As one of the core visual symbols of Chinese traditional culture,the communication history of auspicious cloud patterns on Central Plains ancient ceramics has great significance.Its contemporary value can be summarize...As one of the core visual symbols of Chinese traditional culture,the communication history of auspicious cloud patterns on Central Plains ancient ceramics has great significance.Its contemporary value can be summarized into four aspects,namely the carrier of cultural inheritance and national identity,the innovative resources of modern design,the media of international cultural exchange and the enlightenment of ecological philosophy.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
Y_(3)Al_(2)Ga_(3)O_(12):Ce^(3+),Cr^(3+)(YAGG:Ce^(3+),Cr^(3+)),as a persistent luminescent material,has advantages of high initial luminescence intensity and long persistent time,which is promising in persistent lumine...Y_(3)Al_(2)Ga_(3)O_(12):Ce^(3+),Cr^(3+)(YAGG:Ce^(3+),Cr^(3+)),as a persistent luminescent material,has advantages of high initial luminescence intensity and long persistent time,which is promising in persistent luminescent material applications.At present,YAGG:Ce^(3+),Cr^(3+)powders exhibit good persistent performance,but their persistent performance of ceramics still needs to be further improved to meet the new requirements.In this work,(Y_(0.998)Ce_(0.002))_(3)(Al_(1-x)Cr_(x))_(2)Ga_(3)O_(12) ceramics with different Cr^(3+)doping concentrations were prepared by solid-state reaction,including air pre-sintering,hot isostatic pressing(HIP)post-treatment and air annealing,to investigate the effects of Cr^(3+)doping concentration on the microstructure,optical properties and persistent performance of the ceramics.The results showed that as the doping concentration of Cr^(3+)increased from 0.025%to 0.2%(in atom),no significant effect of Cr^(3+)concentration on the morphology of pre-sintered ceramics or HIP post-treatment ceramics was observed,but the in-line transmittance gradually increased while the persistent performance gradually decreased.Among them,YAGG:Ce^(3+),Cr^(3+)ceramics doped with 0.025%Cr^(3+)showed the strongest initial luminescence intensity exceeding 6055 mcd/m^(2) and a persistent time of 1030 min after air pre-sintering combined with HIP post-treatment and air annealing.By optimizing the Cr^(3+)doping concentration and the fabrication process,the persistent luminescence(PersL)performance of the YAGG:Ce^(3+),Cr^(3+)ceramics was obviously improved.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
The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy beco...The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy becomes defect dipole,which prevents the domain rotation.In this field,a serious problem is that generally,Qm decreases as the temperature(T)increases,since the oxygen vacancies are decoupled from the defect dipoles.In this work,Q_(m) of Pb_(0.95)Sr_(0.05)(Zr_(0.53)Ti_(0.47))O_(3)(PSZT)ceramics doped by 0.40%Fe_(2)O_(3)(in mole)abnormally increases as T increases,of which the Qm and piezoelectric coefficient(d_(33))at room temperature and Curie temperature(TC)are 507,292 pC/N,and 345℃,respectively.The maximum Qm of 824 was achieved in the range of 120–160℃,which is 62.52%higher than that at room temperature,while the dynamic piezoelectric constant(d_(31))was just slightly decreased by 3.85%.X-ray diffraction(XRD)and piezoresponse force microscopy results show that the interplanar spacing and the fine domains form as temperature increases,and the thermally stimulated depolarization current shows that the defect dipoles are stable even the temperature up to 240℃.It can be deduced that the aggregation of oxygen vacancies near the fine domains and defect dipole can be stable up to 240℃,which pins domain rotation,resulting in the enhanced Q_(m) with the increasing temperature.These results give a potential path to design high Q_(m) at high temperature.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
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
Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certa...Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certain range,consequently leading to some superb material properties,e.g.,ripple suppression,elec-trocaloric cooling,and dielectric energy storage.However,there are many cognitive blanks about how this exotic multi-field relationε(E_(DC),T)is influenced and manipulated via microscopic structures in the anti-ferroelectrics.In this work,the classic antiferroelectric ceramics PLZT were selected to see this intelligent effect,based on a quad-parameterizedε(E_(DC))relation on the dependence of T.εrelations were studied under different material compositions,temperature,frequency,AC electric field,and DC electric field,re-vealing lattice/domain structure evolution and the underlying mechanism.The inherent phase stability,introduced random field,and hierarchical hysteresis states were found to co-dominate this multi-field nonlinear relation.This work would not only contribute to future progress in the current applications(ripple suppression/electrocaloric cooling/dielectric energy storage)but imply the possibility of co-sensing temperature and electric potential simply and smartly.展开更多
