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
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
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
High-temperature piezoelectric vibration sensors are the preferred choice for structural health monitoring in harsh environments such as high temperatures and complex vibrations.Bismuth layer-structured CaBi_(4)Ti_(4)...High-temperature piezoelectric vibration sensors are the preferred choice for structural health monitoring in harsh environments such as high temperatures and complex vibrations.Bismuth layer-structured CaBi_(4)Ti_(4)O_(15)(CBT)high-temperature piezoelectric ceramics,with high Curie temperature(TC),are the key components for piezoelectric vibration sensors operating at temperatures exceeding 500℃.However,their low piezoelectric coefficient(d_(33))greatly limits their high-temperature applications.In this work,a novel Bi^(3+)self-doping strategy was employed to enhance the piezoelectric performance of CBT ceramics.The enhancement is attributed to an increase in the number of grain boundaries,providing more sites for space charge accumulation and promoting formation of space charge polarization.Furthermore,given that space charge polarization predominantly occurs at low frequencies,dielectric temperature spectra at different frequencies were used to elucidate the mechanism by which space charge polarization enhances piezoelectric properties of CBT ceramics.Excellent overall performance was achieved for the CBT-based high-temperature piezoelectric ceramics.Among them,TC reached 778℃,d_(33) increased by more than 30%,reaching 20.1 pC/N,and the electrical resistivity improved by one order of magnitude(reaching 6.33×10^(6)Ω·cm at 500℃).These advancements provide a key functional material with excellent performance for practical applications of piezoelectric vibration sensors at 500℃and above.展开更多
Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2...Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.展开更多
The role of the adhesive layer in the ballistic performance of ceramic multi-layer armour system is complex and multi-faceted,often with trade-offs between single-and multi-hit performance.However,research focused on ...The role of the adhesive layer in the ballistic performance of ceramic multi-layer armour system is complex and multi-faceted,often with trade-offs between single-and multi-hit performance.However,research focused on untangling the underlying impact of varying adhesive cohesive or adhesion properties is limited and sometimes appears to provide conflicting conclusions.Comparison between the available studies is also often difficult due to variations in armour systems or ballistic testing being conducted.This review scrutinises the available research,identifying six critical properties of an adhesive layer in determining ballistic performance:elastic modulus,fracture strain,acoustic impedance,tensile bond strength,shear bond strength,and thickness.The impact of each of these properties on ballistic performance is discussed in detail,with clear description of the underlying processes involved,allowing clear optimisation goals to be established depending on the ceramic armour specification.展开更多
The ballistic resistance and failure pattern of a bi-layer alumina 99.5%-aluminium alloy 1100-H12 target against steel 4340 ogival nosed projectile has been explored in the present experimental cum numerical study.In ...The ballistic resistance and failure pattern of a bi-layer alumina 99.5%-aluminium alloy 1100-H12 target against steel 4340 ogival nosed projectile has been explored in the present experimental cum numerical study.In the experimental investigation,damage induced in the ceramic layer has been quantified in terms of number of cracks developed and failure zone dimensions.The resultant damage in the backing layer has been studied with variation in the bulge and perforation hole in the backing layer with the varying incidence velocity.The discussion of the experimental results has been further followed by three dimensional finite element computations using ABAQUS/Explicit finite code to investigate the behaviour of different types of bi-layer targets under multi-hit projectile impact.The JH-2 constitutive model has been used to reproduce the behaviour of alumina 99.5%and JC constitutive model has been used for steel 4340 and aluminium alloy 1100-H12.The total energy dissipation has been noted to be of lesser magnitude in case of sub-sequential impact in comparison to simultaneous impact of two projectiles.The distance between the impact points of two projectiles also effected the ballistic resistance of bi-layer target.The ballistic resistance of single tile ceramic front layer and four tile ceramic of equivalent area found to be dependent upon the boundary conditions provided to the target.展开更多
ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to...ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2)and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2)phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2)oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2)is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2)particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2)increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2)in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.展开更多
