The interfacial chemistry of solid electrolyte interphases(SEI)on lithium(Li)electrode is directly determined by the structural chemistry of the electric double layer(EDL)at the interface.Herein,a strategy for regulat...The interfacial chemistry of solid electrolyte interphases(SEI)on lithium(Li)electrode is directly determined by the structural chemistry of the electric double layer(EDL)at the interface.Herein,a strategy for regulating the structural chemistry of EDL via the introduction of intermolecular hydrogen bonds has been proposed(p-hydroxybenzoic acid(pHA)is selected as proof-of-concept).According to the molecular dynamics(MD)simulation and density functional theory(DFT)calculation results,the existence of hydrogen bonds realizes the anion structural rearrangement in the EDL,reduces the lowest unoccupied molecular orbital(LUMO)energy level of anions in the EDL,and the number of free solvent molecules,which promotes the formation of inorganic species-enriched SEI and eventually achieves the dendrite-free Li deposition.Based on this strategy,Li‖Cu cells can stably run over 185 cycles with an accumulated active Li loss of only 2.27 mAh cm^(-2),and the long-term cycle stability of Li‖Li cells is increased to 1200 h.In addition,the full cell pairing with the commercial LiFePO_(4)(LFP)cathodes exhibits stable cycling performance at 1C,with a capacity retention close to 90%after 200 cycles.展开更多
Covalent organic frameworks(COFs)are promising materials for converting solar energy into green hydrogen.However,limited charge separation and transport in COFs impede their application in the photocatalytic hydrogen ...Covalent organic frameworks(COFs)are promising materials for converting solar energy into green hydrogen.However,limited charge separation and transport in COFs impede their application in the photocatalytic hydrogen evolution reaction(HER).In this study,the intrinsically tunable internal bond electric field(IBEF)at the imine bonds of COFs was manipulated to cooperate with the internal molecular electric field(IMEF)induced by the donor-acceptor(D-A)structure for an efficient HER.The aligned orientation of IBEF and IMEF resulted in a remarkable H_(2) evolution rate of 57.3 mmol·g^(-1)·h^(-1)on TNCA,which was approximately 520 times higher than that of TCNA(0.11 mmol·g^(-1)·h^(-1))with the opposing electric field orientation.The superposition of the dual electric fields enables the IBEF to function as an accelerating field for electron transfer,kinetically facilitat-ing the migration of photogenerated electrons from D to A.Furthermore,theoretical calculations indicate that the inhomogeneous charge distribution at the C and N atoms in TNCA not only pro-vides a strong driving force for carrier transfer but also effectively hinders the return of free elec-trons to the valence band,improving the utilization of photoelectrons.This strategy of fabricating dual electric fields in COFs offers a novel approach to designing photocatalysts for clean energy synthesis.展开更多
Arc erosion behavior of Ag/Ni materials with different operation numbers was investigated by OM,3DOP and SEM.The results indicated that the arc erosion of Ag/10Ni electrical contact material fabricated by sintering−ex...Arc erosion behavior of Ag/Ni materials with different operation numbers was investigated by OM,3DOP and SEM.The results indicated that the arc erosion of Ag/10Ni electrical contact material fabricated by sintering−extrusion technology was more and more serious with the operation numbers increasing from 1000 to 40000.With the same operation numbers,the arc erosion on anode was more serious than that on cathode.Besides,the pores preferred to emerge around the arc effect spot during the first 10000 operations.And the morphology of the molten silver on cathode and anode was different due to the action of gravity and arc erosion.Furthermore,the relationships among arc energy,arc time,welding force,electric resistivity,temperature and mass change on contacts were discussed,which indicated that the mass loss on cathode was mainly caused by the fracture of molten bridge.展开更多
Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems.However,the previous studies have been focused on the macro mechanica...Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems.However,the previous studies have been focused on the macro mechanical performance of diffusion bonded joint,especially diffusion bonding conditions effects on tensile strength,shearing strength and fatigue strength.The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints.An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation.The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results.Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints.For the purpose of identifying the failure mechanisms of the joints,both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system.Based on the microscopic observations,the mechanism of interfacial failure is addressed.The observation result shows that for 316LSS diffusion-bonded joints,microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism.Finally,a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results.The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.展开更多
