Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric const...Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2) as the core,MXene as the intermediate layer,and MoS_(2) as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2) nanosheets.Notably,the synergistic combination of SiO_(2) and MoS_(2) with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”展开更多
As a literary slogan given to a special meaning by history, ‘reality＇ has constituted a dominant clue in the evolution of the ideological trend of realism in 20th Century Chinese Literature. In the ‘New Literature ...As a literary slogan given to a special meaning by history, ‘reality＇ has constituted a dominant clue in the evolution of the ideological trend of realism in 20th Century Chinese Literature. In the ‘New Literature Movement＇ of May 4th Movement,‘reality＇, as the characterization of scientific rationality spirit and an imposition on the description of the objective reality, has been incorporated into the perspective of Modern Chinese literature： In the 1950s and 1960s, it protested to obtain an independent literary discourse as a saving weapon; in the early 1980s, it‘restored＇ realism as a theory starting point of ‘re-enlightenment＇. In the late 1980s, with the conversion of historical context, and the subversion and reconstruction of Western ‘refer to＇ concept to ＂reality＂ concept of traditional epistemology, ‘reality＇ ended its historic mission, and thus to retire展开更多
Alumina whisker reinforced zirconia ceramic composite was prepared by both hot oscillatory pressing(HOP)and conventional hot pressing(HP).The results show that compared with HP,HOP can significantly increase the final...Alumina whisker reinforced zirconia ceramic composite was prepared by both hot oscillatory pressing(HOP)and conventional hot pressing(HP).The results show that compared with HP,HOP can significantly increase the final density and densification rate of the material.Analysis of densification kinetics reveals that the predominant densification mechanism transits from grain boundary sliding in the beginning to the diffusion in the later stage.The main effect of the oscillating pressure is to increase the densification rate in the process of grain boundary sliding.The current study suggests that HOP is a promising technique for densifying whisker reinforced ceramics.展开更多
In this work,a novel process,oscillatory pressure-assisted sinter forging(OPSF),for the preparation of high-performance ceramic composites was reported.Compared with the samples made by conventional sinter forging(SF)...In this work,a novel process,oscillatory pressure-assisted sinter forging(OPSF),for the preparation of high-performance ceramic composites was reported.Compared with the samples made by conventional sinter forging(SF)and hot oscillatory pressing(HOP),the SiC whisker reinforced Al_(2)O_(3) composites(SiCw–Al_(2)O_(3))prepared by OPSF at the same temperature exhibited a higher density and significantly improved the mechanical properties.The improvements in densification and performance are attributed to simultaneous enhanced shear deformation at both macro-and micro-scales,resulting from the combination of die-free configuration and oscillatory pressure of OPSF.And the strength of grain boundary is greatly increased when the temperature reaches 1600℃ of OPSF,due to that the grain-boundary sliding became pronounced at higher temperatures.The current results shed light on a powerful technique for preparing ceramic composites,which is likely applicable to other systems.展开更多
In order to prevent the microwave leakage and mutual interference,more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation.In this work,we have success...In order to prevent the microwave leakage and mutual interference,more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation.In this work,we have successfully prepared MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties.Supported by comprehensive characterizations,M0S_(2) nanosheets were proved to be anchored on the surface and interlayer of Ti_(3)C_(2)T_(x) through a hydrothermal process.Additionally,TiO_(2) nanoparticles were obtained in situ.Due to these hierarchical structures,the MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites showed greatly enhanced microwave absorbing performance.The MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites exhibit a maximum reflection loss value of -33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1GHz(13.9-17 GHz)at the thickness of 1.0 mm,implying the features of wide frequency and light weight.This work in the hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.展开更多
Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to...Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to prevent unexpected overgrowth and aggregation of noble nanometals.However,the surfactants are hard to remove and may interfere with plasmonic and catalytic studies,remaining surfactant-free synthesis of noble nanometals a challenge.Herein,we report an approach to epitaxial growth of sizecontrolled noble nanometals on MXenes.As piloted by density functional theory calculations,along with work function experimental determination,kinetic and spectroscopic studies,epitaxial growth of noble nanometals is initiated via a mechanism that involves an in situ redox reaction.In the redox,MXenes as two-dimensional solid reductants whose work functions are compatible with the reduction potentials of noble metal cations,enable spontaneous donation of electrons from the MXenes to noble metal cations and reduce the cations into nanoscale metallic metals on the outmost surface of MXenes.Neither surfactants nor external reductants are used during the whole synthesis process,which addresses a long-standing interference issue of surfactant and external reductant in the conventional wet-chemical synthesis.Moreover,the MXenes induced noble nanometals are size-controlled.Impressively,noble nanometals firmly anchored on MXenes exhibit excellent performance towards surface enhanced Raman scattering.Our developed strategy will promote the nanostructure-controlled synthesis of noble nanometals,offering new opportunities to further improve advanced functional properties towards practical applications.展开更多
A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scan...A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550℃.The relative density and hardness of the ES(Ca,Sr,Ba)ZrO_(3) ceramic sintered at 1550℃are 97.79%and 10.840.33 GPa,re s pectively.This ES(Ca,Sr,Ba)ZrO_(3) exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates,CaZrO_(3),SrZrO_(3) and BaZrO_(3).Most importantly,the ES(Ca,Sr,Ba)ZrO_(3) ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES(Ca,Sr,Ba)ZrO_(3) ceramic in the contact region.The combination of these properties indicates that ES(Ca,Sr,Ba)ZrO_(3) ceramic is promising for use as a novel crucible material for the melting of titanium alloys.展开更多
Pressure measurement with excellent stability and long time durability is highly desired,especially at high temperature and harsh environments.A polymer-derived silicoboron carbonitride(SiBCN)ceramic pressure sensor w...Pressure measurement with excellent stability and long time durability is highly desired,especially at high temperature and harsh environments.A polymer-derived silicoboron carbonitride(SiBCN)ceramic pressure sensor with excellent stability,accuracy,and repeatability is designed based on the giant piezoresistivity of SiBCN ceramics.The SiBCN ceramic sensor was packaged in a stainless steel case and tested using half Wheatstone bridge with the uniaxial pressure up to 10 MPa.The SiBCN ceramic showed a remarkable piezoresistive effect with the gauge factor(K)as high as 5500.The output voltage of packed SiBCN ceramic sensor changes monotonically and smoothly versus external pressure.The as received SiBCN pressure sensor possesses features of short response time,excellent repeatability,stability,sensitivity,and accuracy.Taking the excellent high temperature thermo-mechanical properties of polymer-derived SiBCN ceramics(e.g.,high temperature stability,oxidation/corrosion resistance)into account,SiBCN ceramic sensor has significant potential for pressure measurement at high temperature and harsh environments.展开更多
Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is ...Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.展开更多
基金Joint Fund of Research and Development Program of Henan Province,Grant/Award Number:222301420002National Natural Science Foundation of China,Grant/Award Number:U21A2064Scientific and Technological Innovation Talents in Colleges and Universities in Henan Province,Grant/Award Number:22HASTIT001。
文摘Material composition and structural design are important factors influencing the electromagnetic wave(EMW)absorption performance of materials.To alleviate the impedance mismatch attributed to the high dielectric constant of Ti_(3)C_(2)T_(x)MXene,we have successfully synthesized core‐shell structured SiO_(2)@MXene@MoS_(2)nanospheres.This architecture,comprising SiO_(2) as the core,MXene as the intermediate layer,and MoS_(2) as the outer shell,is achieved through an electrostatic self‐assembly method combined with a hydrothermal process.This complex core‐shell structure not only provides a variety of loss mechanisms that effectively dissipate electromagnetic energy but also prevents self‐aggregation of MXene and MoS_(2) nanosheets.Notably,the synergistic combination of SiO_(2) and MoS_(2) with highly conductive MXene enables the suitable dielectric constant of the composites,ensuring optimal impedance matching.Therefore,the core‐shell structured SiO_(2)@MXene@MoS_(2) nanospheres exhibit excellent EMW absorption performance,featuring a remarkable minimum reflection loss(RL_(min))of−52.11 dB(2.4 mm).It is noteworthy that these nanospheres achieve an ultra‐wide effective absorption bandwidth(EAB)of 6.72 GHz.This work provides a novel approach for designing and synthesizing high‐performance EMW absorbers characterized by“wide bandwidth and strong reflection loss.”
