SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum ...SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.展开更多
Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C-M_(t)C composite ceramic was prepared by hot press sintering,with the Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C high-entropy carbide as the main phase.Secondary phase M_(x)C(M...Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C-M_(t)C composite ceramic was prepared by hot press sintering,with the Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C high-entropy carbide as the main phase.Secondary phase M_(x)C(M=Ti,Zr,Hf,Nb,Ta) was found to be distributed relatively uniform in the composite ceramic.The oxidation behavior of the ceramic was examined after exposure to 923 K and 1173 K.Morphology of the surface and cross sections of all oxidation samples were observed.The characteristics of the oxidation behavior of the high-entropy carbide and the secondary phase M_(x)C were compared and analyzed.The secondary phases(such as Ti-rich carbide or Hf-rich carbide) in the material were seriously oxidized at 923 K and 1173 K,which reflects the superior oxidation performance of the high-entropy carbide.The nano high-entropy oxides with Ti,Zr,Hf,Nb,Ta,and O elements were discovered by oxidation of the composite ceramic.This research will help deepen the understanding of the oxidation mechanism of high-entropy carbide and composite ceramic.展开更多
Nominal (Li0.5Ce0.5)x(Na0.5Bi0.5)(1-x)Na0.5Bi4.5Ti5O18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase wa...Nominal (Li0.5Ce0.5)x(Na0.5Bi0.5)(1-x)Na0.5Bi4.5Ti5O18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase was determined in these ceramics using XRD technique. At room temperature, the x=0.11 sample showed the largest piezoelectric constant, d33, of about 26.5 pC/N and the largest electromechanical coupling factor, kt, of about 30%. Even after annealing at 500 ℃, the value of d33 was still about 19 pC/N, in x=0.08-0.11 samples. Moreover these composite ceramics showed low temperature coefficients of dielectric constant and high electrical resistivity in the temperature region of 450-550 ℃. These results indicated that (Li, Ce) modified NaBi5Ti5O18 composite ceramics were promising piezoelectric materials for high-temperature applications.展开更多
We successfully obtain a high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight piano-concave cavity. The temperature distribution in composite cera...We successfully obtain a high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight piano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By using a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.展开更多
For improving the properties of SiC-mullite composite ceramics used for solar sensible thermal storage, MnO2 was introduced as sintering additive when preparing. The composite ceramics were synthesized by using SiC, a...For improving the properties of SiC-mullite composite ceramics used for solar sensible thermal storage, MnO2 was introduced as sintering additive when preparing. The composite ceramics were synthesized by using SiC, andalusite, a-Al2O3 as the starting materials with non-contact graphite-buried sintering method. Phase composition and microstructure of the composites were investigated by XRD and SEM, and the effect of MnOz on the properties of SiC composites was studied. Results indicated that samples SM1 with 0.2 wt% MnO2 addition achieved the optimum properties: bending strength of 70.96 MPa, heat capacity of 1.02 J.(g.K)-1, thermal conductivity of 9.05 W-(m.K)-1. Proper addition of MnO2 was found to weaken the volume effect of the composites and improve the thermal shock resistance with an increased rate of 27.84% for bending strength after 30 cycles of thermal shock (air cooling from 1 100 ℃ to RT). Key words: SiC-mullite composite ceramics; MnO2; solar sensible thermal storage; non-contact graphite-buried sintering; thermal shock resistance展开更多
The Al2O3-ZrO2(3Y)-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength ...The Al2O3-ZrO2(3Y)-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests (quenching from 1000℃ to 25℃ in air medium) is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2(3Y)-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2(3Y)-SiC composite ceramic has promising potential application in solar thermal power.展开更多
ZrN-SiAlON composite materials were synthesized at 1 550 ℃ for 6 h via a carbothermal reduction nitridation route using fly ash (≤74 μm),zircon (≤ 44 μm) and active carbon as starting materials.The processed ...ZrN-SiAlON composite materials were synthesized at 1 550 ℃ for 6 h via a carbothermal reduction nitridation route using fly ash (≤74 μm),zircon (≤ 44 μm) and active carbon as starting materials.The processed ZrN-SiAlON composite micropowders were mixed with polyvinyl alcohol as binder to prepare ZrN (ZrON)-SiAlON composite ceramics by carbon-embedded pressureless firing at 1 450,1 500 and 1 550 ℃ for 1 h,respectively.Influences of firing temperature on the phase compositions,microstructure and sintering properties of the ceramics were investigated.The results show that:(1) β-SiAlON based composite ceramics with different compositions can be prepared by controlling firing temperature,and the main crystalline phases of the specimen fired at 1 550 ℃ for 1 h involve ZrN,ZrON and β-SiAlON (z =2,Si4Al2O2N6); (2) ZrN (ZrON),β-SiAlON and a Fe-Si based compound can be observed in the microstructures of the specimens fired at different temperatures.ZrN (ZrON) particles distribute homogeneously in the β-SiAlON matrix; (3) raising firing temperature can increase the shrinkage ratio of the ceramics,and the volume shrinkage ratio increases from 19.4% to 40.3% when the firing temperature rises from 1 450 to 1 550 ℃.展开更多
Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based(DED-LB)te...Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based(DED-LB)technology.However,the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions.The shaping quality,microstructure,and mechanical properties of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13)(6 mol%TiO_(2))composite ceramics were systematically investigated as a function of energy input in an extensive process window.On this basis,the formation mechanism of solidification defects and the evolution process of microstructure were revealed,and the optimized process parameters were determined.Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases,thus,facilitating the elimination of solidification defects,such as pores and strip gaps.In addition,the microstructure size is strongly dependent on the energy input,increasing when the energy input increases.Moreover,the morphology of theα-Al_(2)O_(3) phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions.Under the comprehensive influence of solidification defects and microstructure size,the fracture toughness and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics present a parabolic law behavior as the energy input increases.Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min^(2) g^(-1) mm^(-1).Within this process window,the average microhardness,fracture toughness,and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics are up to 1640 Hv,3.87 MPa m^(1/2),and 227 MPa,respectively.This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics.展开更多
The grain growing dynamics including the growing process, the growing exponent and the growing activation energy is obtained for the MgO-CaO composite ceramics with the additions of Fe2O3, CeO2 and/or ZrO2 as fluxes b...The grain growing dynamics including the growing process, the growing exponent and the growing activation energy is obtained for the MgO-CaO composite ceramics with the additions of Fe2O3, CeO2 and/or ZrO2 as fluxes by measuring the size of grains with the method of Straight Line Across. The results show that all of the additions, in which Fe2O3 is the strongest, have notable effects on the grain growing dynamics by reducing the growing activation energy and promoting the grain growing. The research gives a good reference for the additions of fluxes to the matrix of ceramic filter.展开更多
Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is ...Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is studied.Experimental results show that the vickers hardness,wear resistance and thermal conductivity of the samples increase with the increase in the SiC content,and the hardness of the sample reaches 16.22 GPa,and thermal conductivity of the sample reaches 25.41 W/(m.K)at room temperature when the SiC content is 20 wt%(B5)and the sintering temperature is at 1640℃.Higher hardness means higher scour resistance,and it indicates that the B5 material is expected to be used for the solar heat absorber of third generation solar thermal generation.The results indicate the mechanism of improving mechanical properties of Al_(2)O_(3)/SiC composite ceramics:SiC plays a role in grain refinement that the grain of SiC inhibits the grain growth of Al_(2)O_(3),while the addition of SiC changes the fracture mode from the intergranular to the intergranular-transgranular.展开更多
The influence of Mn doping on the formation and dielectric properties of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) composite ceramics were investigated. The Mn was doped according to the formula 0.7BaO&...The influence of Mn doping on the formation and dielectric properties of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) composite ceramics were investigated. The Mn was doped according to the formula 0.7BaO·0.3SrO·(0.7-z)TiO2·0.3Nb2O5·zMnO2 (BSTNM). The results show the two phases, perovskite phase BST and the tungsten bronze phase SBN, are coexistence in BSTNM as they are in BSTN composite ceramics. The Mn ions doped in BSTN substitute for Nb5+ ions in the tungsten bronze phase, and then, the Nb5+ ions substitute for Ti4+ ions in the perovskite phase. With the increasing of Mn dopant, the content of the perovskite phase increases while that of the tungsten bronze phase decreases, and the grain size of the perovskite phase decreases. As well as, the phase transition temperature of tungsten bronze phase increases with value z increasing from 0 to about 0.05.展开更多
Strontium barium niobate/barium strontium titanate composite ceramics of xSrO·(1-x)BaO·0.5Nb2O5·0.5TiO2 (BSTN in short) with a range of Sr/Ba ratios were fabricated using a modified sol-gel method with ...Strontium barium niobate/barium strontium titanate composite ceramics of xSrO·(1-x)BaO·0.5Nb2O5·0.5TiO2 (BSTN in short) with a range of Sr/Ba ratios were fabricated using a modified sol-gel method with Nb2O5 fine powders suspended in the barium strontium titanate (BST in short) sol solution. Powders obtained from dried gels were calcined at 800 ℃ for 3 h. After preparing bulk ceramics from these powders by sintering at 1200 ℃ for 3 h, the tetragonal tungsten bronze(TTB) phase and perivoskite phase were co-present in compositions between 0.25≤x≤0.75, with the increasing of x value, the peaks of pervoskite phase shift to the high angle position slightly while no changes happened in the peak position of TTB phase. The peak intensity of both two phases were also changed.展开更多