TiAl intermetallic compound was synthesized and bonded together with Ti substrate synchronously by using fieldactivated and pressure-assisted synthesis (FAPAS) process. The effect of electric field on the microstruc...TiAl intermetallic compound was synthesized and bonded together with Ti substrate synchronously by using fieldactivated and pressure-assisted synthesis (FAPAS) process. The effect of electric field on the microstructure and growth pattern of the diffusion dissolution layer of TiA1/Ti interface was mainly studied. The microstructure of the diffusion dissolution layer was investigated by optical microscope (OM) and scanning electron microscope (SEM). The elements distribution of the diffusion dissolution layer was investigated by energy dispersive spectroscopy (EDS). The results show that a fine and homogeneous grain structure is obtained in sintered TiA1 intermetallic compound. Metallurgical bond is formed at the TiAl/Ti interface. The thickness of diffusion dissolution layer between TiAl and Ti changes with conduction time and current density.展开更多
Reconstruction of liquid free slosh modes by curved quiet free surface was investigated in the case of small Bond number by means of modal part analysis method in this paper. It is shown that the curved liquid quiet f...Reconstruction of liquid free slosh modes by curved quiet free surface was investigated in the case of small Bond number by means of modal part analysis method in this paper. It is shown that the curved liquid quiet free surface would couple the modes to form new eigen-modes while the orthogonality of the modes which participate the liquid slosh are given only by their Bessel modal parts and it would change their eigen-frequencies respectively while the orthogonality are given by their triangle function modal parts. By studying the laterally forced slosh of the liquid in a cylindrical container based on the new eigen-modes, a characteristic of modes-choosing was found.展开更多
Poisson-Boltzmann equation for EDL (electric double layer) and Navier- Stokes equation for liquid flows were numerically solved to investigate resistance effect of electric double layer on liquid flow in microchanne...Poisson-Boltzmann equation for EDL (electric double layer) and Navier- Stokes equation for liquid flows were numerically solved to investigate resistance effect of electric double layer on liquid flow in microchannel. The dimension analysis indicates that the resistance effect of electric double layer can be estimated by an electric resistance number, which is proportional to the square of the liquid dielectric constant and the solid surface zeta potential, and inverse-proportional to the liquid dynamic viscosity, electric conductivity and the square of the channel width. An "electric current density balancing" (ECDB) condition was proposed to evaluate the flow-induced streaming potential, instead of conventional "electric current balancing" (ECB) condition which may induce spurious local backflow in neighborhood of the solid wall of the microchannel. The numerical results of the flow rate loss ratio and velocity profile are also given to demonstrate the resistance effect of electric double layer in microchannel.展开更多
To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validat...To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validated through ground tests.The fake gyroscopic torque is first proposed,which the vector mechanism should overcome besides the inertial torque and the gravitational torque.The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane,appears only when the propeller is rotating and is proportional with the rotation speed.It is a sinusoidal pulse,with a frequency that is twice of the rotation speed.Considering the fake gyroscope torque pulse and aerodynamic efficiency,three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.展开更多
The linear Rayleigh-Bénard electro-convective stability of the Newtonian dielectric liquid is determined theoretically subject to the temperature modulation with time.A perturbation method is used to compute the ...The linear Rayleigh-Bénard electro-convective stability of the Newtonian dielectric liquid is determined theoretically subject to the temperature modulation with time.A perturbation method is used to compute the critical Rayleigh number and the wave number.The critical Rayleigh number is calculated as a function of the frequency of modulation,the temperature-dependent variable viscosity,the electric field dependent variable viscosity,the Prandtl number,and the electric Rayleigh number.The effects of all three cases of modulations are established to delay or advance the onset of the convection process.In addition,how the effect of variable viscosity controls the onset of convection is studied.展开更多
This study presents the results of a research into the developing a methodology for assessing the adequacy of advanced electric power systems characterized by the integration of various innovative technologies,which c...This study presents the results of a research into the developing a methodology for assessing the adequacy of advanced electric power systems characterized by the integration of various innovative technologies,which complicates their analysis.The methodology development is aimed at solving two main problems:(1)increase the adequacy of modeling the processes that occur in the electric power system and (2)enhance the computational efficiency of the adequacy assessment methodology.This study proposes a new mathematical model to minimize the power shortage and enhance the adequacy of modeling the processes.The model considers quadratic power transmission losses and network coefficients.The computational efficiency of the adequacy assessment methodology is enhanced using efficient random-number generators to form the calculated states of electric power systems and machine learning methods to assess power shortages and other reliability characteristics in the calculated states.展开更多