文摘As a literary slogan given to a special meaning by history, ‘reality＇ has constituted a dominant clue in the evolution of the ideological trend of realism in 20th Century Chinese Literature. In the ‘New Literature Movement＇ of May 4th Movement,‘reality＇, as the characterization of scientific rationality spirit and an imposition on the description of the objective reality, has been incorporated into the perspective of Modern Chinese literature： In the 1950s and 1960s, it protested to obtain an independent literary discourse as a saving weapon; in the early 1980s, it‘restored＇ realism as a theory starting point of ‘re-enlightenment＇. In the late 1980s, with the conversion of historical context, and the subversion and reconstruction of Western ‘refer to＇ concept to ＂reality＂ concept of traditional epistemology, ‘reality＇ ended its historic mission, and thus to retire
基金We thank the financial support from the National Natural Science Foundation of China(Grant Nos.52072344 and U1904180)Excellent Young Scientists Fund of Henan Province(Grant No.202300410369)Henan Province University Innovation Talents Support Program(Grant No.21HASTIT001).
文摘Alumina whisker reinforced zirconia ceramic composite was prepared by both hot oscillatory pressing(HOP)and conventional hot pressing(HP).The results show that compared with HP,HOP can significantly increase the final density and densification rate of the material.Analysis of densification kinetics reveals that the predominant densification mechanism transits from grain boundary sliding in the beginning to the diffusion in the later stage.The main effect of the oscillating pressure is to increase the densification rate in the process of grain boundary sliding.The current study suggests that HOP is a promising technique for densifying whisker reinforced ceramics.
基金support from the National Natural Science Foundation of China (Grant Nos.52072344 and U1904180)Excellent Young Scientists Fund of Henan Province (Grant No.202300410369)Henan Province University Innovation Talents Support Program (Grant No.21HASTIT001).
文摘In this work,a novel process,oscillatory pressure-assisted sinter forging(OPSF),for the preparation of high-performance ceramic composites was reported.Compared with the samples made by conventional sinter forging(SF)and hot oscillatory pressing(HOP),the SiC whisker reinforced Al_(2)O_(3) composites(SiCw–Al_(2)O_(3))prepared by OPSF at the same temperature exhibited a higher density and significantly improved the mechanical properties.The improvements in densification and performance are attributed to simultaneous enhanced shear deformation at both macro-and micro-scales,resulting from the combination of die-free configuration and oscillatory pressure of OPSF.And the strength of grain boundary is greatly increased when the temperature reaches 1600℃ of OPSF,due to that the grain-boundary sliding became pronounced at higher temperatures.The current results shed light on a powerful technique for preparing ceramic composites,which is likely applicable to other systems.
基金financially supported by the National Natural Science Foundation of China(No.U2004177)Outstanding Youth Fund of Henan Province(No.212300410081)Natural Science Research Project of Henan Educational Committee(No.20A43001).
文摘In order to prevent the microwave leakage and mutual interference,more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation.In this work,we have successfully prepared MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties.Supported by comprehensive characterizations,M0S_(2) nanosheets were proved to be anchored on the surface and interlayer of Ti_(3)C_(2)T_(x) through a hydrothermal process.Additionally,TiO_(2) nanoparticles were obtained in situ.Due to these hierarchical structures,the MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites showed greatly enhanced microwave absorbing performance.The MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites exhibit a maximum reflection loss value of -33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1GHz(13.9-17 GHz)at the thickness of 1.0 mm,implying the features of wide frequency and light weight.This work in the hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.
基金supported by the National Natural Science Foundation of China(No.51972310)the Shenyang National Laboratory for Materials Science,Institute of Metal Research,Chinese Academy of Sciences(CAS)+1 种基金the Youth Innovation Promotion Association,CAS(No.2011152)the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(the second phase)(No.U1501501).