The performance of composite ceramic armor penetrated by rod projectile was studied by both numerical simulation and experiment.The penetration and damage mechanisms of the projectile-armor after high-speed collision ...The performance of composite ceramic armor penetrated by rod projectile was studied by both numerical simulation and experiment.The penetration and damage mechanisms of the projectile-armor after high-speed collision were also observed by high-speed photography.The experimental results showed that the ballistic performance of composite ceramic armor was highly affected by the density,hardness and toughness of bulletproof ceramic.The flow stress of the failed bulletproof ceramic is not only related to the pressure but also related to the strain rate.The phenomenological method based on Bodner-Partom ceramic model was introduced to derive the growth rate of damage.Numerical simulation results show good agreement with the experimental results.展开更多
Al 2O 3-SiO 2-TiO 2-ZrO 2 supported membranes were prepar ed by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al 2O 3, TiO...Al 2O 3-SiO 2-TiO 2-ZrO 2 supported membranes were prepar ed by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al 2O 3, TiO 2(a natase), Al 2SiO 5, and ZrO 2 in these membranes. Changing the molar ratio of Al∶Si∶Ti∶Zr,the kinds and content of crystal phases of composite membranes could be different, which may lead to a variety of microstructure of membranes. The surface nanoscale topography and microstructure of membranes were investiga ted by XRD,SEM,AFM,EPMA. The effects of additives and heat treatments on the sur face nanoscale topography and microstructure of composite ceramic membranes were also analyzed.展开更多
The synthesis process of TiN/AlON composite ceramics was studied, the thermodynamics, mechanical properties and micro-structures of TiN/AlON have also been investigated. The TiN/AlON composite ceramics has been synthe...The synthesis process of TiN/AlON composite ceramics was studied, the thermodynamics, mechanical properties and micro-structures of TiN/AlON have also been investigated. The TiN/AlON composite ceramics has been synthesized by both hot-pressing and pressureless sintering. The characterizations of the material synthesized were analyzed with XRD (X-ray diffraction) and TEM (transmission electronic microscope). The density and toughness strength of TiN/AlON are 3.57g/cm3 and 4.74MPa.m1/2, respectively. The bending strength was measured at both room temperature and high temperatures and the results are 399 MPa (room temperature), 406 MPa (1 073 K), 417 MPa (1 273 K) and 323 MPa (1 573 K). Pattern Recognition (PR) and Artificial Neural Network (ANN) were used to optimize the parameters and to predict the expected values. A proper parameter for pressureless sintering of TiN/AlON has been obtained and testified, the parameters are temperature (1 978 K), AlN / (AlN + Al2O3) ratio (0.22), MgO (4.7%) and TiO2 (7.2%).展开更多
The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was disc...The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (Ⅳ) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al203 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.展开更多
Aluminum oxide(Al_(2)O_(3))ceramics have been widely utilized as circuit substrates owing to their exceptional performance.In this study,boron nitride microribbon(BNMR)/Al_(2)O_(3)composite ceramics are prepared using...Aluminum oxide(Al_(2)O_(3))ceramics have been widely utilized as circuit substrates owing to their exceptional performance.In this study,boron nitride microribbon(BNMR)/Al_(2)O_(3)composite ceramics are prepared using spark plasma sintering(SPS).This study examines the effect of varying the amount of toughened phase BNMR on the density,mechanical properties,dielectric constant,and thermal conductivity of BNMR/Al_(2)O_(3)composite ceramics while also exploring the mechanisms behind the toughening and increased thermal conductivity of the fabricated ceramics.The results showed that for a BNMR content of 5 wt%,BNMR/Al_(2)O_(3)composite ceramics displayed more enhanced characteristics than pure Al_(2)O_(3)ceramics.In particular,the relative density,hardness,fracture toughness,and bending strength were 99.95%±0.025%,34.11±1.5 GPa,5.42±0.21 MPa·m1/2,and 375±2.5 MPa,respectively.These values represent increases of 0.76%,70%,35%,and 25%,respectively,compared with the corresponding values for pure Al_(2)O_(3)ceramics.Furthermore,during the SPS process,BNMRs are subjected to high temperatures and pressures,resulting in the bending and deformation of the Al_(2)O_(3)matrix;this leads to the formation of special thermal pathways within it.The dielectric constant of the composite ceramics decreased by 25.6%,whereas the thermal conductivity increased by 45.6%compared with that of the pure Al_(2)O_(3)ceramics.The results of this study provide valuable insights into ways of enhancing the performance of Al_(2)O_(3)-based ceramic substrates by incorporating novel BNMRs as a second phase.These improvements are significant for potential applications in circuit substrates and related fields that require high-performance materials with improved mechanical properties and thermal conductivities.展开更多
