The nonstoichiometric β-SIC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD ...The nonstoichiometric β-SIC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SIC powder are smaller than the standard value of β-SIC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content. The effect of CSi defects on dielectric property of β-SiC powder has been discussed.展开更多
Metal-based electromagnetic interference(EMI)shielding composites are essential for ensuring electromagnetic compatibility but are often compromised by susceptibility to corrosion,especially in harsh environments.Exis...Metal-based electromagnetic interference(EMI)shielding composites are essential for ensuring electromagnetic compatibility but are often compromised by susceptibility to corrosion,especially in harsh environments.Existing strategies to mitigate coupling corrosion typically involve physical barriers,which inevitably hinder conductivity.In this study,we introduce a novel interface doping approach to fabricate lightweight Graphite@PDA/Ag@Ag composites that simultaneously enhance EMI shielding and corrosion resistance.The PDA/Ag layer selectively regulates electrons with different migration directions and energies to migrate,increasing charge transfer resistance at Ag/graphite interfaces and ensuring conductivity through a tunneling effect.This design achieves an ultralow corrosion rate of 4.313×10–8µm/y(a billionth that of 316 L stainless steel)alongside superior EMI shielding effectiveness of 109 dB in the X-band at 1.5 mm thickness.Remarkably,the composite maintains over 90 dB shielding efficiency after 7 d in NaCl solutions across various pH levels.Furthermore,simulated corrosion under South China Sea conditions predicts a coating loss of less than 0.026µm over 7 years.This work presents a transformative approach to mitigating coupling corrosion in EMI shielding materials,offering a practical route to high-performance,corrosion-resistant composites without the need for a protective topcoat.展开更多
The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured y...The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured yttria stabilized zirconia(YSZ)(nYSZ)thermal barrier coatings.To address these challenges,this study introduces an innovative approach that involves coating nanoparticles with carbon films to prevent them from melting and merging during the plasma spraying process.This method substantially increases the nanoparticle content within the coating,and nanopores formed at the nanoparticle surfaces when the carbon film is removed at 800℃.These nanopores,in combination with nanoparticles,enhance thermal radiation scattering,improving the scattering coefficient and thermal radiation blocking capability of the coating.In contrast to that of conventional thermal barrier coatings(TBCs)of YSZ,the simulated temperature of the substrate under service conditions decreases by up to 26.26 K due to decreased radiative heat transfer and by 111.2 K when the thermal conductivity is reduced.Additionally,the scattering coefficients remain stable within the 1-5μm range even after heat treatment at 1300°C for 100 h,as the coarsened nanoparticle size approaches the wavelength of thermal radiation.Thus,nYSZ TBCs with enhanced thermal radiation blocking ability and high temperature stability can be created by this approach for higher temperature applications.展开更多
Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ...Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ℃ and dwell time for 2 h.The samples were characterized by X-ray diffraction and scanning electron microscopy,respectively.The dielectric properties of the 0.98KNN-0.02 LF ceramics were also investigated.The results show that all the ceramics sintered at different sintering temperatures are a pure pseudo-cubic perovskite phase,and it is effective to improve the density and dielectric properties when the sintering temperature increases.However,the properties of the ceramics can be deteriorated when the sintering temperature exceeds the optimum value.The 0.98KNN-0.02 LF ceramics sintered at1150 ℃ for 2 h show the optimum dielectric properties,i.e.,the high dielectric permittivity(near 2000) and low dielectric loss(<5%) in the temperature range of 100-400 ℃ and the capacitance variation(AC/C_(150℃)) of ±15%,indicating a potential application in high-temperature ceramics capacitors.展开更多
