The removal of boron from metallurgical silicon in slag system of CaO-SiO2-10%CaF2 was investigated. The partition coefficient of boron (LB) between slag and silicon phase was studied under different conditions of s...The removal of boron from metallurgical silicon in slag system of CaO-SiO2-10%CaF2 was investigated. The partition coefficient of boron (LB) between slag and silicon phase was studied under different conditions of slag basicity (CaO/SiO2 ratio), temperature, mass ratio of slag to silicon and gas blowing. The results show that LB has a maximum value of 4.61 when the CaO/SiO2 mass ratio is around 2 at l 873 K. The logarithm of LB is linear to the reciprocal of temperatures in the range of 1 773-1 973 K. LB increases with the increase of mass ratio of slag to silicon, but it does not increase markedly when the ratio excesses 3. Gas blowing can sionificantlv increase the removal of boron, and LR increases with the increase of water vapor content.展开更多
Boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of...Boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of CaO-SiO2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron (LB) and the activities of SiO2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of LB reaches 1.57 with a slag composition of 60%CaO-40%SiO2 (mass fraction). The boron content in the refined silicon is reduced from 18×10^-6 to 1.8×10^-6 using slag refining at 1600 ℃ for 3 h with a CaO-SiO2/MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.展开更多
The hole injection,the radiative recombination and the device luminescent efficiencies of amorphous silicon carbide thin film p-i-n junction light emitting diodes are quantitatively calculated,and the effect of the ca...The hole injection,the radiative recombination and the device luminescent efficiencies of amorphous silicon carbide thin film p-i-n junction light emitting diodes are quantitatively calculated,and the effect of the carrier(especially the hole) injection and recombination processes on the device luminescent characteristics are revealed.Without considering the device junction temperature,it is found that the device luminescent efficiency mainly depends on the hole injection efficiency at low field and the hole radiative recombination efficiency at high field respectively.The theoretical analyses are in well agreement with the experimental results.展开更多
A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dime...A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation.The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications.The correlation between the solute diffusivity D and solvent viscosity μ is examined.In terms of Eyring's activation theory,the activation in the air-silicone-oil diffusion process is quite different from that in the momentum transport of the silicone oil:the activation entropy of the former is positive while that of latter is negative.However,the activation enthalpies of the two processes are in the same order of magnitude,which leads to the observation that Dμ/T is roughly constant.展开更多
Experimental investigations were carried out to determine the Al2O3/water and SiO2/water nanofluids flowing through a circular tube. convective heat transfer performance and pressure drop of Measurements show that the...Experimental investigations were carried out to determine the Al2O3/water and SiO2/water nanofluids flowing through a circular tube. convective heat transfer performance and pressure drop of Measurements show that the addition of small amounts of nano-sized Al2O3 particles to the base fluid increases heat transfer coefficients considerably, while the result for the silica nanofluids contradicts with the alumina nanofluids and this leads to some interesting results. In the case of alumina nanofluids, an average increase of 16% in convective heat transfer coefficient is observed with an average penalty of 28% in pressure drop. Moreover, flow resistance increases significantly compared to the base fluid even at very low concentrations of nanofluids. Finally, measured heat transfer coefficients are compared with predicted ones from the correlation of Shah under the same conditions.展开更多
In the present article, we study the electrical resistivity ρ, the thermoelectric power (TEP) α, thermal conductivity σ, Knight-Shifts and temperature coefficient of the Knight-Shifts of the liquid Si and Ge usin...In the present article, we study the electrical resistivity ρ, the thermoelectric power (TEP) α, thermal conductivity σ, Knight-Shifts and temperature coefficient of the Knight-Shifts of the liquid Si and Ge using the well known model potential for the first time. The structure factor used in the present work is derived from the Percus-Yevick (PY) theory. Various local field correction functions are used to study the screening influence. The present results of resistivity are found in qualitative agreement with available experimental and theoretical whenever exists.展开更多
The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years.This study investigates the gas-membrane solution equilibrium,for which Henry's...The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years.This study investigates the gas-membrane solution equilibrium,for which Henry's law is not applicable if the gas phase is a mixture.This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane.A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model.By the experiments of gas permeation through polydimethylsiloxane PDMS membrane,the solubility coefficients of some gases(N2,CO2,CH4) were measured.Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature(H2,O2,C3H8),the gas-membrane interaction parameters for these gases were obtained.Based on these parameters,the activity coefficients of the dissolved gas were calculated by UNIQUAC model,and their values agree well with the experimental data.These results confirm the feasibility and effectiveness of the proposed method,which makes it possible to better predict gas-membrane solution equilibrium.展开更多