In this paper, the concept of incorporating core–shell structured units as secondary phases totoughen Al_(2)O_(3) ceramics is proposed. Al_(2)O_(3) composite ceramics toughened by B_(4)C@TiB_(2) core–shellunits are ...In this paper, the concept of incorporating core–shell structured units as secondary phases totoughen Al_(2)O_(3) ceramics is proposed. Al_(2)O_(3) composite ceramics toughened by B_(4)C@TiB_(2) core–shellunits are successfully synthesized using a combination of molten salt methodology and spark plasmasintering. The synthesis of B_(4)C@TiB_(2) core–shell toughening units stems from the prior production ofcore–shell structural B_(4)C@TiB_(2) powders, and this core–shell structure is effectively preserved withinthe Al_(2)O_(3) matrix after sintering. The B_(4)C@TiB_(2) core–shell toughening unit consists of a micron-sizedB4C core enclosed by a shell approximately 500 nm in thickness, composed of numerous nanosizedTiB2 grains. The regions surrounding these core–shell units exhibit distinct geometric structures andencompass multidimensional variations in phase composition, grain dimensions, and thermal expansioncoefficients. Consequently, intricate stress distributions emerge, fostering the propagation of cracks inmultiple dimensions. This behavior consumes a considerable amount of crack propagation energy,thereby enhancing the fracture toughness of the Al_(2)O_(3) matrix. The resulting Al_(2)O_(3) composite ceramicsdisplay relative density of 99.7%±0.2%, Vickers hardness of 21.5±0.8 GPa, and fracture toughness6.92±0.22 MPa·m1/2.展开更多
Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formati...Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.展开更多
Composite ceramics thermal barrier coatings(TBCs) are widely used in the aero-engines field due to their excellent thermal insulation, which improves the service life and durability of the inherent hot components. The...Composite ceramics thermal barrier coatings(TBCs) are widely used in the aero-engines field due to their excellent thermal insulation, which improves the service life and durability of the inherent hot components. The most typical, successful and widely used TBCs material is yttria stabilized zirconia(YSZ). In this paper, fabrication methods, coating structures, materials, failure mechanism and major challenges of YSZ TBCs are introduced and reviewed. The research tendency is put forward as well. This review provides a good understanding of the YSZ TBCs and inspires researchers to discover versatile ideas to improve the TBCs systems.展开更多
基金Funded by the National Key R&D Program of China(No.2018YFB1501002)。
文摘SiC composite ceramics for solar absorber and storage integration are new concentrating solar power materials.SiC composite ceramics for solar absorber and storage integration were fabricated using SiC,black corundum and kaolin as the raw materials,Co_(2)O_(3)as the additive via pressureless graphite-buried sintering method in this study.Influences of Co_(2)O_(3)on the microstructure and properties of SiC composite ceramics for solar absorber and storage integration were studied.The results indicate that sample D2(5wt%Co_(2)O_(3))sintered at 1480℃exhibits optimal performances for 119.91 MPa bending strength,93%solar absorption,981.5 kJ/kg(25-800℃)thermal storage density.The weight gain ratio is 12.58 mg/cm2after 100 h oxidation at 1000℃.The Co_(2)O_(3)can decrease the liquid phase formation temperature and reduce the viscosity of liquid phase during sintering.The liquid with low viscosity not only promotes the elimination of pores to achieve densification,but also increases bending strength,solar absorption,thermal storage density and oxidation resistance.A dense SiO_(2) layer was formed on the surface of SiC after 100 h oxidation at 1000℃,which protects the sample from further oxidation.However,excessive Co_(2)O_(3)will make the microstructure loose,which is disadvantageous to the performances of samples.
基金Project supported by the Doctoral Research Fund of Southwest University of Science and Technology(Grant No.20zx7104)the Sichuan Science and Technology Program(Grant No.2020ZYD055)the National Natural Science Foundation of China(Grant Nos.11905206 and 12075194)。
文摘Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C-M_(t)C composite ceramic was prepared by hot press sintering,with the Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2)C high-entropy carbide as the main phase.Secondary phase M_(x)C(M=Ti,Zr,Hf,Nb,Ta) was found to be distributed relatively uniform in the composite ceramic.The oxidation behavior of the ceramic was examined after exposure to 923 K and 1173 K.Morphology of the surface and cross sections of all oxidation samples were observed.The characteristics of the oxidation behavior of the high-entropy carbide and the secondary phase M_(x)C were compared and analyzed.The secondary phases(such as Ti-rich carbide or Hf-rich carbide) in the material were seriously oxidized at 923 K and 1173 K,which reflects the superior oxidation performance of the high-entropy carbide.The nano high-entropy oxides with Ti,Zr,Hf,Nb,Ta,and O elements were discovered by oxidation of the composite ceramic.This research will help deepen the understanding of the oxidation mechanism of high-entropy carbide and composite ceramic.