Any product must undergo precise manufacturing before use.The damage incurred during the manufacturing process can significantly impact the residual strength of the product post-manufacturing.However,the relationship ...Any product must undergo precise manufacturing before use.The damage incurred during the manufacturing process can significantly impact the residual strength of the product post-manufacturing.However,the relationship between residual bending strength and manufacturing-induced damage remains unclear,despite being a crucial parameter for assessing material service life and performance,leading to a decrease in product performance reliability.This study focuses on investigating the impact of crack generation on residual bending strength through theoretical and experimental analyses of scratching,grinding,and three-point bending.The research first elucidates the forms and mechanisms of material damage through scratch experiments.Subsequently,using resin-bonded and electroplated wheels as case studies,the influence of different process parameters on grinding damage and residual bending strength is explored.The reduction of brittle removal can lead to a 50%–60%decrease in residual bending strength.Lastly,a model is developed to delineate the relationship between processing parameters and the residual bending strength of the product,with the model exhibiting an error margin of less than 11%.This model clearly reveals the effect of crack generation under different process parameters on residual flexural strength.展开更多
Porous ultra-high temperature ceramics(UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In o...Porous ultra-high temperature ceramics(UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and partial sintering has been developed for preparing porous Zr C and Hf C with low conductivity. In this process, porous Zr C and Hf C are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The asprepared porous Zr C and Hf C exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m-1 K-1, and compressive strength of 8.28 and 5.51 MPa, respectively.These features render porous Zr C and Hf C promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous Nb C, Ta C as well as Ti C have been prepared by this method.展开更多
Porous ultrahigh temperature ceramics(UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main li...Porous ultrahigh temperature ceramics(UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/partial sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa.The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.展开更多
The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and inc...The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.展开更多
Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity a...Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy(HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm2 s^-1 and 0.51 W m^-1K^-1, respectively. In addition, it exhibits high compressive strength of3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is a novel strategy in making UHTCs thermal insulating.展开更多
Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffr...Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffractometry,scanning electron microscopy,and mercury porosimetry measurements,etc.It is found that although the decomposition of MgCO3 and CaCO3 has little contribution to the porosity,the double addition of MgCO3 and CaCO3 strongly affects the formation of liquid phase,and then changes the phase compositions,pore characterization,and strength.The appropriate mode is the sample containing 1.17wt% MgCO3 and 1.17wt% CaCO3,which has high apparent porosity（41.0%）,high crushing strength（53.5 MPa）,high mullite content（76wt%）,and small average pore size（3.24 μm）.展开更多
