Silicone rubber(SR)exhibits superior breathability and high-temperature resistance.However,SR is prone to degradation under extreme heat or combustion,limiting its effectiveness in mitigating secondary hazards.In this...Silicone rubber(SR)exhibits superior breathability and high-temperature resistance.However,SR is prone to degradation under extreme heat or combustion,limiting its effectiveness in mitigating secondary hazards.In this study,phosphate glass powder was used to calcinate zinc borate,lanthanum oxide,and cerium oxide.Methylphenyl polysiloxane was then grafted onto the surface of the glass powder,resulting in the modified pow-ders designated as Methylphenyl polysiloxane-grafted zinc borate-modified phosphate glass powder(GF-ZnBM),Methylphenyl polysiloxane-grafted lanthanum oxide-modified phosphate glass powder(GF-LaM),and Methylphenyl polysiloxane-grafted cerium oxide-modified phosphate glass powder(GF-CeM).The modified powders were sub-sequently incorporated into silicone rubber composites to enhance the ceramicization capability of silicone rubber at high temperatures.Specifically,GF-CeM and GF-LaM significantly increased the limiting oxygen index(LOI)to 33%and reduced the tendency for combustion propagation.Additionally,GF-CeM notably contributed to enhancing ceramicization strength.The presence of cerium oxide helps in the melting of the glass powder and enhances its adhesion to the silicone rubber matrix.SR/ZnB-GF exhibited the lowest activation energy among the tested composites,along with the best protective capability.The inclusion of modified glass powder has a minor impact on the rheological properties,indicating that the composite retains its ability to flow and deform under stress.This confirms that the material remains flexible under normal conditions and forms a ceramic structure when heated,thereby exhibiting self-supporting properties.This study provides a practical methodology for the targeted modification of glass powders,thereby further enhancing the fire safety of silicone-based composites.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
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
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
Unmanned combat aerial vehicles require lightweight,stealth-capable exhaust systems.However,traditional metallic nozzles increase radar detectability and reduce range,while advanced composites offer high performance b...Unmanned combat aerial vehicles require lightweight,stealth-capable exhaust systems.However,traditional metallic nozzles increase radar detectability and reduce range,while advanced composites offer high performance but are expensive.Therefore,to improve the operational range and survivability of unmanned combat aerial vehicles,a lightweight,high-temperature-resistant,oxidation-resistant,and low-observable composite exhaust nozzle is developed to replace conventional metallic straight-type nozzles.The nozzle features a double serpentine shape to reduce radar and infrared signatures and is manufactured as a monolithic structure using the filament winding process,accommodating the complex geometry and large size(length:1.8 m,width:0.8 m).The exhaust nozzle consists of a ceramic matrix composite made of silicon carbide fibers and a silicon oxycarbide matrix,which absorbs and scatters radio frequency signals while withstanding prolonged exposure to high-temperature(700℃)oxidizing environments typical of engine exhaust gases.The polysiloxane resin used to produce the silicon oxycarbide matrix poses significant challenges owing to its low tackiness and high viscosity variations depending on the presence of nanoparticles,making filament winding difficult.These challenges are addressed by optimizing resin viscosity and winding pattern design.As a result,the tensile strength of the composite specimens fabricated with the optimized viscosity increases by 228.03% before pyrolysis and 97.68%after pyrolysis,compared with that of the non-optimized specimens.In addition,the density and tensile strength of the composite processed via three cycles of polymer infiltration and pyrolysis increased by 13.08% and 80.37%,respectively,compared to those of the non-densified composite.High-temperature oxidation and flame tests demonstrate exceptional thermal and oxidative stability.Furthermore,when compared with carbon fiber-reinforced ceramic matrix composites,the developed composite exhibits a permittivity at least two levels lower and a reflection loss below7 dB within the frequency range of 9.3-10.9 GHz,underscoring its superior electromagnetic stealth performance.展开更多
