homoepitaxy on GaAs （001） by theo- retical calculation, a half-terrace diffusion model based on thermodynamics is used to calculate the...In order to predict the actual quantity of non-bulk GaAs layers after long-time homoepitaxy on GaAs （001） by theo- retical calculation, a half-terrace diffusion model based on thermodynamics is used to calculate the ripening time of GaAs layers to form a fiat morphology in annealing. To verify the accuracy of the calculation, real space scanning tunneling microscopy images of GaAs surface after different annealing times are obtained and the roughness of the GaAs surface is measured. The results suggest that the half terrace model is an accurate method with a relative error of about 4.1%.展开更多
In the development of Li-ion batteries(LIBs)with high energy/power density,long cycle-life,fast charging,and high safety,an insight into charge transfer reactions is required.Although electrochemical impedance spectro...In the development of Li-ion batteries(LIBs)with high energy/power density,long cycle-life,fast charging,and high safety,an insight into charge transfer reactions is required.Although electrochemical impedance spectroscopy(EIS)is regarded as a powerful diagnosis tool,it is not a direct but an indirect measurement.With respect to this,some critical questions need to be answered:(i)why EIS can reflect the kinetics of charge transfer reactions;(ii)what the inherent logical relationship between impedance models under different physical scenes is;(iii)how charge transfer reactions compete with each other at multiple scales.This work aims at answering these questions via developing a theory framework so as to mitigate the blindness and uncertainty in unveiling charge transfer reactions in LIBs.To systematically answer the above questions,this article is organized into a three-in-one(review,tutorial,and research)type and the following contributions are made:(i)a brief review is given for impedance model development of the LIBs over the past half century;(ii)an open source code toolbox is developed based on the unified impedance model;(iii)the competive mechanisms of charge transfer reactions are unveiled based on the developed EIS-Toolbox@LIB.This work not only clarifies theoretical fundamentals,but also provides an easy-to-use open source code for EIS-Toolbox@LIB to optimize fast charge/discharge,mitigate cycle aging,and improve energy/power density.展开更多
The present paper discusses our investigation of InGaAs surface morphology annealed for different lengths of time.After annealing for 15 min,the ripening of InGaAs islands is completed.The real space scanning tunnelin...The present paper discusses our investigation of InGaAs surface morphology annealed for different lengths of time.After annealing for 15 min,the ripening of InGaAs islands is completed.The real space scanning tunneling microscopy（STM） images show the evolution of InGaAs surface morphology.A half-terrace diffusion theoretical model based on thermodynamic theory is proposed to estimate the annealing time for obtaining flat morphology.The annealing time calculated by the proposed theory is in agreement with the experimental results.展开更多
The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today.Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective t...The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today.Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants,especially,single-atom catalysts(SACs)are promising candidates.Herein,we comprehensively summarizes the atomic diffusion strategy,which is considered as an effective method to prepare a series of SACs.According to the different diffusion forms of the precursors,we review the synthesis pathways of SACs from three aspects:gas diffusion,solid diffusion and liquid diffusion.The gaseous diffusion method mainly discusses atomic layer deposition(ALD)and chemical vapor deposition(CVD),both of which carry out gas phase mass transfer at high temperatures.The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration.Liquid diffusion mainly describes the electrochemical method and the molten salt method.We hope this review can trigger the rational design of SACs.展开更多
Centrifugal compressors for the fuel cell vehicles often operate near the surge line compared with the turbocharger compressors.Low solidity and half vaned diffusers are recognized as good ways to improve the stabilit...Centrifugal compressors for the fuel cell vehicles often operate near the surge line compared with the turbocharger compressors.Low solidity and half vaned diffusers are recognized as good ways to improve the stability of the centrifugal compressor.The presented work investigated four diffuser configurations (i.e.,the vaneless diffuser (VLD),full-height low solidity vaned diffuser (LSVD),hub-side half vaned diffuser (HVD) and shroud-side half vaned diffuser (SVD)) through steady-state and unsteady numerical simulations.The results show that the best performance is achieved by the LSVD,HVD and SVD at the design,surge and choke conditions.The flow rate at the surge operating point of the HVD has decreased by 15.53% compared with the LSVD,and 9.21% compared with the VLD.At near surge operating point,a longitudinal suction side passage vortex is formed on the hub of the LSVD and rotates as circumferential stall cells.A hairpin vortex is formed along the leading edge and is dragged by the main flow along the suction side as a local vortex shedding.The mechanism of the stability improvement by half vaned diffusers is that the tip leakage vortex migrates from the clearance side to the vane mounting side and replenishes the low-momentum zone on the mounting side.The best position where the half vaned diffuser should be mounted is based on the impeller outlet flow conditions,namely,the location of the wake region,where the meridional velocity and relative stagnation pressure is low.展开更多