High-thermal-conductivity silicon nitride ceramic substrates are indispensable components for nextgeneration high-power electronic devices because of their excellent mechanical properties and high thermal conductiviti...High-thermal-conductivity silicon nitride ceramic substrates are indispensable components for nextgeneration high-power electronic devices because of their excellent mechanical properties and high thermal conductivities, which make them suitable for applications in complex and extreme environments. Here, we present an overview of the recent developments in the preparation of high-thermal-conductivity silicon nitride ceramics. First,the factors affecting the thermal conductivity of silicon nitride ceramics are described. These include lattice oxygen and grain boundary phases, as well the oxygen content of the crystal lattice, which is the main influencing factor.Then, the methods to prepare high-thermal-conductivity silicon nitride ceramics are presented. Recent work on the preparation of high-thermal-conductivity silicon nitride is described in detail, including the raw materials used and the forming and sintering processes. Although great progress has been made, the development of a high-quality,low-cost fabrication process remains a challenge. Nevertheless, we believe that high-thermal-conductivity silicon nitride substrates are promising for massive practical applications in the next generation of high-power electronic devices.展开更多
Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders w...Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders were consolidated by a hot pressing (HP) technique at 1800 °C under a pressure of 30 MPa in argon and nitrogen. The sintering atmosphere had a great influence on the microstructures and mechanical properties of the ceramics. The two ceramics had different phase compositions and fracture surface morphologies. For the ceramics sintered in argon, flexural strength, fracture toughness, elastic modulus and Vickers hardness were 421.90 MPa, 3.40 MPa·m1/2, 174.10 GPa, and 12.74 GPa, respectively. For the ceramics sintered in nitrogen, the mechanical properties increased, except for the Vickers hardness, and the values of the above properties were 526.80 MPa, 5.25 MPa·m1/2, 222.10 GPa, and 11.63 GPa, respectively.展开更多
The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperat...The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.展开更多
Transparent polyerystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0μm and narrow size distribution was selec...Transparent polyerystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0μm and narrow size distribution was selected as the starting material. Transparent polyerystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700℃for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ~ 40μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.展开更多
To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 ℃ a pure single-phase solid solution yb3＋：（LaxY1-x）2O3 was f...To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 ℃ a pure single-phase solid solution yb3＋：（LaxY1-x）2O3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb3＋ at moderate temperatures about 1650 ℃. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb0.11 La0.23Y1.66O3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.展开更多
The effect of heating rates during vacuum debinding on the microstructure and mechanical properties of alumina ceramics are discussed in this paper.The threedimensional(3D)-printed alumina ceramics examined in this st...The effect of heating rates during vacuum debinding on the microstructure and mechanical properties of alumina ceramics are discussed in this paper.The threedimensional(3D)-printed alumina ceramics examined in this study were found to have a layered structure,and interlayer spacing increased as the heating rate increased The pore diameter,shrinkage,flexural strength and hardness were found to decrease as the heating rate increased due to weak interfacial bonding between alumina particles Shrinkage was found to be much larger along the Z direction than along the X or Y directions due to the layer-bylayer forming mode during 3D printing.0.5°C·min-1is considered the optimum heating rate,yielding ceramics with interlayer spacing of 0.65 lm,shrinkage of 2.6%2.3%and 4.0%along the X,Y and Z directions,respectively,flexural strength of 27.5 MPa,hardness of29.8 GPa,Vickers hardness of HV 266.5,pore diameter of356.8 nm,bulk density of 2.5 g·cm-3,and open porosity of38.4%.The debinding procedure used in this study could be used to produce a high-quality ceramic which can be used for fabricating alumina ceramic cores.展开更多
基金Supported by Open Project of Henan Key Laboratory of Research for Central Plains Ancient Ceramics in 2018(ZYGTCXN2018-05).
文摘As one of the core visual symbols of Chinese traditional culture,the communication history of auspicious cloud patterns on Central Plains ancient ceramics has great significance.Its contemporary value can be summarized into four aspects,namely the carrier of cultural inheritance and national identity,the innovative resources of modern design,the media of international cultural exchange and the enlightenment of ecological philosophy.