Er^(3+),Na^(+)co-doped CaF_(2) transparent ceramics with Er^(3+)dopant concentration of 3% and Na^(+) of 0%,0.5%,1.0%,1.5% and 2.0% were fabricated by the vacuum hot pressing method with 16 mm in diameter and 3 mm in ...Er^(3+),Na^(+)co-doped CaF_(2) transparent ceramics with Er^(3+)dopant concentration of 3% and Na^(+) of 0%,0.5%,1.0%,1.5% and 2.0% were fabricated by the vacuum hot pressing method with 16 mm in diameter and 3 mm in thickness.The average grain size of the obtained Er,Na∶CaF_(2) powders varied from 28 nm to 36 nm with the shape of sphere.The effects of Na^(+) doping on the transmittance,microstructure and spectral properties of Er^(3+)∶CaF_(2) transparent ceramics were investigated.The transmittance of all the obtained ceramic samples is above 84%in the wavelength of 1000 nm.The results show that after introducing Na^(+)into Er^(3+)∶CaF_(2) transparent ceramics,charge-neutralized Er^(3+)-Na^(+) structure formed which prevent Er^(3+) from clustering.The emission spectra of Er^(3+) in CaF_(2) transparent ceramics at around 1.5 and 2.7μm could be modulated by adjusting the concentration of Na^(+) and the near-infrared fluorescence lifetime at around 1.5μm increase with the increasing of Na^(+) concentration,reaching a maximum of 56.75 ms.展开更多
Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the lengt...Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper.Here,the influence of confinement and prestress on cone cracking and transition velocity is investigated.The hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been determined.The transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic material.Both experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.展开更多
In order to improve the penetration of projectiles into ceramic composite armors,the nose of 30 mm standard projectile was replaced by a toughened ceramic nose,and the performance of ceramic-nose projectiles penetrati...In order to improve the penetration of projectiles into ceramic composite armors,the nose of 30 mm standard projectile was replaced by a toughened ceramic nose,and the performance of ceramic-nose projectiles penetrating into ceramic/A3 steel composite targets has been experimentally researched.According to impact dynamics theory,,the performances of 30 mm ceramic-nose projectile and 30 mm standard projectile penetrating into the ceramic/A3 steel composite targets were analyzed and compared using DOP method,especially focusing on the effects made by different nose structures and materials.The aperture and depth of perforation of projectile into the armor plates as well as the residual mass of bullet core under the same conditions were comparatively analyzed.A numerical simulation was built and computed by ANSYS/LS-DYNA.Based on the simulated results,the penetration performance was further analyzed in terms of the residual mass of bullet core.The results show that the ceramic nose has a great effect on the protection of bullet core.展开更多
Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in th...Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.展开更多
In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the...In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the view on the crater zone and the tip of a projectile penetrating a ceramic is rapidly getting obscured by damaged material,a flash X-ray technique has to be applied in order to visualize projectile penetration.For this purpose,usually several flash X-ray tubes are arranged around the target and the radiographs are recorded on film.At EMI a flash X-ray imaging method has been developed,which provides up to eight flash radiographs in one experiment.A multi-anode 450 k V flash X-ray tube is utilized with this method.The radiation transmitted through the target is then detected on a fluorescent screen.The fluorescent screen converts the radiograph into an image in the visible wavelength range,which is photographed by means of a high-speed camera.This technique has been applied to visualize and analyze the penetration of 7.62 mm AP projectiles into three different types of Si C ceramics.Two commercial Si C grades and MICASIC(Metal Infiltrated Carbon derived Si C),a C-Si Si C ceramic developed by DLR,have been studied.The influences,not only of the ceramic but also the backing material,on dwell time and projectile erosion have been studied.Penetration curves have been determined and their relevance to the ballistic resistance is discussed.展开更多
Principles of dimensional analysis are applied in a new interpretation of penetration of ceramic targets subjected to hypervelocity impact. The analysis results in a power series representation – in terms of inverse ...Principles of dimensional analysis are applied in a new interpretation of penetration of ceramic targets subjected to hypervelocity impact. The analysis results in a power series representation – in terms of inverse velocity – of normalized depth of penetration that reduces to the hydrodynamic solution at high impact velocities. Specifically considered are test data from four literature sources involving penetration of confined thick ceramic targets by tungsten long rod projectiles. The ceramics are AD-995 alumina, aluminum nitride, silicon carbide, and boron carbide.Test data can be accurately represented by the linear form of the power series, whereby the same value of a single fitting parameter