Continuous silicon carbide fiber reinforced silicon carbide matrix(SiC_f/SiC) composites are attractive candidate materials for aerospace engine system and nuclear reactor system. In this paper, SiC_f/SiC composites w...Continuous silicon carbide fiber reinforced silicon carbide matrix(SiC_f/SiC) composites are attractive candidate materials for aerospace engine system and nuclear reactor system. In this paper, SiC_f/SiC composites were fabricated by polymer infiltration and pyrolysis(PIP) process using KD-S fiber as the reinforcement and the LPVCS as the precursor, while the BN interface layer was introduced by chemical vapor deposition(CVD) process using borazine as the single precursor. The effect of the BN interface layer on the structure and properties of the SiC_f/SiC composites was comprehensively investigated. The results showed that the BN interface layer significantly improved the mechanical properties of the KD-S SiC_f/SiC composites. The flexure strength and fracture toughness of the KD-S SiC_f/SiC composites were evidently improved from 314±44.8 to 818±39.6 MPa and 8.6± 0.5 to 23.0±2.2 MPa·m^(1/2), respectively. The observation of TEM analysis displayed a turbostratic structure of the CVD-BN interface layer that facilitated the improvement of the fracture toughness of the SiC_f/SiC composites. The thermal conductivity of KD-S SiC_f/SiC composites with BN interface layer was lower than that of KD-S SiC_f/SiC composites without BN interface layer, which could be attributed to the relative low thermal conductivity of BN interface layer with low crystallinity.展开更多
The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties f...The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.展开更多
It is possible to improve the machinability of aluminum nitride-hexagonal boron nitride(AlN-h-BN)ceramics while maintaining high strength and high thermal conductivity.The composite ceramics with 0-30 wt%BN as seconda...It is possible to improve the machinability of aluminum nitride-hexagonal boron nitride(AlN-h-BN)ceramics while maintaining high strength and high thermal conductivity.The composite ceramics with 0-30 wt%BN as secondary phase were prepared by hot pressed sintering,using yttrium oxide(Y_(2)O_(3))as sintering aid.The phase composition,density,microstructure,mechanical properties,thermal conductivity,and dielectric properties were investigated.The sintering additives were favorable to purify the grain boundaries and improve densification,reacting with oxide impurities on the surface of raw material powder particles.The optimum BN content improved the flexural strength and fracture toughness of composite ceramics with 475 MPa and 4.86 MPa·m^(1/2),respectively.With increasing the amount of BN,the thermal conductivity and hardness of composites gradually decreased,but the minimum value of thermal conductivity was still 85.6 W·m^(-1)·K^(-1) The relative dielectric constant and dielectric loss tangent of the samples ranged from 6.8 to 8.3 and from 2.4×10^(3) to 6.4×10^(3),respectively,in 22-26 GHz.展开更多
Efficient and environmentally friendly production of high-quality continuous fiber coatings using current preparation methods is highly challenging due to issues such as scale and batch processing restrictions,low dep...Efficient and environmentally friendly production of high-quality continuous fiber coatings using current preparation methods is highly challenging due to issues such as scale and batch processing restrictions,low deposition rate,high energy consumption,and utilization of multiple environmentally hazardous steps.To address these challenges,we propose a stable and efficient wet chemical deposition coating method for high-throughput online continuous preparation of boron nitride(BN)coatings on ceramic fibers under an ambient environment.Our process involves surface modification,in-situ wet chemical deposition,and heat treatment,and all seamlessly connecting with the ceramic fiber preparation process through continuous stretching.Hydrophilic groups were introduced via surface modification enhancing wettability of the fiber surface with impregnating solution.An in-situ reaction and atom migration improve uniformity and binding of the coating.As a result,outstanding impregnation and adhesion properties are achieved.A comprehensive analysis to evaluate the impact of the BN coatings was conducted,which demonstrates that the BN-coated fibers exhibit a remarkable 36%increase in tensile strength,a 133%increase in fracture toughness,and enhanced temperature resistance of up to 1600℃.It provides a secure and efficient platform for cost-effective production of functional and high-quality coatings through targeted surface modification and rapid stretching impregnation.展开更多