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(2023YFB3506600)。
文摘Y_(3)Al_(2)Ga_(3)O_(12):Ce^(3+),Cr^(3+)(YAGG:Ce^(3+),Cr^(3+)),as a persistent luminescent material,has advantages of high initial luminescence intensity and long persistent time,which is promising in persistent luminescent material applications.At present,YAGG:Ce^(3+),Cr^(3+)powders exhibit good persistent performance,but their persistent performance of ceramics still needs to be further improved to meet the new requirements.In this work,(Y_(0.998)Ce_(0.002))_(3)(Al_(1-x)Cr_(x))_(2)Ga_(3)O_(12) ceramics with different Cr^(3+)doping concentrations were prepared by solid-state reaction,including air pre-sintering,hot isostatic pressing(HIP)post-treatment and air annealing,to investigate the effects of Cr^(3+)doping concentration on the microstructure,optical properties and persistent performance of the ceramics.The results showed that as the doping concentration of Cr^(3+)increased from 0.025%to 0.2%(in atom),no significant effect of Cr^(3+)concentration on the morphology of pre-sintered ceramics or HIP post-treatment ceramics was observed,but the in-line transmittance gradually increased while the persistent performance gradually decreased.Among them,YAGG:Ce^(3+),Cr^(3+)ceramics doped with 0.025%Cr^(3+)showed the strongest initial luminescence intensity exceeding 6055 mcd/m^(2) and a persistent time of 1030 min after air pre-sintering combined with HIP post-treatment and air annealing.By optimizing the Cr^(3+)doping concentration and the fabrication process,the persistent luminescence(PersL)performance of the YAGG:Ce^(3+),Cr^(3+)ceramics was obviously improved.
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(U2241242)National Key R&D Program of China(2023YFB3812000,2021YFA0716502)。
文摘The accepted doping ion in Ti^(4+)-site of PbZr_(y)Ti_(1–y)O_(3)(PZT)-based piezoelectric ceramics is a well-known method to increase mechanical quality factor(Q_(m)),since the acceptor coupled by oxygen vacancy becomes defect dipole,which prevents the domain rotation.In this field,a serious problem is that generally,Qm decreases as the temperature(T)increases,since the oxygen vacancies are decoupled from the defect dipoles.In this work,Q_(m) of Pb_(0.95)Sr_(0.05)(Zr_(0.53)Ti_(0.47))O_(3)(PSZT)ceramics doped by 0.40%Fe_(2)O_(3)(in mole)abnormally increases as T increases,of which the Qm and piezoelectric coefficient(d_(33))at room temperature and Curie temperature(TC)are 507,292 pC/N,and 345℃,respectively.The maximum Qm of 824 was achieved in the range of 120–160℃,which is 62.52%higher than that at room temperature,while the dynamic piezoelectric constant(d_(31))was just slightly decreased by 3.85%.X-ray diffraction(XRD)and piezoresponse force microscopy results show that the interplanar spacing and the fine domains form as temperature increases,and the thermally stimulated depolarization current shows that the defect dipoles are stable even the temperature up to 240℃.It can be deduced that the aggregation of oxygen vacancies near the fine domains and defect dipole can be stable up to 240℃,which pins domain rotation,resulting in the enhanced Q_(m) with the increasing temperature.These results give a potential path to design high Q_(m) at high temperature.
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 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supported by the National Natural Science Foun-dation of China(Grant Nos.U2002217,11774366 and 52102342).
文摘Due to the atomic-level centrosymmetric spontaneous polarization,antiferroelectric materials exhibit a sensitively nonlinear capacitive response to plural physic fields(mainly electric field and temperature)in a certain range,consequently leading to some superb material properties,e.g.,ripple suppression,elec-trocaloric cooling,and dielectric energy storage.However,there are many cognitive blanks about how this exotic multi-field relationε(E_(DC),T)is influenced and manipulated via microscopic structures in the anti-ferroelectrics.In this work,the classic antiferroelectric ceramics PLZT were selected to see this intelligent effect,based on a quad-parameterizedε(E_(DC))relation on the dependence of T.εrelations were studied under different material compositions,temperature,frequency,AC electric field,and DC electric field,re-vealing lattice/domain structure evolution and the underlying mechanism.The inherent phase stability,introduced random field,and hierarchical hysteresis states were found to co-dominate this multi-field nonlinear relation.This work would not only contribute to future progress in the current applications(ripple suppression/electrocaloric cooling/dielectric energy storage)but imply the possibility of co-sensing temperature and electric potential simply and smartly.