Ceramic cells promise ideal energy conversion and storage devices,making the development of efficient and robust air electrodes crucial for their application.In this study,a Ba_(0.4)Sr_(0.5)Cs_(0.1)Co_(0.7)Fe_(0.2)Nb_...Ceramic cells promise ideal energy conversion and storage devices,making the development of efficient and robust air electrodes crucial for their application.In this study,a Ba_(0.4)Sr_(0.5)Cs_(0.1)Co_(0.7)Fe_(0.2)Nb_(0.1)O_(3−δ)(BSCCFN)air electrode,based on Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3−δ)(BSCF),is designed using a perovskite A-B-site ionic Lewis acid strength(ISA)polarization distribution strategy and is successfully applied in both oxygen-ion conducting solid oxide fuel cells(O-SOFCs)and proton-conducting reversible protonic ceramic cells(R-PCCs).When BSCCFN is used as the air electrode in O-SOFCs,a peak power density(PPD)of 1.45 W cm^(−2)is achieved at 650°C,whereas in R-PCCs,a PPD of 1.13 W cm^(−2)and a current density of−1.8 A cm^(−2)at 1.3 V are achieved at the same temperature and show stable reversibility over 100 h.Experimental measurements and theoretical calculations demonstrate that low-ISA Cs+doping accelerates the reaction kinetics of both oxygen ions and protons,while high-ISA Nb^(5+)doping enhances electrode stability.The synergistic effect of Cs^(+)and Nb^(5+)co-doping in the BSCCFN electrode lies in the ISA polarization distribution,which weakens the Co/Fe–O bond covalency,thereby promoting oxygen vacancy formation and facilitating the conduction of oxygen ions and protons.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
SiC_(f)/SiC ceramic matrix composites(SiC_(f)/SiC composites)are difficult to drill small holes due to their heterogeneity,high hardness,and low electrical conductivity.In order to solve the difficulties of poor quali...SiC_(f)/SiC ceramic matrix composites(SiC_(f)/SiC composites)are difficult to drill small holes due to their heterogeneity,high hardness,and low electrical conductivity.In order to solve the difficulties of poor quality and low efficiency when drilling small holes,a novel femtosecond laser rotary drilling(FLRD)technique is proposed.Beam kinematic paths and experimental studies were carried out to analyze the effects of processing parameters on the drilling results in the two-step drilling process.In the through-hole drilling stage,the material removal rate increases with increasing laser power,decreasing feed speed and decreasing pitch.As for the finishing stage of drilling,the exit diameter increased with increasing laser power and decreasing feed speed.The drilling parameters were selected by taking the processing efficiency of through-hole and the quality of finished hole as the constraint criteria.Holes with a diameter of 500μm were drilled using FLRD in 3 mm thick SiC_(f)/SiC composites with a drilling time<150 s.The hole aspect ratio was 6,the taper<0.2°,and there was no significant thermal damage at the orifice or the wall of the hole.The FLRD provides a solution for precision machining of small holes in difficult-to-machine materials by offering the advantages of high processing quality and short drilling times.展开更多
As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancin...As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancing performances.In the domain of manufacturing melt-grown oxide ceramics,it encounters substantial challenges in suppressing crack defects during the rapid solidification process.The strategic integration of high entropy alloys(HEA),leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles.The ingenious doping of HEA parti-cles preserves the eutectic microstructures of the Al_(2)O_(3)/GdAlO_(3)(GAP)/ZrO_(2)ceramic composite.The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF,effectively reducing crack initiation and growth.Due to in-creased curvature forces and intense Marangoni convection at the top of the molt pool,particle collision intensifies,leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool.However,this phenomenon can be effectively alleviated in the remelting process of subsequent layer de-position.Furthermore,a portion of the HEA particles partially dissolves and sinks into the molten pool,acting as heterogeneous nucleation particles,inducing the formation of equiaxed eutectic and leading pri-mary phase nucleation.Some HEA particles diffuse into the lamellar ternary eutectic structures,further promoting the refinement of eutectic microstructures due to increased undercooling.The innovative dop-ing of HEA particles has effectively facilitated the fabrication of turbine-structured,conical,and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm,demonstrating significant developmental potential in the field of ceramic composite manufacturing.展开更多