In order to reduce the sulfur compounds in diesel fuel,boron nitride(BN)has been used as a novel metal-free catalyst in the present research.This nanocatalyst was synthesized via template-free approach followed by hea...In order to reduce the sulfur compounds in diesel fuel,boron nitride(BN)has been used as a novel metal-free catalyst in the present research.This nanocatalyst was synthesized via template-free approach followed by heating treatment at 900℃ in nitrogen atmosphere that the characteristics of the sample were identified by the X-ray diffraction,Fourier-transform infrared spectroscopy,Raman spectroscopy,field emission scanning electron microscopy,transmission electron microscopy,atomic force microscopy,and N2 adsorption-desorption isotherms.The results of structural and morphological analysis represented that BN has been successfully synthesized.The efficacy of the main operating parameters on the process was studied by using response surface methodology based on the Box-Behnken design method.The prepared catalyst showed high efficiency in oxidative desulfurization of diesel fuel with initial sulfur content of 8040 mg·kg^(-1)S.From statistical analysis,a significant quadratic model was obtained to predict the sulfur removal as a function of efficient parameters.The maximum efficiency of 72.4%was achieved under optimized conditions at oxidant/sulfur molar ratio of 10.2,temperature of 71℃,reaction time of 113 min,and catalyst dosage of 0.36 g.Also,the reusability of the BN was studied,and the result showed little reduction in activity of the catalyst after 10 times regeneration.Moreover,a plausible mechanism was proposed for oxidation of sulfur compounds on the surface of the catalyst.The present study shows that BN materials can be selected as promising metal-free catalysts for desulfurization process.展开更多
Orientation control of anisotropic one-dimensional(1D)and two-dimensional(2D)materials in solutions is of great importance in many fields ranging from structural materials design,the thermal management,to energy stora...Orientation control of anisotropic one-dimensional(1D)and two-dimensional(2D)materials in solutions is of great importance in many fields ranging from structural materials design,the thermal management,to energy storage.Achieving fine control of vertical alignment of anisotropic fillers(such as graphene,boron nitride(BN),and carbon fiber)remains challenging.This work presents a universal and scalable method for constructing vertically aligned structures of anisotropic fillers in composites assisted by the expansion flow(using2D BN platelets as a proof-of-concept).BN platelets in the silicone gel strip are oriented in a curved shape that includes vertical alignment in the central area and horizontal alignment close to strip surfaces.Due to the vertical orientation of BN in the central area of strips,a throughplane thermal conductivity as high as 5.65 W m^(-1) K^(-1) was obtained,which can be further improved to 6.54 W m^(-1) K^(-1) by combining BN and pitch-based carbon fibers.The expansion-flow-assisted alignment can be extended to the manufacture of a variety of polymer composites filled with 1D and 2D materials,which can find wide applications in batteries,electronics,and energy storage devices.展开更多
Polytetrafluoroethylene(PTFE)blended with polyimide(PI)and filled with boron nitride(BN)is prepared through cold pressing and sintering for composites with remarkable wear resistance and reduced coefficient of frictio...Polytetrafluoroethylene(PTFE)blended with polyimide(PI)and filled with boron nitride(BN)is prepared through cold pressing and sintering for composites with remarkable wear resistance and reduced coefficient of friction(COF).The characterizations show that BN and PI at different levels,improve the hardness,dynamic thermo-mechanical modulus,thermal conductivity,and tribological properties of PTFE.PI boosts the dispersion and bonding of BN in PTFE.In dry sliding friction of a block-on-ring tribometer,the wear rate and COF of 10:10:80 BN/PI/PTFE reduce to almost 1/300 and 80%of those of pure PTFE,respectively,as the wear mechanism transition from being adhesive to partially abrasive.This occurs only when the additives BN and PI induce a synergistic effect,that is,at concentrations that are not higher than ca.10 wt%and 15 wt%,respectively.The obvious agglomeration at high percentages of added PI and severe conditions(400 N and 400 rpm)induce strong adhesive failure.The variations in the tensile properties,hardness,crystallization,and microstructure of the composites correspond to different effects.The multiple parameters of the plots of wear and friction are transformed into their contour curves.The mechanism transition maps aid in understanding the influence of various test conditions and composite compositions on the contact surfaces in the space-time framework of wear.展开更多
