Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly ...Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly been studied,whereas the in-plane thermal conductivity has received less attention due to their limited thickness.展开更多
The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp...The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.展开更多
Silicon is being investigated extensively as an anodic material for next-generation lithium ion batteries for portable energy storage and electric vehicles.However,the large changes in volume during cycling lead to th...Silicon is being investigated extensively as an anodic material for next-generation lithium ion batteries for portable energy storage and electric vehicles.However,the large changes in volume during cycling lead to the breakdown of the conductive network in Si anodes and the formation of an unstable solid-electrolyte interface,resulting in capacity fading.Here,we demonstrate nanoparticles with a Si@Mn22.6Si5.4C4@C double-shell structure and the formation of self-organized Si-Mn-C nanocomposite anodes during the lithiation/delithiation process.The anode consists of amorphous Si particles less than 10 nm in diameter and separated by an interconnected conductive/buffer network,which exhibits excellent charge transfer kinetics and charge/discharge performances.A stable specific capacity of 1100 mAh·g-1 at 100 mA·g-1 and a coulombic efficiency of 99.2%after 30 cycles are achieved.Additionally,a rate capacity of 343 mAh·g-1 and a coulombic efficiency of 99.4%at 12000 mA·g-1 are also attainable.Owing to its simplicity and applicability,this strategy for improving electrode performance paves a way for the development of high-performance Si-based anodic materials for lithium ion batteries.展开更多
Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjust...Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjusting pH values of suspensions. Remarkable increase in flexural strength at room temperatures was obtained by adding nanoparticles in Si3N4 matrix with 10% （wt pct） of nano-Si3N4 and 15% of nano-TiC. The flexural strength, fracture toughness and hardness were 1025 MPa, 7.5 MPa.m^1/2 and 15.6 GPa, respectively. The microstructures of materials were analyzed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）, which indicated that TiC nanoparticles distribute in the matrix and at the grain boundaries. According to the fracture form, low contents of nano particles could refine matrix grains and lead to the crack deflection as well as crack pinning. The multiplex microstructure was formed by mixing nano-Si3N4 particles. The crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out.展开更多
In the present study,the electrophoretic deposition method was successfully applied as a binder-free and scalable approach to deposit carbonaceous nanomaterials on carbon fiber paper(CFP)for cathode applications in Li...In the present study,the electrophoretic deposition method was successfully applied as a binder-free and scalable approach to deposit carbonaceous nanomaterials on carbon fiber paper(CFP)for cathode applications in Li-S batteries.The microstructural studies of the EPD-CNT film using scanning electron microscopy(SEM)revealed the formation of a crack-free and porous layer of CNTs being uniformly distributed on the CFP surface.The EPD:CFP/CNT/S cathode delivered a capacity around 2.2 times higher than that obtained in the absence of the EPD-CNT film(CFP/S cell)after 50 cycles and a capacity of935 mAh g^-1 after 100 cycles at 0.1 C.The EPD method was then employed to fabricate layer-by-layer structures where the EPD-CNT film was decorated with carbon black particles.The initial capacity as well as the reversible capacity after 100 cycles was further increased by the EPD:CFP/CNT/KB/S layer-by-layer structure to 1473 and 1033 mAh g^-1,respectively,indicating effective suppression of the shuttle effect.In addition,the rate performance of CFP/S was improved by depositing the EPD-CNT and EPD-CNT/carbon black architectures on CFP surface,and even further enhanced through the co-deposition of CNT and Pt nanoparticles by EPD,delivering a specific capacity of around 730 mAh g^-1 at 1 C.Finally,the cathodes fabricated by EPD were observed to outperform those made by the conventional casting method in terms of cycling performance,internal resistance,and polarization.This difference was ascribed to the non-uniform microstructure of the Cast-CNT film,which resulted in poor interfacial connection between the CNT agglomerates,hindering uniform sulfide/sulfur deposition during cycling.The obtained results suggested that the binder-free C/S nanocomposite cathode made by EPD is key to further enhance the specific capacity and energy density of Li-S batteries.展开更多