applies remarkably well for all four ceramics. Comparison of the present model with others in the literature(e.g., Tate's theory) demonstrates a target resistance stress that depends on impact velocity, linearly in the limiting case. Comparison of the present analysis with recent research involving penetration of thin ceramic tiles at lower typical impact velocities confirms the importance of target properties related to fracture and shear strength at the Hugoniot Elastic Limit(HEL) only in the latter. In contrast, in the former(i.e., hypervelocity and thick target) experiments, the current analysis demonstrates dominant dependence of penetration depth only by target mass density. Such comparisons suggest transitions from microstructure-controlled to density-controlled penetration resistance with increasing impact velocity and ceramic target thickness.Production and hosting by Elsevier B.V. on behalf of China Ordnance Society.展开更多
Wollastonite glass ceramics were prepared using the reactive crystallization sintering method by mixing waste glass powders with gehlenite.The crystallization property,thermodynamics,and kinetics of the prepared wolla...Wollastonite glass ceramics were prepared using the reactive crystallization sintering method by mixing waste glass powders with gehlenite.The crystallization property,thermodynamics,and kinetics of the prepared wollastonite glass ceramics were determined by X-ray diffraction analysis,scanning electron microscopy,energy-dispersive spectroscopy,high-resolution transmission electron microscopy,and differential thermal analysis.Results showed that crystals of wollastonite and alumina could be found in the gehlenite through its reaction with silicon dioxide.The wollastonite crystals showed a lath shape with a certain length-to-diameter ratio.The crystals exhibited excellent bridging and reinforcing effects.In the crystallization process,the aluminum ions in gehlenite diffused into the glass and the silicon ions in the glass diffused into gehlenite.Consequently,the three-dimensional frame structure of gehlenite was partially damaged to form a chain-like wollastonite.The results of crystallization thermodynamics and kinetics indicated that crystallization reaction could occur spontaneously under a low temperature(1173 K),with 20 wt%gehlenite added as the reactive crystallization promoter.The crystallization activation energy was evaluated as 261.99 kJ/mol by using the Kissinger method.The compression strength of the wollastonite glass ceramic samples(7.5 cm×7.5 cm)reached 251 MPa.展开更多
The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and mi...The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.展开更多
In order to study the performance of ceramic composite projectile penetrating into ceramic composite target,the contrast test and numerical simulations of the penetration of standard projectile and the ceramic composi...In order to study the performance of ceramic composite projectile penetrating into ceramic composite target,the contrast test and numerical simulations of the penetration of standard projectile and the ceramic composite projectile into a ceramic composite target were conducted.The results show that the penetration performance of ceramic composite projectile is obvious superior to that of standard projectile for ceramic composite target.The ceramic nose of ceramic composite projectile fully destroys the ceramic panels anterior to its following armor-piercing projectile body,thus maintaining the penetration ability of the following armor-piercing projectile body.展开更多
ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were...ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, ZnTSbaOl2-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/nun and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1-22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 ℃ have the best electrical characteristics.展开更多
Alumina ceramics are widely used in many fields such as cutting tools,laser shock materials,roadbed board and refractory.Herein,Al_(2)O_(3)ceramics are prepared by a low-cost pressureless sintering technology,using th...Alumina ceramics are widely used in many fields such as cutting tools,laser shock materials,roadbed board and refractory.Herein,Al_(2)O_(3)ceramics are prepared by a low-cost pressureless sintering technology,using the binary sintering aids of MgO and SiO_(2).The effects of sintering temperature and the ratio of binary sintering aids on the mechanical properties and microstructure of Al_(2)O_(3)ceramics are investigated.A spinel second phase(MgAl_(2)O_(4))is found out by the analysis of the results of XRD and EDS when MgO and SiO_(2)are introduced in the samples.The optimum properties are found when MgO content is 20 wt.%based on the total sintering aids and the sintering temperature is 1550℃.The bending strength and the bulk density reach a maximum value of 314 MPa and 3.73 g/cm^(3),respectively.The addition of appropriate amount of SiO_(2)makes the formation of liquid phase sintering and the removal of large pores.Meanwhile,a small amount of magnesium oxide doping has an effect on the grain refinement from the microstructure of the sample.Therefore,it is believed that MgO and SiO_(2)are the ideal sintering aids for promoting the densification and property of alumina ceramics.展开更多
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.