基金Supported by National Key Research and Development Program of China(Grant No.2023YFB3711100)National Natural Science Foundation of China(Grant Nos.52275458,52275207)Tianjin Municipal Natural Science Foundation(Grant No.22JCZDJC00050)。
文摘Any product must undergo precise manufacturing before use.The damage incurred during the manufacturing process can significantly impact the residual strength of the product post-manufacturing.However,the relationship between residual bending strength and manufacturing-induced damage remains unclear,despite being a crucial parameter for assessing material service life and performance,leading to a decrease in product performance reliability.This study focuses on investigating the impact of crack generation on residual bending strength through theoretical and experimental analyses of scratching,grinding,and three-point bending.The research first elucidates the forms and mechanisms of material damage through scratch experiments.Subsequently,using resin-bonded and electroplated wheels as case studies,the influence of different process parameters on grinding damage and residual bending strength is explored.The reduction of brittle removal can lead to a 50%–60%decrease in residual bending strength.Lastly,a model is developed to delineate the relationship between processing parameters and the residual bending strength of the product,with the model exhibiting an error margin of less than 11%.This model clearly reveals the effect of crack generation under different process parameters on residual flexural strength.
基金financially supported by the National Natural Science Foundation of China under Grant Nos. 51672064 and U1435206the Beijing Municipal Science & Technology Commission under Grant No. D161100002416001
文摘Porous ultra-high temperature ceramics(UHTCs) are potential candidates as high-temperature thermal insulation materials. However, high thermal conductivity is the main obstacle to the application of porous UHTCs. In order to address this problem, herein, a new method combining in-situ reaction and partial sintering has been developed for preparing porous Zr C and Hf C with low conductivity. In this process, porous Zr C and Hf C are directly obtained from ZrO2/C and HfO2/C green bodies without adding any pore-forming agents. The release of reaction gas can not only increase the porosity but also block the shrinkage. The asprepared porous Zr C and Hf C exhibit homogeneous porous microstructure with grain sizes in the range of 300–600 nm and 200–500 nm, high porosity of 68.74% and 77.82%, low room temperature thermal conductivity of 1.12 and 1.01 W·m-1 K-1, and compressive strength of 8.28 and 5.51 MPa, respectively.These features render porous Zr C and Hf C promising as light-weight thermal insulation materials for ultrahigh temperature applications. Furthermore, the feasibility of this method has been demonstrated and porous Nb C, Ta C as well as Ti C have been prepared by this method.
基金supported by the National Natural Science Foundation of China under Grant Nos. U1435206 and 51672064by the Beijing Municipal Science & Technology Commission under Grant No. D161100002416001
文摘Porous ultrahigh temperature ceramics(UHTCs) are potential candidates as reusable thermal protection materials of transpiration cooling system in scramjet engine. However, low strength and low porosity are the main limitations of porous UHTCs. To overcome these problems, herein, a new and simple in-situ reaction/partial sintering process has been developed for preparing high strength and high porosity porous YB2C2. In this process, a simple gas-releasing in-situ reaction has been designed, and the formation and escape of gases can block the shrinkage during sintering process, which is favorable to increase the porosity of porous YB2C2. In order to demonstrate the advantages of the new method, porous YB2C2 ceramics have been fabricated from Y2O3, BN and graphite powders for the first time. The as-prepared porous YB2C2 ceramics possess high porosity of 57.17%–75.26% and high compressive strength of 9.32–34.78 MPa.The porosity, sintered density, radical shrinkage and compressive strength of porous YB2C2 ceramics can be controlled simply by changing the green density. Due to utilization of graphite as the carbon source, the porous YB2C2 ceramics show anisotropy in microstructure and mechanical behavior. These features render the porous YB2C2 ceramics promising as a thermal-insulating light-weight component for transpiration cooling system.