The spark plasma sintering(SPS) method was used to study the mechanism of reaction interface between Zr and Ti3AlC2 with electric current going through it. It was found that electric current greatly reduced the bond...The spark plasma sintering(SPS) method was used to study the mechanism of reaction interface between Zr and Ti3AlC2 with electric current going through it. It was found that electric current greatly reduced the bonding temperature of Zr and Ti3AlC2. By the micro-structure analysis of the interface through SEM/EDS, it was found that Al atoms diffused from the Ti3AlC2 substrate into the Zr side and reacted with Zr to form the Zr-Al compounds at the interface, which is the strengthening mechanism of Ti3AlC2-Zr bonding. The thickness of reaction layers(Zr-Al alloy) was from 0.879 to 13.945 mm depending on different sintering condition. Current direction, heating rate, soaking time, pulse patterns all influenced the diffusion of Al atoms which affected the joining quality of Zr and Ti3AlC2.展开更多
This letter proposes a novel design of a Micro Electro Mechanical System (MEMS) device featuring a metal grating vibratory mierostructure driven by electrostatic force to sense the spatial electric field. Due to the...This letter proposes a novel design of a Micro Electro Mechanical System (MEMS) device featuring a metal grating vibratory mierostructure driven by electrostatic force to sense the spatial electric field. Due to the advantages in slide-film damping and large vibration amplitude, such a device makes atmospheric packaging a low-cost option for practical manufacture. In this letter, we present the operating principles and specifications, the design structure, as well as the finite element simulation. Computational analysis shows that our design obtains good results in device parameters setting, while its simplicity and low-cost features make it an attractive solution for applications.展开更多
For many years, a Lorentz factor of L = 1/3 has been used to describe the local electric field in thin amorphous dielectrics. However, the exact meaning of thin has been unclear. The local electric field E<sub>l...For many years, a Lorentz factor of L = 1/3 has been used to describe the local electric field in thin amorphous dielectrics. However, the exact meaning of thin has been unclear. The local electric field E<sub>loc</sub> modeling presented in this work indicates that L = 1/3 is indeed valid for very thin solid dielectrics (t<sub>diel</sub> ≤ 20 monolayers) but significant deviations from L = 1/3 start to occur for thicker dielectrics. For example, L ≈ 2/3 for dielectric thicknesses of t<sub>diel</sub> = 50 monolayers and increases to L ≈ 1 for dielectric thicknesses t<sub>diel</sub> > 200 monolayers. The increase in L with t<sub>diel</sub> means that the local electric fields are significantly higher in thicker dielectrics and explains why the breakdown strength E<sub>bd</sub> of solid polar dielectrics generally reduces with dielectric thickness t<sub>diel</sub>. For example, E<sub>bd</sub> for SiO<sub>2</sub> reduces from approximately E<sub>bd</sub> ≈ 25 MV/cm at t<sub>diel</sub> = 2 nm to E<sub>bd</sub> ≈ 10 MV/cm at t<sub>diel</sub> = 50 nm. However, while E<sub>bd</sub> for SiO<sub>2</sub> reduces with t<sub>diel</sub>, all SiO<sub>2</sub> thicknesses are found to breakdown at approximately the same local electric field (E<sub>loc</sub>)<sub>bd</sub> ≈ 40 MV/cm. This corresponds to a coordination bond strength of 2.7 eV for the silicon-ion to transition from four-fold to three-fold coordination in the tetrahedral structure.展开更多
A recent technique, using to potentially replace the conventional impregnating one in low voltage electric motors, has been studied in this communication. The conventional technique that uses?both primary and secondar...A recent technique, using to potentially replace the conventional impregnating one in low voltage electric motors, has been studied in this communication. The conventional technique that uses?both primary and secondary insulations;?i.e.: enamel and varnish, has been compared to this recent technique which only uses one component,?i.e.: self-bonding wires. Self-bonding wires polymerization is very quick compared to that of the conventional technique. Environmental impact and both dielectric and mechanical properties of these two techniques have been estimated and compared. The goal is to estimate if this recent technique has not only a better environmental footprint but also good technical properties. The dielectric properties that have been measured are the dielectric strength and?the lifetime under pulse?voltage while mechanical consists in measuring the bonding strength that is crucial for impregnation.?For that purpose, a Life Cycle Assessment (LCA) that can simultaneously evaluatenumerous impacts on ground, water and air,?has been performed. The results show clearly that the recent technique significantly reduces the environmental footprint. Both mechanical and dielectric properties are then compared and analyzed.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.21905033,52271201)the Key Research and DevelopmentProgram of Sichuan Province(Grant No.2022YFG0100)+1 种基金the Central Government Funds of Guiding Local Scientific and Technological Development for Sichuan Province(Grant No.2022ZYD0045)the State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization(Grant No.2020P4FZG02A)