This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip ...This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.展开更多
A numerical procedure for hydrodynamic redesign of the conventional vaned diffuser into the low solidity vaned diffuser by means of a real-coded genetic algorithm with Boltzmann, Tournament and Roulette Wheel selectio...A numerical procedure for hydrodynamic redesign of the conventional vaned diffuser into the low solidity vaned diffuser by means of a real-coded genetic algorithm with Boltzmann, Tournament and Roulette Wheel selection is presented. In the first part, an investigation on the relative efficiency of the different real-coded genetic algorithm is carried out on a typical mathematical test function. The real-coded genetic algorithm with Boltzmann selection shows the best optimization performance compared to the Tournament and Roulette Wheel selection. In the second part, an approach to redesign the vaned diffuser profile is introduced. Goal of the optimum design is to search the highest static pressure recovery coefficient and low solidity vaned diffuser. The result of the low solidity vaned diffuser optimum design confirms that the efficiency and optimization performance of the real-coded Boltzmann selection genetic algorithm outperforms the other selection methods. A comparison between the designed low solidity vaned diffuser and original vaned diffuser shows that the diffuser pump with the redesigned low solidity vaned diffuser has the higher static pressure recovery and improved total hydrodynamic performance. In addition, the smaller outlet diameter of designed vaned diffuser tends to a more compact size of diffuser pump compared to the original diffuser pump. The obtained results also demonstrate the real-coded Boltzmann selection genetic algorithm is a promising optimization algorithm for centrifugal pumps design.展开更多
基金This work was supported by NNSF of China(No.20406024)the Postdoctoral Science Foundation of Central South University(No.76600).
文摘In this paper, the capacity titration technique （CT technique） was developed on basis of the RPG （ratio of potentio-charge capacity to galvano-charge capacity） method to continuously determine the solid diffusion coefficient D of the intercalary species within insertion-host materials with a small voltage region. The linear equations of D vs. q （value of ratio of the potentio-charge capacity to the galvano-charge capacity） were given in different range of q. By the CT technique,the Li^＋ solid diffusion coefficients D within LiMn2O4 at different voltages were determined. The results showed that the values of D varied from 3.447×10^-9 cm^2/s to 7.60×10^-11 cm^2/s in the voltage range of charge from 3.3V to 4.3V as a function of voltage with “W” shape.
文摘The stable and crystalline phase of pure nano- structured CeO2 was directly synthesized by flame-assisted spray pyrolysis and solid state diffusion route. Different characterization techniques, including X-ray diffraction （XRD）, scanning electron microscopy （SEM）, Fourier trans- form infrared spectroscopy （FTIR）, ultraviolet-visible （UV- Vis）, and thermo gravimetric analysis （TGA） were employed to examine the structural, morphological, optical, and thermal properties of the final product. Similarly, the comparative carbon dioxide （CO2）-sensing response of as-synthesized CeO2 nanoparticles by both routes was also reported. The CeO2 nanoparticles synthesized by solid state diffusion method exhibit good sensitivity （3.38 %） at room temperature, low operating temperature （398 K）, fast response time （32 s）, and recovery time （36 s） along with good stability.
基金supported by the National Science and Technology Major Project(Grant No.J2019-VI-0019-0134)the National Natural Science Foundation of China(Grant No.52203301)+1 种基金the China Postdoctoral Science Foundation(Grant No.2021TQ0335)the Liaoning Province Science and Technology Plan Joint Fund(Doctoral Research Initiation Project)(Grant No.2024-BSLH-195).
文摘This work studies the impact of the carbon diffusion on the growth kinetics of austenite and the solute segregation,by utilizing the phase-field(PF)method to simulate the solidification of a Fe-C binary alloy.It is revealed that increasing the ratio of the carbon diffusion coefficient in solid to that in liquid is advantageous in reducing the solute segregation,and a novel microsegregation model is developed based on the quantitative analysis of the results from PF simulations.The simplified one-dimensional diffusion simulation is employed to analyse the quantitative relationship between the parameters of the proposed microsegregation model and the properties of materials.The universality and reliability of the new microsegregation model are then validated by comparing with the experimental data of various alloy systems.These findings contribute to our comprehension of the fundamental theory of solidification and also provide a potential and promising approach to controlling the solidification microstructure.