Novel graphene-like boron nitride(BN)/Bi_(3)O_(4)Br photocatalysts have been controllably synthesized through a facile solvothermal method for the first time. Layer contact stacking between graphene-like BN and ultrat...Novel graphene-like boron nitride(BN)/Bi_(3)O_(4)Br photocatalysts have been controllably synthesized through a facile solvothermal method for the first time. Layer contact stacking between graphene-like BN and ultrathin Bi_(3)O_(4)Br was achieved with strong interaction. Dehalogenation is designed to harvest more visible light, and the ultrathin structure of Bi_(3)O_(4)Br is designed to accelerate charge transfer from inside to the surface. After graphene-like BN was engineered, photocatalytic performance greatly improved under visible light irradiation. Graphene-like BN can act as a surface electron-withdrawing center and adsorption center, facilitating molecular oxygen activation. O_(2)^(·-)was determined to be the main active species during the degradation process through analyses of electron spin resonance and XPS valence band spectra.展开更多
Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehen...Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN,BN-molybdenum disulfide,and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory.The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107±0.062 and 0.999±0.053 times that at BN-BN interface,respectively,while increase to 1.195±0.076 and 1.085±0.075 a.u.after exposure of the tip to radiation in scanning electron microscopy,with data repeatability higher than 86%.The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method,whereas the effect of radiation comes from the introduced charges in the tip,indicating the crucial roles of both dispersion and electrostatic interactions in construction,manipulation and device application of two-dimensional heterostructures.展开更多
基金supported by the National Natural Science Foundation of China with Grant Nos.51502343 and 91426304
文摘Continuous silicon carbide fiber reinforced silicon carbide matrix(SiC_f/SiC) composites are attractive candidate materials for aerospace engine system and nuclear reactor system. In this paper, SiC_f/SiC composites were fabricated by polymer infiltration and pyrolysis(PIP) process using KD-S fiber as the reinforcement and the LPVCS as the precursor, while the BN interface layer was introduced by chemical vapor deposition(CVD) process using borazine as the single precursor. The effect of the BN interface layer on the structure and properties of the SiC_f/SiC composites was comprehensively investigated. The results showed that the BN interface layer significantly improved the mechanical properties of the KD-S SiC_f/SiC composites. The flexure strength and fracture toughness of the KD-S SiC_f/SiC composites were evidently improved from 314±44.8 to 818±39.6 MPa and 8.6± 0.5 to 23.0±2.2 MPa·m^(1/2), respectively. The observation of TEM analysis displayed a turbostratic structure of the CVD-BN interface layer that facilitated the improvement of the fracture toughness of the SiC_f/SiC composites. The thermal conductivity of KD-S SiC_f/SiC composites with BN interface layer was lower than that of KD-S SiC_f/SiC composites without BN interface layer, which could be attributed to the relative low thermal conductivity of BN interface layer with low crystallinity.
文摘The benefits of reinforcing polyimide （PI） films with boron nitride （BN） particles and boron nitride nanosheets （BNNSs） were assessed with the aim of enhancing their thermal, optical, and mechanical properties for flexible device applications. BNNSs were prepared from BN particles using a liquid-phase exfoliation method assisted by an ultrasonic probe-type sonicator and centrifugator. PI-based composite films blended with BNNSs and BN particles were fabricated at various concentrations via mechanical stirring and spin coating. The transparency of the PI/BNNS composite films remained almost the same as that of pure PI films up to 3 wt.% whereas the transparency of the PI/BN composite films decreased with increasing concentration of the BN fillers at 550 nm. The thermal stability improved significantly with increasing concentrations of both BN and BNNS relative to that of pure PI films. The temperature for 5% weight loss of the PI/BNNS composite film was higher than that of the PI/BN composite film at the same filler concentration. The composite films with 2 wt.% BN or BNNS showed the lowest wear rate, and the PI/BNNS composite films showed more stable frictional behavior compared to the PI/BN composite films. In addition, bending tests showed that the PI/BNNS composite films exhibited excellent flexibility compared to the PI/BN composite films. Overall, the results indicate that the BNNS can be effectively used as a filler that can enhance the thermal and mechanical properties of polymer materials for flexible device applications.