文摘The interfacial chemistry of solid electrolyte interphases(SEI)on lithium(Li)electrode is directly determined by the structural chemistry of the electric double layer(EDL)at the interface.Herein,a strategy for regulating the structural chemistry of EDL via the introduction of intermolecular hydrogen bonds has been proposed(p-hydroxybenzoic acid(pHA)is selected as proof-of-concept).According to the molecular dynamics(MD)simulation and density functional theory(DFT)calculation results,the existence of hydrogen bonds realizes the anion structural rearrangement in the EDL,reduces the lowest unoccupied molecular orbital(LUMO)energy level of anions in the EDL,and the number of free solvent molecules,which promotes the formation of inorganic species-enriched SEI and eventually achieves the dendrite-free Li deposition.Based on this strategy,Li‖Cu cells can stably run over 185 cycles with an accumulated active Li loss of only 2.27 mAh cm^(-2),and the long-term cycle stability of Li‖Li cells is increased to 1200 h.In addition,the full cell pairing with the commercial LiFePO_(4)(LFP)cathodes exhibits stable cycling performance at 1C,with a capacity retention close to 90%after 200 cycles.
文摘Covalent organic frameworks(COFs)are promising materials for converting solar energy into green hydrogen.However,limited charge separation and transport in COFs impede their application in the photocatalytic hydrogen evolution reaction(HER).In this study,the intrinsically tunable internal bond electric field(IBEF)at the imine bonds of COFs was manipulated to cooperate with the internal molecular electric field(IMEF)induced by the donor-acceptor(D-A)structure for an efficient HER.The aligned orientation of IBEF and IMEF resulted in a remarkable H_(2) evolution rate of 57.3 mmol·g^(-1)·h^(-1)on TNCA,which was approximately 520 times higher than that of TCNA(0.11 mmol·g^(-1)·h^(-1))with the opposing electric field orientation.The superposition of the dual electric fields enables the IBEF to function as an accelerating field for electron transfer,kinetically facilitat-ing the migration of photogenerated electrons from D to A.Furthermore,theoretical calculations indicate that the inhomogeneous charge distribution at the C and N atoms in TNCA not only pro-vides a strong driving force for carrier transfer but also effectively hinders the return of free elec-trons to the valence band,improving the utilization of photoelectrons.This strategy of fabricating dual electric fields in COFs offers a novel approach to designing photocatalysts for clean energy synthesis.
基金supported by the National Natural Science Foundation of China (No.51601225)Hunan Provincial Natural Science Foundation,China (No.2020JJ5742)。
文摘Arc erosion behavior of Ag/Ni materials with different operation numbers was investigated by OM,3DOP and SEM.The results indicated that the arc erosion of Ag/10Ni electrical contact material fabricated by sintering−extrusion technology was more and more serious with the operation numbers increasing from 1000 to 40000.With the same operation numbers,the arc erosion on anode was more serious than that on cathode.Besides,the pores preferred to emerge around the arc effect spot during the first 10000 operations.And the morphology of the molten silver on cathode and anode was different due to the action of gravity and arc erosion.Furthermore,the relationships among arc energy,arc time,welding force,electric resistivity,temperature and mass change on contacts were discussed,which indicated that the mass loss on cathode was mainly caused by the fracture of molten bridge.
基金supported by National Natural Science Foundation of China(Grant No.50475068)
文摘Micro-structure related behavior of diffusion bonding joints is a crucial issue in device and reactor fabrication of Micro Chemo Mechanical Systems.However,the previous studies have been focused on the macro mechanical performance of diffusion bonded joint,especially diffusion bonding conditions effects on tensile strength,shearing strength and fatigue strength.The research of interfacial micro-voids and microstructures evolution for failure mechanism has not been carried out for diffusion-bonded joints.An interfacial electrical resistance measuring method is proposed to evaluate the quality of bonded joints and verified by using two-dimensional finite-element simulation.The influences of micro void geometry on increments of resistance are analyzed and the relationship between bonded area fraction and resistance increment is established by theoretical analysis combined with simulated results.Metallographic inspections and micro-hardness testing are conducted near the interface of diffusion bonded joints.For the purpose of identifying the failure mechanisms of the joints,both microscopic tensile and fatigue tests are conducted on the self-developed in-situ microscopic fatigue testing system.Based on the microscopic observations,the mechanism of interfacial failure is addressed.The observation result shows that for 316LSS diffusion-bonded joints,microstructure evolution and effect of micro-voids play a key role in interfacial failure mechanism.Finally,a new life prediction model in terms of the increment of electrical resistance is developed and confirmed by the experimental results.The proposed study is initiated that constituted a primary interfacial failure mechanism on micron scale and provide the life prediction for reliability of components sealed by diffusion bonding.