In recent years,photochromic(PC)materials have garnered widespread interest due to their potential applications in next-generation optical storage devices and photocatalysis.These materials,which control luminescence ...In recent years,photochromic(PC)materials have garnered widespread interest due to their potential applications in next-generation optical storage devices and photocatalysis.These materials,which control luminescence intensity via PC reactions,are not only suitable for optical switches and information storage but also play a crucial role in enhancing catalytic efficiency in photocatalytic applications.However,quantifying the PC effect on performance in these applications is challenging,complicating the material design needed to meet performance specifications.This study reports on a multifunctional Na_(0.5)Bi_(4.5)Ti_(4)O_(15)(NBT)material that achieves adjustable photoluminescence(PL)and photocatalytic(PCA)performance through precise control of the PC reaction.Under alternating exposure to 405 nm light and thermal annealing,the Er/Yb co-doped NBT samples display remarkable photochromic(PC)behavior,capable of reversible color transitions between yellow and gray.After 30 s of 405 nm irradiation,strong energy transfer facilitates a high up-conversion(UC)luminescence contrast of 78.02%.Additionally,the PC reaction promotes the ideal separation of photoexcited carriers and significantly enhances the utilization of electron-hole pairs,nearly doubling the PCA efficiency of the NBT samples by 1.9 times.Furthermore,the luminescence contrast and PCA efficiency controlled by PC can be regulated through varying Er/Yb doping levels,maintaining consistent trends.This study provides theoretical and experimental foundations for the performance modulation of rare-earth-doped multifunctional photochromic materials.展开更多
Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A2B2O7 ceramic for environmental/thermal barrier coating applications.To collaboratively tailor the mechanical and thermal propert...Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A2B2O7 ceramic for environmental/thermal barrier coating applications.To collaboratively tailor the mechanical and thermal properties of A2B2O7 ceramic,a novel high entropy pyrochlore ceramic(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) with significant atomic radius and mass fluctuation is proposed by simultaneously introducing various elements with different valence states at A and B cation sites.The as-synthesized(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) exhibits enhanced fracture toughness(1.68 MPa m^(1/2)),amorphous-like low thermal conductivity(1.45 W m^(-1) K^(-1) at 900℃)and matched thermal expansion coefficient(9.0×10^(-6) K^(-1) at 1200℃)with Al_(2)O_(3)/Al_(2)O_(3) CMCs.The extensive misfits in atomic weight,ionic radius among the substitutional cations in combination with the intrinsic oxygen vacancies in the anion sublattice play significant roles in the thermal conductivity reduction of(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) ceramic.The combination of outstanding mechanical and thermal properties indicates that this type of material has a good application prospect for environmental/thermal barrier coatings.展开更多
To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg...To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg-Zr composite was fabricated using LPBF. The results indicated that a dense sample with a maximum relative density of 99.85% could be obtained by adjusting the LPBF process parameters. Incorporating TiB_(2) nanoparticles enhanced the powder's laser absorption rate, thereby raising the alloy's intrinsic heat treatment temperature and consequently facilitating the precipitation of Si and βʺ nanoparticles in the α-Al cells. Moreover, the rapid cooling process during LPBF resulted in numerous alloying elements with low-stacking fault energy dissolving in the α-Al matrix, thus promoting the formation of the 9R phase. After a 48 h direct aging treatment at 150℃, the strength of the alloy slightly increased due to the increase of nanoprecipitates. Both yield strength and ultimate tensile strength of the LPBF TiB_(2)/Al-Si-Mg-Zr alloy were significantly higher than that of other LPBF TiB_(2)-modified aluminum alloys with external addition.展开更多
Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession r...Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession rate of 0.15μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m^(2)(2000℃)for 300 s.Associated with the temperature gradient of the ablation surface,the oxidation products at different locations mainly consist of(TiZrHfNbTa)O_(x),(Zr_(x)Hf_(1-x))6(NbyTa_(1-y))_(2)O_(17),Ti(Nb_(x)Ta_(1-x))_(2)O_(7),(Hf_(x)Zr_(1-x))SiO_(4),and SiO_(2).Due to the synergistic effect of the multi-component oxides,oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases.It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring.It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.展开更多
The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this wor...The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.展开更多
ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(...ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.展开更多
Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suita...Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.展开更多
基金supported by National Natural Science Foundation of China(51991352 and 51874266).