基金supported by the Basic Science Center Project of NSFC(Grant No.51788104)as well as the National Natural Science Foundation of China(Grant Nos.51532004 and 11704216).
文摘It is possible to improve the machinability of aluminum nitride-hexagonal boron nitride(AlN-h-BN)ceramics while maintaining high strength and high thermal conductivity.The composite ceramics with 0-30 wt%BN as secondary phase were prepared by hot pressed sintering,using yttrium oxide(Y_(2)O_(3))as sintering aid.The phase composition,density,microstructure,mechanical properties,thermal conductivity,and dielectric properties were investigated.The sintering additives were favorable to purify the grain boundaries and improve densification,reacting with oxide impurities on the surface of raw material powder particles.The optimum BN content improved the flexural strength and fracture toughness of composite ceramics with 475 MPa and 4.86 MPa·m^(1/2),respectively.With increasing the amount of BN,the thermal conductivity and hardness of composites gradually decreased,but the minimum value of thermal conductivity was still 85.6 W·m^(-1)·K^(-1) The relative dielectric constant and dielectric loss tangent of the samples ranged from 6.8 to 8.3 and from 2.4×10^(3) to 6.4×10^(3),respectively,in 22-26 GHz.
基金This work was supported by the Natural Science Foundation for Excellent Young Scholars of Hunan Province(No.2021JJ20048).
文摘Efficient and environmentally friendly production of high-quality continuous fiber coatings using current preparation methods is highly challenging due to issues such as scale and batch processing restrictions,low deposition rate,high energy consumption,and utilization of multiple environmentally hazardous steps.To address these challenges,we propose a stable and efficient wet chemical deposition coating method for high-throughput online continuous preparation of boron nitride(BN)coatings on ceramic fibers under an ambient environment.Our process involves surface modification,in-situ wet chemical deposition,and heat treatment,and all seamlessly connecting with the ceramic fiber preparation process through continuous stretching.Hydrophilic groups were introduced via surface modification enhancing wettability of the fiber surface with impregnating solution.An in-situ reaction and atom migration improve uniformity and binding of the coating.As a result,outstanding impregnation and adhesion properties are achieved.A comprehensive analysis to evaluate the impact of the BN coatings was conducted,which demonstrates that the BN-coated fibers exhibit a remarkable 36%increase in tensile strength,a 133%increase in fracture toughness,and enhanced temperature resistance of up to 1600℃.It provides a secure and efficient platform for cost-effective production of functional and high-quality coatings through targeted surface modification and rapid stretching impregnation.
文摘In order to reduce the sulfur compounds in diesel fuel,boron nitride(BN)has been used as a novel metal-free catalyst in the present research.This nanocatalyst was synthesized via template-free approach followed by heating treatment at 900℃ in nitrogen atmosphere that the characteristics of the sample were identified by the X-ray diffraction,Fourier-transform infrared spectroscopy,Raman spectroscopy,field emission scanning electron microscopy,transmission electron microscopy,atomic force microscopy,and N2 adsorption-desorption isotherms.The results of structural and morphological analysis represented that BN has been successfully synthesized.The efficacy of the main operating parameters on the process was studied by using response surface methodology based on the Box-Behnken design method.The prepared catalyst showed high efficiency in oxidative desulfurization of diesel fuel with initial sulfur content of 8040 mg·kg^(-1)S.From statistical analysis,a significant quadratic model was obtained to predict the sulfur removal as a function of efficient parameters.The maximum efficiency of 72.4%was achieved under optimized conditions at oxidant/sulfur molar ratio of 10.2,temperature of 71℃,reaction time of 113 min,and catalyst dosage of 0.36 g.Also,the reusability of the BN was studied,and the result showed little reduction in activity of the catalyst after 10 times regeneration.Moreover,a plausible mechanism was proposed for oxidation of sulfur compounds on the surface of the catalyst.The present study shows that BN materials can be selected as promising metal-free catalysts for desulfurization process.