基金supported by the National Natural Science Foundation of China (50702030)National Fund for Fostering Talents of Basic Science (J0730318)
文摘Nominal (Li0.5Ce0.5)x(Na0.5Bi0.5)(1-x)Na0.5Bi4.5Ti5O18 composite ceramics were fabricated using conventional solid-state reaction method. The coexistence of bismuth layer-structured phase and perovskite phase was determined in these ceramics using XRD technique. At room temperature, the x=0.11 sample showed the largest piezoelectric constant, d33, of about 26.5 pC/N and the largest electromechanical coupling factor, kt, of about 30%. Even after annealing at 500 ℃, the value of d33 was still about 19 pC/N, in x=0.08-0.11 samples. Moreover these composite ceramics showed low temperature coefficients of dielectric constant and high electrical resistivity in the temperature region of 450-550 ℃. These results indicated that (Li, Ce) modified NaBi5Ti5O18 composite ceramics were promising piezoelectric materials for high-temperature applications.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61107086, 61172010, and 61101058)the Science and Technology Committee of Tianjin, China (Grant No. 11JCYBJC01100)the National High Technology Research and Development Program of China (Grant No. 2011AA010205)
文摘We successfully obtain a high-average-power high-stability Q-switched green laser based on diode-side-pumped composite ceramic Nd:YAG in a straight piano-concave cavity. The temperature distribution in composite ceramic Nd:YAG crystal is numerically analyzed and compared with that of conventional Nd:YAG crystal. By using a composite ceramic Nd:YAG rod and a type-II high gray track resistance KTP (HGTR-KTP) crystal, a green laser with an average output power of 165 W is obtained at a repetition rate of 25 kHz, with a diode-to-green optical conversion of 14.68%, and a pulse width of 162 ns. To the best of our knowledge, both the output power and optical-to-optical efficiency are the highest values for green laser systems with intracavity frequency doubling of this novel composite ceramic Nd:YAG laser to date. The power fluctuation at around 160 W is lower than 0.3% in 2.5 hours.
基金Funded by the Major State Basic Research Development Program of China(973 Program)(No.2010CB227105)
文摘For improving the properties of SiC-mullite composite ceramics used for solar sensible thermal storage, MnO2 was introduced as sintering additive when preparing. The composite ceramics were synthesized by using SiC, andalusite, a-Al2O3 as the starting materials with non-contact graphite-buried sintering method. Phase composition and microstructure of the composites were investigated by XRD and SEM, and the effect of MnOz on the properties of SiC composites was studied. Results indicated that samples SM1 with 0.2 wt% MnO2 addition achieved the optimum properties: bending strength of 70.96 MPa, heat capacity of 1.02 J.(g.K)-1, thermal conductivity of 9.05 W-(m.K)-1. Proper addition of MnO2 was found to weaken the volume effect of the composites and improve the thermal shock resistance with an increased rate of 27.84% for bending strength after 30 cycles of thermal shock (air cooling from 1 100 ℃ to RT). Key words: SiC-mullite composite ceramics; MnO2; solar sensible thermal storage; non-contact graphite-buried sintering; thermal shock resistance
文摘The Al2O3-ZrO2(3Y)-SiC composite ceramics used in solar thermal power were prepared by micrometric Al2O3,nano-ZrO2 and SiC powders under the condition of pressureless sintering.The bulk density and bending strength of samples with 10vol% nano-ZrO2 sintered at 1480℃ were 3.222 g/cm3 and 160.4MPa,respectively.The bending strength of samples after 7 times thermal shock tests (quenching from 1000℃ to 25℃ in air medium) is 132.0MPa,loss rate of bending strength is only 17%.The effect of nano-ZrO2 content on the microstructure and performance of Al2O3-ZrO2(3Y)-SiC composite ceramic was investigated.The experimental results show that the bending strength of samples with above 10vol% nano-ZrO2 content has decreased,because the volume expansion resulting from t-ZrO2 to m-ZrO2 phase transformation is excessive;Adding proper nano-ZrO2 would be contributed to improve the thermal shock resistance of the composite ceramics.The Al2O3-ZrO2(3Y)-SiC composite ceramic has promising potential application in solar thermal power.
