Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix compo...Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix composites at low cost.However,the low mechanical properties as well as the intrinsic brittleness limit their technological implementations,and it is necessary to enhance the mechanical properties of geopolymers by adopting various kinds of reinforcements.In this work,therefore,two⁃dimensional continuous carbon fiber(Cf)reinforced phosphate⁃based geopolymer composites(Cf/geopolymer)were prepared through ultrasonic⁃assisted impregnation method.Effects of acetone treatment and high⁃temperature treatment on the properties of Cf/geopolymer composites were studied by X⁃ray photoelectron spectroscopy(XPS),X⁃ray diffraction(XRD),and scanning electron microscopy(SEM).Results of the study proved that acetone treatment plays a key role in ameliorating the interfacial interaction between Cf and phosphate matrix,which can thus enhance the mechanical properties of Cf/geopolymer composites.The Cf/geopolymer composites prepared by acetone⁃treated Cf had a flexural strength of 156.1 MPa and an elastic modulus of 39.7 GPa in Y direction.Moreover,an additional Sol⁃SiO2 re⁃impregnation treatment could further enhance the mechanical properties of the acetone⁃treated Cf/geopolymer composites by repairing the cracks and filling the pores.The results in this paper not only provide insights into the surface modification of Cf,but also report a facile and low⁃cost preparation route for Cf/geopolymer composites with potential applications in aerospace and defense technology.展开更多
A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 c...A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 content on phase microstructure,mechanical and dielectric properties of the SiBON ceramics were investigated.展开更多
The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and micr...The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and microstructure evolution of the prepared ceramics were展开更多
We demonstrate a high power,Er:Lu AG single-longitudinal-mode laser in an anti-misaligned resonator.Based on the Faraday effect,a 1.61 W single-longitudinal-mode(SLM)laser is obtained with the double corner-cube-retro...We demonstrate a high power,Er:Lu AG single-longitudinal-mode laser in an anti-misaligned resonator.Based on the Faraday effect,a 1.61 W single-longitudinal-mode(SLM)laser is obtained with the double corner-cube-retroreflector(CCR)structure,and the tunable wavelength is 1649.2-1650.3 nm.Additionally,we investigate the anti-misalignment characteristics when the CCR moves and rotates along the optical axis.Furthermore,by utilizing the Er:Lu AG amplifier,the maximum 2.32 W single-longitudinal-mode laser at 1649.6 nm is achieved.The beam quality factors M^(2) of the 2.32 W Er:Lu AG single-longitudinal-mode laser are 1.23 and 1.25 along the horizontal(x)and vertical(y)directions,respectively.展开更多
Over time,natural materials have evolved to be lightweight,high-strength,tough,and damage-tolerant due to their unique biological structures.Therefore,combining biological inspiration and structural design would provi...Over time,natural materials have evolved to be lightweight,high-strength,tough,and damage-tolerant due to their unique biological structures.Therefore,combining biological inspiration and structural design would provide traditional materials with a broader range of performance and applications.Here,the application of an ink-based three-dimensional(3D)printing strategy to the structural design of a Lunar regolith simulant-based geopolymer(HIT-LRS-1 GP)was first reported,and high-precision carbon fiber/quartz sand-reinforced biomimetic patterns inspired by the cellular sandwich structure of plant stems were fabricated.This study demonstrated how different cellular sandwich structures can balance the structure–property relationship and how to achieve unprecedented damage tolerance for a geopolymer composite.The results presented that components based on these biomimetic architectures exhibited stable non-catastrophic fracture characteristics regardless of the compression direction,and each structure possessed effective damage tolerance and anisotropy of mechanical properties.The results showed that the compressive strengths of honeycomb sandwich patterns,triangular sandwich patterns,wave sandwich patterns,and rectangular sandwich patterns in the Y-axis(Z-axis)direction were 15.6,17.9,11.3,and 20.1 MPa(46.7,26.5,23.8,and 34.4 MPa),respectively,and the maximum fracture strain corresponding to the above four structures could reach 10.2%,6.7%,5.8%,and 5.9%(12.1%,13.7%,13.6%,and 13.9%),respectively.展开更多