基金supported by Shaan Xi Provincial Natural Science Foundation of China(No.2004E111).
文摘The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time （8, 16, and 24h）. The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test （in 3.0% NaCl solution, temperature is （28±1）℃, and time is 96h）. Optical microscopy （OM） and EDS （energy dispersive spectrum） composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones （especially the samples treated for 24h at 480℃）, was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase （WP-zone） of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10647008 and 50971099)the Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20096101110017)
文摘A theoretical prediction of ion conductivity for solid state HfO2 is carried out in analogy to ZrO2 based on the density functional calculation. Geometric and electronic structures of pure bulks exhibit similarity for the two materials. Negative formation enthalpy and negative vacancy formation energy are found for YSH （yttria-stabilized hafnia） and YSZ （yttria- stabilized zirconia）, suggesting the stability of both materials. Low activation energies （below 0.7 eV） of diffusion are found in both materials, and YSH＇s is a little higher than that of YSZ. In addition, for both HfO2 and ZrO2, the supercells with native oxygen vacancies are also studied. The so-called defect states are observed in the supercells with neutral and ＋1 charge native vacancy but not in the ＋2 charge one. It can give an explanation to the relatively lower activation energies of yttria-doped oxides and ＋2 charge vacancy supercells. A brief discussion is presented to explain the different YSH ion conductivities in the experiment and obtained by us, and we attribute this to the different ion vibrations at different temperatures.
基金supported by the Fundamental Research Funds for the Central Universities (FRF-TP-15-009A2)the Project Funded by China Postdoctoral Science Foundation (2015M570931)+1 种基金the National Natural Science Fund Project of China (91534121)the National Major Scientific Instruments Special Plan (2011YQ12003907)
文摘Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles＇ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 k J/mol, respectively.
基金University Grants Commission (UGC), New Delhi, for sanctioning the leave under Faculty Improvement program (FIP) to carry out this research work
文摘BaGdB9O16：Eu^3＋ and Ba（Gd,Ln）B9O16：Eu^3＋（Ln=La, Y） phosphors were synthesized by solid state diffusion method. The X-ray diffraction, scanning electron microscopy（SEM） and photoluminescence properties were investigated. The as-synthesized BaGdB9O16：Eu^3＋ and Ba（Gd,Ln）B9O16：Eu^3＋（Ln=La, Y） phosphors showed strong red emission under ultraviolet light excitation. By partially substituting Gd^3＋ by La^3＋ and Y^3＋ ions in the host BaGdB9O16：Eu^3＋ materials, the maximum emission intensity was observed for the optimum composition of BaGd0.91La0.8B9O16Eu0.01 phosphor. The experimental results indicated that the Eu doped BaGdB9O16 and Ba（Gd,Ln）B9O16（Ln=La, Y） phosphors were promising red phosphors, which might find potential applications in near-UV excited LED lighting as well as display devices. Comparison of as-synthesized phosphors with standard phosphor used in CFL（compact fluorescent lamp） was also done. Energy transfer mechanism of Gd^3＋ to Eu^3＋ was also discussed in this paper.
基金supported by the State Key Basic Research Program of China(No.2011CB201202)
文摘The adsorption of methane onto five dry coal samples was measured at 298 K over the pressure range from 0 to 3.5 MPa using a volumetric method.The isotherm data were fitted to the Langmuir and the Freundlich equations.The kinetic data were fitted to a pseudo second order equation,the linear driving force equation(LDF),and an intra-particle diffusion model.These results showed that higher methane adsorption is correlated with larger micro-pore volumes and specific surface areas.The adsorption was related to the narrow micro-pore size distribution when the previous two parameters are large.The kinetics study showed that the kinetics of methane adsorption onto these five dry coal samples followed a pseudo second order model very well.Methane adsorption rates are controlled by intra-particle diffusion.The faster the intra-particle diffusion,the faster the methane adsorption rate will be.
文摘The self-preservation of methane hydrate is a key process in its engineering applications because the hydrate can survive for a significant period under atmospheric pressure and moderate temperature. Some experiments have predicted that the shielding ice formed on the hydrate surface after initial dissociation of the hydrate plays an important role in the self-preservation effect. We propose ice-shielding models of gas hydrates to investigate the dissociation rates quantitatively, including the self-preservation process, at temperatures below the ice-melting point and at atmospheric pressure. Three general models are constructed for two temperature ranges The rate-determining process for the lower temperature range is hydrate dissociation, and those for the higher range are gas diffusion through ice or hydrate layers, which depend on the thickness of the shielding-ice layer. Our models suggest that the extent of self-preservation depends on temperature, original hydrate size, and vip substances, which can explain the experimental results.
