Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the ...Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the main chain and fabricate HfC_(x)N_(1-x)ceramics after pyrolysis of the precursor.The synthesis,ceramic conversion,and microstructural evolution of the single-source precursor as well as the derived HfC_(x)N_(1-x)ceramics treated under various atmospheres were investigated.The results indicate that in an argon atmosphere,the nitrogen content within HfC_(x)N_(1-x)decreases with rising temperature.While under a nitrogen atmosphere,the high concentration of N_(2)facilitates the rapid conversion of HfO2 to Hf7O8N4,which subsequently promotes the transformation of the HfC_(x)N_(1-x)solid solution ceramics.During this process,there is also an inhibitory effect of N_(2)on the tendency of HfN into HfC.Moreover,the desired chemical composition of HfC_(x)N_(1-x)can be regulated by adjusting the N_(2)concentration in the heat treat-ment atmosphere.The present work proposes a novel strategy for the single-source precursor-derived carbonitride ceramics and provides a deep understanding of the preparation and property modulation of HfC_(x)N_(1-x)ceramics.展开更多
Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interact...Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interactions among the constituent nanoparticles,coupled with the limited toughness of traditional CAs,make them susceptible to structural collapse or even catastrophic failure when exposed to complex mechanical external forces.Unlike 0D building units,1D ceramic nanofibers(CNFs)possess a high aspect ratio and exceptional flexibility simultaneously,which are desirable building blocks for elastic CAs.This review presents the recent progress in electrospun ceramic nanofibrous aerogels(ECNFAs)that are constructed using ECNFs as building blocks,focusing on the various preparation methods and corresponding structural characteristics,strategies for optimizing mechanical performance,and a wide range of applications.The methods for preparing ECNFs and ECNFAs with diverse structures were initially explored,followed by the implementation of optimization strategies for enhancing ECNFAs,emphasizing the improvement of reinforcing the ECNFs,establishing the bonding effects between ECNFs,and designing the aggregate structures of the aerogels.Moreover,the applications of ECNFAs across various fields are also discussed.Finally,it highlights the existing challenges and potential opportunities for ECNFAs to achieve superior properties and realize promising prospects.展开更多
Ceramic thin plates were prepared using kaolin,potassium sodium feldspar and quartz powder as the main raw materials and kaolin,α-Al_(2)O_(3),MoO_(3) and AlF_(3)·3H_(2)O as additives.The experiment examined the ...Ceramic thin plates were prepared using kaolin,potassium sodium feldspar and quartz powder as the main raw materials and kaolin,α-Al_(2)O_(3),MoO_(3) and AlF_(3)·3H_(2)O as additives.The experiment examined the effects of different additives on mullite formation,as well as the microstructure and properties of the ceramic thin plates.Additionally,the study explored the toughening and strengthening mechanisms induced by the additives,providing a theoretical foundation for further optimizing the toughness of ceramic thin plates.The results showed that the D4 sample fired at 1220℃(with an addition of 20 wt% α-Al_(2)O_(3))exhibited the best performance,with a water absorption rate of 0.07%,apparent porosity of 0.18%,bulk density of 2.75 g·cm^(-3),firing shrinkage of 12.76%,bending strength reaching 101.93 MPa,and fracture toughness of 2.51 MPa·m^(1/2).As the amount ofα-Al_(2)O_(3) additive increased,the ceramic thin plates exhibited a greater abundance of short rod-like mullite and corundum grains,which were tightly packed together,forming a framework for the ceramic thin plates.This microstructure enhanced pathways for crack propagation,dispersed internal stresses,and increased fracture surface energy,resulting in significant improvements in both strength and fracture toughness of the ceramic thin plates.展开更多
(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperatu...(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.展开更多
In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of co...In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.展开更多
In this study,the design,analysis,manufacturing,and testing of a 3D-printed conformal microstrip array antenna for high-temperature environments is presented.3D printing technology is used to fabricate a curved cerami...In this study,the design,analysis,manufacturing,and testing of a 3D-printed conformal microstrip array antenna for high-temperature environments is presented.3D printing technology is used to fabricate a curved ceramic substrate,and laser sintering and microdroplet spraying processes are used to add the conductive metal on the curved substrate.The problems of gain loss,bandwidth reduction,and frequency shift caused by high temperatures are addressed by using a proper antenna design,with parasitic patches,slots,and metal resonant cavities.The antenna prototype is characterized by the curved substrates and the conductive metals for the power dividers,the patch,and the ground plane;its performance is examined up to a temperature of 600℃in a muffle furnace and compared with the results from the numerical analysis.The results show that the antenna can effectively function at 600℃and even higher temperatures.展开更多