A high-energy,alignment-insensitive,injection-seeded Q-switched Ho:yttrium aluminum garnet(YAG)singlefrequency laser is developed.Both the slave Q-switched laser and the seed laser are Ho:YAG ring lasers based on a pa...A high-energy,alignment-insensitive,injection-seeded Q-switched Ho:yttrium aluminum garnet(YAG)singlefrequency laser is developed.Both the slave Q-switched laser and the seed laser are Ho:YAG ring lasers based on a pair of corner cubic reflectors.The seed laser has an available power of 830 mW at 2096.667 nm.At 100 Hz,the Q-switched Ho:YAG laser provides a single-frequency pulsed output using injection-seeded technology.The 7.3 mJ single-frequency pulse energy from the slave laser has a pulse width of 161.2 ns and is scaled to 33.3 mJ after passing through the Ho:YAG single-pass amplifier.According to the measurement results of the heterodyne beating technique,the single-frequency pulse has a half-width of 4.12 MHz.展开更多
Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. ...Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth(TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented.展开更多
In the past twenty years,Si-B-C-N ceramic has attracted wide attention due to its special structure and outstanding properties.The ceramic generally has an amorphous or a nano-crystalline structure,and has excellent s...In the past twenty years,Si-B-C-N ceramic has attracted wide attention due to its special structure and outstanding properties.The ceramic generally has an amorphous or a nano-crystalline structure,and has excellent structural stability,oxidation resistance,creep resistance and high-temperature mechanical properties,etc.Thus,Si-B-C-N ceramic attracts many researchers and finds potential applications in transportation,aerocraft,energy,information,microelectronics and environment,etc.Much work has been carried out on its raw materials,preparation processes,structural evolution,phase equilibrium and high-temperature properties.In recent years,many researchers focus on its new preparation methods,the preparation of dense ceramic sample with large dimensions,ceramic matrix composites reinforced by carbon fiber or SiC whisker,or components with various applications.Research on Si-B-C-N ceramic will develop our insight into the relationship between structures and properties of ceramics,and will be helpful to the development of novel high-performance ceramics.This paper reviews the preparation processes,general microstructures,mechanical,chemical,electrical and optical properties,and potential applications of Si-B-C-N ceramic,as well as its matrix composites.展开更多
BN/La-Al-Si-O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride(h-BN),lanthanum oxide(La_(2)O_(3)),aluminia(Al_(2)O_(3)),and amorphous silica(SiO_(2))as the raw materials.The ef...BN/La-Al-Si-O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride(h-BN),lanthanum oxide(La_(2)O_(3)),aluminia(Al_(2)O_(3)),and amorphous silica(SiO_(2))as the raw materials.The effects of sintering temperature on microstructural evolution,bulk density,apparent porosity,and mechanical properties of the h-BN composite ceramics were investigated.The results indicated that La-Al-Si-O liquid phase was formed during sintering process,which provided an environment for the growth of h-BN grains.With increasing sintering temperature,the cristobalite phase precipitation and h-BN grain growth occurred at the same time,which had a significant influence on the densification and mechanical properties of h-BN composite ceramics.The best mechanical properties of BN/La-Al-Si-O composite ceramics were obtained under the sintering temperature of 1700℃.The elastic modulus,flexural strength,and fracture toughness were 80.5 GPa,266.4 MPa,and 3.25 MPa·m^(1/2),respectively.展开更多
The active/passive Q-switching operation of a 2 [tm a-cut Tm,Ho：YAP laser was experimentally demonstrated with an acousto-optical Q-switch/MoS2 saturable absorber mirror. The active Q-switch laser was operated for th...The active/passive Q-switching operation of a 2 [tm a-cut Tm,Ho：YAP laser was experimentally demonstrated with an acousto-optical Q-switch/MoS2 saturable absorber mirror. The active Q-switch laser was operated for the first time, to the best of our knowledge, with an average output power of 12.3 W and a maximum pulse energy of 10.3 mJ. The passive Q-switch laser was also the first acquired with an average output power of 3.3 W and per pulse energy of 23.31 μJ, and the beam quality factors of Mx^2 = 1.06 and My^2 = 1.06 were measured at the average output power of 2 W.展开更多
