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
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
The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear ...The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear resistance.Cu–Ti3SiC2 co-continuous composites have superior performance due to the continuous distribution of 3 D network structures.In this paper,the Cu/Ti3SiC2(Ti C/Si C)co-continuous composites are formed via vacuum infiltration process from Cu and Ti3SiC2 porous ceramics.The co-continuous composites have significantly improved the flexural strength and conductivity of Ti3SiC2 due to the addition of Cu,with the conductivity up to 5.73×10^5 S/m,twice as high as the Ti3SiC2 porous ceramics and five times higher than graphite.The reaction between ingredients leads to an increase in the friction coefficient,while the hard reaction products(Ti Cx,Si C)lower the overall wear rate(1×10^–3 mm^3/(N·m)).Excellent electrical conductivity and wear resistance make co-continuous composites more advantageous in areas such as rail transit.展开更多
Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. I...Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. In this work, a novel high-entropy(HE) rare-earth phosphate monazite ceramic (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al2O3, without reaction with Al2O3 as high as 1600℃ in air. Moreover, the thermal expansion coefficient(TEC) of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4(8.9 × 10^-6/℃ at 300–1000℃) is close to that of Al2O3. The thermal conductivity of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 at room temperature is as low as 2.08 W·m^-1·K^-1, which is about 42% lower than that of La PO4. Good chemical compatibility, close TEC to that of Al2O3, and low thermal conductivity indicate that HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is suitable as a candidate EBC/TBC material and an interphase for Al2O3 f/Al2O3 composites.展开更多
Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forc...Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coating applications.展开更多
Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrins...Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrinsically sluggish electron/ion transport.Herein,in-situ encapsulation ofα-Fe_(2)O_(3) nanoparticles into micro-sized ZnFe_(2)O_(4) capsules is facilely fulfilled through a co-precipitation process and followed by heat-treatment at optimal calcination temperature.The porous ZnFe_(2)O_(4) scaffold affords a synergistic confinement effect to suppress the grain growth ofα-Fe2 O3 nanocrystals during the calcination process and to accommodate the stress generated by volume expansion during the charge/discharge process,leading to an enhanced interfacial conductivity and inhibit electrode pulverization and mechanical failure in the active material.With these merits,the preparedα-Fe_(2)O_(3)/Fe_(2)O_(4) composite delivers prolonged cycling stability and improved rate capability with a higher specific capacity than soleα-Fe_(2)O_(3) and Fe_(2)O_(4).The discharge capacity is retained at 700 mAh g-1 after 500 cycles at 200 mA g^(-1) and 940 mAh g^(-1) after 50 cycles at 100 m A g^(-1).This work provides a new perspective in designing transition metal oxides for advanced lithium-ion batteries with superior electrochemical properties.展开更多
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.
文摘The MAX phase Ti3SiC2 has broad application prospects in the field of rail transit,nuclear protective materials and electrode materials due to its excellent electrical conductivity,selflubricating properties and wear resistance.Cu–Ti3SiC2 co-continuous composites have superior performance due to the continuous distribution of 3 D network structures.In this paper,the Cu/Ti3SiC2(Ti C/Si C)co-continuous composites are formed via vacuum infiltration process from Cu and Ti3SiC2 porous ceramics.The co-continuous composites have significantly improved the flexural strength and conductivity of Ti3SiC2 due to the addition of Cu,with the conductivity up to 5.73×10^5 S/m,twice as high as the Ti3SiC2 porous ceramics and five times higher than graphite.The reaction between ingredients leads to an increase in the friction coefficient,while the hard reaction products(Ti Cx,Si C)lower the overall wear rate(1×10^–3 mm^3/(N·m)).Excellent electrical conductivity and wear resistance make co-continuous composites more advantageous in areas such as rail transit.
基金financially supported by the National Natural Science Foundation of China (Nos. 51672064 and U1435206)
文摘Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. In this work, a novel high-entropy(HE) rare-earth phosphate monazite ceramic (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al2O3, without reaction with Al2O3 as high as 1600℃ in air. Moreover, the thermal expansion coefficient(TEC) of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4(8.9 × 10^-6/℃ at 300–1000℃) is close to that of Al2O3. The thermal conductivity of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 at room temperature is as low as 2.08 W·m^-1·K^-1, which is about 42% lower than that of La PO4. Good chemical compatibility, close TEC to that of Al2O3, and low thermal conductivity indicate that HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is suitable as a candidate EBC/TBC material and an interphase for Al2O3 f/Al2O3 composites.