The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiNx) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering inv...The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiNx) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particle size-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results.展开更多
A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface...A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface. It is found that the increased conductivities in both doped and undoped regions help reduce the temperature difference across the wafer surface. However, the doped layer conductivity has little effect on the overall temperature distribution and difference. The temperature level and difference on the top surface drop suddenly when absorption coefficient changes from 104 to 103 m-1. When the absorption coefficient is less or equal to 103 m-1, the temperature level and difference do not change much. The emissivity has the dominant effect on the top surface temperature level and difference. Higher surface emissivity can easily increase the temperature level of the wafer surface. After using the improved property data, the overall temperature level reduces by about 200 K from the basis case. The results will help improve the current understanding of the energy transport in the rapid thermal processing and the wafer temperature monitor and control level.展开更多
Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,...Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,we develop an advanced approach of surface gel conversion for synthesis of submicron-thick pure silica MFI(silicalite-1)zeolite membranes.Viscous gel is prepared by finely adjusting the precursor composition,enabling its reduced wettability.The unfavorable wetting of the support surface can effectively prevent gel penetration into alumina support voids.Aided by the seeds,the surface gel is directly and fully crystallized into an MFI zeolite membrane with minimal water steam.A membrane with a thickness of 500 nm is successfully acquired and it is free of visible cracks.Additionally,the as-synthesized membranes exhibit rapid and selective separation of hexane isomers by virtue of unprecedentedly high n-hexane permeance of 24.5×10^−7 mol m^−2 s^−1 Pa^−1 and impressive separation factors of 13.3-22.6 for n-hexane over its isomers.This developed approach is of practical interest for sustainable synthesis of high-quality zeolite membranes.展开更多
Superlattices have great application potentials in thermo-electric materials and solid laser techniques.Their complicated heat transport mechanisms due to size effects,multi-interfaces and mini-band are very important...Superlattices have great application potentials in thermo-electric materials and solid laser techniques.Their complicated heat transport mechanisms due to size effects,multi-interfaces and mini-band are very important issues for the prediction of thermal conductivity.In this paper,the short-period Si/Ge superlattices are investigated by a modified series model based on the Debye-Callaway description.The Lambert Law is used to describe the phonon emission within hemisphere space.In addition,the phonon interface transmission coefficients obtained from the phonon wave packet simulation are incorporated into boundary condition of the model,which removes the fitting parameters in the model.Better agreement with experiment is obtained.The effects of temperature,wavelength-dependent phonon transmission,superlattice periods,as well as the thickness of Ge layer are considered in this paper.展开更多
In this paper, it is proved that the intemal porous structure of alumina-silicate refractory fiber has fractal characteristics, which is reconstructed by the computer and the reconstructed structure further proved to ...In this paper, it is proved that the intemal porous structure of alumina-silicate refractory fiber has fractal characteristics, which is reconstructed by the computer and the reconstructed structure further proved to have fractal characteristics. Based on the reconstructed structure, the network-thermal-resistance model is established to calculate the thermal conductivity of the fiber. It is shown that the calculated results agree well with the previous experimental ones, proving the correctness of the method.展开更多
The experimental phase equilibria of the Mn-Si-Zn system available in the literature were critically evaluated.Thermodynamic assessment of the Mn-Si-Zn system was then performed in the framework of CALPHAD(CALculation...The experimental phase equilibria of the Mn-Si-Zn system available in the literature were critically evaluated.Thermodynamic assessment of the Mn-Si-Zn system was then performed in the framework of CALPHAD(CALculation of PHAse Diagram) method on the basis of the experimental data in the literature.The optimal thermodynamic parameters of the ternary system were then obtained,yielding a good agreement with most of the experimental data.The complete liquidus projection and reaction scheme was also presented for the Mn-Si-Zn system.It is noteworthy that a stable closed liquid miscibility gap appears in the computed ternary phase diagrams,even though it is metastable in three boundary binaries.The occurrence of such a closed miscibility gap can be predicted by a criterion considering the general thermodynamic rules and the features of the three constituent binary systems.展开更多