文摘Silicone rubber(SR)exhibits superior breathability and high-temperature resistance.However,SR is prone to degradation under extreme heat or combustion,limiting its effectiveness in mitigating secondary hazards.In this study,phosphate glass powder was used to calcinate zinc borate,lanthanum oxide,and cerium oxide.Methylphenyl polysiloxane was then grafted onto the surface of the glass powder,resulting in the modified pow-ders designated as Methylphenyl polysiloxane-grafted zinc borate-modified phosphate glass powder(GF-ZnBM),Methylphenyl polysiloxane-grafted lanthanum oxide-modified phosphate glass powder(GF-LaM),and Methylphenyl polysiloxane-grafted cerium oxide-modified phosphate glass powder(GF-CeM).The modified powders were sub-sequently incorporated into silicone rubber composites to enhance the ceramicization capability of silicone rubber at high temperatures.Specifically,GF-CeM and GF-LaM significantly increased the limiting oxygen index(LOI)to 33%and reduced the tendency for combustion propagation.Additionally,GF-CeM notably contributed to enhancing ceramicization strength.The presence of cerium oxide helps in the melting of the glass powder and enhances its adhesion to the silicone rubber matrix.SR/ZnB-GF exhibited the lowest activation energy among the tested composites,along with the best protective capability.The inclusion of modified glass powder has a minor impact on the rheological properties,indicating that the composite retains its ability to flow and deform under stress.This confirms that the material remains flexible under normal conditions and forms a ceramic structure when heated,thereby exhibiting self-supporting properties.This study provides a practical methodology for the targeted modification of glass powders,thereby further enhancing the fire safety of silicone-based composites.
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.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supported by the Agency for Defense Development Grant Funded by the Korean Government(Grant No.912822501).
文摘Unmanned combat aerial vehicles require lightweight,stealth-capable exhaust systems.However,traditional metallic nozzles increase radar detectability and reduce range,while advanced composites offer high performance but are expensive.Therefore,to improve the operational range and survivability of unmanned combat aerial vehicles,a lightweight,high-temperature-resistant,oxidation-resistant,and low-observable composite exhaust nozzle is developed to replace conventional metallic straight-type nozzles.The nozzle features a double serpentine shape to reduce radar and infrared signatures and is manufactured as a monolithic structure using the filament winding process,accommodating the complex geometry and large size(length:1.8 m,width:0.8 m).The exhaust nozzle consists of a ceramic matrix composite made of silicon carbide fibers and a silicon oxycarbide matrix,which absorbs and scatters radio frequency signals while withstanding prolonged exposure to high-temperature(700℃)oxidizing environments typical of engine exhaust gases.The polysiloxane resin used to produce the silicon oxycarbide matrix poses significant challenges owing to its low tackiness and high viscosity variations depending on the presence of nanoparticles,making filament winding difficult.These challenges are addressed by optimizing resin viscosity and winding pattern design.As a result,the tensile strength of the composite specimens fabricated with the optimized viscosity increases by 228.03% before pyrolysis and 97.68%after pyrolysis,compared with that of the non-optimized specimens.In addition,the density and tensile strength of the composite processed via three cycles of polymer infiltration and pyrolysis increased by 13.08% and 80.37%,respectively,compared to those of the non-densified composite.High-temperature oxidation and flame tests demonstrate exceptional thermal and oxidative stability.Furthermore,when compared with carbon fiber-reinforced ceramic matrix composites,the developed composite exhibits a permittivity at least two levels lower and a reflection loss below7 dB within the frequency range of 9.3-10.9 GHz,underscoring its superior electromagnetic stealth performance.
基金funding from the National Natural Science Foundation of China (Award 91745203) supplemented by Central Universities’ Basic Research Funds.