The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear...The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.展开更多
A novel 4H-Si C trench insulated gate bipolar transistor(IGBT)with a controllable hole-extracting(CHE)path is proposed and investigated in this paper.The CHE path is controlled by metal semiconductor gate(MES gate)and...A novel 4H-Si C trench insulated gate bipolar transistor(IGBT)with a controllable hole-extracting(CHE)path is proposed and investigated in this paper.The CHE path is controlled by metal semiconductor gate(MES gate)and metal oxide semiconductor gate(MOS gate)in the p-shield region.The grounded p-shield region can significantly suppress the high electric field around gate oxide in Si C devices,but it weakens the conductivity modulation in the Si C trench IGBT by rapidly sweeping out holes.This effect can be eliminated by introducing the CHE path.The CHE path is pinched off by the high gate bias voltage at on-state to maintain high conductivity modulation and obtain a comparatively low on-state voltage(VON).During the turn-off transient,the CHE path is formed,which contributes to a decreased turn-off loss(EOFF).Based on numerical simulation,the EOFFof the proposed IGBT is reduced by 89%compared with the conventional IGBT at the same VONand the VONof the proposed IGBT is reduced by 50%compared to the grounded p-shield IGBT at the same EOFF.In addition,the average power reduction for the proposed device can be 51.0%to 81.7%and 58.2%to 72.1%with its counterparts at a wide frequency range of 500 Hz to 10 k Hz,revealing a great improvement of frequency characteristics.展开更多
A novel silicon carbide gate-controlled bipolar field effect composite transistor with poly silicon region(SiC GCBTP)is proposed.Different from the traditional electrode connection mode of SiC vertical diffused MOS(VD...A novel silicon carbide gate-controlled bipolar field effect composite transistor with poly silicon region(SiC GCBTP)is proposed.Different from the traditional electrode connection mode of SiC vertical diffused MOS(VDMOS),the P+region of P-well is connected with the gate in SiC GCBTP,and the polysilicon region is added between the P+region and the gate.By this method,additional minority carriers can be injected into the drift region at on-state,and the distribution of minority carriers in the drift region will be optimized,so the on-state current is increased.In terms of static characteristics,it has the same high breakdown voltage(811 V)as SiC VDMOS whose length of drift is 5.5μm.The on-state current of SiC GCBTP is 2.47×10^(-3)A/μm(V_(G)=10 V,V_(D)=10 V)which is 5.7 times of that of SiC IGBT and 36.4 times of that of SiC VDMOS.In terms of dynamic characteristics,the turn-on time of SiC GCBTP is only 0.425 ns.And the turn-off time of SiC GCBTP is similar to that of SIC insulated gate bipolar transistor(IGBT),which is 114.72 ns.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52276086 and 52130604)the Basic Research Program of China(Grant No.514010303-102)the K.C.Wong Education Foundation。
文摘Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution.In C/Si C composites,the out-of-plane thermal conductivity has mainly been studied,whereas the in-plane thermal conductivity has received less attention due to their limited thickness.
基金the Key Projects of Equipment Pre-research Foundation of the Ministry of Equipment Development of the Central Military Commission of China (No.6140922010201)the Key R&D Plan of Zhenjiang in 2018(No.GY2018021)。
文摘The performance of solid solution aging treatment on aluminum matrix composites prepared by powder metallurgy and reinforced with 6061 aluminum alloy powder as matrix;meanwhile, nano silicon carbide particles(nm Si Cp), submicron silicon carbide particles(1 μm Si Cp) and Ti particles were studied. The Al/Si Cp composite powder was prepared by high-energy ball milling, and then cold-pressed, sintered, hotextruded, and then heat-treated with different solution temperatures and aging times for the extruded composites. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy(EDS), X-ray diffractometer(XRD) and extrusion testing were used to analyze and test the microstructure and mechanical properties of aluminum matrix composites. The results show that after the multi-stage solid solution at 530 ℃×2 h+535 ℃×2 h+540 ℃×2 h, the particles are mainly equiaxed grains and uniformly distributed. There is no reinforcement agglomeration, and the surface is dense and the insoluble phase is basically dissolved. In the matrix, the strengthening effect is good, and the hardness and compressive strength are 179.43 HV and 680.42 MPa, respectively. Under this solution process, when the aluminum matrix composites are aged at 170 ℃ for 10 h, the hardness and compressive strength can reach their peaks and increase to 195.82 HV and 721.48 MPa, respectively.