基金the financial supports from the National Natural Science Foundation of China ( 51274057 )Fundamental Research Funds for the Central Universities ( N120402006)Educational Commission of Liaoning Province of China ( L2012079)
文摘ZrN-SiAlON composite materials were synthesized at 1 550 ℃ for 6 h via a carbothermal reduction nitridation route using fly ash (≤74 μm),zircon (≤ 44 μm) and active carbon as starting materials.The processed ZrN-SiAlON composite micropowders were mixed with polyvinyl alcohol as binder to prepare ZrN (ZrON)-SiAlON composite ceramics by carbon-embedded pressureless firing at 1 450,1 500 and 1 550 ℃ for 1 h,respectively.Influences of firing temperature on the phase compositions,microstructure and sintering properties of the ceramics were investigated.The results show that:(1) β-SiAlON based composite ceramics with different compositions can be prepared by controlling firing temperature,and the main crystalline phases of the specimen fired at 1 550 ℃ for 1 h involve ZrN,ZrON and β-SiAlON (z =2,Si4Al2O2N6); (2) ZrN (ZrON),β-SiAlON and a Fe-Si based compound can be observed in the microstructures of the specimens fired at different temperatures.ZrN (ZrON) particles distribute homogeneously in the β-SiAlON matrix; (3) raising firing temperature can increase the shrinkage ratio of the ceramics,and the volume shrinkage ratio increases from 19.4% to 40.3% when the firing temperature rises from 1 450 to 1 550 ℃.
基金funded by the National Natural Science Foundation of China(Nos.51805070,51790172)the Liaoning Province Natural Science Foundation Guidance Program(Nos.2019-ZD-0010,2020-BS-057)the Fundamental Research Funds for the Central Universities(No.DUT19RC(3)060)。
文摘Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based(DED-LB)technology.However,the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions.The shaping quality,microstructure,and mechanical properties of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13)(6 mol%TiO_(2))composite ceramics were systematically investigated as a function of energy input in an extensive process window.On this basis,the formation mechanism of solidification defects and the evolution process of microstructure were revealed,and the optimized process parameters were determined.Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases,thus,facilitating the elimination of solidification defects,such as pores and strip gaps.In addition,the microstructure size is strongly dependent on the energy input,increasing when the energy input increases.Moreover,the morphology of theα-Al_(2)O_(3) phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions.Under the comprehensive influence of solidification defects and microstructure size,the fracture toughness and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics present a parabolic law behavior as the energy input increases.Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min^(2) g^(-1) mm^(-1).Within this process window,the average microhardness,fracture toughness,and flexural strength of Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics are up to 1640 Hv,3.87 MPa m^(1/2),and 227 MPa,respectively.This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al_(2)O_(3)/Al_(6)Ti_(2)O_(13) composite ceramics.
文摘The grain growing dynamics including the growing process, the growing exponent and the growing activation energy is obtained for the MgO-CaO composite ceramics with the additions of Fe2O3, CeO2 and/or ZrO2 as fluxes by measuring the size of grains with the method of Straight Line Across. The results show that all of the additions, in which Fe2O3 is the strongest, have notable effects on the grain growing dynamics by reducing the growing activation energy and promoting the grain growing. The research gives a good reference for the additions of fluxes to the matrix of ceramic filter.
基金Funded by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No.2018YFB1501002)。
文摘Al_(2)O_(3)/SiC composite ceramics were prepared fromα-Al_(2)O_(3) and SiC by a pressureless sinter method in this study.The effect of SiC contents on the mechanic properties,phase compositions and microstructure is studied.Experimental results show that the vickers hardness,wear resistance and thermal conductivity of the samples increase with the increase in the SiC content,and the hardness of the sample reaches 16.22 GPa,and thermal conductivity of the sample reaches 25.41 W/(m.K)at room temperature when the SiC content is 20 wt%(B5)and the sintering temperature is at 1640℃.Higher hardness means higher scour resistance,and it indicates that the B5 material is expected to be used for the solar heat absorber of third generation solar thermal generation.The results indicate the mechanism of improving mechanical properties of Al_(2)O_(3)/SiC composite ceramics:SiC plays a role in grain refinement that the grain of SiC inhibits the grain growth of Al_(2)O_(3),while the addition of SiC changes the fracture mode from the intergranular to the intergranular-transgranular.
基金Supported by the Research Fund of the Doctoral Program of University of Jinan
文摘The influence of Mn doping on the formation and dielectric properties of 0.7BaO·0.3SrO·(1-y)TiO2·yNb2O5 (BSTN) composite ceramics were investigated. The Mn was doped according to the formula 0.7BaO·0.3SrO·(0.7-z)TiO2·0.3Nb2O5·zMnO2 (BSTNM). The results show the two phases, perovskite phase BST and the tungsten bronze phase SBN, are coexistence in BSTNM as they are in BSTN composite ceramics. The Mn ions doped in BSTN substitute for Nb5+ ions in the tungsten bronze phase, and then, the Nb5+ ions substitute for Ti4+ ions in the perovskite phase. With the increasing of Mn dopant, the content of the perovskite phase increases while that of the tungsten bronze phase decreases, and the grain size of the perovskite phase decreases. As well as, the phase transition temperature of tungsten bronze phase increases with value z increasing from 0 to about 0.05.