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National Natural Science Foundation of China (51932010)。
文摘High-temperature piezoelectric vibration sensors are the preferred choice for structural health monitoring in harsh environments such as high temperatures and complex vibrations.Bismuth layer-structured CaBi_(4)Ti_(4)O_(15)(CBT)high-temperature piezoelectric ceramics,with high Curie temperature(TC),are the key components for piezoelectric vibration sensors operating at temperatures exceeding 500℃.However,their low piezoelectric coefficient(d_(33))greatly limits their high-temperature applications.In this work,a novel Bi^(3+)self-doping strategy was employed to enhance the piezoelectric performance of CBT ceramics.The enhancement is attributed to an increase in the number of grain boundaries,providing more sites for space charge accumulation and promoting formation of space charge polarization.Furthermore,given that space charge polarization predominantly occurs at low frequencies,dielectric temperature spectra at different frequencies were used to elucidate the mechanism by which space charge polarization enhances piezoelectric properties of CBT ceramics.Excellent overall performance was achieved for the CBT-based high-temperature piezoelectric ceramics.Among them,TC reached 778℃,d_(33) increased by more than 30%,reaching 20.1 pC/N,and the electrical resistivity improved by one order of magnitude(reaching 6.33×10^(6)Ω·cm at 500℃).These advancements provide a key functional material with excellent performance for practical applications of piezoelectric vibration sensors at 500℃and above.
基金National Key R&D Program of China(2023YFE3812005)International Partnership Program of Chinese Academy of Sciences(121631KYSB20200039)+1 种基金National Center for Research and Development(WPC2/1/SCAPOL/2021)Chinese Academy of Sciences President’s International Fellowship Initiative(2024VEA0005,2024VEA0014)。
文摘Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.
基金funding for this research was provided by Netherlands Ministry of Defence
文摘The role of the adhesive layer in the ballistic performance of ceramic multi-layer armour system is complex and multi-faceted,often with trade-offs between single-and multi-hit performance.However,research focused on untangling the underlying impact of varying adhesive cohesive or adhesion properties is limited and sometimes appears to provide conflicting conclusions.Comparison between the available studies is also often difficult due to variations in armour systems or ballistic testing being conducted.This review scrutinises the available research,identifying six critical properties of an adhesive layer in determining ballistic performance:elastic modulus,fracture strain,acoustic impedance,tensile bond strength,shear bond strength,and thickness.The impact of each of these properties on ballistic performance is discussed in detail,with clear description of the underlying processes involved,allowing clear optimisation goals to be established depending on the ceramic armour specification.
文摘The ballistic resistance and failure pattern of a bi-layer alumina 99.5%-aluminium alloy 1100-H12 target against steel 4340 ogival nosed projectile has been explored in the present experimental cum numerical study.In the experimental investigation,damage induced in the ceramic layer has been quantified in terms of number of cracks developed and failure zone dimensions.The resultant damage in the backing layer has been studied with variation in the bulge and perforation hole in the backing layer with the varying incidence velocity.The discussion of the experimental results has been further followed by three dimensional finite element computations using ABAQUS/Explicit finite code to investigate the behaviour of different types of bi-layer targets under multi-hit projectile impact.The JH-2 constitutive model has been used to reproduce the behaviour of alumina 99.5%and JC constitutive model has been used for steel 4340 and aluminium alloy 1100-H12.The total energy dissipation has been noted to be of lesser magnitude in case of sub-sequential impact in comparison to simultaneous impact of two projectiles.The distance between the impact points of two projectiles also effected the ballistic resistance of bi-layer target.The ballistic resistance of single tile ceramic front layer and four tile ceramic of equivalent area found to be dependent upon the boundary conditions provided to the target.