文摘Ceramic cells promise ideal energy conversion and storage devices,making the development of efficient and robust air electrodes crucial for their application.In this study,a Ba_(0.4)Sr_(0.5)Cs_(0.1)Co_(0.7)Fe_(0.2)Nb_(0.1)O_(3−δ)(BSCCFN)air electrode,based on Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3−δ)(BSCF),is designed using a perovskite A-B-site ionic Lewis acid strength(ISA)polarization distribution strategy and is successfully applied in both oxygen-ion conducting solid oxide fuel cells(O-SOFCs)and proton-conducting reversible protonic ceramic cells(R-PCCs).When BSCCFN is used as the air electrode in O-SOFCs,a peak power density(PPD)of 1.45 W cm^(−2)is achieved at 650°C,whereas in R-PCCs,a PPD of 1.13 W cm^(−2)and a current density of−1.8 A cm^(−2)at 1.3 V are achieved at the same temperature and show stable reversibility over 100 h.Experimental measurements and theoretical calculations demonstrate that low-ISA Cs+doping accelerates the reaction kinetics of both oxygen ions and protons,while high-ISA Nb^(5+)doping enhances electrode stability.The synergistic effect of Cs^(+)and Nb^(5+)co-doping in the BSCCFN electrode lies in the ISA polarization distribution,which weakens the Co/Fe–O bond covalency,thereby promoting oxygen vacancy formation and facilitating the conduction of oxygen ions and protons.
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.
基金the support of the Xingliao Talent Program of Liaoning Province(No.XLYC2001004)the High Level Talents Innovation Plan of Dalian(No.2020RD02)the Fundamental Research Funds for the Central Universities(No.DUT22LAB501).
文摘SiC_(f)/SiC ceramic matrix composites(SiC_(f)/SiC composites)are difficult to drill small holes due to their heterogeneity,high hardness,and low electrical conductivity.In order to solve the difficulties of poor quality and low efficiency when drilling small holes,a novel femtosecond laser rotary drilling(FLRD)technique is proposed.Beam kinematic paths and experimental studies were carried out to analyze the effects of processing parameters on the drilling results in the two-step drilling process.In the through-hole drilling stage,the material removal rate increases with increasing laser power,decreasing feed speed and decreasing pitch.As for the finishing stage of drilling,the exit diameter increased with increasing laser power and decreasing feed speed.The drilling parameters were selected by taking the processing efficiency of through-hole and the quality of finished hole as the constraint criteria.Holes with a diameter of 500μm were drilled using FLRD in 3 mm thick SiC_(f)/SiC composites with a drilling time<150 s.The hole aspect ratio was 6,the taper<0.2°,and there was no significant thermal damage at the orifice or the wall of the hole.The FLRD provides a solution for precision machining of small holes in difficult-to-machine materials by offering the advantages of high processing quality and short drilling times.
基金supported by the National Natural Science Foundation of China(Nos.52130204,52174376,52202070,51822405)Guangdong Basic and Applied Basic Research Foundation(No.2021B1515120028)+6 种基金TQ Innovation Foundation(No.23-TQ09-02-ZT-01-005)Aeronautical Science Foundation of China(No.20220042053001)Science and Technology Innovation Team Plan of Shaanxi Province(No.2021TD-17)Key R&D Project of Shaanxi Province(No.2024GX-YBXM-220)Thousands Person Plan of Jiangxi Province(JXSQ2020102131)Fundamental Research Funds for the Central Universities(Nos.D5000230348,D5000220057)China Scholarship Council(Nos.202206290133,202306290190).
文摘As a 3D printing method,laser powder bed fusion(LPBF)technology has been extensively proven to offer significant advantages in fabricating complex structured specimens,achieving ultra-fine microstructures,and enhancing performances.In the domain of manufacturing melt-grown oxide ceramics,it encounters substantial challenges in suppressing crack defects during the rapid solidification process.The strategic integration of high entropy alloys(HEA),leveraging the significant ductility and toughness into ceramic powders represents a major innovation in overcoming the obstacles.The ingenious doping of HEA parti-cles preserves the eutectic microstructures of the Al_(2)O_(3)/GdAlO_(3)(GAP)/ZrO_(2)ceramic composite.The high damage tolerance of the HEA alloy under high strain rates enables the absorption of crack energy and alleviation of internal stresses during LPBF,effectively reducing crack initiation and growth.Due to in-creased curvature forces and intense Marangoni convection at the top of the molt pool,particle collision intensifies,leading to the tendency of HEA particles to agglomerate at the upper part of the molt pool.However,this phenomenon can be effectively alleviated in the remelting process of subsequent layer de-position.Furthermore,a portion of the HEA particles partially dissolves and sinks into the molten pool,acting as heterogeneous nucleation particles,inducing the formation of equiaxed eutectic and leading pri-mary phase nucleation.Some HEA particles diffuse into the lamellar ternary eutectic structures,further promoting the refinement of eutectic microstructures due to increased undercooling.The innovative dop-ing of HEA particles has effectively facilitated the fabrication of turbine-structured,conical,and cylindrical ternary eutectic ceramic composite specimens with diameters of about 70 mm,demonstrating significant developmental potential in the field of ceramic composite manufacturing.