We investigate the thermoelectric energy conversion efficiency of Si and Ge nanowires, and in particular, that of Si/Ge core-shell nanowires. We show how the presence of a thin Ge shell on a Si core nanowire increases...We investigate the thermoelectric energy conversion efficiency of Si and Ge nanowires, and in particular, that of Si/Ge core-shell nanowires. We show how the presence of a thin Ge shell on a Si core nanowire increases the overall figure of merit. We find the optimal thickness of the Ge shell to provide the largest figure of merit for the devices. We also consider Ge core/Si shell nanowires, and show that an optimal thickness of the Si shell does not exist, since the figure of merit is a monotonically decreasing function of the radius of the nanowire. Finally, we verify the empirical law relating the electron energy gap to the optimal working temperature that maximizes the efficiency of the device.展开更多
TiA1SiN nano-composite coatings with Silicon contents from 4.1 to 23.9 at.% were deposited on Silicon wafers. The nano- hardness, microstructure, and adhesion force of the coatings were deeply affected by Silicon cont...TiA1SiN nano-composite coatings with Silicon contents from 4.1 to 23.9 at.% were deposited on Silicon wafers. The nano- hardness, microstructure, and adhesion force of the coatings were deeply affected by Silicon contents. The TiA1SiN with 9.0 at.% Silicon has a maximum hardness of 40.9 GPa, a highest adhesion force of 67 N and a lowest friction coefficient of 0.5. Microstructures show that Silicon doping increases the hardness of coating due to solid solution hardening effect and grain boundary enhancement effect. The amorphous Si3N4 matrix, which contains (Ti,Al)N nano-crystals, is formed as the Silicon content is increased. The matrix contributes to the nano-hardness and helps to resist surface oxidization. Especially, the matrix induces low surface roughness and decreases the friction coefficient.展开更多
The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a sy...The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in CuxSi phase after the removal of oxygen atoms in Cn2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.展开更多
基金Project(2007J0012)supported by the Natural Science Foundation of Fujian Province,ChinaProject(2007HZ0005-2)supported by the Key Technological Program of Fujian Province,China
文摘The removal of boron from metallurgical silicon in slag system of CaO-SiO2-10%CaF2 was investigated. The partition coefficient of boron (LB) between slag and silicon phase was studied under different conditions of slag basicity (CaO/SiO2 ratio), temperature, mass ratio of slag to silicon and gas blowing. The results show that LB has a maximum value of 4.61 when the CaO/SiO2 mass ratio is around 2 at l 873 K. The logarithm of LB is linear to the reciprocal of temperatures in the range of 1 773-1 973 K. LB increases with the increase of mass ratio of slag to silicon, but it does not increase markedly when the ratio excesses 3. Gas blowing can sionificantlv increase the removal of boron, and LR increases with the increase of water vapor content.
基金Projects (51104080,u1137601) supported by the National Natural Science Foundation of ChinaProject (14118557) supported by the Personnel Training Foundation of Kunming University of Science and Technology in China
文摘Boron removal from metallurgical grade silicon (MG-Si) using a calcium silicate slag was studied. The results show that it is impossible basically to remove boron using a pure SiO2 refining. The oxidizing ability of CaO-SiO2 slag for boron removal was characterized by establishing the thermodynamic relationship between the distribution coefficient of boron (LB) and the activities of SiO2 and CaO. The experimental results show that the distribution coefficient and the removal efficiency of boron are greatly improved with the increase of CaO proportion in the slag. The maximal value of LB reaches 1.57 with a slag composition of 60%CaO-40%SiO2 (mass fraction). The boron content in the refined silicon is reduced from 18×10^-6 to 1.8×10^-6 using slag refining at 1600 ℃ for 3 h with a CaO-SiO2/MG-Si ratio of 2.5, and the removal efficiency of boron reaches 90%.
文摘The hole injection,the radiative recombination and the device luminescent efficiencies of amorphous silicon carbide thin film p-i-n junction light emitting diodes are quantitatively calculated,and the effect of the carrier(especially the hole) injection and recombination processes on the device luminescent characteristics are revealed.Without considering the device junction temperature,it is found that the device luminescent efficiency mainly depends on the hole injection efficiency at low field and the hole radiative recombination efficiency at high field respectively.The theoretical analyses are in well agreement with the experimental results.
基金Supported by the National Natural Science Foundation of China (50675202)
文摘A piston-cylinder apparatus was established to measure the solubility and diffusivity of air in dimethyl silicone oils and in hydraulic oils based on the PVT state equation of air and the solution of unsteady one-dimensional diffusion equation.The measured diffusivity-temperature relation can be well fitted by the Arrhenius equation for engineering applications.The correlation between the solute diffusivity D and solvent viscosity μ is examined.In terms of Eyring's activation theory,the activation in the air-silicone-oil diffusion process is quite different from that in the momentum transport of the silicone oil:the activation entropy of the former is positive while that of latter is negative.However,the activation enthalpies of the two processes are in the same order of magnitude,which leads to the observation that Dμ/T is roughly constant.