基金supported by The National Key Research and Development Program of China(2020YFA0210704)。
文摘Orientation control of anisotropic one-dimensional(1D)and two-dimensional(2D)materials in solutions is of great importance in many fields ranging from structural materials design,the thermal management,to energy storage.Achieving fine control of vertical alignment of anisotropic fillers(such as graphene,boron nitride(BN),and carbon fiber)remains challenging.This work presents a universal and scalable method for constructing vertically aligned structures of anisotropic fillers in composites assisted by the expansion flow(using2D BN platelets as a proof-of-concept).BN platelets in the silicone gel strip are oriented in a curved shape that includes vertical alignment in the central area and horizontal alignment close to strip surfaces.Due to the vertical orientation of BN in the central area of strips,a throughplane thermal conductivity as high as 5.65 W m^(-1) K^(-1) was obtained,which can be further improved to 6.54 W m^(-1) K^(-1) by combining BN and pitch-based carbon fibers.The expansion-flow-assisted alignment can be extended to the manufacture of a variety of polymer composites filled with 1D and 2D materials,which can find wide applications in batteries,electronics,and energy storage devices.
基金This work was supported by the National Natural Science Foundation of China(No.51073021).
文摘Polytetrafluoroethylene(PTFE)blended with polyimide(PI)and filled with boron nitride(BN)is prepared through cold pressing and sintering for composites with remarkable wear resistance and reduced coefficient of friction(COF).The characterizations show that BN and PI at different levels,improve the hardness,dynamic thermo-mechanical modulus,thermal conductivity,and tribological properties of PTFE.PI boosts the dispersion and bonding of BN in PTFE.In dry sliding friction of a block-on-ring tribometer,the wear rate and COF of 10:10:80 BN/PI/PTFE reduce to almost 1/300 and 80%of those of pure PTFE,respectively,as the wear mechanism transition from being adhesive to partially abrasive.This occurs only when the additives BN and PI induce a synergistic effect,that is,at concentrations that are not higher than ca.10 wt%and 15 wt%,respectively.The obvious agglomeration at high percentages of added PI and severe conditions(400 N and 400 rpm)induce strong adhesive failure.The variations in the tensile properties,hardness,crystallization,and microstructure of the composites correspond to different effects.The multiple parameters of the plots of wear and friction are transformed into their contour curves.The mechanism transition maps aid in understanding the influence of various test conditions and composite compositions on the contact surfaces in the space-time framework of wear.
基金financially supported by the Fundamental Research Funds for the Central Universities (No.30922010302)the Start-Up Grant from Nanjing University of Science and Technology (AE89991/397)。
文摘Novel graphene-like boron nitride(BN)/Bi_(3)O_(4)Br photocatalysts have been controllably synthesized through a facile solvothermal method for the first time. Layer contact stacking between graphene-like BN and ultrathin Bi_(3)O_(4)Br was achieved with strong interaction. Dehalogenation is designed to harvest more visible light, and the ultrathin structure of Bi_(3)O_(4)Br is designed to accelerate charge transfer from inside to the surface. After graphene-like BN was engineered, photocatalytic performance greatly improved under visible light irradiation. Graphene-like BN can act as a surface electron-withdrawing center and adsorption center, facilitating molecular oxygen activation. O_(2)^(·-)was determined to be the main active species during the degradation process through analyses of electron spin resonance and XPS valence band spectra.
基金This work was supported by National Key Research and Development Program of China(No.2019YFA0705400)National Natural Science Foundation of China(Nos.51535005 and 11702132)+4 种基金The authors also thank for supports from the China Postdoctoral Science Foundation(Nos.2016M600408 and 2017T100362)the Natural Science Foundation of Jiangsu Province(No.BK20170770)the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Nos.MCMS-I-0418K01 and MCMS-I-0419K01)the Fundamental Research Funds for the Central Universities(Nos.NZ2020001,NC2018001,NP2019301,and NJ2019002)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN,BN-molybdenum disulfide,and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory.The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107±0.062 and 0.999±0.053 times that at BN-BN interface,respectively,while increase to 1.195±0.076 and 1.085±0.075 a.u.after exposure of the tip to radiation in scanning electron microscopy,with data repeatability higher than 86%.The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method,whereas the effect of radiation comes from the introduced charges in the tip,indicating the crucial roles of both dispersion and electrostatic interactions in construction,manipulation and device application of two-dimensional heterostructures.