Some active metal oxides(Al_(2)O_(3),TiO_(2),and Cr_(2)O_(3))were selected as dopants to the Al_(2)O_(3)-based ceramic shells for investment casting of K417G superalloy.The effects of dopant types and contents(0,2,5,a...Some active metal oxides(Al_(2)O_(3),TiO_(2),and Cr_(2)O_(3))were selected as dopants to the Al_(2)O_(3)-based ceramic shells for investment casting of K417G superalloy.The effects of dopant types and contents(0,2,5,and 8 wt.%)on the wettability and interfacial reaction between the alloy and shell were investigated by a sessile-drop experiment.The results show that increasing the Al_(2)O_(3) doping contents(0−8 wt.%)reduces the porosity(21.74%−10.08%)and roughness(3.22−1.34μm)of the shell surface.The increase in Cr_(2)O_(3) dopant content(2−8 wt.%)further exacerbates the interfacial reaction,leading to an increase in the thickness of the reaction layer(2.6−3.1μm)and a decrease in the wetting angle(93.9°−91.0°).The addition of Al_(2)O_(3) and TiO_(2) dopants leads to the formation of Al_(2)TiO_(5) composite oxides in the reaction products,which effectively inhibits the interfacial reaction.The increase in TiO_(2) dopant contents(0−8 wt.%)further promotes the formation of Al_(2)TiO_(5),which decreases the thickness of the interfacial reaction layer(3.9−1.2μm)and increases the wetting angle(95.0°−103.8°).The introduced dopants enhance the packing density of the shell surface,while simultaneously suppress the diffusion of active metal elements from the alloy matrix to the interface.展开更多
Two polyborosiloxanes （PBSis） with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeati...Two polyborosiloxanes （PBSis） with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as ^1H-, ^29Si- and ^11B-NMR. PBSi modified phenol-formaldehyde resins （PBSi/PFs） were prepared at different PBSi/PF mass ratios and were cured at 150 ℃. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4：1 had char yield up to 70.83% at 800 ℃. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide （SiBOC） ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.展开更多
Electromagnetic(EM)wave-absorbing materials with high-temperature-resistance are urgently desirable to eliminate EM interference in extreme conditions.Precursor derived ceramics(PDC)route is being evolved as an effect...Electromagnetic(EM)wave-absorbing materials with high-temperature-resistance are urgently desirable to eliminate EM interference in extreme conditions.Precursor derived ceramics(PDC)route is being evolved as an effective strategy to solve the puzzle.Herein,a single source hyperbranched polyborosi-lazane precursor containing hafnium(hb-PBSZ-Hf)is introduced and the SiBCNHf ceramic is obtained by further pyrolysis.The micro-sized tissues including HfC,SiC,HfB 2 nanocrystals and segregated carbons are in situ generated during annealing which not only increase EM wave absorption ability(minimum re-flection coefficient(RC_(min))is-56.71 dB with a thickness of 2.5 mm,effective absorption bandwidth(EAB)is 3.4 GHz),but also improve antioxidation property(less than 2 wt.%mass fluctuation at 1400℃in air).Theoretical simulation of complex permittivity suggests that SiBCNHf ceramic has an RC_(min)of less than-5 dB for the whole X-band even at 1100℃.Such SiBCNHf ceramic with superior high-temperature-resistance and antioxidation performance derived from single source precursors possesses great potential for EM wave absorbing coatings in high-temperature and harsh environments.展开更多
Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after ther...Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after thermolysis specimens were heat treated at a temperature of 1400℃ for 10 h in nitrogen atmosphere. The thermal expansion coefficient of VT50-derived amorphous Si-C-N ceramic increases from 1.98×10-6/K at 400℃ to 3.09×10-6/K at 1000℃, of NCP200-derived amorphous Si-C-N ceramic increases from 2.35×10-6/K at 400℃ to 3.45×10-6/K at 1000℃, and of T2-l-derived amorphous Si-B-C-N ceramic increases from 2.08×10-6/K at 400℃ to 3.18×10-6/K at 1000℃. No glass transition for these amorphous ceramic materials was detected, indicating that as-thermolyzed precursor-derived Si-(B-)C-N ceramic materials are amorphous solids, but not glasses.展开更多