文摘The effect of Tb407 on electrical behavior of the ZnO-Pr6Oll-based varistor ceramics was investigated. Microstructural analysis indicated that the addition of Tb407 decreased average grain size from 3.6 to 3.2 and increased the sintered density from 5.58 to 5.68 g/cm3. As the amount ofTb407 increased, the breakdown field increased from 9393 to 12437 V/cm and the nonlinear coefficient increased from 50 to 65. The varistor ceramics added with 0.5 mol.% in the amount of Tb407 exhibited an excellent stability by exhibiting 0. 1% in the variation rate of the breakdown field, 0% in the variation rate of the nonlinear coefficient, and 8.8% in the variation rate of the leakage current density for DC-accelerated aging stress of 0.85 E1 mA/115 ℃/24 h.
基金supported by the National Natural Science Foundation of China (Nos. 51672064 and U1435206)
文摘Transition metal diborides based ultrahigh temperature ceramics(UHTCs) are characterized by high melting point, high strength and hardness, and high electrical and thermal conductivity. The high thermal conductivity arises from both electronic and phonon contributions. Thus electronic and phonon contributions must be controlled simultaneously in reducing the thermal conductivity of transition metal diborides. In high entropy(HE) materials, both electrons and phonons are scattered such that the thermal conductivity can significantly be reduced, which opens a new window to design novel insulating materials. Inspired by the high entropy effect, porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is designed in this work as a new thermal insulting ultrahigh temperature material and is synthesized by an in-situ thermal borocarbon reduction/partial sintering process. The porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 possesses high porosity of 75.67%, pore size of 0.3–1.2 μm, homogeneous microstructure with small grain size of 400–800 nm, which results in low room temperature thermal diffusivity and thermal conductivity of 0.74 mm2 s^-1 and 0.51 W m^-1K^-1, respectively. In addition, it exhibits high compressive strength of3.93 MPa. The combination of these properties indicates that exploring porous high entropy ceramics such as porous HE(Zr0.2Hf0.2Ti0.2Nb0.2Ta0.2)B2 is a novel strategy in making UHTCs thermal insulating.
基金Puyang Re-fractories Co. Ltd. for financially supporting
文摘Porous ceramics were prepared from kaolinite gangue and Al（OH）3 with double addition of MgCO3 and CaCO3 by the pore-forming in-situ technique.The characterizations of porous ceramics were investigated by X-ray diffractometry,scanning electron microscopy,and mercury porosimetry measurements,etc.It is found that although the decomposition of MgCO3 and CaCO3 has little contribution to the porosity,the double addition of MgCO3 and CaCO3 strongly affects the formation of liquid phase,and then changes the phase compositions,pore characterization,and strength.The appropriate mode is the sample containing 1.17wt% MgCO3 and 1.17wt% CaCO3,which has high apparent porosity（41.0%）,high crushing strength（53.5 MPa）,high mullite content（76wt%）,and small average pore size（3.24 μm）.
基金financially supported by the National Key Research and Development Program of China (No.2017YFB0310400)the National Natural Science Foundation of China (No.51427802)。
文摘High-thermal-conductivity silicon nitride ceramic substrates are indispensable components for nextgeneration high-power electronic devices because of their excellent mechanical properties and high thermal conductivities, which make them suitable for applications in complex and extreme environments. Here, we present an overview of the recent developments in the preparation of high-thermal-conductivity silicon nitride ceramics. First,the factors affecting the thermal conductivity of silicon nitride ceramics are described. These include lattice oxygen and grain boundary phases, as well the oxygen content of the crystal lattice, which is the main influencing factor.Then, the methods to prepare high-thermal-conductivity silicon nitride ceramics are presented. Recent work on the preparation of high-thermal-conductivity silicon nitride is described in detail, including the raw materials used and the forming and sintering processes. Although great progress has been made, the development of a high-quality,low-cost fabrication process remains a challenge. Nevertheless, we believe that high-thermal-conductivity silicon nitride substrates are promising for massive practical applications in the next generation of high-power electronic devices.