基金Project supported by the Jiangsu Province Graduate Research and Innovation Program(KYCX24_0329)。
文摘In recent years,photochromic(PC)materials have garnered widespread interest due to their potential applications in next-generation optical storage devices and photocatalysis.These materials,which control luminescence intensity via PC reactions,are not only suitable for optical switches and information storage but also play a crucial role in enhancing catalytic efficiency in photocatalytic applications.However,quantifying the PC effect on performance in these applications is challenging,complicating the material design needed to meet performance specifications.This study reports on a multifunctional Na_(0.5)Bi_(4.5)Ti_(4)O_(15)(NBT)material that achieves adjustable photoluminescence(PL)and photocatalytic(PCA)performance through precise control of the PC reaction.Under alternating exposure to 405 nm light and thermal annealing,the Er/Yb co-doped NBT samples display remarkable photochromic(PC)behavior,capable of reversible color transitions between yellow and gray.After 30 s of 405 nm irradiation,strong energy transfer facilitates a high up-conversion(UC)luminescence contrast of 78.02%.Additionally,the PC reaction promotes the ideal separation of photoexcited carriers and significantly enhances the utilization of electron-hole pairs,nearly doubling the PCA efficiency of the NBT samples by 1.9 times.Furthermore,the luminescence contrast and PCA efficiency controlled by PC can be regulated through varying Er/Yb doping levels,maintaining consistent trends.This study provides theoretical and experimental foundations for the performance modulation of rare-earth-doped multifunctional photochromic materials.
基金support from the National Natural Science Foundation of China under grant No.52302065the Yunnan Fundamental Research Projects under grant Nos.202201BE070001-008 and 202201AU070142the National Key Research and Development Program of China under grant No.2023YFB3711200.
文摘Low thermal conductivity and excellent mechanical strength are essential to pyrochlore A2B2O7 ceramic for environmental/thermal barrier coating applications.To collaboratively tailor the mechanical and thermal properties of A2B2O7 ceramic,a novel high entropy pyrochlore ceramic(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) with significant atomic radius and mass fluctuation is proposed by simultaneously introducing various elements with different valence states at A and B cation sites.The as-synthesized(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) exhibits enhanced fracture toughness(1.68 MPa m^(1/2)),amorphous-like low thermal conductivity(1.45 W m^(-1) K^(-1) at 900℃)and matched thermal expansion coefficient(9.0×10^(-6) K^(-1) at 1200℃)with Al_(2)O_(3)/Al_(2)O_(3) CMCs.The extensive misfits in atomic weight,ionic radius among the substitutional cations in combination with the intrinsic oxygen vacancies in the anion sublattice play significant roles in the thermal conductivity reduction of(La_(0.3)Gd_(0.3)Ca_(0.4))_(2)(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))_(2)O_(7) ceramic.The combination of outstanding mechanical and thermal properties indicates that this type of material has a good application prospect for environmental/thermal barrier coatings.
基金supported by the National Natural Science Foundation of China(Nos.51801079 and 52001140)the National Science Centre,Poland(Narodowe Centrum Nauki)(No.UMO-2021/42/E/ST5/00339).
文摘To increase the strength of the laser powder-bed fusion (LPBF) Al-Si-based aluminum alloy, TiB_(2) ceramic particles were selected to be mixed with high-Mg content Al-Si-Mg-Zr powder, and then a novel TiB_(2)/Al-Si-Mg-Zr composite was fabricated using LPBF. The results indicated that a dense sample with a maximum relative density of 99.85% could be obtained by adjusting the LPBF process parameters. Incorporating TiB_(2) nanoparticles enhanced the powder's laser absorption rate, thereby raising the alloy's intrinsic heat treatment temperature and consequently facilitating the precipitation of Si and βʺ nanoparticles in the α-Al cells. Moreover, the rapid cooling process during LPBF resulted in numerous alloying elements with low-stacking fault energy dissolving in the α-Al matrix, thus promoting the formation of the 9R phase. After a 48 h direct aging treatment at 150℃, the strength of the alloy slightly increased due to the increase of nanoprecipitates. Both yield strength and ultimate tensile strength of the LPBF TiB_(2)/Al-Si-Mg-Zr alloy were significantly higher than that of other LPBF TiB_(2)-modified aluminum alloys with external addition.