A machinable Y TZP/LaPO 4 composite ceramic was prepared by infiltrating LaPO 4 liquid precursor into Y TZP porous ceramic. Sintered Y TZP ceramic preformed with 35% (volume fraction) open pore volume was made by...A machinable Y TZP/LaPO 4 composite ceramic was prepared by infiltrating LaPO 4 liquid precursor into Y TZP porous ceramic. Sintered Y TZP ceramic preformed with 35% (volume fraction) open pore volume was made by adding graphite (30%, volume fraction). The Y TZP/LaPO 4 composite ceramics containing different LaPO 4 contents were obtained by infiltration and pyrolysis cycles. The machinability and mechanical properties of materials were investigated. The results show that the machinable Y TZP/LaPO 4 composite ceramics containing 2 3% to 7.5% (volume fraction) LaPO 4 has good machinability as well as outstanding mechanical properties.展开更多
Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy(TEM) combined with spatially-resolved e...Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy(TEM) combined with spatially-resolved electron energy-loss spectroscopy(EELS) analysis. The ceramics were pyrolyzed at1000℃ followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200℃ and dominate at 1500℃. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5 nm at 1400℃. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCxand Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400℃. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCxlayers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.展开更多
The deposition rate, phase, chemical composition and microstructure of deposits were determined from 950 to 1100 ℃. With increasing temperature, the deposition rate increases, and the morphology changes from smooth t...The deposition rate, phase, chemical composition and microstructure of deposits were determined from 950 to 1100 ℃. With increasing temperature, the deposition rate increases, and the morphology changes from smooth to coarse, meanwhile, the concentration of silicon increases while that of boron decreases. The deposition process is controlled by chemical reactions, and the activation energy is 271 kJ/mol. At relatively lower temperature （below 1000 ℃）, the deposition process is dominated by formation of BaC. While at higher temperature （above 1000 ℃）, it is governed by formation of SiC. BaC and SiC disperse uniformly in the Si-B-C co-deposition system and form a dense network structure.展开更多
In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymer...In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.展开更多
We report the laser output of transparent Nd：YAG （Nd：Y3Al5O12） ceramics fabricated from Nd：YAG precursors through the microwave-assisted homogenous precipitation （MAHP） method. Pure phase and uniform Nd：YAG na...We report the laser output of transparent Nd：YAG （Nd：Y3Al5O12） ceramics fabricated from Nd：YAG precursors through the microwave-assisted homogenous precipitation （MAHP） method. Pure phase and uniform Nd：YAG nano-powders with average sizes less than 100 nm were obtained by heating treatment of.the Nd：YAG precursor particles aged for 6 d in vessel with humidity of 30%-50% at 25℃. Transparent Nd：YAG ceramic pellets were obtained by vacuum sintering at 1730℃ for 10 h. Laser output （305 roW） with a slope efficiency of 5.1% was realized through an end-pumped configuration. Our results indicate that the MAHP method could potentially be used for the fabrication of laser ceramic products,展开更多
Polyaluminocarbosilane（PACS） was synthesized by the reaction of aluminum acetylacetonate（（Al（AcAc）3）） with polysilacarbosilane （PSCS）, which was prepared by thermolysis and condensation of polydimethylsilane...Polyaluminocarbosilane（PACS） was synthesized by the reaction of aluminum acetylacetonate（（Al（AcAc）3）） with polysilacarbosilane （PSCS）, which was prepared by thermolysis and condensation of polydimethylsilane （PDMS）. The sublimation of Al（AcAc）3 could be avoided by the use of PSCS as reactant. The empirical formula of PACS was SiC2.01H7.66O0.13Al0.02, which has the relative molecular mass of 2 265. When the reaction of PSCS with Al（AcAc）3 proceeds, an enormous decrease in the number of Si—H bonds in PSCS is observed, at the same time, gas acetylacetonate is a by-product of the reaction based on the ligands of Al（AcAc）3. The reaction mechanism is found to be related to the increase in the molecular mass of PACS by the cross-linking reaction of （Si—H） bonds in PSCS with Al（AcAc）3, which leads to the formation of Si—Al bonds.展开更多
A new kind of polytitanosilazane precursor PTSZ for Si/C/N/Ti-based ceramic was synthesized from the condensation reaction of silazane lithium salt and titanium tetrachloride (TiCl4). The results indicated that the c...A new kind of polytitanosilazane precursor PTSZ for Si/C/N/Ti-based ceramic was synthesized from the condensation reaction of silazane lithium salt and titanium tetrachloride (TiCl4). The results indicated that the ceramic yield of PTSZ was much higher than that of corresponding silazane oligomer.展开更多