基金National Key R&D Program of China(2022YFB3707700)Shanghai Science and Technology Innovation Action Plan(21511104800)+3 种基金National Natural Science Foundation of China(52172111)National Science and Technology Major Project(2017-IV-0005-0042)Key Research Program of the Chinese Academy of Sciences(ZDRW-CN-2021-2-2)Science Center for Gas Turbine Project(P2022-B-IV-001-001)。
文摘ZrB_(2)-based ceramics typically necessitate high temperature and pressure for sintering,whereas ZrB_(2)-SiC ceramics can be fabricated at 1500℃using the process of reactive melt infiltration with Si.In comparison to the conventional preparation method,reactive synthesis allows for the more facile production of ultra-high temperature ceramics with fine particle size and homogeneous composition.In this work,ZrSi_(2),B4C,and C were used as raw materials to prepare ZrB_(2)-SiC via combination of tape casting and reactive melt infiltration herein referred to as ZBC ceramics.Control sample of ZrB_(2)-SiC was also prepared using ZrB_(2)and SiC as raw materials through an identical process designated as ZS ceramics.Microscopic analysis of both ceramic groups revealed smaller and more uniformly distributed particles of the ZrB_(2)phase in ZBC ceramics compared to the larger particles in ZS ceramics.Both sets of ceramics underwent cyclic oxidation testing in the air at 1600℃for a cumulative duration of 5 cycles,each cycle lasting 2 h.Analysis of the oxidation behavior showed that both ZBC ceramics and ZS ceramics developed a glassy SiO_(2)-ZrO_(2)oxide layer on their surfaces during the oxidation.This layer severed as a barrier against oxygen.In ZBC ceramics,ZrO_(2)is finely distributed in SiO_(2),whereas in ZS ceramics,larger ZrO_(2)particles coexist with glassy SiO_(2).The surface oxide layer of ZBC ceramics maintains a dense structure because the well-dispersed ZrO_(2)increases the viscosity of glassy SiO_(2),preventing its crystallization during the cooling.Conversely,some SiO_(2)in the oxide layer of ZS ceramics may crystallize and form a eutectic with ZrO_(2),leading to the formation of ZrSiO_(4).This leads to cracking of the oxide layer due to differences in thermal expansion coefficients,weakening its barrier effect.An analysis of the oxidation resistance shows that ZBC ceramics exhibit less increase in oxide layer thickness and mass compared to ZS ceramics,suggesting superior oxidation resistance of ZBC ceramics.
基金National Key R&D Program of China(2023YFB3507400)。
文摘Er^(3+),Na^(+)co-doped CaF_(2) transparent ceramics with Er^(3+)dopant concentration of 3% and Na^(+) of 0%,0.5%,1.0%,1.5% and 2.0% were fabricated by the vacuum hot pressing method with 16 mm in diameter and 3 mm in thickness.The average grain size of the obtained Er,Na∶CaF_(2) powders varied from 28 nm to 36 nm with the shape of sphere.The effects of Na^(+) doping on the transmittance,microstructure and spectral properties of Er^(3+)∶CaF_(2) transparent ceramics were investigated.The transmittance of all the obtained ceramic samples is above 84%in the wavelength of 1000 nm.The results show that after introducing Na^(+)into Er^(3+)∶CaF_(2) transparent ceramics,charge-neutralized Er^(3+)-Na^(+) structure formed which prevent Er^(3+) from clustering.The emission spectra of Er^(3+) in CaF_(2) transparent ceramics at around 1.5 and 2.7μm could be modulated by adjusting the concentration of Na^(+) and the near-infrared fluorescence lifetime at around 1.5μm increase with the increasing of Na^(+) concentration,reaching a maximum of 56.75 ms.
基金funded by the Swedish Armed Forces and by the Army Research Laboratory through US Naval Regional Contracting Centre,Contract No.W911NF0810271
文摘Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper.Here,the influence of confinement and prestress on cone cracking and transition velocity is investigated.The hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been determined.The transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic material.Both experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.
文摘In order to improve the penetration of projectiles into ceramic composite armors,the nose of 30 mm standard projectile was replaced by a toughened ceramic nose,and the performance of ceramic-nose projectiles penetrating into ceramic/A3 steel composite targets has been experimentally researched.According to impact dynamics theory,,the performances of 30 mm ceramic-nose projectile and 30 mm standard projectile penetrating into the ceramic/A3 steel composite targets were analyzed and compared using DOP method,especially focusing on the effects made by different nose structures and materials.The aperture and depth of perforation of projectile into the armor plates as well as the residual mass of bullet core under the same conditions were comparatively analyzed.A numerical simulation was built and computed by ANSYS/LS-DYNA.Based on the simulated results,the penetration performance was further analyzed in terms of the residual mass of bullet core.The results show that the ceramic nose has a great effect on the protection of bullet core.
文摘Based on the deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution was presented in this paper, according to which an Al 2O 3-TiC functionally gradient ceramic tool material FG-1 was synthesized by powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al 2O 3-TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al 2O 3-TiC ceramics. Functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to homogeneous ceramics, indicating the higher thermal shock resistance. The experimental results were supported by the calculation of transient thermal stress field. The cutting performance of the Al 2O 3-TiC functionally gradient ceramic tool FG-1 was also investigated in rough turning the cylindrical surface of exhaust valve of diesel engine in comparison with that of a common Al 2O 3-TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50 percent over that of LT55. Tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock. While tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.