SiC fiber reinforced SiBCN ceramic matrix composites(CMCs)have been prepared by mechanical alloying and consolidated by hot pressing.During the sintering process,amorphous SiC fibers crystallized seriously and transfo...SiC fiber reinforced SiBCN ceramic matrix composites(CMCs)have been prepared by mechanical alloying and consolidated by hot pressing.During the sintering process,amorphous SiC fibers crystallized seriously and transformed into-SiC.Meanwhile,the interfacial carbothermal reactions caused the strong bonding between the matrix and fibers.As a result,SiCf/SiBCN fractured in a typical catastrophic manner.Room-temperature mechanical properties reached the maximums for the CMC samples sintered at 1900℃/60 MPa/30 min.The density,flexural strength,Young’s modulus and fracture toughness are 2.56±0.02 g/cm^(3),284.3±17.9 MPa,183.5±11.1 GPa and 2.78±0.14 MPa·m^(1/2),respectively.展开更多
CoCO_(3) with high theoretical capacity has been considered as a candidate anode for the next generation of lithium-ion batteries(LIBs).However,the electrochemical performance of CoCO_(3) itself,especially the cyclic ...CoCO_(3) with high theoretical capacity has been considered as a candidate anode for the next generation of lithium-ion batteries(LIBs).However,the electrochemical performance of CoCO_(3) itself,especially the cyclic stability at high current density,hinders its application.Herein,pure phase CoCO_(3) particles with different particle and pore sizes were prepared by adjusting the solvents(diethylene glycol,ethylene glycol,and deionized water).Among them,CoCO_(3) synthesized with diethylene glycol(DG-CC)as the solvent shows the best electrochemical performance owing to the smaller particle size and abundant mesoporous structure to maintain robust structural stability.A high specific capacity of 690.7 mAh/g after 1000 cycles was achieved,and an excellent capacity retention was presented.The capacity was contributed by diverse electrochemical reactions and the impedance of DG-CC under different cycles was further compared.Those results provide an important reference for the structural design and stable cycle performance of pure CoCO_(3).展开更多
The thermal expansion coefficient(TEC)and thermal conductivity(k)of thermal fillers are key factors for designing thermal management and thermal protection composite materials.Due to its unique advantages,hexagonal bo...The thermal expansion coefficient(TEC)and thermal conductivity(k)of thermal fillers are key factors for designing thermal management and thermal protection composite materials.Due to its unique advantages,hexagonal boron nitride(h-BN)is one of the most commonly used thermal fillers.However,its TEC and k values are still unclear due to the inconsistency of characterization techniques and sample preparations.In this work,these disputes were addressed using the quasi-harmonic approximation(QHA)method and phonon Boltzmann transport equation(BTE)theory based on the density functional theory(DFT),respectively.The accuracy of our calculated TEC and k values was confirmed by previously reported experimental results,and the underlying physical principles were analyzed from the phonon behaviors.Our TEC results show that the h-BN has small in-plane negative value and large cross-plane positive value,which are-2.4×10^(-6) and 36.4×10^(-6) K^(-1) at 300 K,respectively.And the anisotropic TEC is mainly determined by the anisotropic isothermal bulk modulus and the low-frequency out-of-plane longitudinal phonon modes.We found that the convergence of cutoff radius and q-grid size have significant effect on the accuracy of k of h-BN.Our results show that the in-plane k is much higher than the cross-plane k,and the values at 300 K are 286.6 and 2.7 W m^(-1) K^(-1),respectively.The anisotropic phonon group velocity arising from the vibration behaviors of acoustic phonon modes should be primarily responsible for the anisotropic k.Our calculated TEC and k values will provide important references for the design of h-BN composite materials.展开更多
We demonstrated a high-power long-wave infrared laser based on a polarization beam coupling technique.An average output power at 8.3µm of 7.0 W was achieved at a maximum available pump power of 107.6 W,correspond...We demonstrated a high-power long-wave infrared laser based on a polarization beam coupling technique.An average output power at 8.3µm of 7.0 W was achieved at a maximum available pump power of 107.6 W,corresponding to an optical-to-optical conversion of 6.5%.The coupling efficiency of the polarization coupling system was calculated to be approximately 97.2%.With idler single resonance operation,a good beam quality factor of^1.8 combined with an output wavelength of 8.3µm was obtained at the maximum output power.展开更多