Three new borazine derivatives,2,4,6-tri（allylamino）borazine （CH 2 =CHCH 2 NHBNH） 3 （1）,2,4,6-tri（3ethynylanilino）borazine （CH≡CC 6 H 4 NHBNH） 3 （2）,and 2,4,6-tri（4-propargyl oxyanilino）borazine （CH≡ ...Three new borazine derivatives,2,4,6-tri（allylamino）borazine （CH 2 =CHCH 2 NHBNH） 3 （1）,2,4,6-tri（3ethynylanilino）borazine （CH≡CC 6 H 4 NHBNH） 3 （2）,and 2,4,6-tri（4-propargyl oxyanilino）borazine （CH≡ CCH 2 OC 6 H 4 NHBNH） 3 （3） were synthesized by reaction of 2,4,6-trichloro-borazine Cl 3 B 3 N 3 H 3 （TCB） with corresponding primary amines,respectively.Their thermal behavior was studied by differential scanning calorimetry （DSC） and thermogravimetric analysis （TGA）.These molecules were easily crosslinked via thermal polymerization of reactive ethynyl or vinyl groups.The pyrolytic residues of borazines were investigated by X-ray photoelectron spectroscopy （XPS）,powder X-ray diffraction （XRD）,and scanning electron microscopy （SEM）.The analytic results indicated that B-C-N ceramics were formed upon pyrolysis of the borazines under an inert atmosphere.展开更多
A new kind of organometallic precursor for Si/Zr/C/N-based ceramics was synthesized from the amine exchangereaction of hexamethylcyclotrisilazane (D_3~N) and tetrakis(diethylamino) zirconium (Zr[NEt_2]_4). Pyrolysis w...A new kind of organometallic precursor for Si/Zr/C/N-based ceramics was synthesized from the amine exchangereaction of hexamethylcyclotrisilazane (D_3~N) and tetrakis(diethylamino) zirconium (Zr[NEt_2]_4). Pyrolysis was performedunder nitrogen at 800℃ in a tube furnace equipped with a temperature program controller. The highest pyrolytic yield was67.5%.展开更多
In the present work,novel NbC-SiC-C ceramic nanocomposite powders were successfully synthesized by a polymer-derived ceramic approach with the allylhydridopolycarbosilane(AHPCS)and niobium pentachloride(NbCl5)as start...In the present work,novel NbC-SiC-C ceramic nanocomposite powders were successfully synthesized by a polymer-derived ceramic approach with the allylhydridopolycarbosilane(AHPCS)and niobium pentachloride(NbCl5)as starting materials.A single-source-precursor was first synthesized by chemical reaction between AHPCS and NbCl5 and then pyrolyzed at 900℃ to obtain amorphous ceramic powders.After further annealing amorphous ceramics at higher temperatures in the range of 1100-1500℃,the NbC-SiC-C ceramic nanocomposite powders were finally obtained.The single-source-precursor synthesis and polymer-to-ceramic transformation were characterized by Fourier transform infrared spectra(FT-IR)and thermal gravimetric analysis(TGA).The phase evolution of resulting ceramics was investigated by X-ray diffraction(XRD)and transmission electron microscopy(TEM).Interestingly,both the NbC@C and SiC@C core−shell structured nanoparticles were in-situ formed at 1300℃ to form NbC-SiC-C ceramic nanocomposites.With the highest NbCl5 content in the feed,the contents of NbC andβ-SiC obtained by Rietveld refinement of the XRD patterns from the 1500℃ ceramics are 68.41wt.%and 31.59wt.%,respectively,indicating that the ultra-high temperature resistant NbC is the main phase.In general,the resultant NbC-SiC-C nanocomposite with NbC as main phase can be considered as candidate material for structure−function integrated applications in harsh environment.展开更多
基金supported by the National Key R&D Program of China(Grant No.2021YFA0715803)the National Natural Science Foundation of China(Grant Nos.52293373 and 52130205)+3 种基金the Special Funds of the National Natural Science Foun-dation of China(Grant No.52342207)the National Science and Technology Major Project(Grant No.J2022-VI-0011-0042)the Joint Fund of Henan Province Science and Technology R&D Program(Grant No.225200810002)the Research Foundation of the Science and Technology on Thermostructural Composite Materials Laboratory(Grant No.JCKYS2024607001-1).
文摘Hafnium carbonitride(HfC_(x)N_(1-x))ceramics have drawn considerable interest due to their exceptional me-chanical and thermophysical properties.Herein,we report a novel single-source precursor with Hf-N bonds as the main chain and fabricate HfC_(x)N_(1-x)ceramics after pyrolysis of the precursor.The synthesis,ceramic conversion,and microstructural evolution of the single-source precursor as well as the derived HfC_(x)N_(1-x)ceramics treated under various atmospheres were investigated.The results indicate that in an argon atmosphere,the nitrogen content within HfC_(x)N_(1-x)decreases with rising temperature.While under a nitrogen atmosphere,the high concentration of N_(2)facilitates the rapid conversion of HfO2 to Hf7O8N4,which subsequently promotes the transformation of the HfC_(x)N_(1-x)solid solution ceramics.During this process,there is also an inhibitory effect of N_(2)on the tendency of HfN into HfC.Moreover,the desired chemical composition of HfC_(x)N_(1-x)can be regulated by adjusting the N_(2)concentration in the heat treat-ment atmosphere.The present work proposes a novel strategy for the single-source precursor-derived carbonitride ceramics and provides a deep understanding of the preparation and property modulation of HfC_(x)N_(1-x)ceramics.
基金supported by the National Natural Science Foundation of China(Nos.92371110 and 52373281)Weiqiao Science Foundation(H2872302 and H2872303)the Scientific Research Innovation Capability Support Project for Young Faculty.
