The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(S...The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(SiC_(nws))/SiC composites are fabricated with in-situ SiC interface on one-dimensional oriented SiC_(nws)skeleton,which collaborative configuration by 3D printing and freeze casting assembly.The con-structed porous structure optimizes the impedance matching degree and scattering intensity,the maximum effective absorption bandwidth(EAB_(max))of 5.9 GHz and the minimum reflection loss(RL_(min))of−41.4 dB can be realized.Considering the inherent oxidation resistance of SiC,the composites present well-maintained absorption performance at 600℃.Even at 1100℃,the EAB_(max)of 4.9 GHz and RLmin of−30.4 dB also demonstrate the high-temperature absorption stability of the composites,indicating exceptional wave absorption properties and thermal stability.The slight attenuation can be attributed to the decrease in impedance matching capability accompanying the elevated dielectric constant.This work clarifies the impact of structure and component synergy on wave absorption behavior,and offers a novel approach to producing high-performance and high-temperature resistance ceramic-based electromagnetic wave absorption materials suitable for extreme environments.展开更多
To further improve the performance of binders,a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics(PDC)route using TiB2,Polysiloxane(PSO)and short SiC nanowires ...To further improve the performance of binders,a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics(PDC)route using TiB2,Polysiloxane(PSO)and short SiC nanowires as fillers.The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature,as well as the reinforcing mechanism was studied.Compared with the adhesive without SiC nanowires,after curing(at 170℃)and pyrolysis(at 1000℃)in air,the appropriate adding of SiC nanowires upgrades the room temperature and high temperature(at 1000℃ in air)adhesive strength to(12.50±0.67)MPa(up by about 32%)and(13.11±0.79)MPa(up by about 106%),respectively.Attractively,under the synergistic impact of the nanowire bridging,nanowire breaking,nanowire drawing and crack deflection,the optimized adhesive exhibits multi-stage fracture,causing the increscent fracture displacement.展开更多
The Mahabad rhyolitic complex,mostly composed of rhyolite but also including granite and granodiorite,is exposed in NW Iran as a part of the Central Iran Block.Porphyritic,hyalo-porphyritic and spheroidal are the main...The Mahabad rhyolitic complex,mostly composed of rhyolite but also including granite and granodiorite,is exposed in NW Iran as a part of the Central Iran Block.Porphyritic,hyalo-porphyritic and spheroidal are the main textures of the studied samples of rhyolite.U-Pb zircon chronology on three samples of Mahabad rhyolitic complex yielded Cambrian to Ediacaran ages of 537.6±6.6 Ma,547.4±6.5 Ma and 556.2±7.1 Ma.Based on geochemical analyses,the original magma was high potassium calc-alkaline to shoshonitic.The rocks are enriched in LREEs relative to HREEs.Trace element patterns of Mahabad rhyolite normalized to chondrites show negative anomalies of high-fi eld-strength elements(Ti,Nb,Ta,Hf,Yb,Y and Zr)and high LREEs and large ion lithophile element contents(Rb,K,Th and Ba).^(208)Pb/^(204) Pb(36.7219–39.0367),^(207) Pb/^(204) Pb(15.4963–15.7669)and ^(206) Pb/^(204) Pb(16.9405–19.9567)ratios indicate an EM-II enriched mantle source for the rhyolite magma.Large variation ofεHf(t)from−5.2 to+4.5 points to a mantle source with crustal material contribution in the magma genesis.The rhyolitic magma erupted in an active continental margin.The formation of calc-alkaline high potassium magma was probably related to metasomatism of the mantle because of the north to south subduction of Proto-Tethys oceanic crust beneath the northern margin of Gondwana continental crust.展开更多
The Kashmir Basin,shaped by the collision of the Indian and Eurasian tectonic plates,features prominent faults,including the Balapur fault and other fault zones.This study focuses on the Gulmarg fault within the North...The Kashmir Basin,shaped by the collision of the Indian and Eurasian tectonic plates,features prominent faults,including the Balapur fault and other fault zones.This study focuses on the Gulmarg fault within the Northwestern Himalaya,using advanced geomagnetic techniques for delineation.Geomagnetic measurements reveal the characteristics of the newly identified Gulmarg fault.Ground magnetic surveys with Proton Precession Magnetometers along linear profiles and a magnetic grid highlight fault-related anomalies.The results indicate a fault running through the Gulmarg meadows,approximately 1.6 km from the Balapur fault,suggesting a potential coupling between the two.Three profiles across the fault exhibit distinctive magnetic variations,highlighting the intricate nature of the fault structure.Gridding methods also reveal anomalies associated with subsurface water and hydraulic activities,underscoring the importance of advanced geophysical techniques.This study emphasizes the significance of detailed investigations to unravel the complex geological processes shaping the Kashmir Basin.The study provides valuable insights into the tectonic activity in the Gulmarg region,underscoring the role of geophysical studies in enhancing our understanding of dynamic geological structures like the Gulmarg fault zone.展开更多
The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） ...The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） exerts a more evident influence on the band gap of the ZnO NWs. However, the effect will be weakened with the increase of the diameter. In addition, the energy band shifts downward due to the existence of VOand the offset decreases with the reduction of the VOconcentration. As the concentration of surface Zn atoms decreases, the conduction band shifts downward, while 2p electrons are lost in the oxygen vacancy, resulting in the split of valence band and the formation of an impurity level. Our findings agree well with the previous observations and will be of great importance for theoretical research based on ZnO NWs.展开更多
基金supported by the National Key R&D Program of China(No.2022YFB3707700)National Natural Science Foundation of China(No.52302121)+3 种基金Shanghai Sailing Program(No.23YF1454700)Shanghai Natural Science Foundation(No.23ZR1472700)Shanghai Post-doctoral Excellent Program(No.2022664)Shanghai Science and Technology Innovation Action Plan(No.21511104800).