文摘TiAl intermetallic compound was synthesized and bonded together with Ti substrate synchronously by using fieldactivated and pressure-assisted synthesis (FAPAS) process. The effect of electric field on the microstructure and growth pattern of the diffusion dissolution layer of TiA1/Ti interface was mainly studied. The microstructure of the diffusion dissolution layer was investigated by optical microscope (OM) and scanning electron microscope (SEM). The elements distribution of the diffusion dissolution layer was investigated by energy dispersive spectroscopy (EDS). The results show that a fine and homogeneous grain structure is obtained in sintered TiA1 intermetallic compound. Metallurgical bond is formed at the TiAl/Ti interface. The thickness of diffusion dissolution layer between TiAl and Ti changes with conduction time and current density.
文摘Reconstruction of liquid free slosh modes by curved quiet free surface was investigated in the case of small Bond number by means of modal part analysis method in this paper. It is shown that the curved liquid quiet free surface would couple the modes to form new eigen-modes while the orthogonality of the modes which participate the liquid slosh are given only by their Bessel modal parts and it would change their eigen-frequencies respectively while the orthogonality are given by their triangle function modal parts. By studying the laterally forced slosh of the liquid in a cylindrical container based on the new eigen-modes, a characteristic of modes-choosing was found.
基金Project supported by the National Natural Science Foundation of China (No. 10472036)
文摘Poisson-Boltzmann equation for EDL (electric double layer) and Navier- Stokes equation for liquid flows were numerically solved to investigate resistance effect of electric double layer on liquid flow in microchannel. The dimension analysis indicates that the resistance effect of electric double layer can be estimated by an electric resistance number, which is proportional to the square of the liquid dielectric constant and the solid surface zeta potential, and inverse-proportional to the liquid dynamic viscosity, electric conductivity and the square of the channel width. An "electric current density balancing" (ECDB) condition was proposed to evaluate the flow-induced streaming potential, instead of conventional "electric current balancing" (ECB) condition which may induce spurious local backflow in neighborhood of the solid wall of the microchannel. The numerical results of the flow rate loss ratio and velocity profile are also given to demonstrate the resistance effect of electric double layer in microchannel.
文摘To enhance the controllability of stratosphere airship,a vectored electric propulsion system is used.By using the Lagrangian method,a kinetic model of the vectored electric propulsion system is established and validated through ground tests.The fake gyroscopic torque is first proposed,which the vector mechanism should overcome besides the inertial torque and the gravitational torque.The fake gyroscopic torque is caused by the difference between inertial moments about two principal inertial axes of the propeller in the rotating plane,appears only when the propeller is rotating and is proportional with the rotation speed.It is a sinusoidal pulse,with a frequency that is twice of the rotation speed.Considering the fake gyroscope torque pulse and aerodynamic efficiency,three blade propeller is recommended for the vectored propulsion system used for stratosphere airship.
文摘The linear Rayleigh-Bénard electro-convective stability of the Newtonian dielectric liquid is determined theoretically subject to the temperature modulation with time.A perturbation method is used to compute the critical Rayleigh number and the wave number.The critical Rayleigh number is calculated as a function of the frequency of modulation,the temperature-dependent variable viscosity,the electric field dependent variable viscosity,the Prandtl number,and the electric Rayleigh number.The effects of all three cases of modulations are established to delay or advance the onset of the convection process.In addition,how the effect of variable viscosity controls the onset of convection is studied.
基金the framework of the project under state assignment (No. FWEU-2021-0003) of the RF Basic Research Program for 2021-2030financial support from the Russian Foundation for Basic Research within the framework of the scientific project No 20-08-00550
文摘This study presents the results of a research into the developing a methodology for assessing the adequacy of advanced electric power systems characterized by the integration of various innovative technologies,which complicates their analysis.The methodology development is aimed at solving two main problems:(1)increase the adequacy of modeling the processes that occur in the electric power system and (2)enhance the computational efficiency of the adequacy assessment methodology.This study proposes a new mathematical model to minimize the power shortage and enhance the adequacy of modeling the processes.The model considers quadratic power transmission losses and network coefficients.The computational efficiency of the adequacy assessment methodology is enhanced using efficient random-number generators to form the calculated states of electric power systems and machine learning methods to assess power shortages and other reliability characteristics in the calculated states.