基金National Magnetic Confinement Fusion Energy Research Project,Ministry of Science and Technology of China(Grant No.2015GB109002)the Innovation Fund of Postgraduate,Xihua University,China(Grant No.ycjj2018017)the National Natural Science Foundation of China(Grant No.21401173).
文摘The retention and release of deuterium in W–2%Y2O3 composite materials and commercially pure tungsten after they have been implanted by deuterium plasma(flux ~ 3.71 × 1021 D/m2·s, energy ~ 25 eV, and fluence up to 1.3 × 1026D/m2)are studied. The results show that the total amount of deuterium released from W–2%Y2O3 is 5.23 × 1020 D/m2(2.5 K/min),about 2.5 times higher than that from the pure tungsten. Thermal desorption spectra(TDS) at different heating rates(2.5 K/min–20 K/min) reveal that both W and W–2%Y2O3 have two main deuterium trapped sites. For the low temperature trap, the deuterium desorption activation energy is 0.85 eV(grain boundary) in W, while for high temperature trap, the desorption activation energy is 1.57 eV(vacancy) in W and 1.73 eV(vacancy) in W–2%Y2O3.
基金Project supported by the National Natural Science Foundation of China(Grant No.60866001)the Doctorate Foundation of the Education Ministry of China(Grant No.20105201110003)
文摘In order to predict the actual quantity of non-bulk GaAs layers after long-time homoepitaxy on GaAs （001） by theo- retical calculation, a half-terrace diffusion model based on thermodynamics is used to calculate the ripening time of GaAs layers to form a fiat morphology in annealing. To verify the accuracy of the calculation, real space scanning tunneling microscopy images of GaAs surface after different annealing times are obtained and the roughness of the GaAs surface is measured. The results suggest that the half terrace model is an accurate method with a relative error of about 4.1%.
基金the financial support from the National Science Foundation of China(22078190)the National Key R&D Plan of China(2020YFB1505802)。
文摘In the development of Li-ion batteries(LIBs)with high energy/power density,long cycle-life,fast charging,and high safety,an insight into charge transfer reactions is required.Although electrochemical impedance spectroscopy(EIS)is regarded as a powerful diagnosis tool,it is not a direct but an indirect measurement.With respect to this,some critical questions need to be answered:(i)why EIS can reflect the kinetics of charge transfer reactions;(ii)what the inherent logical relationship between impedance models under different physical scenes is;(iii)how charge transfer reactions compete with each other at multiple scales.This work aims at answering these questions via developing a theory framework so as to mitigate the blindness and uncertainty in unveiling charge transfer reactions in LIBs.To systematically answer the above questions,this article is organized into a three-in-one(review,tutorial,and research)type and the following contributions are made:(i)a brief review is given for impedance model development of the LIBs over the past half century;(ii)an open source code toolbox is developed based on the unified impedance model;(iii)the competive mechanisms of charge transfer reactions are unveiled based on the developed EIS-Toolbox@LIB.This work not only clarifies theoretical fundamentals,but also provides an easy-to-use open source code for EIS-Toolbox@LIB to optimize fast charge/discharge,mitigate cycle aging,and improve energy/power density.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60866001 and 61076049)the Science and Technology Projects for Overseas Researchers of Guizhou Province (Grant No. (2007) 03)+5 种基金the Foundation of Guizhou Provincial Science and Technology Department (Grant No. QKH-J[2007]2176)the Special Assistant to the High-Level Personnel Research Projects of Guizhou Provincial Committee,Organization Department(Grant No. TZJF-200610)the Doctorate Foundation of the Education Ministry of China (Grant No. 20105201110003)the Science and Technology Projects for Overseas Researchers of Guizhou Province (Grant No. Z103233)Special Governor Fund for Outstanding Professionals in Science & Technology and Education of Guizhou Province (Grant No. 2009114)the Innovation Funds for Graduates of Guizhou University (Grant No. LG2012019)
文摘The present paper discusses our investigation of InGaAs surface morphology annealed for different lengths of time.After annealing for 15 min,the ripening of InGaAs islands is completed.The real space scanning tunneling microscopy（STM） images show the evolution of InGaAs surface morphology.A half-terrace diffusion theoretical model based on thermodynamic theory is proposed to estimate the annealing time for obtaining flat morphology.The annealing time calculated by the proposed theory is in agreement with the experimental results.
基金This work was supported by the National Natural Science Foundation of China(No.21801015)Beijing Institute of Technology Research Fund Program for Young Scholars.