文摘Experimental investigations were carried out to determine the Al2O3/water and SiO2/water nanofluids flowing through a circular tube. convective heat transfer performance and pressure drop of Measurements show that the addition of small amounts of nano-sized Al2O3 particles to the base fluid increases heat transfer coefficients considerably, while the result for the silica nanofluids contradicts with the alumina nanofluids and this leads to some interesting results. In the case of alumina nanofluids, an average increase of 16% in convective heat transfer coefficient is observed with an average penalty of 28% in pressure drop. Moreover, flow resistance increases significantly compared to the base fluid even at very low concentrations of nanofluids. Finally, measured heat transfer coefficients are compared with predicted ones from the correlation of Shah under the same conditions.
文摘In the present article, we study the electrical resistivity ρ, the thermoelectric power (TEP) α, thermal conductivity σ, Knight-Shifts and temperature coefficient of the Knight-Shifts of the liquid Si and Ge using the well known model potential for the first time. The structure factor used in the present work is derived from the Percus-Yevick (PY) theory. Various local field correction functions are used to study the screening influence. The present results of resistivity are found in qualitative agreement with available experimental and theoretical whenever exists.
文摘The recovery or capture of one or more components from gas mixture by membrane separation has become a research focus in recent years.This study investigates the gas-membrane solution equilibrium,for which Henry's law is not applicable if the gas phase is a mixture.This problem can be solved by using UNIQUAC model to calculate the activity coefficient of gas dissolved in the membrane.A method was proposed in this study to obtain the gas-membrane interaction parameter for UNIQUAC model.By the experiments of gas permeation through polydimethylsiloxane PDMS membrane,the solubility coefficients of some gases(N2,CO2,CH4) were measured.Through non-linear fitting UNIQUAC model to the experimental results from this study and in literature(H2,O2,C3H8),the gas-membrane interaction parameters for these gases were obtained.Based on these parameters,the activity coefficients of the dissolved gas were calculated by UNIQUAC model,and their values agree well with the experimental data.These results confirm the feasibility and effectiveness of the proposed method,which makes it possible to better predict gas-membrane solution equilibrium.
基金Supported by the National Natural Science Foundation of China under Grant No.60940020the Natural Foundation of Hebei Province under Grant No.E2008000619
文摘The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiNx) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particle size-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results.
基金Project(N110204015)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2012M510075)supported by the China Postdoctoral Science Foundation
文摘A combined conduction and radiation heat transfer model was used to simulate the heat transfer within wafer and investigate the effect of thermal transport properties on temperature non-uniformity within wafer surface. It is found that the increased conductivities in both doped and undoped regions help reduce the temperature difference across the wafer surface. However, the doped layer conductivity has little effect on the overall temperature distribution and difference. The temperature level and difference on the top surface drop suddenly when absorption coefficient changes from 104 to 103 m-1. When the absorption coefficient is less or equal to 103 m-1, the temperature level and difference do not change much. The emissivity has the dominant effect on the top surface temperature level and difference. Higher surface emissivity can easily increase the temperature level of the wafer surface. After using the improved property data, the overall temperature level reduces by about 200 K from the basis case. The results will help improve the current understanding of the energy transport in the rapid thermal processing and the wafer temperature monitor and control level.
基金the National Natural Science Foundation of China(21531003,21501024 and 21971035)Jilin Scientific and Technological Development Program(20170101198JC and 20190103017JH)+2 种基金Jilin Education Office(JJKH20180015KJ)“111”Program(B18012)open projects from the State Key Laboratory of Inorganic Synthesis&Preparative Chemistry and State Key Laboratory of Heavy Oil Processing(2018-8,SKLOP201902003)。
文摘Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,we develop an advanced approach of surface gel conversion for synthesis of submicron-thick pure silica MFI(silicalite-1)zeolite membranes.Viscous gel is prepared by finely adjusting the precursor composition,enabling its reduced wettability.The unfavorable wetting of the support surface can effectively prevent gel penetration into alumina support voids.Aided by the seeds,the surface gel is directly and fully crystallized into an MFI zeolite membrane with minimal water steam.A membrane with a thickness of 500 nm is successfully acquired and it is free of visible cracks.Additionally,the as-synthesized membranes exhibit rapid and selective separation of hexane isomers by virtue of unprecedentedly high n-hexane permeance of 24.5×10^−7 mol m^−2 s^−1 Pa^−1 and impressive separation factors of 13.3-22.6 for n-hexane over its isomers.This developed approach is of practical interest for sustainable synthesis of high-quality zeolite membranes.