基金financial support of the study by the Bundeswehr Research Institute for Materials, Fuels and Lubricants (WIWe B) (grant number E/E210/AB015/9F120)
文摘In order to improve the performance of ceramic composite armor it is essential to know the mechanisms during each phase of the projectile–target interaction and their influence on the penetration resistance.Since the view on the crater zone and the tip of a projectile penetrating a ceramic is rapidly getting obscured by damaged material,a flash X-ray technique has to be applied in order to visualize projectile penetration.For this purpose,usually several flash X-ray tubes are arranged around the target and the radiographs are recorded on film.At EMI a flash X-ray imaging method has been developed,which provides up to eight flash radiographs in one experiment.A multi-anode 450 k V flash X-ray tube is utilized with this method.The radiation transmitted through the target is then detected on a fluorescent screen.The fluorescent screen converts the radiograph into an image in the visible wavelength range,which is photographed by means of a high-speed camera.This technique has been applied to visualize and analyze the penetration of 7.62 mm AP projectiles into three different types of Si C ceramics.Two commercial Si C grades and MICASIC(Metal Infiltrated Carbon derived Si C),a C-Si Si C ceramic developed by DLR,have been studied.The influences,not only of the ceramic but also the backing material,on dwell time and projectile erosion have been studied.Penetration curves have been determined and their relevance to the ballistic resistance is discussed.
文摘Principles of dimensional analysis are applied in a new interpretation of penetration of ceramic targets subjected to hypervelocity impact. The analysis results in a power series representation – in terms of inverse velocity – of normalized depth of penetration that reduces to the hydrodynamic solution at high impact velocities. Specifically considered are test data from four literature sources involving penetration of confined thick ceramic targets by tungsten long rod projectiles. The ceramics are AD-995 alumina, aluminum nitride, silicon carbide, and boron carbide.Test data can be accurately represented by the linear form of the power series, whereby the same value of a single fitting parameter applies remarkably well for all four ceramics. Comparison of the present model with others in the literature(e.g., Tate's theory) demonstrates a target resistance stress that depends on impact velocity, linearly in the limiting case. Comparison of the present analysis with recent research involving penetration of thin ceramic tiles at lower typical impact velocities confirms the importance of target properties related to fracture and shear strength at the Hugoniot Elastic Limit(HEL) only in the latter. In contrast, in the former(i.e., hypervelocity and thick target) experiments, the current analysis demonstrates dominant dependence of penetration depth only by target mass density. Such comparisons suggest transitions from microstructure-controlled to density-controlled penetration resistance with increasing impact velocity and ceramic target thickness.Production and hosting by Elsevier B.V. on behalf of China Ordnance Society.
基金Project(51308086)supported by the National Natural Science Foundation of ChinaProject(LJQ2015020)supported by the Program for Liaoning Excellent Talents in University,ChinaProject(2016RQ051)supported by the Program of Science-Technology Star for Young Scholars by the Dalian Municipality,China
文摘Wollastonite glass ceramics were prepared using the reactive crystallization sintering method by mixing waste glass powders with gehlenite.The crystallization property,thermodynamics,and kinetics of the prepared wollastonite glass ceramics were determined by X-ray diffraction analysis,scanning electron microscopy,energy-dispersive spectroscopy,high-resolution transmission electron microscopy,and differential thermal analysis.Results showed that crystals of wollastonite and alumina could be found in the gehlenite through its reaction with silicon dioxide.The wollastonite crystals showed a lath shape with a certain length-to-diameter ratio.The crystals exhibited excellent bridging and reinforcing effects.In the crystallization process,the aluminum ions in gehlenite diffused into the glass and the silicon ions in the glass diffused into gehlenite.Consequently,the three-dimensional frame structure of gehlenite was partially damaged to form a chain-like wollastonite.The results of crystallization thermodynamics and kinetics indicated that crystallization reaction could occur spontaneously under a low temperature(1173 K),with 20 wt%gehlenite added as the reactive crystallization promoter.The crystallization activation energy was evaluated as 261.99 kJ/mol by using the Kissinger method.The compression strength of the wollastonite glass ceramic samples(7.5 cm×7.5 cm)reached 251 MPa.