文摘The depletion of energy and increasing environmental pressure have become one of the main challenges in the world today.Synthetic high-efficiency catalysts bring hope for efficient conversion of energy and effective treatment of pollutants,especially,single-atom catalysts(SACs)are promising candidates.Herein,we comprehensively summarizes the atomic diffusion strategy,which is considered as an effective method to prepare a series of SACs.According to the different diffusion forms of the precursors,we review the synthesis pathways of SACs from three aspects:gas diffusion,solid diffusion and liquid diffusion.The gaseous diffusion method mainly discusses atomic layer deposition(ALD)and chemical vapor deposition(CVD),both of which carry out gas phase mass transfer at high temperatures.The solid-state diffusion method can be divided into nanoparticle transformation into single atoms and solid atom migration.Liquid diffusion mainly describes the electrochemical method and the molten salt method.We hope this review can trigger the rational design of SACs.
基金The research is supported by National Natural Science Foundation of China(51875410).
文摘Centrifugal compressors for the fuel cell vehicles often operate near the surge line compared with the turbocharger compressors.Low solidity and half vaned diffusers are recognized as good ways to improve the stability of the centrifugal compressor.The presented work investigated four diffuser configurations (i.e.,the vaneless diffuser (VLD),full-height low solidity vaned diffuser (LSVD),hub-side half vaned diffuser (HVD) and shroud-side half vaned diffuser (SVD)) through steady-state and unsteady numerical simulations.The results show that the best performance is achieved by the LSVD,HVD and SVD at the design,surge and choke conditions.The flow rate at the surge operating point of the HVD has decreased by 15.53% compared with the LSVD,and 9.21% compared with the VLD.At near surge operating point,a longitudinal suction side passage vortex is formed on the hub of the LSVD and rotates as circumferential stall cells.A hairpin vortex is formed along the leading edge and is dragged by the main flow along the suction side as a local vortex shedding.The mechanism of the stability improvement by half vaned diffusers is that the tip leakage vortex migrates from the clearance side to the vane mounting side and replenishes the low-momentum zone on the mounting side.The best position where the half vaned diffuser should be mounted is based on the impeller outlet flow conditions,namely,the location of the wake region,where the meridional velocity and relative stagnation pressure is low.
文摘This paper deals with the effect of the blade tip-groove of the low solidity cascade diffuser (LSD) on the blowercharacteristic and the noise generated by the LSD. The small grooves were set up at the root and/or tip near theleading edge of the LSD blade. In order to clarify the mechanism of noise increase due to LSD and also to reducethe noise, the relationships between the noise increase based on the LSD, the LSD performance and the secondaryflow formed additionally by the tip-groove were investigated experimentally as well as numerically, especiallyanalyzing flow behaviors in the LSD in view points of flow separation on the suction surface of the LSD bladeand the secondary flow on the side walls. By reducing the stagnation region smaller near the root and/or tip of theLSD blade leading edge, the secondary flow behavior changes remarkably around the LSD blade, as a result, thenoise level and the blower characteristics vary. It can be concluded that, by means of a small tip-groove locatedonly at the shroud side near the LSD blade leading edge, the noise generated by the LSD can be reduced withoutdeteriorations of the LSD performance and the blower characteristics as well.
文摘A numerical procedure for hydrodynamic redesign of the conventional vaned diffuser into the low solidity vaned diffuser by means of a real-coded genetic algorithm with Boltzmann, Tournament and Roulette Wheel selection is presented. In the first part, an investigation on the relative efficiency of the different real-coded genetic algorithm is carried out on a typical mathematical test function. The real-coded genetic algorithm with Boltzmann selection shows the best optimization performance compared to the Tournament and Roulette Wheel selection. In the second part, an approach to redesign the vaned diffuser profile is introduced. Goal of the optimum design is to search the highest static pressure recovery coefficient and low solidity vaned diffuser. The result of the low solidity vaned diffuser optimum design confirms that the efficiency and optimization performance of the real-coded Boltzmann selection genetic algorithm outperforms the other selection methods. A comparison between the designed low solidity vaned diffuser and original vaned diffuser shows that the diffuser pump with the redesigned low solidity vaned diffuser has the higher static pressure recovery and improved total hydrodynamic performance. In addition, the smaller outlet diameter of designed vaned diffuser tends to a more compact size of diffuser pump compared to the original diffuser pump. The obtained results also demonstrate the real-coded Boltzmann selection genetic algorithm is a promising optimization algorithm for centrifugal pumps design.