Dielectric-magnetic composite material that incorporate both dielectric and magnetic loss mechanisms are progressively emerging as the design paradigm for high-performance electromagnetic wave(EMW)absorbing materials....Dielectric-magnetic composite material that incorporate both dielectric and magnetic loss mechanisms are progressively emerging as the design paradigm for high-performance electromagnetic wave(EMW)absorbing materials.However,it remains challenging to combine dielectric and magnetic materials through a convenient structural design.Here,we report a core-shell structured Fe_(3)O_(4)@copper sulfide with multiple loss mechanisms,combining the typical magnetic component Fe_(3)O_(4),which has excellent magnetic loss and impedance matching,with the dielectric component copper sulfide,which has high electrical conductivity and rich interfaces.Unlike the conventional hydrothermal synthesis method,the Fe_(3)O_(4)@copper sulfide core-shell structure is formed using the polymer-assisted electrodeless metal deposition(PAMD)method and a subsequent solution based sulfidation reaction.Attributed to the strong dielectric loss capacity introduced by copper sulfide nanosheets,Fe_(3)O_(4)@copper sulfide has an effective absorption bandwidth(EAB)of 5 GHz within 2-18 GHz at a filling ratio of 65 wt.%and a thickness of only 1.4 mm.In addition,we used the same possess to synthesize FeSiCr@copper sulfide,which also exhibited EMW absorption performance superior to that of the original magnetic component,verifying that the PAMD method is also applicable to other magnetic particles.Therefore,the proposed PAMD method provides a new solution-based strategy for constructing high-performance EMW absorbing materials with multi-component and multi-loss mechanisms.展开更多
基金supported by the National Natural Science Foundation of China under grant No. 50572090the fund of the Slate Key Laboratory of Solidification Processing in NWPU, No. KP200901
文摘The nonstoichiometric β-SIC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SIC powder are smaller than the standard value of β-SIC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content. The effect of CSi defects on dielectric property of β-SiC powder has been discussed.
基金supported by the National Science and Technology Major Project(No.J2019-VI-0015-013)Innovative Talent Promotion Program-Youth Science and Technology Emerging Project(No.2021KJXX-101)+5 种基金Science Fund for Distinguished Young Scholars of Shannxi Province(No.2023-JC-JQ-35)Fundamental Research Project of National Defense(No.2021-JCJQ-ZD-046-00)Northwestern Polytechnical University College Student Innovation and Entrepreneurship Training Program(No.S202310699574)National Natural Science Foundation of China(No.52302367)“Fundamental Research Funds for the Central Universities”(No.G2023KY05101)Special thanks to Dr.Minghui Fang(School of Materials Science and Engineering,Northwestern Polytechnical Uni-versity)for illustration production.
文摘Metal-based electromagnetic interference(EMI)shielding composites are essential for ensuring electromagnetic compatibility but are often compromised by susceptibility to corrosion,especially in harsh environments.Existing strategies to mitigate coupling corrosion typically involve physical barriers,which inevitably hinder conductivity.In this study,we introduce a novel interface doping approach to fabricate lightweight Graphite@PDA/Ag@Ag composites that simultaneously enhance EMI shielding and corrosion resistance.The PDA/Ag layer selectively regulates electrons with different migration directions and energies to migrate,increasing charge transfer resistance at Ag/graphite interfaces and ensuring conductivity through a tunneling effect.This design achieves an ultralow corrosion rate of 4.313×10–8µm/y(a billionth that of 316 L stainless steel)alongside superior EMI shielding effectiveness of 109 dB in the X-band at 1.5 mm thickness.Remarkably,the composite maintains over 90 dB shielding efficiency after 7 d in NaCl solutions across various pH levels.Furthermore,simulated corrosion under South China Sea conditions predicts a coating loss of less than 0.026µm over 7 years.This work presents a transformative approach to mitigating coupling corrosion in EMI shielding materials,offering a practical route to high-performance,corrosion-resistant composites without the need for a protective topcoat.
基金supported by the National Science and Technology Major Project(No.J2019-VI-0015-0130)the Shaanxi Provincial Innovative Talent Promotion Plan Youth Science and Technology New Star Project(Talent)(No.2023KJXX-075)the Youth Innovation Team of Shaanxi Universities Project(No.23JP072).