基金Project(2010GXNSFA013029) supported by the Natural Science Foundation of Guangxi Province,ChinaProject(101059529) supported by National Undergraduate Innovation Program of the Ministry of Education of China
文摘The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.
文摘In order to study the performance of ceramic composite projectile penetrating into ceramic composite target,the contrast test and numerical simulations of the penetration of standard projectile and the ceramic composite projectile into a ceramic composite target were conducted.The results show that the penetration performance of ceramic composite projectile is obvious superior to that of standard projectile for ceramic composite target.The ceramic nose of ceramic composite projectile fully destroys the ceramic panels anterior to its following armor-piercing projectile body,thus maintaining the penetration ability of the following armor-piercing projectile body.
基金Project(BK2011243) supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(2007DA10512711408) supported by the Visiting Scholarship of State Key Laboratory of Power Transmission Equipment & System Security and New Technology (Chongqing University),China+4 种基金Project(EIPE11204) supported by the State Key Laboratory of Electrical Insulation and Power Equipment,ChinaProject(KF201104) supported by the State Key Laboratory of New Ceramic and Fine Processing,ChinaProject(KFJJ201105) supported by the Opening Project of State Key Laboratory of Electronic Thin Films and Integrated Devices,ChinaProject(10KJD430002) supported by the Universities Natural Science Research Project of Jiangsu Province,ChinaProject(11JDG084) supported by the Research Foundation of Jiangsu University,China
文摘ZnO-Bi2O3-based varistor ceramics doped with Yb2O3 in the range from 0 to 0.4% （molar fraction） were obtained by a solid reaction route. The X-ray diffractometry （XRD） and scanning electron microscopy （SEM） were applied to characterize the phases and microstructure of the varistor ceramics, and a DC parameter instrument for varistor ceramics was applied to investigate their electrical properties and V-I characteristics. The XRD analysis of the samples shows that the ZnO phase, Bi2O3 phase, ZnTSbaOl2-type spinel phase and Zn2Bi3Sb3O14-type pyrochlore are present, and the Yb2O3 phases and Sb2O4 phases are found in varistor ceramics with increasing amounts of Yb2O3. The average size of ZnO grain firstly increases and then decreases with the increase of Yb2O3 content. The result also shows that the threshold voltage is between 656 V/nun and 1 232 V/mm, the nonlinear coefficient is in the range of 14.1-22.3, and the leakage current is between 0.60 μA and 19.6 μA. The 0.20% Yb2O3-added ZnO-Bi2O3-based varistor ceramics sintered at 900 ℃ have the best electrical characteristics.
基金Projects(11772207,U2130128)supported by the National Natural Science Foundation of ChinaProjects(E2019210042,E2017210065)supported by the Natural Science Foundation of Hebei Province,China+3 种基金Project(QN2019137)supported by the Natural Science Foundation of the Hebei Education Department,ChinaProject(A2019210204)supported by the Natural Science Foundation of Hebei Province for Distinguished Young Scholars,ChinaProject(216Z4302G)supported by Central Government Guiding Local Science and Technology Development,ChinaProject supported by Youth Top-notch Talents Supporting Plan of Hebei Province,China。
文摘Alumina ceramics are widely used in many fields such as cutting tools,laser shock materials,roadbed board and refractory.Herein,Al_(2)O_(3)ceramics are prepared by a low-cost pressureless sintering technology,using the binary sintering aids of MgO and SiO_(2).The effects of sintering temperature and the ratio of binary sintering aids on the mechanical properties and microstructure of Al_(2)O_(3)ceramics are investigated.A spinel second phase(MgAl_(2)O_(4))is found out by the analysis of the results of XRD and EDS when MgO and SiO_(2)are introduced in the samples.The optimum properties are found when MgO content is 20 wt.%based on the total sintering aids and the sintering temperature is 1550℃.The bending strength and the bulk density reach a maximum value of 314 MPa and 3.73 g/cm^(3),respectively.The addition of appropriate amount of SiO_(2)makes the formation of liquid phase sintering and the removal of large pores.Meanwhile,a small amount of magnesium oxide doping has an effect on the grain refinement from the microstructure of the sample.Therefore,it is believed that MgO and SiO_(2)are the ideal sintering aids for promoting the densification and property of alumina ceramics.