文摘Ceramic aerogels(CAs)have emerged as a significant research frontier across various applications due to their lightweight,high porosity,and easily tunable structural characteristics.However,the intrinsic weak interactions among the constituent nanoparticles,coupled with the limited toughness of traditional CAs,make them susceptible to structural collapse or even catastrophic failure when exposed to complex mechanical external forces.Unlike 0D building units,1D ceramic nanofibers(CNFs)possess a high aspect ratio and exceptional flexibility simultaneously,which are desirable building blocks for elastic CAs.This review presents the recent progress in electrospun ceramic nanofibrous aerogels(ECNFAs)that are constructed using ECNFs as building blocks,focusing on the various preparation methods and corresponding structural characteristics,strategies for optimizing mechanical performance,and a wide range of applications.The methods for preparing ECNFs and ECNFAs with diverse structures were initially explored,followed by the implementation of optimization strategies for enhancing ECNFAs,emphasizing the improvement of reinforcing the ECNFs,establishing the bonding effects between ECNFs,and designing the aggregate structures of the aerogels.Moreover,the applications of ECNFAs across various fields are also discussed.Finally,it highlights the existing challenges and potential opportunities for ECNFAs to achieve superior properties and realize promising prospects.
基金Funded by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2023YFB4204302)。
文摘Ceramic thin plates were prepared using kaolin,potassium sodium feldspar and quartz powder as the main raw materials and kaolin,α-Al_(2)O_(3),MoO_(3) and AlF_(3)·3H_(2)O as additives.The experiment examined the effects of different additives on mullite formation,as well as the microstructure and properties of the ceramic thin plates.Additionally,the study explored the toughening and strengthening mechanisms induced by the additives,providing a theoretical foundation for further optimizing the toughness of ceramic thin plates.The results showed that the D4 sample fired at 1220℃(with an addition of 20 wt% α-Al_(2)O_(3))exhibited the best performance,with a water absorption rate of 0.07%,apparent porosity of 0.18%,bulk density of 2.75 g·cm^(-3),firing shrinkage of 12.76%,bending strength reaching 101.93 MPa,and fracture toughness of 2.51 MPa·m^(1/2).As the amount ofα-Al_(2)O_(3) additive increased,the ceramic thin plates exhibited a greater abundance of short rod-like mullite and corundum grains,which were tightly packed together,forming a framework for the ceramic thin plates.This microstructure enhanced pathways for crack propagation,dispersed internal stresses,and increased fracture surface energy,resulting in significant improvements in both strength and fracture toughness of the ceramic thin plates.
基金supported by the National Natural Science Foundation of China(Nos.92166105 and 52005053)High-Tech Industry Science and Technology Innovation Leading Program of Hunan Province(No.2020GK2085)the Science and Technology Innovation Program of Hunan Province(No.2021RC3096).
文摘(NbZrHfTi)C high-entropy ceramics,as an emerging class of ultra-high-temperature materials,have garnered significant interest due to their unique multi-principal-element crystal structure and exceptional hightemperature properties.This study systematically investigates the mechanical properties of(NbZrHfTi)C high-entropy ceramics by employing first-principles density functional theory,combined with the Debye-Grüneisen model,to explore the variations in their thermophysical properties with temperature(0–2000 K)and pressure(0–30 GPa).Thermodynamically,the calculated mixing enthalpy and Gibbs free energy confirm the feasibility of forming a stable single-phase solid solution in(NbZrHfTi)C.The calculated results of the elastic stiffness constant indicate that the material meets the mechanical stability criteria of the cubic crystal system,further confirming the structural stability.Through evaluation of key mechanical parameters—bulk modulus,shear modulus,Young’s modulus,and Poisson’s ratio—we provide comprehensive insight into the macro-mechanical behaviour of the material and its correlation with the underlying microstructure.Notably,compared to traditional binary carbides and their average properties,(NbZrHfTi)C exhibits higher Vickers hardness(Approximately 28.5 GPa)and fracture toughness(Approximately 3.4 MPa⋅m^(1/2)),which can be primarily attributed to the lattice distortion and solid-solution strengthening mechanism.The study also utilizes the quasi-harmonic approximation method to predict the material’s thermophysical properties,including Debye temperature(initial value around 563 K),thermal expansion coefficient(approximately 8.9×10^(−6) K−1 at 2000 K),and other key parameters such as heat capacity at constant volume.The results show that within the studied pressure and temperature ranges,(NbZrHfTi)C consistently maintains a stable phase structure and good thermomechanical properties.The thermal expansion coefficient increasing with temperature,while heat capacity approaches the Dulong-Petit limit at elevated temperatures.These findings underscore the potential of(NbZrHfTi)C applications in ultra-high temperature thermal protection systems,cutting tool coatings,and nuclear structural materials.
基金supported by the Guangdong Basic and Applied Basic Research Foundation,China(No.2021B1515140007).