文摘Noble nanometals are of significance in both scientific interest and technological applications,which are usually obtained by conventional wet-chemical synthesis.Organic surfactants are always used in the synthesis to prevent unexpected overgrowth and aggregation of noble nanometals.However,the surfactants are hard to remove and may interfere with plasmonic and catalytic studies,remaining surfactant-free synthesis of noble nanometals a challenge.Herein,we report an approach to epitaxial growth of sizecontrolled noble nanometals on MXenes.As piloted by density functional theory calculations,along with work function experimental determination,kinetic and spectroscopic studies,epitaxial growth of noble nanometals is initiated via a mechanism that involves an in situ redox reaction.In the redox,MXenes as two-dimensional solid reductants whose work functions are compatible with the reduction potentials of noble metal cations,enable spontaneous donation of electrons from the MXenes to noble metal cations and reduce the cations into nanoscale metallic metals on the outmost surface of MXenes.Neither surfactants nor external reductants are used during the whole synthesis process,which addresses a long-standing interference issue of surfactant and external reductant in the conventional wet-chemical synthesis.Moreover,the MXenes induced noble nanometals are size-controlled.Impressively,noble nanometals firmly anchored on MXenes exhibit excellent performance towards surface enhanced Raman scattering.Our developed strategy will promote the nanostructure-controlled synthesis of noble nanometals,offering new opportunities to further improve advanced functional properties towards practical applications.
基金financially supported by the National Natural Science Foundation of China(No.51772275)。
文摘A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550℃.The relative density and hardness of the ES(Ca,Sr,Ba)ZrO_(3) ceramic sintered at 1550℃are 97.79%and 10.840.33 GPa,re s pectively.This ES(Ca,Sr,Ba)ZrO_(3) exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates,CaZrO_(3),SrZrO_(3) and BaZrO_(3).Most importantly,the ES(Ca,Sr,Ba)ZrO_(3) ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES(Ca,Sr,Ba)ZrO_(3) ceramic in the contact region.The combination of these properties indicates that ES(Ca,Sr,Ba)ZrO_(3) ceramic is promising for use as a novel crucible material for the melting of titanium alloys.
基金The authors appreciate the financial support from the National Natural Science Foundation of China(No.U1904180)Key Scientific Research Projects of High Education Institutions of Henan province(No.19A430025).
文摘Pressure measurement with excellent stability and long time durability is highly desired,especially at high temperature and harsh environments.A polymer-derived silicoboron carbonitride(SiBCN)ceramic pressure sensor with excellent stability,accuracy,and repeatability is designed based on the giant piezoresistivity of SiBCN ceramics.The SiBCN ceramic sensor was packaged in a stainless steel case and tested using half Wheatstone bridge with the uniaxial pressure up to 10 MPa.The SiBCN ceramic showed a remarkable piezoresistive effect with the gauge factor(K)as high as 5500.The output voltage of packed SiBCN ceramic sensor changes monotonically and smoothly versus external pressure.The as received SiBCN pressure sensor possesses features of short response time,excellent repeatability,stability,sensitivity,and accuracy.Taking the excellent high temperature thermo-mechanical properties of polymer-derived SiBCN ceramics(e.g.,high temperature stability,oxidation/corrosion resistance)into account,SiBCN ceramic sensor has significant potential for pressure measurement at high temperature and harsh environments.
基金the financial support from the National Natural Science Foundation of China(Nos.U1904180 and 52072344)Excellent Young Scientists Fund of Henan Province(No.202300410369)+1 种基金Henan Province University Innovation Talents Support Program(No.21HASTIT001)China Postdoctoral Science Foundation(No.2021M692897).
文摘Electromagnetic absorption(EMA)materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles.However,meeting these two requirements is always a great challenge,which excluded the most attractive lightweight candidates,such as carbon-based materials.In this study,SiC_(nw)-reinfbrced SiCNO(SiC_(nw)/SiCNO)composite aerogels were fabricated through the in-situ growth of SiC_(nw) in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time.The phase composition,microstructure,and EMA property of the SiC_(nw)/SiCNO composite aerogels were systematically investigated.The results indicated that the morphology and phase composition of SiC_(nw)/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature.The composite aerogels show excellent EMA property with minimum reflection loss of -23.9 dB@13.8 GHz,-26.5 dB@10.9 GHz,and -20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz,3.2 GHz,and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600℃,800℃,and 1000℃,respectively,which is much better than that of SiCN ceramic aerogels.The superior EMA performance is mainly attributed to the improved impedance matching,multireflection,multi-interfacial polarization,and micro current caused by migration of hopping electrons.