基金supported by the National Basic Research Program of China(Grant No.2012CB933200)the National Natural Science Foundation of China(Grant No.51176091)Science Fund for Creative Research Groups of China(Grant No.51321002)
文摘Superlattices have great application potentials in thermo-electric materials and solid laser techniques.Their complicated heat transport mechanisms due to size effects,multi-interfaces and mini-band are very important issues for the prediction of thermal conductivity.In this paper,the short-period Si/Ge superlattices are investigated by a modified series model based on the Debye-Callaway description.The Lambert Law is used to describe the phonon emission within hemisphere space.In addition,the phonon interface transmission coefficients obtained from the phonon wave packet simulation are incorporated into boundary condition of the model,which removes the fitting parameters in the model.Better agreement with experiment is obtained.The effects of temperature,wavelength-dependent phonon transmission,superlattice periods,as well as the thickness of Ge layer are considered in this paper.
文摘In this paper, it is proved that the intemal porous structure of alumina-silicate refractory fiber has fractal characteristics, which is reconstructed by the computer and the reconstructed structure further proved to have fractal characteristics. Based on the reconstructed structure, the network-thermal-resistance model is established to calculate the thermal conductivity of the fiber. It is shown that the calculated results agree well with the previous experimental ones, proving the correctness of the method.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50831007 and 51071179) National Basic Research Program of China (Grant No. 2011CB610401)
文摘The experimental phase equilibria of the Mn-Si-Zn system available in the literature were critically evaluated.Thermodynamic assessment of the Mn-Si-Zn system was then performed in the framework of CALPHAD(CALculation of PHAse Diagram) method on the basis of the experimental data in the literature.The optimal thermodynamic parameters of the ternary system were then obtained,yielding a good agreement with most of the experimental data.The complete liquidus projection and reaction scheme was also presented for the Mn-Si-Zn system.It is noteworthy that a stable closed liquid miscibility gap appears in the computed ternary phase diagrams,even though it is metastable in three boundary binaries.The occurrence of such a closed miscibility gap can be predicted by a criterion considering the general thermodynamic rules and the features of the three constituent binary systems.
文摘We investigate the thermoelectric energy conversion efficiency of Si and Ge nanowires, and in particular, that of Si/Ge core-shell nanowires. We show how the presence of a thin Ge shell on a Si core nanowire increases the overall figure of merit. We find the optimal thickness of the Ge shell to provide the largest figure of merit for the devices. We also consider Ge core/Si shell nanowires, and show that an optimal thickness of the Si shell does not exist, since the figure of merit is a monotonically decreasing function of the radius of the nanowire. Finally, we verify the empirical law relating the electron energy gap to the optimal working temperature that maximizes the efficiency of the device.
基金supported by the National Natural Science Foundation of China(Grant No.51105222)the State Key Basic Research Program of China(Grant No.2012CB934101)+1 种基金the Science Fund of the State Key Laboratory of Tribology at Tsinghua University SKLT12A01Beijing Research Program(Grant No.100322002)
文摘TiA1SiN nano-composite coatings with Silicon contents from 4.1 to 23.9 at.% were deposited on Silicon wafers. The nano- hardness, microstructure, and adhesion force of the coatings were deeply affected by Silicon contents. The TiA1SiN with 9.0 at.% Silicon has a maximum hardness of 40.9 GPa, a highest adhesion force of 67 N and a lowest friction coefficient of 0.5. Microstructures show that Silicon doping increases the hardness of coating due to solid solution hardening effect and grain boundary enhancement effect. The amorphous Si3N4 matrix, which contains (Ti,Al)N nano-crystals, is formed as the Silicon content is increased. The matrix contributes to the nano-hardness and helps to resist surface oxidization. Especially, the matrix induces low surface roughness and decreases the friction coefficient.
基金supported by the National Natural Science Foundation of China (21506224)the Institute of Chemical and Engineering Sciences (ICES) for the kind support of the collaboration
文摘The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in CuxSi phase after the removal of oxygen atoms in Cn2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.