文摘In a rapid cycling synchrotron(RCS),the magnetic field is synchronized with the beam energy,creating a highly dynamic magnetic environment.A ceramic chamber with a shielding layer(RF shield),composed of a series of copper strips connected to a capacitor at either end,is typically employed as a vacuum chamber to mitigate eddy current effects and beam coupling impedance.Consequently,the ceramic chamber exhibits a thin-walled multilayered complex structure.Previous theoretical studies have suggested that the impedance of such a structure has a negligible impact on the beam.However,recent impedance measurements of the ceramic chamber in the China Spallation Neutron Source(CSNS)RCS revealed a resonance in the low-frequency range,which was confirmed by further theoretical analysis as a source of beam instability in the RCS.Currently,the magnitude of this impedance cannot be accurately assessed using theoretical calculations.In this study,we used the CST Microwave Studio to confirm the impedance of the ceramic chamber.Further simulations covering six different types of ceramic chambers were conducted to develop an impedance model in the RCS.Additionally,this study investigates the resonant characteristics of the ceramic chamber impedance,finding that the resonant frequency is closely related to the capacitance of the capacitors.This finding provides clear directions for further impedance optimization and is crucial for achieving a beam power of 500 kW for the CSNS Phase-Ⅱ project(CSNS-Ⅱ).However,careful attention must be paid to the voltage across the capacitors.
基金National Natural Science Foundation of china(No.U2241205)the Natural Science Basic Research Program of Shaanxi(Nos.2022JC-33,2023-GHZD-35,and 2024JC-ZDXM-25)+1 种基金the Fundamental Research Funds for the Central Universitiesthe National 111 Project to provide fund for conducting experiments。
文摘In this study,the design,analysis,manufacturing,and testing of a 3D-printed conformal microstrip array antenna for high-temperature environments is presented.3D printing technology is used to fabricate a curved ceramic substrate,and laser sintering and microdroplet spraying processes are used to add the conductive metal on the curved substrate.The problems of gain loss,bandwidth reduction,and frequency shift caused by high temperatures are addressed by using a proper antenna design,with parasitic patches,slots,and metal resonant cavities.The antenna prototype is characterized by the curved substrates and the conductive metals for the power dividers,the patch,and the ground plane;its performance is examined up to a temperature of 600℃in a muffle furnace and compared with the results from the numerical analysis.The results show that the antenna can effectively function at 600℃and even higher temperatures.
基金supported by the National Natural Science Foundation of China (No. 52374292)China Baowu Low Carbon Metallurgy Innovation Foundation, China (No. BWLCF202309)the Natural Science Foundation of Changsha City, China (No. KQ2208271)。
文摘Some active metal oxides(Al_(2)O_(3),TiO_(2),and Cr_(2)O_(3))were selected as dopants to the Al_(2)O_(3)-based ceramic shells for investment casting of K417G superalloy.The effects of dopant types and contents(0,2,5,and 8 wt.%)on the wettability and interfacial reaction between the alloy and shell were investigated by a sessile-drop experiment.The results show that increasing the Al_(2)O_(3) doping contents(0−8 wt.%)reduces the porosity(21.74%−10.08%)and roughness(3.22−1.34μm)of the shell surface.The increase in Cr_(2)O_(3) dopant content(2−8 wt.%)further exacerbates the interfacial reaction,leading to an increase in the thickness of the reaction layer(2.6−3.1μm)and a decrease in the wetting angle(93.9°−91.0°).The addition of Al_(2)O_(3) and TiO_(2) dopants leads to the formation of Al_(2)TiO_(5) composite oxides in the reaction products,which effectively inhibits the interfacial reaction.The increase in TiO_(2) dopant contents(0−8 wt.%)further promotes the formation of Al_(2)TiO_(5),which decreases the thickness of the interfacial reaction layer(3.9−1.2μm)and increases the wetting angle(95.0°−103.8°).The introduced dopants enhance the packing density of the shell surface,while simultaneously suppress the diffusion of active metal elements from the alloy matrix to the interface.
文摘Two polyborosiloxanes （PBSis） with char yield up to 74.13% at 800 ℃ were synthesized by the direct polycondensation of boric acid with phenyltrimethoxysilane in diglyme. The PBSis were characterized by gel permeation chromatography, IR spectroscopy as well as ^1H-, ^29Si- and ^11B-NMR. PBSi modified phenol-formaldehyde resins （PBSi/PFs） were prepared at different PBSi/PF mass ratios and were cured at 150 ℃. The PBSi/PFs were characterized by IR spectroscopy, scanning electron microscopy, thermogravimetric analysis and tensile test. The results revealed that the cured PBSi/PFs had sea-island morphology and higher char yield than the common PF. PBSi/PF blend with PBSi/PF mass ratio of 0.4：1 had char yield up to 70.83% at 800 ℃. The PBSi/PFs had tensile strength similar to PF. The ceramization of PBSi/PFs was also studied. The silicon boron oxycarbide （SiBOC） ceramics formed were characterized by IR spectroscopy and elemental analysis. This method provided a valuable way to prepare easily shapeable polymer blends as ceramic precursors.