基金Supported by National Natural Science Foundation of China(Nos.91226202,91426304)CAS Interdisciplinary Innovation Team Project
文摘The spark plasma sintering(SPS) method was used to study the mechanism of reaction interface between Zr and Ti3AlC2 with electric current going through it. It was found that electric current greatly reduced the bonding temperature of Zr and Ti3AlC2. By the micro-structure analysis of the interface through SEM/EDS, it was found that Al atoms diffused from the Ti3AlC2 substrate into the Zr side and reacted with Zr to form the Zr-Al compounds at the interface, which is the strengthening mechanism of Ti3AlC2-Zr bonding. The thickness of reaction layers(Zr-Al alloy) was from 0.879 to 13.945 mm depending on different sintering condition. Current direction, heating rate, soaking time, pulse patterns all influenced the diffusion of Al atoms which affected the joining quality of Zr and Ti3AlC2.
基金Supported by the National Natural Science Foundation of China (No.60172001).
文摘This letter proposes a novel design of a Micro Electro Mechanical System (MEMS) device featuring a metal grating vibratory mierostructure driven by electrostatic force to sense the spatial electric field. Due to the advantages in slide-film damping and large vibration amplitude, such a device makes atmospheric packaging a low-cost option for practical manufacture. In this letter, we present the operating principles and specifications, the design structure, as well as the finite element simulation. Computational analysis shows that our design obtains good results in device parameters setting, while its simplicity and low-cost features make it an attractive solution for applications.
文摘For many years, a Lorentz factor of L = 1/3 has been used to describe the local electric field in thin amorphous dielectrics. However, the exact meaning of thin has been unclear. The local electric field E<sub>loc</sub> modeling presented in this work indicates that L = 1/3 is indeed valid for very thin solid dielectrics (t<sub>diel</sub> ≤ 20 monolayers) but significant deviations from L = 1/3 start to occur for thicker dielectrics. For example, L ≈ 2/3 for dielectric thicknesses of t<sub>diel</sub> = 50 monolayers and increases to L ≈ 1 for dielectric thicknesses t<sub>diel</sub> > 200 monolayers. The increase in L with t<sub>diel</sub> means that the local electric fields are significantly higher in thicker dielectrics and explains why the breakdown strength E<sub>bd</sub> of solid polar dielectrics generally reduces with dielectric thickness t<sub>diel</sub>. For example, E<sub>bd</sub> for SiO<sub>2</sub> reduces from approximately E<sub>bd</sub> ≈ 25 MV/cm at t<sub>diel</sub> = 2 nm to E<sub>bd</sub> ≈ 10 MV/cm at t<sub>diel</sub> = 50 nm. However, while E<sub>bd</sub> for SiO<sub>2</sub> reduces with t<sub>diel</sub>, all SiO<sub>2</sub> thicknesses are found to breakdown at approximately the same local electric field (E<sub>loc</sub>)<sub>bd</sub> ≈ 40 MV/cm. This corresponds to a coordination bond strength of 2.7 eV for the silicon-ion to transition from four-fold to three-fold coordination in the tetrahedral structure.
文摘A recent technique, using to potentially replace the conventional impregnating one in low voltage electric motors, has been studied in this communication. The conventional technique that uses?both primary and secondary insulations;?i.e.: enamel and varnish, has been compared to this recent technique which only uses one component,?i.e.: self-bonding wires. Self-bonding wires polymerization is very quick compared to that of the conventional technique. Environmental impact and both dielectric and mechanical properties of these two techniques have been estimated and compared. The goal is to estimate if this recent technique has not only a better environmental footprint but also good technical properties. The dielectric properties that have been measured are the dielectric strength and?the lifetime under pulse?voltage while mechanical consists in measuring the bonding strength that is crucial for impregnation.?For that purpose, a Life Cycle Assessment (LCA) that can simultaneously evaluatenumerous impacts on ground, water and air,?has been performed. The results show clearly that the recent technique significantly reduces the environmental footprint. Both mechanical and dielectric properties are then compared and analyzed.