We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating(VBG)as an output coupler at room temperature.Two kinds of active heat dissipation methods were used for the VBG to suppress the shift o...We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating(VBG)as an output coupler at room temperature.Two kinds of active heat dissipation methods were used for the VBG to suppress the shift of wavelength caused by its increasing temperature.The maximum continuous wave(CW)output power of 202 W using the microchannel cooling was obtained under the total incident pump power of 553 W,the corresponding slope efficiency and optical-to-optical conversion efficiency were 39.7%and 36.5%,respectively.The central wavelength was 1908.5 nm with the linewidth(full width at half maximum)of 0.57 nm.Meanwhile,with the laser output increasing from 30 to 202 W,the total shift was about 1.0 nm,and the wavelength was limited to two water absorption lines near 1908 nm.The beam quality factors M;were measured to be 2.3 and 4.0 in x and y directions at 202 W.展开更多
Textured hexagonal boron nitride(h-BN)matrix composite ceramics were prepared by hotpressing using different contents of 3Y_(2)O_(3)–5Al_(2)O_(3)(molar ratio of 3:5)as the sintering additive.During hot-pressing,the l...Textured hexagonal boron nitride(h-BN)matrix composite ceramics were prepared by hotpressing using different contents of 3Y_(2)O_(3)–5Al_(2)O_(3)(molar ratio of 3:5)as the sintering additive.During hot-pressing,the liquid Y_(3)Al_(5)O_(12)(YAG)phase showing good wettability to h-BN grains was in situ formed through the reaction between Y_(2)O_(3) and Al_(2)O_(3),and a coherent relationship between h-BN and YAG was observed with[010]_(h-BN)//[111]_(YAG) and(002)_(h-BN)//(321)_(YAG).In the YAG liquid phase environment formed during hot-pressing,plate-like h-BN grains were rotated under the uniaxial sintering pressure and preferentially oriented with their basal surfaces perpendicular to the sintering pressure direction,forming textured microstructures with the c-axis of h-BN grains oriented parallel to the sintering pressure direction,which give these composite ceramics anisotropy in their mechanical and thermal properties.The highest texture degree was found in the specimen with 30 wt%YAG,which also possesses the highest anisotropy degree in thermal conductivity.The aggregation of YAG phase was observed in the specimen with 40 wt%YAG,which resulted in the buckling of h-BN plates and significantly reduced the texture degree.展开更多
The in situ nano Ta_(4)HfC_(5) reinforced SiBCN-Ta_(4)HfC_(5) composite ceramics were prepared by a combination of two-step mechanical alloying and reactive hot-pressing sintering.The microstructural evolution and mec...The in situ nano Ta_(4)HfC_(5) reinforced SiBCN-Ta_(4)HfC_(5) composite ceramics were prepared by a combination of two-step mechanical alloying and reactive hot-pressing sintering.The microstructural evolution and mechanical properties of the resulting SiBCN-Ta_(4)HfC_(5) were studied.After the first-step milling of 30 h,the raw materials of TaC and HfC underwent crushing,cold sintering,and short-range interdiffusion to finally obtain the high pure nano Ta_(4)HfC_(5).A hybrid structure of amorphous SiBCN and nano Ta_(4)HfC_(5) was obtained by adopting a second-step ball-milling.After reactive hot-pressing sintering,amorphous SiBCN has crystallized to 3C-SiC,6H-SiC,and turbostratic BN(C)phases and Ta_(4)HfC_(5) retained the form of the nanostructure.With the in situ generations of 2.5 wt% Ta_(4)HfC_(5),Ta_(4)HfC_(5) is preferentially distributed within the turbostratic BN(C);however,as Ta_(4)HfC_(5) content further raised to 10 wt%,it mainly distributed in the grain-boundary of BN(C) and SiC.The introduction of Ta_(4)HfC_(5) nanocrystals can effectively improve the flexural strength and fracture toughness of SiBCN ceramics,reaching to 344.1 MPa and 4.52 MPa·m^(1/2),respectively.This work has solved the problems of uneven distribution of ultra-high temperature phases in the ceramic matrix,which is beneficial to the real applications of SiBCN ceramics.展开更多
基金National Natural Science Foundation of China(Grant Nos.51872063,51832002 and 51621091)the Natural Science Foundation of Heilongjiang Province(Grant No.YQ2019E002)the National Key Research and Development Program of China(Grant No.2017YFB0703200)。
