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
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
Nd2O3 doped BaTiO3ceramics（the additive content was respectively 0.001, 0.002, 0.003, 0.005, 0.01 molar ratio）were prepared by Sol-Gel method to study their dielectric characteristics and electric conductivities thr...Nd2O3 doped BaTiO3ceramics（the additive content was respectively 0.001, 0.002, 0.003, 0.005, 0.01 molar ratio）were prepared by Sol-Gel method to study their dielectric characteristics and electric conductivities through X-ray photoelectron spectrum （XPS）. The results showed that the dielectric characteristics of Nd2O3 doped BaTiO3 ceramics were improved by doping. When Nd2O3 content was 0.003 mol, the results were even better, the dielectric constant was increased, the dielectric loss was decreased, the Curie-temperature （Tc） was 110 ℃, and the frequency characteristic was also good. The resistivity of Nd2O3 doped BaTiO3 ceramics was lower than that of pure BaTiO3 ceramics, when Nd2O3 content was 0.001 mol,the resistivity was （2.364×）108 Ω·m, the smallest. The grain resistance of Nd2O3 doped BaTiO3 ceramics exhibited NTC effect, but the grain boundary resistance showed PTC effect, and the grain boundary resistance was larger than that of the grain resistance, so the PTC effect originated from the grain boundary. The analysis of the element binding energy through X-ray photoelectron spectrum were indicated that the quantivalence of Ba2+and Ti4+in Nd2O3 doped BaTiO3 ceramics was variable, and resulted in the improvement of the conductibility of BaTiO3 ceramics.展开更多
The composites were prepared by ball-milling ZrO_2(3%Y_2O_3) and γ-Al_2O_3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO_2 in composites ...The composites were prepared by ball-milling ZrO_2(3%Y_2O_3) and γ-Al_2O_3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO_2 in composites were examined by X-ray diffraction. The microstructure of Al_2O_3/3Y-TZP composites was observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) respectively. The X-ray analysis reveals that ZrO_2 of both surface and fracture surface is mainly t-ZrO_2. The SEM image shows that there are some intragranular particles in large granulars. The fracture toughness K_ 1c of Al_2O_3/70%ZrO_2(3%Y_2O_3(mole fraction)) composite tested by single-edge notched bending is 13.5 MPa·m 1/2. Being toughened by the ferroelastic domain switching and the intragranular microstructure explains high toughness of the composite.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 major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance.However,phosphors usually suffer laser-induced luminescence saturation,which limits the peak lum...The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance.However,phosphors usually suffer laser-induced luminescence saturation,which limits the peak luminance of laser lighting devices.The aim of the present study is to develop LuAG:Ce/Al_(2)O_(3)composite ceramics(LACCs)with a high saturation threshold for high-luminance laser lighting.Owning to the rigid crystal structure,proper synthetic process,and optimized thermal design,the LACCs possess small thermal quenching(16%loss in luminescence at 225℃),high quantum yield(>95%),and excellent luminescence properties.When the LACCs are irradiated by blue laser diodes in a reflection mode,a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W^(−1)are realized.Furthermore,they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm^(−2).With these favorable properties,the designed LACCs show great potential in high-luminance laser lighting.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
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·m^(1/2),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
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.
文摘Nd2O3 doped BaTiO3ceramics（the additive content was respectively 0.001, 0.002, 0.003, 0.005, 0.01 molar ratio）were prepared by Sol-Gel method to study their dielectric characteristics and electric conductivities through X-ray photoelectron spectrum （XPS）. The results showed that the dielectric characteristics of Nd2O3 doped BaTiO3 ceramics were improved by doping. When Nd2O3 content was 0.003 mol, the results were even better, the dielectric constant was increased, the dielectric loss was decreased, the Curie-temperature （Tc） was 110 ℃, and the frequency characteristic was also good. The resistivity of Nd2O3 doped BaTiO3 ceramics was lower than that of pure BaTiO3 ceramics, when Nd2O3 content was 0.001 mol,the resistivity was （2.364×）108 Ω·m, the smallest. The grain resistance of Nd2O3 doped BaTiO3 ceramics exhibited NTC effect, but the grain boundary resistance showed PTC effect, and the grain boundary resistance was larger than that of the grain resistance, so the PTC effect originated from the grain boundary. The analysis of the element binding energy through X-ray photoelectron spectrum were indicated that the quantivalence of Ba2+and Ti4+in Nd2O3 doped BaTiO3 ceramics was variable, and resulted in the improvement of the conductibility of BaTiO3 ceramics.
文摘The composites were prepared by ball-milling ZrO_2(3%Y_2O_3) and γ-Al_2O_3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO_2 in composites were examined by X-ray diffraction. The microstructure of Al_2O_3/3Y-TZP composites was observed by scanning electron microscope (SEM) and transmission electron microscopy (TEM) respectively. The X-ray analysis reveals that ZrO_2 of both surface and fracture surface is mainly t-ZrO_2. The SEM image shows that there are some intragranular particles in large granulars. The fracture toughness K_ 1c of Al_2O_3/70%ZrO_2(3%Y_2O_3(mole fraction)) composite tested by single-edge notched bending is 13.5 MPa·m 1/2. Being toughened by the ferroelastic domain switching and the intragranular microstructure explains high toughness of the composite.
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.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA22010301)the key research project of the frontier science of the Chinese Academy of Sciences(Grant No.QYZDB-SSW-JSC022).
文摘The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance.However,phosphors usually suffer laser-induced luminescence saturation,which limits the peak luminance of laser lighting devices.The aim of the present study is to develop LuAG:Ce/Al_(2)O_(3)composite ceramics(LACCs)with a high saturation threshold for high-luminance laser lighting.Owning to the rigid crystal structure,proper synthetic process,and optimized thermal design,the LACCs possess small thermal quenching(16%loss in luminescence at 225℃),high quantum yield(>95%),and excellent luminescence properties.When the LACCs are irradiated by blue laser diodes in a reflection mode,a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W^(−1)are realized.Furthermore,they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm^(−2).With these favorable properties,the designed LACCs show great potential in high-luminance laser lighting.
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·m^(1/2),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.