文摘The research on high-performance electromagnetic wave absorption materials with high-temperature and oxidative stability in extreme environments is gaining popularity.Herein,the lightweight silicon carbide nanowires(SiC_(nws))/SiC composites are fabricated with in-situ SiC interface on one-dimensional oriented SiC_(nws)skeleton,which collaborative configuration by 3D printing and freeze casting assembly.The con-structed porous structure optimizes the impedance matching degree and scattering intensity,the maximum effective absorption bandwidth(EAB_(max))of 5.9 GHz and the minimum reflection loss(RL_(min))of−41.4 dB can be realized.Considering the inherent oxidation resistance of SiC,the composites present well-maintained absorption performance at 600℃.Even at 1100℃,the EAB_(max)of 4.9 GHz and RLmin of−30.4 dB also demonstrate the high-temperature absorption stability of the composites,indicating exceptional wave absorption properties and thermal stability.The slight attenuation can be attributed to the decrease in impedance matching capability accompanying the elevated dielectric constant.This work clarifies the impact of structure and component synergy on wave absorption behavior,and offers a novel approach to producing high-performance and high-temperature resistance ceramic-based electromagnetic wave absorption materials suitable for extreme environments.
基金co-supported by the National Natural Science Foundation of China (No. 52061135102)the Innovation Training Foundation for College Students of Northwestern Polytechnical University, China (No. 202310699180)the Creative Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory
文摘To further improve the performance of binders,a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics(PDC)route using TiB2,Polysiloxane(PSO)and short SiC nanowires as fillers.The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature,as well as the reinforcing mechanism was studied.Compared with the adhesive without SiC nanowires,after curing(at 170℃)and pyrolysis(at 1000℃)in air,the appropriate adding of SiC nanowires upgrades the room temperature and high temperature(at 1000℃ in air)adhesive strength to(12.50±0.67)MPa(up by about 32%)and(13.11±0.79)MPa(up by about 106%),respectively.Attractively,under the synergistic impact of the nanowire bridging,nanowire breaking,nanowire drawing and crack deflection,the optimized adhesive exhibits multi-stage fracture,causing the increscent fracture displacement.
文摘The Mahabad rhyolitic complex,mostly composed of rhyolite but also including granite and granodiorite,is exposed in NW Iran as a part of the Central Iran Block.Porphyritic,hyalo-porphyritic and spheroidal are the main textures of the studied samples of rhyolite.U-Pb zircon chronology on three samples of Mahabad rhyolitic complex yielded Cambrian to Ediacaran ages of 537.6±6.6 Ma,547.4±6.5 Ma and 556.2±7.1 Ma.Based on geochemical analyses,the original magma was high potassium calc-alkaline to shoshonitic.The rocks are enriched in LREEs relative to HREEs.Trace element patterns of Mahabad rhyolite normalized to chondrites show negative anomalies of high-fi eld-strength elements(Ti,Nb,Ta,Hf,Yb,Y and Zr)and high LREEs and large ion lithophile element contents(Rb,K,Th and Ba).^(208)Pb/^(204) Pb(36.7219–39.0367),^(207) Pb/^(204) Pb(15.4963–15.7669)and ^(206) Pb/^(204) Pb(16.9405–19.9567)ratios indicate an EM-II enriched mantle source for the rhyolite magma.Large variation ofεHf(t)from−5.2 to+4.5 points to a mantle source with crustal material contribution in the magma genesis.The rhyolitic magma erupted in an active continental margin.The formation of calc-alkaline high potassium magma was probably related to metasomatism of the mantle because of the north to south subduction of Proto-Tethys oceanic crust beneath the northern margin of Gondwana continental crust.
文摘The Kashmir Basin,shaped by the collision of the Indian and Eurasian tectonic plates,features prominent faults,including the Balapur fault and other fault zones.This study focuses on the Gulmarg fault within the Northwestern Himalaya,using advanced geomagnetic techniques for delineation.Geomagnetic measurements reveal the characteristics of the newly identified Gulmarg fault.Ground magnetic surveys with Proton Precession Magnetometers along linear profiles and a magnetic grid highlight fault-related anomalies.The results indicate a fault running through the Gulmarg meadows,approximately 1.6 km from the Balapur fault,suggesting a potential coupling between the two.Three profiles across the fault exhibit distinctive magnetic variations,highlighting the intricate nature of the fault structure.Gridding methods also reveal anomalies associated with subsurface water and hydraulic activities,underscoring the importance of advanced geophysical techniques.This study emphasizes the significance of detailed investigations to unravel the complex geological processes shaping the Kashmir Basin.The study provides valuable insights into the tectonic activity in the Gulmarg region,underscoring the role of geophysical studies in enhancing our understanding of dynamic geological structures like the Gulmarg fault zone.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51132002 and 11574261)the Natural Science Foundation of Hebei ProvinceChina(Grant No.A2015203261)
文摘The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） exerts a more evident influence on the band gap of the ZnO NWs. However, the effect will be weakened with the increase of the diameter. In addition, the energy band shifts downward due to the existence of VOand the offset decreases with the reduction of the VOconcentration. As the concentration of surface Zn atoms decreases, the conduction band shifts downward, while 2p electrons are lost in the oxygen vacancy, resulting in the split of valence band and the formation of an impurity level. Our findings agree well with the previous observations and will be of great importance for theoretical research based on ZnO NWs.