文摘Geopolymers are an important class of materials with potential applications because of their heat resistance,flame resistance,environmental friendliness,and possibilities of being transformed into ceramic matrix composites at low cost.However,the low mechanical properties as well as the intrinsic brittleness limit their technological implementations,and it is necessary to enhance the mechanical properties of geopolymers by adopting various kinds of reinforcements.In this work,therefore,two⁃dimensional continuous carbon fiber(Cf)reinforced phosphate⁃based geopolymer composites(Cf/geopolymer)were prepared through ultrasonic⁃assisted impregnation method.Effects of acetone treatment and high⁃temperature treatment on the properties of Cf/geopolymer composites were studied by X⁃ray photoelectron spectroscopy(XPS),X⁃ray diffraction(XRD),and scanning electron microscopy(SEM).Results of the study proved that acetone treatment plays a key role in ameliorating the interfacial interaction between Cf and phosphate matrix,which can thus enhance the mechanical properties of Cf/geopolymer composites.The Cf/geopolymer composites prepared by acetone⁃treated Cf had a flexural strength of 156.1 MPa and an elastic modulus of 39.7 GPa in Y direction.Moreover,an additional Sol⁃SiO2 re⁃impregnation treatment could further enhance the mechanical properties of the acetone⁃treated Cf/geopolymer composites by repairing the cracks and filling the pores.The results in this paper not only provide insights into the surface modification of Cf,but also report a facile and low⁃cost preparation route for Cf/geopolymer composites with potential applications in aerospace and defense technology.
文摘A novel composite ceramics with excellen mechanical and dielectric properties was fabricated by means of low temperature hot-pressing using mechanically alloyed SiBON powders as raw materials.The influences of SiO_2 content on phase microstructure,mechanical and dielectric properties of the SiBON ceramics were investigated.
文摘The fully dense amorphous Si-B-C-N monoliths were fabricated at 1000°-1600°C under5 GPa for 30 min where the mechanically alloyed amorphous Si-B-C-N powders were used as raw material.Crystallization and microstructure evolution of the prepared ceramics were
基金supported by the National Natural Science Foundation of China(Nos.U20A20214 and 62275067)。
文摘We demonstrate a high power,Er:Lu AG single-longitudinal-mode laser in an anti-misaligned resonator.Based on the Faraday effect,a 1.61 W single-longitudinal-mode(SLM)laser is obtained with the double corner-cube-retroreflector(CCR)structure,and the tunable wavelength is 1649.2-1650.3 nm.Additionally,we investigate the anti-misalignment characteristics when the CCR moves and rotates along the optical axis.Furthermore,by utilizing the Er:Lu AG amplifier,the maximum 2.32 W single-longitudinal-mode laser at 1649.6 nm is achieved.The beam quality factors M^(2) of the 2.32 W Er:Lu AG single-longitudinal-mode laser are 1.23 and 1.25 along the horizontal(x)and vertical(y)directions,respectively.
基金support from the National Natural Science Foundation of China(Nos.52072090 and 51872063)the Heilongjiang Touyan Innovation Team Program and the Natural Science Foundation of Heilongjiang Province(No.YQ2019E002)the Advanced Talents Scientific Research Foundation of Shenzhen:Yu Zhou,and the Sichuan Provincial Science and Technology Program Project(No.21SYSX0170).
文摘Over time,natural materials have evolved to be lightweight,high-strength,tough,and damage-tolerant due to their unique biological structures.Therefore,combining biological inspiration and structural design would provide traditional materials with a broader range of performance and applications.Here,the application of an ink-based three-dimensional(3D)printing strategy to the structural design of a Lunar regolith simulant-based geopolymer(HIT-LRS-1 GP)was first reported,and high-precision carbon fiber/quartz sand-reinforced biomimetic patterns inspired by the cellular sandwich structure of plant stems were fabricated.This study demonstrated how different cellular sandwich structures can balance the structure–property relationship and how to achieve unprecedented damage tolerance for a geopolymer composite.The results presented that components based on these biomimetic architectures exhibited stable non-catastrophic fracture characteristics regardless of the compression direction,and each structure possessed effective damage tolerance and anisotropy of mechanical properties.The results showed that the compressive strengths of honeycomb sandwich patterns,triangular sandwich patterns,wave sandwich patterns,and rectangular sandwich patterns in the Y-axis(Z-axis)direction were 15.6,17.9,11.3,and 20.1 MPa(46.7,26.5,23.8,and 34.4 MPa),respectively,and the maximum fracture strain corresponding to the above four structures could reach 10.2%,6.7%,5.8%,and 5.9%(12.1%,13.7%,13.6%,and 13.9%),respectively.