文摘The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured yttria stabilized zirconia(YSZ)(nYSZ)thermal barrier coatings.To address these challenges,this study introduces an innovative approach that involves coating nanoparticles with carbon films to prevent them from melting and merging during the plasma spraying process.This method substantially increases the nanoparticle content within the coating,and nanopores formed at the nanoparticle surfaces when the carbon film is removed at 800℃.These nanopores,in combination with nanoparticles,enhance thermal radiation scattering,improving the scattering coefficient and thermal radiation blocking capability of the coating.In contrast to that of conventional thermal barrier coatings(TBCs)of YSZ,the simulated temperature of the substrate under service conditions decreases by up to 26.26 K due to decreased radiative heat transfer and by 111.2 K when the thermal conductivity is reduced.Additionally,the scattering coefficients remain stable within the 1-5μm range even after heat treatment at 1300°C for 100 h,as the coarsened nanoparticle size approaches the wavelength of thermal radiation.Thus,nYSZ TBCs with enhanced thermal radiation blocking ability and high temperature stability can be created by this approach for higher temperature applications.
基金supported by the National Natural Science Foundation of China(51072165)the fund of State Key Laboratory of Solidification Processing in NWPU(KP201307)+1 种基金Doctor Start fund of Baoji University of Arts.&Sci.(ZK15044)the fund of Shaanxi Key Laboratory of Phytochemistry(13JS006)
文摘Lead-free 0.98(K_(0.5)Na_(0.5))NbO_3-0.02LaFeO_3(abbreviated as 0.98KNN-0.02LF) ceramics were prepared by a conventional solid-state sintering method at various sintering temperatures of 1140,1145,1150,1155 and 1160 ℃ and dwell time for 2 h.The samples were characterized by X-ray diffraction and scanning electron microscopy,respectively.The dielectric properties of the 0.98KNN-0.02 LF ceramics were also investigated.The results show that all the ceramics sintered at different sintering temperatures are a pure pseudo-cubic perovskite phase,and it is effective to improve the density and dielectric properties when the sintering temperature increases.However,the properties of the ceramics can be deteriorated when the sintering temperature exceeds the optimum value.The 0.98KNN-0.02 LF ceramics sintered at1150 ℃ for 2 h show the optimum dielectric properties,i.e.,the high dielectric permittivity(near 2000) and low dielectric loss(<5%) in the temperature range of 100-400 ℃ and the capacitance variation(AC/C_(150℃)) of ±15%,indicating a potential application in high-temperature ceramics capacitors.
基金supported by the National Natural Science Foundation of China(Nos.52302367 and 52203094)the National Key Laboratory of Electromagnetic Information Control and Effects Open Fund(No.SYS1W2023010304)+1 种基金the State Key Laboratory of Solidification Processing in NPU(No.2025-TS-08)We are grateful to Gao Qianwen(Analytical&Testing Center of NPU)for her help in the microstructure characterization.
文摘Dielectric-magnetic composite material that incorporate both dielectric and magnetic loss mechanisms are progressively emerging as the design paradigm for high-performance electromagnetic wave(EMW)absorbing materials.However,it remains challenging to combine dielectric and magnetic materials through a convenient structural design.Here,we report a core-shell structured Fe_(3)O_(4)@copper sulfide with multiple loss mechanisms,combining the typical magnetic component Fe_(3)O_(4),which has excellent magnetic loss and impedance matching,with the dielectric component copper sulfide,which has high electrical conductivity and rich interfaces.Unlike the conventional hydrothermal synthesis method,the Fe_(3)O_(4)@copper sulfide core-shell structure is formed using the polymer-assisted electrodeless metal deposition(PAMD)method and a subsequent solution based sulfidation reaction.Attributed to the strong dielectric loss capacity introduced by copper sulfide nanosheets,Fe_(3)O_(4)@copper sulfide has an effective absorption bandwidth(EAB)of 5 GHz within 2-18 GHz at a filling ratio of 65 wt.%and a thickness of only 1.4 mm.In addition,we used the same possess to synthesize FeSiCr@copper sulfide,which also exhibited EMW absorption performance superior to that of the original magnetic component,verifying that the PAMD method is also applicable to other magnetic particles.Therefore,the proposed PAMD method provides a new solution-based strategy for constructing high-performance EMW absorbing materials with multi-component and multi-loss mechanisms.