基金Project supported by the National Natural Science Foundation of China (No 50902031)the Development Program for Outstanding Young Teachers in Harbin Institute of Technology (No HITQNJS2009064)
文摘Amorphous SiBCNAl powders were prepared via a mechanical alloying (MA) technique using crystalline silicon (Si), hexagonal boron nitride (h-BN), graphite (C), and aluminum (Al) as starting materials. SiBCNAl powders were consolidated by a hot pressing (HP) technique at 1800 °C under a pressure of 30 MPa in argon and nitrogen. The sintering atmosphere had a great influence on the microstructures and mechanical properties of the ceramics. The two ceramics had different phase compositions and fracture surface morphologies. For the ceramics sintered in argon, flexural strength, fracture toughness, elastic modulus and Vickers hardness were 421.90 MPa, 3.40 MPa·m1/2, 174.10 GPa, and 12.74 GPa, respectively. For the ceramics sintered in nitrogen, the mechanical properties increased, except for the Vickers hardness, and the values of the above properties were 526.80 MPa, 5.25 MPa·m1/2, 222.10 GPa, and 11.63 GPa, respectively.
文摘The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.
基金Project supported by the National High Technology Research and Development Program of China (2004AA332060)
文摘Transparent polyerystalline yttria is a promising optical ceramics with excellent physical and chemical properties. A commercial yttria powder with a mean particle size of 1.0μm and narrow size distribution was selected as the starting material. Transparent polyerystalline yttria ceramics without any additives were successfully prepared by hot isostatic pressing (HIP) at 1700℃for 2 h under the pressure of 200 MPa in Ar following spark plasma sintering (SPS). The as-prepared specimens consist of uniform grains of ~ 40μm. Scanning electron microscopy (SEM) images show their pore-free structure. The influences of the yttria powder and sintering process on the properties of the yttria ceramics, including the microstructure and optical properties, were further investigated in our study.
基金Project supported by Russian Fund of Basic Research(NSFC-RFBR 512111056/13-02-91173-ГФЕН_а,and 13-02-01237,13-02-96043)Ural branch of Russian Academy of Sciences(13-2-054-РЦЛ)Program of Presidium of Russian Academy of Sciences
文摘To prepare ytterbium doped lanthania yttria nanopowder a method of laser evaporation of mixed oxides was used. After calcinations of the powder at 1200 ℃ a pure single-phase solid solution yb3＋：（LaxY1-x）2O3 was formed in the nanoparticles. Influence of lanthanum oxide as an isovalent additive on the yttria structure was investigated. The lanthanium ions were proved to be a good aid to sinter yttria ceramics doped with Yb3＋ at moderate temperatures about 1650 ℃. The ceramics with relative density higher than 99.99% and grain size about 40 μm were fabricated. Full transmittance of 1.8 mm thick Yb0.11 La0.23Y1.66O3 ceramics reached 82.5% at 800 nm. This material could be a good gain medium for ytterbium high power pulse lasers.
基金financially supported by the National Key Research and Development Program of China(No.2018YFB1106600)the National Natural Science Foundation of China(No.51672217)。
文摘The effect of heating rates during vacuum debinding on the microstructure and mechanical properties of alumina ceramics are discussed in this paper.The threedimensional(3D)-printed alumina ceramics examined in this study were found to have a layered structure,and interlayer spacing increased as the heating rate increased The pore diameter,shrinkage,flexural strength and hardness were found to decrease as the heating rate increased due to weak interfacial bonding between alumina particles Shrinkage was found to be much larger along the Z direction than along the X or Y directions due to the layer-bylayer forming mode during 3D printing.0.5°C·min-1is considered the optimum heating rate,yielding ceramics with interlayer spacing of 0.65 lm,shrinkage of 2.6%2.3%and 4.0%along the X,Y and Z directions,respectively,flexural strength of 27.5 MPa,hardness of29.8 GPa,Vickers hardness of HV 266.5,pore diameter of356.8 nm,bulk density of 2.5 g·cm-3,and open porosity of38.4%.The debinding procedure used in this study could be used to produce a high-quality ceramic which can be used for fabricating alumina ceramic cores.