文摘A high-energy,alignment-insensitive,injection-seeded Q-switched Ho:yttrium aluminum garnet(YAG)singlefrequency laser is developed.Both the slave Q-switched laser and the seed laser are Ho:YAG ring lasers based on a pair of corner cubic reflectors.The seed laser has an available power of 830 mW at 2096.667 nm.At 100 Hz,the Q-switched Ho:YAG laser provides a single-frequency pulsed output using injection-seeded technology.The 7.3 mJ single-frequency pulse energy from the slave laser has a pulse width of 161.2 ns and is scaled to 33.3 mJ after passing through the Ho:YAG single-pass amplifier.According to the measurement results of the heterodyne beating technique,the single-frequency pulse has a half-width of 4.12 MHz.
基金supported by the National Key R&D Program of China (No. 2017YFB0703200)the National Natural Science Foundation of China (Nos. 51672060, 51621091, and 51372050)
文摘Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth(TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented.
基金the National Natural Science Foundation of China(Nos.51072041,50902031 and 51021002)the National Science Foundation for Distinguished Young Scholars of China(No.51225203).
文摘In the past twenty years,Si-B-C-N ceramic has attracted wide attention due to its special structure and outstanding properties.The ceramic generally has an amorphous or a nano-crystalline structure,and has excellent structural stability,oxidation resistance,creep resistance and high-temperature mechanical properties,etc.Thus,Si-B-C-N ceramic attracts many researchers and finds potential applications in transportation,aerocraft,energy,information,microelectronics and environment,etc.Much work has been carried out on its raw materials,preparation processes,structural evolution,phase equilibrium and high-temperature properties.In recent years,many researchers focus on its new preparation methods,the preparation of dense ceramic sample with large dimensions,ceramic matrix composites reinforced by carbon fiber or SiC whisker,or components with various applications.Research on Si-B-C-N ceramic will develop our insight into the relationship between structures and properties of ceramics,and will be helpful to the development of novel high-performance ceramics.This paper reviews the preparation processes,general microstructures,mechanical,chemical,electrical and optical properties,and potential applications of Si-B-C-N ceramic,as well as its matrix composites.
基金This study was financially supported by the National Key Research and Development Program of China(No.2017YFB0310400)the National Natural Science Foundation of China(Nos.52072089,51672060,and 51832002).
文摘BN/La-Al-Si-O composite ceramics were fabricated by hot-pressed sintering using hexagonal boron nitride(h-BN),lanthanum oxide(La_(2)O_(3)),aluminia(Al_(2)O_(3)),and amorphous silica(SiO_(2))as the raw materials.The effects of sintering temperature on microstructural evolution,bulk density,apparent porosity,and mechanical properties of the h-BN composite ceramics were investigated.The results indicated that La-Al-Si-O liquid phase was formed during sintering process,which provided an environment for the growth of h-BN grains.With increasing sintering temperature,the cristobalite phase precipitation and h-BN grain growth occurred at the same time,which had a significant influence on the densification and mechanical properties of h-BN composite ceramics.The best mechanical properties of BN/La-Al-Si-O composite ceramics were obtained under the sintering temperature of 1700℃.The elastic modulus,flexural strength,and fracture toughness were 80.5 GPa,266.4 MPa,and 3.25 MPa·m^(1/2),respectively.
基金National Natural Science Foundation of China(NSFC)(61378029,61775053,51572053,51777046)Science Foundation for Outstanding Youths of Heilongjiang Province(JC2016016)Science Foundation for Youths of Heilongjiang Province(QC2017078)
文摘The active/passive Q-switching operation of a 2 [tm a-cut Tm,Ho：YAP laser was experimentally demonstrated with an acousto-optical Q-switch/MoS2 saturable absorber mirror. The active Q-switch laser was operated for the first time, to the best of our knowledge, with an average output power of 12.3 W and a maximum pulse energy of 10.3 mJ. The passive Q-switch laser was also the first acquired with an average output power of 3.3 W and per pulse energy of 23.31 μJ, and the beam quality factors of Mx^2 = 1.06 and My^2 = 1.06 were measured at the average output power of 2 W.