文摘Strontium barium niobate/barium strontium titanate composite ceramics of xSrO·(1-x)BaO·0.5Nb2O5·0.5TiO2 (BSTN in short) with a range of Sr/Ba ratios were fabricated using a modified sol-gel method with Nb2O5 fine powders suspended in the barium strontium titanate (BST in short) sol solution. Powders obtained from dried gels were calcined at 800 ℃ for 3 h. After preparing bulk ceramics from these powders by sintering at 1200 ℃ for 3 h, the tetragonal tungsten bronze(TTB) phase and perivoskite phase were co-present in compositions between 0.25≤x≤0.75, with the increasing of x value, the peaks of pervoskite phase shift to the high angle position slightly while no changes happened in the peak position of TTB phase. The peak intensity of both two phases were also changed.
文摘The performance of composite ceramic armor penetrated by rod projectile was studied by both numerical simulation and experiment.The penetration and damage mechanisms of the projectile-armor after high-speed collision were also observed by high-speed photography.The experimental results showed that the ballistic performance of composite ceramic armor was highly affected by the density,hardness and toughness of bulletproof ceramic.The flow stress of the failed bulletproof ceramic is not only related to the pressure but also related to the strain rate.The phenomenological method based on Bodner-Partom ceramic model was introduced to derive the growth rate of damage.Numerical simulation results show good agreement with the experimental results.
文摘Al 2O 3-SiO 2-TiO 2-ZrO 2 supported membranes were prepar ed by Sol-Gel method. These composite ceramic membranes are level, even and no macro crack. There exist several crystalline phases such as Al 2O 3, TiO 2(a natase), Al 2SiO 5, and ZrO 2 in these membranes. Changing the molar ratio of Al∶Si∶Ti∶Zr,the kinds and content of crystal phases of composite membranes could be different, which may lead to a variety of microstructure of membranes. The surface nanoscale topography and microstructure of membranes were investiga ted by XRD,SEM,AFM,EPMA. The effects of additives and heat treatments on the sur face nanoscale topography and microstructure of composite ceramic membranes were also analyzed.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50074004).
文摘The synthesis process of TiN/AlON composite ceramics was studied, the thermodynamics, mechanical properties and micro-structures of TiN/AlON have also been investigated. The TiN/AlON composite ceramics has been synthesized by both hot-pressing and pressureless sintering. The characterizations of the material synthesized were analyzed with XRD (X-ray diffraction) and TEM (transmission electronic microscope). The density and toughness strength of TiN/AlON are 3.57g/cm3 and 4.74MPa.m1/2, respectively. The bending strength was measured at both room temperature and high temperatures and the results are 399 MPa (room temperature), 406 MPa (1 073 K), 417 MPa (1 273 K) and 323 MPa (1 573 K). Pattern Recognition (PR) and Artificial Neural Network (ANN) were used to optimize the parameters and to predict the expected values. A proper parameter for pressureless sintering of TiN/AlON has been obtained and testified, the parameters are temperature (1 978 K), AlN / (AlN + Al2O3) ratio (0.22), MgO (4.7%) and TiO2 (7.2%).
文摘The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt.% TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (Ⅳ) on fatigue crack growth (Δa). The mechanical properties and thermal fatigue resistance of TiC/Al203 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites.
基金the financial support from National Natural Science Foundation of China(No.52262010)the Guangxi Natural Science Foundation of China(No.2023GXNSFAA026384)the Guilin Scientific Research and Technology Development Program(No.2020011203-3).
文摘Aluminum oxide(Al_(2)O_(3))ceramics have been widely utilized as circuit substrates owing to their exceptional performance.In this study,boron nitride microribbon(BNMR)/Al_(2)O_(3)composite ceramics are prepared using spark plasma sintering(SPS).This study examines the effect of varying the amount of toughened phase BNMR on the density,mechanical properties,dielectric constant,and thermal conductivity of BNMR/Al_(2)O_(3)composite ceramics while also exploring the mechanisms behind the toughening and increased thermal conductivity of the fabricated ceramics.The results showed that for a BNMR content of 5 wt%,BNMR/Al_(2)O_(3)composite ceramics displayed more enhanced characteristics than pure Al_(2)O_(3)ceramics.In particular,the relative density,hardness,fracture toughness,and bending strength were 99.95%±0.025%,34.11±1.5 GPa,5.42±0.21 MPa·m1/2,and 375±2.5 MPa,respectively.These values represent increases of 0.76%,70%,35%,and 25%,respectively,compared with the corresponding values for pure Al_(2)O_(3)ceramics.Furthermore,during the SPS process,BNMRs are subjected to high temperatures and pressures,resulting in the bending and deformation of the Al_(2)O_(3)matrix;this leads to the formation of special thermal pathways within it.The dielectric constant of the composite ceramics decreased by 25.6%,whereas the thermal conductivity increased by 45.6%compared with that of the pure Al_(2)O_(3)ceramics.The results of this study provide valuable insights into ways of enhancing the performance of Al_(2)O_(3)-based ceramic substrates by incorporating novel BNMRs as a second phase.These improvements are significant for potential applications in circuit substrates and related fields that require high-performance materials with improved mechanical properties and thermal conductivities.