基金supported by the National Key R&D Program of China(No.2022YFB3707700)the Program of Shanghai Academic/Technology Research Leader(No.23XD1424300)the National Natural Science Foundation of China(No.52332003).
文摘Air plasma ablation behavior of Cf/(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C-SiC composite was studied systematically with the surface temperature above 2000℃ at the ablation center.It presents a linear recession rate of 0.15μm/s and a mass recession rate of 2.05 mg/s after ablation at 4 MW/m^(2)(2000℃)for 300 s.Associated with the temperature gradient of the ablation surface,the oxidation products at different locations mainly consist of(TiZrHfNbTa)O_(x),(Zr_(x)Hf_(1-x))6(NbyTa_(1-y))_(2)O_(17),Ti(Nb_(x)Ta_(1-x))_(2)O_(7),(Hf_(x)Zr_(1-x))SiO_(4),and SiO_(2).Due to the synergistic effect of the multi-component oxides,oxidation products form a protective structure composed of high melting point oxide skeleton filled with relatively low melting point phases.It retards oxygen inward diffusion and prevents the composite fragmentation caused by plasma mechanical scouring.It is believed that the results would be helpful for further improving the ablation resistance by component design of high entropy ceramics and their composites.
基金National Natural Science Foundation of China (52302140)Major Scientific and Technological Innovation Project of Wenzhou (ZG2023040, ZG2023042)Joint Funds of the National Natural Science Foundation of China Key Program (U21B2068)。
文摘The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.
基金National Natural Science Foundation of China (U24A2052)Shanghai Eastern Talent Plan。
文摘ZnAl_(2)O_(4) and ZnAl_(2)O_(4)-based ceramics have attracted much attention from researchers due to their good microwave dielectric,thermal and mechanical properties.In this work,the influence of 5%(in mass)CuO-TiO_(2)-Nb_(2)O_(5)(CTN)ternary composite oxide additives with different composition ratios on sintering behavior and properties of ZnAl_(2)O_(4) microwave dielectric ceramics was investigated.When the molar fraction ranges of Cu,Ti and Nb elements in 5%CTN additives are 0.625-0.875,0-0.250 and 0.125-0.625,respectively,sintering temperature of ZnAl_(2)O_(4) ceramics can be reduced from above 1400℃to below 1000℃.The sintering additives CN(Cu:Nb=1:1,molar ratio)and CTN(Cu:Ti:Nb=4:1:3,molar ratio)can reduce sintering temperature of ZnAl_(2)O_(4) ceramics to 975 and 1000℃,respectively,while maintaining good dielectric properties(dielectric constantε_(r)=11.36,quality factor Q׃=8245 GHz andε_(r)=9.52,Q׃=22249 GHz)and flexural strengths(200 and 161 MPa),which are expected to be applied in preparation of low temperature co-fired ceramic(LTCC)materials with copper electrodes.Low-temperature sintering of the ZnAl_(2)O_(4)+CTN system is characterized as activated sintering.Nanometer-level amorphous interfacial films containing Cu,Ti,and Nb elements are observed at the grain boundaries,which may provide fast diffusion pathways for mass transportation during the sintering process.Valence changes of Ti and Cu ions,along with changes of oxygen vacancies,are confirmed,which provides a potential mechanism for reduced sintering temperature of ZnAl_(2)O_(4) ceramics.In addition,a series of reactions occurring at the grain boundaries can activate these boundaries and further promote the sintering densification process.These results suggest a promising way to design a novel LTCC material with excellent properties based on the low temperature sintering of ceramics with the sintering aid of CuO-TiO_(2)-Nb_(2)O_(5) composite oxide.
基金Student Training Program for Innovation and Entrepreneurship of Hangzhou Institute for Advanced Study,UCAS(CXCY20230305)Chinese Academy of Sciences Key Project(ZDRW-CN-2021-3-1-18)。
文摘Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.