基金supported by the National Science Fund for Distinguished Young Scholars(No.52025034)National Science and Technology Major Project of China(No.J2019-VI-0017-0132).
文摘Electromagnetic(EM)wave-absorbing materials with high-temperature-resistance are urgently desirable to eliminate EM interference in extreme conditions.Precursor derived ceramics(PDC)route is being evolved as an effective strategy to solve the puzzle.Herein,a single source hyperbranched polyborosi-lazane precursor containing hafnium(hb-PBSZ-Hf)is introduced and the SiBCNHf ceramic is obtained by further pyrolysis.The micro-sized tissues including HfC,SiC,HfB 2 nanocrystals and segregated carbons are in situ generated during annealing which not only increase EM wave absorption ability(minimum re-flection coefficient(RC_(min))is-56.71 dB with a thickness of 2.5 mm,effective absorption bandwidth(EAB)is 3.4 GHz),but also improve antioxidation property(less than 2 wt.%mass fluctuation at 1400℃in air).Theoretical simulation of complex permittivity suggests that SiBCNHf ceramic has an RC_(min)of less than-5 dB for the whole X-band even at 1100℃.Such SiBCNHf ceramic with superior high-temperature-resistance and antioxidation performance derived from single source precursors possesses great potential for EM wave absorbing coatings in high-temperature and harsh environments.
文摘Thermal expansion behaviors of some precursor-derived amorphous Si-C-N and Si-B-C-N ceramics, which were shaped by plastic forming after crosslink, were studied. To complete the shrinkage and densification, after thermolysis specimens were heat treated at a temperature of 1400℃ for 10 h in nitrogen atmosphere. The thermal expansion coefficient of VT50-derived amorphous Si-C-N ceramic increases from 1.98×10-6/K at 400℃ to 3.09×10-6/K at 1000℃, of NCP200-derived amorphous Si-C-N ceramic increases from 2.35×10-6/K at 400℃ to 3.45×10-6/K at 1000℃, and of T2-l-derived amorphous Si-B-C-N ceramic increases from 2.08×10-6/K at 400℃ to 3.18×10-6/K at 1000℃. No glass transition for these amorphous ceramic materials was detected, indicating that as-thermolyzed precursor-derived Si-(B-)C-N ceramic materials are amorphous solids, but not glasses.
文摘A machinable Y TZP/LaPO 4 composite ceramic was prepared by infiltrating LaPO 4 liquid precursor into Y TZP porous ceramic. Sintered Y TZP ceramic preformed with 35% (volume fraction) open pore volume was made by adding graphite (30%, volume fraction). The Y TZP/LaPO 4 composite ceramics containing different LaPO 4 contents were obtained by infiltration and pyrolysis cycles. The machinability and mechanical properties of materials were investigated. The results show that the machinable Y TZP/LaPO 4 composite ceramics containing 2 3% to 7.5% (volume fraction) LaPO 4 has good machinability as well as outstanding mechanical properties.
基金financially supported by National Natural Science Foundation of China (Grant Nos. 51172255 and 51532006)
文摘Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy(TEM) combined with spatially-resolved electron energy-loss spectroscopy(EELS) analysis. The ceramics were pyrolyzed at1000℃ followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200℃ and dominate at 1500℃. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5 nm at 1400℃. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCxand Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400℃. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCxlayers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.
基金the support of the National Natural Sciences foundation of China (Nos. 51002120 and51032006)supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU), China (No.45-QP-2010)
文摘The deposition rate, phase, chemical composition and microstructure of deposits were determined from 950 to 1100 ℃. With increasing temperature, the deposition rate increases, and the morphology changes from smooth to coarse, meanwhile, the concentration of silicon increases while that of boron decreases. The deposition process is controlled by chemical reactions, and the activation energy is 271 kJ/mol. At relatively lower temperature （below 1000 ℃）, the deposition process is dominated by formation of BaC. While at higher temperature （above 1000 ℃）, it is governed by formation of SiC. BaC and SiC disperse uniformly in the Si-B-C co-deposition system and form a dense network structure.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.21174112 and 51242009)the Research Fund of State Key Laboratory of Solidification Processing(Grant No.82-TZ-2013)+1 种基金the project "111"(B08040)the grant of the New Century Excellent Talents of Education Ministry of China(NCET-110817)
文摘In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene（PS） and converting polysilazane（PSZ） into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m;/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.