基金This work is supported by the National Natural Science Foundation of China(Nos.51865044,52062040)Science and Technology Projects of Inner Mongolia Autonomous Region(Nos.2021PT0008,2022ZD02,2022MS05003)Basic Scientific Research Expenses Program of Universities Directly under Inner Mongolia Autonomous Region(Nos.JY20220041,JY20220062).
文摘Developing new high-entropy rare-earth zirconate(HE-RE_(2)Zr_(2)O_(7))ceramics with low thermal conductivity is essential for thermal barrier coating materials.In this work,the average atomic spacings,interatomic forces,and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A_(2)B_(2)O_(7) crystal structure were calculated by density functional theory.These three physical qualities,as vectors,characterize the corresponding rare-earth elements.The distance between two vectors quantitatively describes the difference between two rare-earth elements.For greater differences between two rare-earth elements,the disorder degree of HE-RE_(2)Zr_(2)O_(7)is greater,and therefore,the thermal conductivity is lower.According to the theoretical calculations,the thermal conductivity of the ceramics gradually increases in the order of(SC_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Ce_(0.2)Nd_(0.2)Eu_(0.2)Gd_(0.2))_(2)Zr_(2)0_(7),(SC_(0.2)Y_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)0_(7),and(Sc_(0.2)Er_(0.2)Tm_(0.2)Yb_(0.2)Lu_(0.2))_(2)Zr_(2)O_(7).Using the solution precursor plasma spray method and pressureless sintering method,four types of HE-RE2Zr2Oz powder and bulk samples were prepared.The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure.The thermal conductivities of the sintered HE-RE_(2)Zr_(2)0_(7) bulk samples ranged from 1.30 to 1.45 Wm^(-1).K^(-1) at 1400℃,and their differences were consistent with the theoretical calculation results.Among the ceramics,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)O_(7) had the lowest thermal conductivity(1.30 W·m^(-1)·K^(-1),1400℃),highest thermal expansion coefficient(10.19×10^(-6) K^(-1),200-1400℃),highest fracture toughness(1.69±0.28 MPa·m^(1/2)),and smallest brttleness index(3.03μm^(1/2)).Therefore,(Sc_(0.2)Y_(0.2)La_(0.2)Ho_(0.2)Yb_(0.2))_(2)Zr_(2)0_(7)is considered to be an ideal candidate material for next-generation thermal barrier coating applications.
基金financially supported by the National Natural Science Foundation of China(No.51702217)the Shenzhen Government’s Plan of Science and Technology(No.JCYJ20190808121407676)+1 种基金the Natural Science Foundation of Guangdong(No.2020A1515011127)the Shenzhen University Initiative Research Program(No.2019005)。
文摘Transition metal oxides as anode materials for high-performance lithium-ion batteries suffer from severe capacity decay,originating primarily from particle pulverization upon volume expansion/shrinkage and the intrinsically sluggish electron/ion transport.Herein,in-situ encapsulation ofα-Fe_(2)O_(3) nanoparticles into micro-sized ZnFe_(2)O_(4) capsules is facilely fulfilled through a co-precipitation process and followed by heat-treatment at optimal calcination temperature.The porous ZnFe_(2)O_(4) scaffold affords a synergistic confinement effect to suppress the grain growth ofα-Fe2 O3 nanocrystals during the calcination process and to accommodate the stress generated by volume expansion during the charge/discharge process,leading to an enhanced interfacial conductivity and inhibit electrode pulverization and mechanical failure in the active material.With these merits,the preparedα-Fe_(2)O_(3)/Fe_(2)O_(4) composite delivers prolonged cycling stability and improved rate capability with a higher specific capacity than soleα-Fe_(2)O_(3) and Fe_(2)O_(4).The discharge capacity is retained at 700 mAh g-1 after 500 cycles at 200 mA g^(-1) and 940 mAh g^(-1) after 50 cycles at 100 m A g^(-1).This work provides a new perspective in designing transition metal oxides for advanced lithium-ion batteries with superior electrochemical properties.