基金supported by the Major Program of Beijing Municipal Natural Science Foundation(No.2110001)the National Natural Science Foundation of China(No.11179001)the National High Technology Research and Development Program(No.2012AA052201)
文摘Silicon is being investigated extensively as an anodic material for next-generation lithium ion batteries for portable energy storage and electric vehicles.However,the large changes in volume during cycling lead to the breakdown of the conductive network in Si anodes and the formation of an unstable solid-electrolyte interface,resulting in capacity fading.Here,we demonstrate nanoparticles with a Si@Mn22.6Si5.4C4@C double-shell structure and the formation of self-organized Si-Mn-C nanocomposite anodes during the lithiation/delithiation process.The anode consists of amorphous Si particles less than 10 nm in diameter and separated by an interconnected conductive/buffer network,which exhibits excellent charge transfer kinetics and charge/discharge performances.A stable specific capacity of 1100 mAh·g-1 at 100 mA·g-1 and a coulombic efficiency of 99.2%after 30 cycles are achieved.Additionally,a rate capacity of 343 mAh·g-1 and a coulombic efficiency of 99.4%at 12000 mA·g-1 are also attainable.Owing to its simplicity and applicability,this strategy for improving electrode performance paves a way for the development of high-performance Si-based anodic materials for lithium ion batteries.
基金supported by the National Natural Sci ence Foundation of China(No.50105011)the Foundation for the author by the National Excellent Doctoral Disserta tion of China(200231)+2 种基金the Natural Science Foundation of Shandong Province(Y2004F14)the SRF for ROCS([2002]247),MOE,Chinathe SRF for ROCS(2002[247]),SEM.
文摘Si3N4/TiC nanocomposite ceramics have been fabricated by hot pressing technique with Al2O3 and Y2O3 as additives. The results showed that well dispersed composite powder was carried out by adding dispersant and adjusting pH values of suspensions. Remarkable increase in flexural strength at room temperatures was obtained by adding nanoparticles in Si3N4 matrix with 10% （wt pct） of nano-Si3N4 and 15% of nano-TiC. The flexural strength, fracture toughness and hardness were 1025 MPa, 7.5 MPa.m^1/2 and 15.6 GPa, respectively. The microstructures of materials were analyzed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）, which indicated that TiC nanoparticles distribute in the matrix and at the grain boundaries. According to the fracture form, low contents of nano particles could refine matrix grains and lead to the crack deflection as well as crack pinning. The multiplex microstructure was formed by mixing nano-Si3N4 particles. The crack trajectories exhibited crack deflection, rod-like grain bridging and pull-out.
基金financially supported by the City University of Hong Kong through the SRG projects#7004545�support from the Research G rants Council(RGC)of Hong Kongthe Hong Kong Ph D Fellowship Scheme(HKPFS)。
文摘In the present study,the electrophoretic deposition method was successfully applied as a binder-free and scalable approach to deposit carbonaceous nanomaterials on carbon fiber paper(CFP)for cathode applications in Li-S batteries.The microstructural studies of the EPD-CNT film using scanning electron microscopy(SEM)revealed the formation of a crack-free and porous layer of CNTs being uniformly distributed on the CFP surface.The EPD:CFP/CNT/S cathode delivered a capacity around 2.2 times higher than that obtained in the absence of the EPD-CNT film(CFP/S cell)after 50 cycles and a capacity of935 mAh g^-1 after 100 cycles at 0.1 C.The EPD method was then employed to fabricate layer-by-layer structures where the EPD-CNT film was decorated with carbon black particles.The initial capacity as well as the reversible capacity after 100 cycles was further increased by the EPD:CFP/CNT/KB/S layer-by-layer structure to 1473 and 1033 mAh g^-1,respectively,indicating effective suppression of the shuttle effect.In addition,the rate performance of CFP/S was improved by depositing the EPD-CNT and EPD-CNT/carbon black architectures on CFP surface,and even further enhanced through the co-deposition of CNT and Pt nanoparticles by EPD,delivering a specific capacity of around 730 mAh g^-1 at 1 C.Finally,the cathodes fabricated by EPD were observed to outperform those made by the conventional casting method in terms of cycling performance,internal resistance,and polarization.This difference was ascribed to the non-uniform microstructure of the Cast-CNT film,which resulted in poor interfacial connection between the CNT agglomerates,hindering uniform sulfide/sulfur deposition during cycling.The obtained results suggested that the binder-free C/S nanocomposite cathode made by EPD is key to further enhance the specific capacity and energy density of Li-S batteries.