基金financially supported by the National Natural Science Foundation of China (No.50702031,60974117,50990303,and 50872070)the Excellent Young Investigators Award Foundation of Shandong Province (No.BS2009CL021)the Major State Basic Research Development Program of China (Nos.2009CB93050 and G2004CB619002)
文摘We report the laser output of transparent Nd：YAG （Nd：Y3Al5O12） ceramics fabricated from Nd：YAG precursors through the microwave-assisted homogenous precipitation （MAHP） method. Pure phase and uniform Nd：YAG nano-powders with average sizes less than 100 nm were obtained by heating treatment of.the Nd：YAG precursor particles aged for 6 d in vessel with humidity of 30%-50% at 25℃. Transparent Nd：YAG ceramic pellets were obtained by vacuum sintering at 1730℃ for 10 h. Laser output （305 roW） with a slope efficiency of 5.1% was realized through an end-pumped configuration. Our results indicate that the MAHP method could potentially be used for the fabrication of laser ceramic products,
文摘Polyaluminocarbosilane（PACS） was synthesized by the reaction of aluminum acetylacetonate（（Al（AcAc）3）） with polysilacarbosilane （PSCS）, which was prepared by thermolysis and condensation of polydimethylsilane （PDMS）. The sublimation of Al（AcAc）3 could be avoided by the use of PSCS as reactant. The empirical formula of PACS was SiC2.01H7.66O0.13Al0.02, which has the relative molecular mass of 2 265. When the reaction of PSCS with Al（AcAc）3 proceeds, an enormous decrease in the number of Si—H bonds in PSCS is observed, at the same time, gas acetylacetonate is a by-product of the reaction based on the ligands of Al（AcAc）3. The reaction mechanism is found to be related to the increase in the molecular mass of PACS by the cross-linking reaction of （Si—H） bonds in PSCS with Al（AcAc）3, which leads to the formation of Si—Al bonds.
基金support of the National Natural Science Foundation of China(No.50072033)the Chinese Academy of Sciences(CXJJ-10).
文摘A new kind of polytitanosilazane precursor PTSZ for Si/C/N/Ti-based ceramic was synthesized from the condensation reaction of silazane lithium salt and titanium tetrachloride (TiCl4). The results indicated that the ceramic yield of PTSZ was much higher than that of corresponding silazane oligomer.
文摘Three new borazine derivatives,2,4,6-tri（allylamino）borazine （CH 2 =CHCH 2 NHBNH） 3 （1）,2,4,6-tri（3ethynylanilino）borazine （CH≡CC 6 H 4 NHBNH） 3 （2）,and 2,4,6-tri（4-propargyl oxyanilino）borazine （CH≡ CCH 2 OC 6 H 4 NHBNH） 3 （3） were synthesized by reaction of 2,4,6-trichloro-borazine Cl 3 B 3 N 3 H 3 （TCB） with corresponding primary amines,respectively.Their thermal behavior was studied by differential scanning calorimetry （DSC） and thermogravimetric analysis （TGA）.These molecules were easily crosslinked via thermal polymerization of reactive ethynyl or vinyl groups.The pyrolytic residues of borazines were investigated by X-ray photoelectron spectroscopy （XPS）,powder X-ray diffraction （XRD）,and scanning electron microscopy （SEM）.The analytic results indicated that B-C-N ceramics were formed upon pyrolysis of the borazines under an inert atmosphere.
基金This work was supported by the National Natural Sciences Foundation of China (No. 50072033).
文摘A new kind of organometallic precursor for Si/Zr/C/N-based ceramics was synthesized from the amine exchangereaction of hexamethylcyclotrisilazane (D_3~N) and tetrakis(diethylamino) zirconium (Zr[NEt_2]_4). Pyrolysis was performedunder nitrogen at 800℃ in a tube furnace equipped with a temperature program controller. The highest pyrolytic yield was67.5%.
基金the Natural Science Foundation of China(Nos.51872246 and 52061135102)for financial support.
文摘In the present work,novel NbC-SiC-C ceramic nanocomposite powders were successfully synthesized by a polymer-derived ceramic approach with the allylhydridopolycarbosilane(AHPCS)and niobium pentachloride(NbCl5)as starting materials.A single-source-precursor was first synthesized by chemical reaction between AHPCS and NbCl5 and then pyrolyzed at 900℃ to obtain amorphous ceramic powders.After further annealing amorphous ceramics at higher temperatures in the range of 1100-1500℃,the NbC-SiC-C ceramic nanocomposite powders were finally obtained.The single-source-precursor synthesis and polymer-to-ceramic transformation were characterized by Fourier transform infrared spectra(FT-IR)and thermal gravimetric analysis(TGA).The phase evolution of resulting ceramics was investigated by X-ray diffraction(XRD)and transmission electron microscopy(TEM).Interestingly,both the NbC@C and SiC@C core−shell structured nanoparticles were in-situ formed at 1300℃ to form NbC-SiC-C ceramic nanocomposites.With the highest NbCl5 content in the feed,the contents of NbC andβ-SiC obtained by Rietveld refinement of the XRD patterns from the 1500℃ ceramics are 68.41wt.%and 31.59wt.%,respectively,indicating that the ultra-high temperature resistant NbC is the main phase.In general,the resultant NbC-SiC-C nanocomposite with NbC as main phase can be considered as candidate material for structure−function integrated applications in harsh environment.