基金supported by the National Natural Science Funds for Distinguished Young Scholar of China under Grant No.51225203supported by the National Natural Science Foundation of China under Grant Nos.51072041,50902031 and 51021002.
文摘SiC fiber reinforced SiBCN ceramic matrix composites(CMCs)have been prepared by mechanical alloying and consolidated by hot pressing.During the sintering process,amorphous SiC fibers crystallized seriously and transformed into-SiC.Meanwhile,the interfacial carbothermal reactions caused the strong bonding between the matrix and fibers.As a result,SiCf/SiBCN fractured in a typical catastrophic manner.Room-temperature mechanical properties reached the maximums for the CMC samples sintered at 1900℃/60 MPa/30 min.The density,flexural strength,Young’s modulus and fracture toughness are 2.56±0.02 g/cm^(3),284.3±17.9 MPa,183.5±11.1 GPa and 2.78±0.14 MPa·m^(1/2),respectively.
基金This work was supported by the National Natural Science Foundation of China(NSFC)(Nos.51772060,51372052,51672059,51621091,and 51902102)Natural Science Foundation of Hunan Province(No.2020JJ5042)Postdoctoral Science Foundation of China(No.2020M672478).
文摘CoCO_(3) with high theoretical capacity has been considered as a candidate anode for the next generation of lithium-ion batteries(LIBs).However,the electrochemical performance of CoCO_(3) itself,especially the cyclic stability at high current density,hinders its application.Herein,pure phase CoCO_(3) particles with different particle and pore sizes were prepared by adjusting the solvents(diethylene glycol,ethylene glycol,and deionized water).Among them,CoCO_(3) synthesized with diethylene glycol(DG-CC)as the solvent shows the best electrochemical performance owing to the smaller particle size and abundant mesoporous structure to maintain robust structural stability.A high specific capacity of 690.7 mAh/g after 1000 cycles was achieved,and an excellent capacity retention was presented.The capacity was contributed by diverse electrochemical reactions and the impedance of DG-CC under different cycles was further compared.Those results provide an important reference for the structural design and stable cycle performance of pure CoCO_(3).
基金the National Natural Science Foundation of China(51621091,51225203,and 51672060)the National Key Research and Development Program of China(2017YFB0310400)。
文摘The thermal expansion coefficient(TEC)and thermal conductivity(k)of thermal fillers are key factors for designing thermal management and thermal protection composite materials.Due to its unique advantages,hexagonal boron nitride(h-BN)is one of the most commonly used thermal fillers.However,its TEC and k values are still unclear due to the inconsistency of characterization techniques and sample preparations.In this work,these disputes were addressed using the quasi-harmonic approximation(QHA)method and phonon Boltzmann transport equation(BTE)theory based on the density functional theory(DFT),respectively.The accuracy of our calculated TEC and k values was confirmed by previously reported experimental results,and the underlying physical principles were analyzed from the phonon behaviors.Our TEC results show that the h-BN has small in-plane negative value and large cross-plane positive value,which are-2.4×10^(-6) and 36.4×10^(-6) K^(-1) at 300 K,respectively.And the anisotropic TEC is mainly determined by the anisotropic isothermal bulk modulus and the low-frequency out-of-plane longitudinal phonon modes.We found that the convergence of cutoff radius and q-grid size have significant effect on the accuracy of k of h-BN.Our results show that the in-plane k is much higher than the cross-plane k,and the values at 300 K are 286.6 and 2.7 W m^(-1) K^(-1),respectively.The anisotropic phonon group velocity arising from the vibration behaviors of acoustic phonon modes should be primarily responsible for the anisotropic k.Our calculated TEC and k values will provide important references for the design of h-BN composite materials.
基金This work was supported by the National Natural Science Foundation of China(NFSC)(Nos.61805209 and 51572053).
文摘We demonstrated a high-power long-wave infrared laser based on a polarization beam coupling technique.An average output power at 8.3µm of 7.0 W was achieved at a maximum available pump power of 107.6 W,corresponding to an optical-to-optical conversion of 6.5%.The coupling efficiency of the polarization coupling system was calculated to be approximately 97.2%.With idler single resonance operation,a good beam quality factor of^1.8 combined with an output wavelength of 8.3µm was obtained at the maximum output power.