基金financial support from the National Key Research and Development Programme (2018YFC1801901)the National Natural Science Foundation of China (21808115, 22108309, 52172093)+1 种基金the Key Research and Development Project (Major Project of Scientific and Technological Innovation) of Shandong Province (2020CXGC010308)the Taishan Scholar Program of Shandong (ts20190919)。
文摘The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.
基金Project supported by the Hunan Provincial Natural Science Foundation of China(Grant No.2021JJ30738)Scientific Research Fund of Hunan Provincial Education Department(Grant No.19K001)Hunan Provincial Key Laboratory of Flexible Electronic Materials Genome Engineering’s Open Fund Project-2020(Grant No.202016)。
文摘A novel 4H-Si C trench insulated gate bipolar transistor(IGBT)with a controllable hole-extracting(CHE)path is proposed and investigated in this paper.The CHE path is controlled by metal semiconductor gate(MES gate)and metal oxide semiconductor gate(MOS gate)in the p-shield region.The grounded p-shield region can significantly suppress the high electric field around gate oxide in Si C devices,but it weakens the conductivity modulation in the Si C trench IGBT by rapidly sweeping out holes.This effect can be eliminated by introducing the CHE path.The CHE path is pinched off by the high gate bias voltage at on-state to maintain high conductivity modulation and obtain a comparatively low on-state voltage(VON).During the turn-off transient,the CHE path is formed,which contributes to a decreased turn-off loss(EOFF).Based on numerical simulation,the EOFFof the proposed IGBT is reduced by 89%compared with the conventional IGBT at the same VONand the VONof the proposed IGBT is reduced by 50%compared to the grounded p-shield IGBT at the same EOFF.In addition,the average power reduction for the proposed device can be 51.0%to 81.7%and 58.2%to 72.1%with its counterparts at a wide frequency range of 500 Hz to 10 k Hz,revealing a great improvement of frequency characteristics.
基金Project supported in part by the Science Foundation for Distinguished Young Scholars of Shaanxi Province,China(Grant No.2018JC-017)111 Project(Grant No.B12026)。
文摘A novel silicon carbide gate-controlled bipolar field effect composite transistor with poly silicon region(SiC GCBTP)is proposed.Different from the traditional electrode connection mode of SiC vertical diffused MOS(VDMOS),the P+region of P-well is connected with the gate in SiC GCBTP,and the polysilicon region is added between the P+region and the gate.By this method,additional minority carriers can be injected into the drift region at on-state,and the distribution of minority carriers in the drift region will be optimized,so the on-state current is increased.In terms of static characteristics,it has the same high breakdown voltage(811 V)as SiC VDMOS whose length of drift is 5.5μm.The on-state current of SiC GCBTP is 2.47×10^(-3)A/μm(V_(G)=10 V,V_(D)=10 V)which is 5.7 times of that of SiC IGBT and 36.4 times of that of SiC VDMOS.In terms of dynamic characteristics,the turn-on time of SiC GCBTP is only 0.425 ns.And the turn-off time of SiC GCBTP is similar to that of SIC insulated gate bipolar transistor(IGBT),which is 114.72 ns.