基金This work was financially supported by the Natural Science Foundation of Hebei Province(Nos.E2021402004,F2020402010,and E2020402075)Central Government Guided Local Science and Technology Development Fund Project(No.226Z1101G)+1 种基金Three Talent Project of Hebei Province(No.A202101019)Postgraduate Innovation Ability Training funding Project of Hebei Province(No.CXZZSS2023120).
文摘In this paper, the concept of incorporating core–shell structured units as secondary phases totoughen Al_(2)O_(3) ceramics is proposed. Al_(2)O_(3) composite ceramics toughened by B_(4)C@TiB_(2) core–shellunits are successfully synthesized using a combination of molten salt methodology and spark plasmasintering. The synthesis of B_(4)C@TiB_(2) core–shell toughening units stems from the prior production ofcore–shell structural B_(4)C@TiB_(2) powders, and this core–shell structure is effectively preserved withinthe Al_(2)O_(3) matrix after sintering. The B_(4)C@TiB_(2) core–shell toughening unit consists of a micron-sizedB4C core enclosed by a shell approximately 500 nm in thickness, composed of numerous nanosizedTiB2 grains. The regions surrounding these core–shell units exhibit distinct geometric structures andencompass multidimensional variations in phase composition, grain dimensions, and thermal expansioncoefficients. Consequently, intricate stress distributions emerge, fostering the propagation of cracks inmultiple dimensions. This behavior consumes a considerable amount of crack propagation energy,thereby enhancing the fracture toughness of the Al_(2)O_(3) matrix. The resulting Al_(2)O_(3) composite ceramicsdisplay relative density of 99.7%±0.2%, Vickers hardness of 21.5±0.8 GPa, and fracture toughness6.92±0.22 MPa·m1/2.
基金supported by the National Natural Science Foundation of China (Nos.52130204,52174376,and 51822405)the Guangdong Basic and Applied Basic Research Foundation (No.2021B1515120028)+2 种基金the Science and Technology Innovation Team Plan of Shaan Xi Province (No.2021TD-17)the Youth Innovation Team of Shaanxi Universities,Fundamental Research Funds for the Central Universities (No.D5000210902)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University (Nos.CX2021056,CX2021066,and CX2022033),China.
文摘Microstructure control is a great challenge in the high-temperature gradient directional solidification of eutectic composite ceramics due to the complex solidification behavior.Herein,the microstructure trans-formation of faceted Al_(2)O_(3)/Er_(3)Al_(5)O_(12) thermal emission eutectic composite ceramics is explored over wide ranges of compositions(13.5 mol%-22.5 mol%Er_(2)O_(3))and solidification rates(2-200μm/s).Entirely cou-pled eutectics with primary phases suppressed are fabricated and the coupled zone is broadened in a wide range of 15.5 mol%-22.5 mol%Er_(2)O_(3) at low solidification rates.The competitive growth between eutectic and dendrite is evaluated on the basis of the maximum interface temperature criterion.In ad-dition,the mechanisms of irregular eutectic spacing selection and adjustment under different solidifi-cation rates are revealed based on Magnin-Kurz model.A successful prediction of lamellar to rod-like eutectics is achieved associated with the dynamic instability of lamellar eutectic and the corresponding enlarged coexistence region is mapped based on the interface undercooling.According to the well mi-crostructure tailoring,the flexural strength of Al_(2)O_(3)/Er_(3)Al_(5)O_(12) eutectic composite ceramics has improved from 508 MPa up to 1800 MPa due to the refined eutectic spacing with low fluctuation.The eutectic composite ceramics show strong selective optical absorption and the intensity increases with the refin-ing microstructure.The as-designed Al_(2)O_(3)/Er_(3)Al_(5)O_(12) composites with microstructural tailoring have great potential as integrations of structural and functional materials.
文摘Composite ceramics thermal barrier coatings(TBCs) are widely used in the aero-engines field due to their excellent thermal insulation, which improves the service life and durability of the inherent hot components. The most typical, successful and widely used TBCs material is yttria stabilized zirconia(YSZ). In this paper, fabrication methods, coating structures, materials, failure mechanism and major challenges of YSZ TBCs are introduced and reviewed. The research tendency is put forward as well. This review provides a good understanding of the YSZ TBCs and inspires researchers to discover versatile ideas to improve the TBCs systems.