基金supported by the National Natural Science Foundation of China(No.U20A20214)。
文摘We demonstrated a 202 W Tm:YLF slab laser using a reflecting volume Bragg grating(VBG)as an output coupler at room temperature.Two kinds of active heat dissipation methods were used for the VBG to suppress the shift of wavelength caused by its increasing temperature.The maximum continuous wave(CW)output power of 202 W using the microchannel cooling was obtained under the total incident pump power of 553 W,the corresponding slope efficiency and optical-to-optical conversion efficiency were 39.7%and 36.5%,respectively.The central wavelength was 1908.5 nm with the linewidth(full width at half maximum)of 0.57 nm.Meanwhile,with the laser output increasing from 30 to 202 W,the total shift was about 1.0 nm,and the wavelength was limited to two water absorption lines near 1908 nm.The beam quality factors M;were measured to be 2.3 and 4.0 in x and y directions at 202 W.
基金This work was supported by the National Natural Science Foundation of China(Nos.52072089,51832002,51602074,and 51672060)the Heilongjiang Touyan Team Program.
文摘Textured hexagonal boron nitride(h-BN)matrix composite ceramics were prepared by hotpressing using different contents of 3Y_(2)O_(3)–5Al_(2)O_(3)(molar ratio of 3:5)as the sintering additive.During hot-pressing,the liquid Y_(3)Al_(5)O_(12)(YAG)phase showing good wettability to h-BN grains was in situ formed through the reaction between Y_(2)O_(3) and Al_(2)O_(3),and a coherent relationship between h-BN and YAG was observed with[010]_(h-BN)//[111]_(YAG) and(002)_(h-BN)//(321)_(YAG).In the YAG liquid phase environment formed during hot-pressing,plate-like h-BN grains were rotated under the uniaxial sintering pressure and preferentially oriented with their basal surfaces perpendicular to the sintering pressure direction,forming textured microstructures with the c-axis of h-BN grains oriented parallel to the sintering pressure direction,which give these composite ceramics anisotropy in their mechanical and thermal properties.The highest texture degree was found in the specimen with 30 wt%YAG,which also possesses the highest anisotropy degree in thermal conductivity.The aggregation of YAG phase was observed in the specimen with 40 wt%YAG,which resulted in the buckling of h-BN plates and significantly reduced the texture degree.
基金the financial support from the National Natural Science Foundation of China(52002092,51621091,51472059,51225203,and 51272300)the National Key Research and Development Program(2017YFB0310400)+2 种基金the Postdoctoral Innovative Talents Support Program(BX20190095)the China Postdoctoral Science Foundation(Grant Nos.LBH-Z19141 and 2019M660072)funded by Advanced Space Propulsion Laboratory of BICE and Beijing Engineering Research center of Efficient and Green Aerospace Propulsion Technology(No.LabASP-2019-08).
文摘The in situ nano Ta_(4)HfC_(5) reinforced SiBCN-Ta_(4)HfC_(5) composite ceramics were prepared by a combination of two-step mechanical alloying and reactive hot-pressing sintering.The microstructural evolution and mechanical properties of the resulting SiBCN-Ta_(4)HfC_(5) were studied.After the first-step milling of 30 h,the raw materials of TaC and HfC underwent crushing,cold sintering,and short-range interdiffusion to finally obtain the high pure nano Ta_(4)HfC_(5).A hybrid structure of amorphous SiBCN and nano Ta_(4)HfC_(5) was obtained by adopting a second-step ball-milling.After reactive hot-pressing sintering,amorphous SiBCN has crystallized to 3C-SiC,6H-SiC,and turbostratic BN(C)phases and Ta_(4)HfC_(5) retained the form of the nanostructure.With the in situ generations of 2.5 wt% Ta_(4)HfC_(5),Ta_(4)HfC_(5) is preferentially distributed within the turbostratic BN(C);however,as Ta_(4)HfC_(5) content further raised to 10 wt%,it mainly distributed in the grain-boundary of BN(C) and SiC.The introduction of Ta_(4)HfC_(5) nanocrystals can effectively improve the flexural strength and fracture toughness of SiBCN ceramics,reaching to 344.1 MPa and 4.52 MPa·m^(1/2),respectively.This work has solved the problems of uneven distribution of ultra-high temperature phases in the ceramic matrix,which is beneficial to the real applications of SiBCN ceramics.
