Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their ...Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.展开更多
A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experime...A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated.The results indicate that the average size ofα-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%.In addition,the eutectic Mg2Si phase in the Mg−10%Al−1%Zn−1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process.With the increasing of compression ratio,the morphology and average size of Mg2Si phases do not change obviously.The morphology modification mechanism of Mg2Si phase in Mg−10%Al−1%Zn−1%Si alloy by SIMA process was also studied.展开更多
Novel Bi_(2)MoO_(6) nanocrystals with tunable oxygen vacancies have been developed via a facile low-cost approach with the assistance of a glyoxal reductant under solvothermal conditions.With the introduction of oxyge...Novel Bi_(2)MoO_(6) nanocrystals with tunable oxygen vacancies have been developed via a facile low-cost approach with the assistance of a glyoxal reductant under solvothermal conditions.With the introduction of oxygen vacancies,the optical absorption of Bi_(2)MoO_(6) is extended and its bandgap narrowed.Oxygen vacancies not only lead to the appearance of a defect band level in the forbidden band but can also result in a minor up-shift of the valence band maximum,promoting the mobility of photogenerated holes.Moreover,oxygen vacancies can act as electron acceptors,temporarily capturing electrons excited by light and reducing the recombination of electrons and holes.At the same time,oxygen vacancies help to capture oxygen,which reacts with the captured photogenerated electrons to generate more superoxide radicals(·O_(2)-)to participate in the reaction,thereby significantly promoting the redox performance of the photocatalyst.From Bi_(2)MoO_(6) containing these oxygen vacancies(OVBMO),excellent photocatalytic performance has been obtained for the oxidation of 1,2,3,4-tetrahydroquinoline to produce quinoline and cause antibiotic degradation.The reaction mechanism of the oxidation of 1,2,3,4-tetrahydroquinoline to quinoline over the OVBMO materials is elucidated in terms of heterogeneous Catal.via a radical pathway.展开更多
Two non-ionic hydro-fluorocarbon hybrid surfactants with and without hydroxyl groups were synthesized and compared.They exhibited good thermal stability and superior surface activity.It was observed that the hydroxyl ...Two non-ionic hydro-fluorocarbon hybrid surfactants with and without hydroxyl groups were synthesized and compared.They exhibited good thermal stability and superior surface activity.It was observed that the hydroxyl group had a profound effect on modifying the surface tension of their solutions and the morphology of the formed micelles.This effect may be attributed to the rearranging of the alkane group from above the air/aqueous surface to below it and the disrupting of the interfacial water structure induced by the hydroxyl groups.This work provides a strategy to weaken the immiscibility between hydrocarbon and fluorocarbon chains by modifying their orientational structure at the interface,thus it is helpful for the design of surfactants with varied interfacial properties.展开更多
Isothermal sections of the Co−Al−Re ternary system at 1100 and 1300℃ were determined experimentally by electron probe microanalysis and X-ray diffraction.The results show that there are seven three-phase regions in t...Isothermal sections of the Co−Al−Re ternary system at 1100 and 1300℃ were determined experimentally by electron probe microanalysis and X-ray diffraction.The results show that there are seven three-phase regions in the 1100℃ isothermal section and five three-phase regions in the 1300℃ isothermal section.The solid solubilities ofαCo,εRe and CoAl increase a little with temperature increasing from 1100 to 1300℃.The solubility of Co in compounds AlRe2,Al11Re4 and Al4Re is negligible,<1.5 at.%.And no ternary compounds are found.展开更多
As social and economic dynamics continue to evolve and the demand for companionship increases,pet ownership has become an increasingly popular lifestyle choice.Pet parks,as a new form of urban public space,are gaining...As social and economic dynamics continue to evolve and the demand for companionship increases,pet ownership has become an increasingly popular lifestyle choice.Pet parks,as a new form of urban public space,are gaining significant attention.This study,grounded in the theory of spatial justice,employs a combination of questionnaires and semi-structured interviews to evaluate four representative pet parks in Hong Kong,China.It explores how pet parks,as inclusive green infrastructure in high-density environments,contribute to urban community well-being and broader spatial justice.The study reveals the conflicts between pet owners and non-pet owners regarding the rights to use public spaces,examining how to guarantee the spatial rights of specific groups while avoiding harm to others.The findings indicate that green space availability,sociability and participation,walkability,safety,and flexibility in pet parks play a positive role in achieving urban spatial justice.However,pet parks also face challenges related to social exclusion and safety,requiring a balance between promoting community integration and ensuring public safety.This study offers valuable insights for the development of pet parks,the creation of vibrant and diverse public spaces,and the promotion of harmonious human-animal environments in cities across China and other Asian countries.展开更多
基金National Natural Science Foundation of China (52072088, 52072089)Natural Science Foundation of Heilongjiang Province (LH2023E061)+1 种基金Scientific and Technological Innovation Leading Talent of Harbin Manufacturing (2022CXRCCG001)Fundamental Research Funds for the Central Universities (3072023CFJ1003)。
文摘Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(Nos.41807235,50674038).
文摘A new Mg−10%Al−1%Zn−1%Si alloy with non-dendritic microstructure was prepared by strain induced melt activation(SIMA)process.The effect of compression ratio on the evolution of semisolid microstructure of the experimental alloy was investigated.The results indicate that the average size ofα-Mg grains decreases and spheroidizing tendency becomes more obvious with the compression ratios increasing from 0 to 40%.In addition,the eutectic Mg2Si phase in the Mg−10%Al−1%Zn−1%Si alloy transforms completely from the initial fishbone shape to globular shape by SIMA process.With the increasing of compression ratio,the morphology and average size of Mg2Si phases do not change obviously.The morphology modification mechanism of Mg2Si phase in Mg−10%Al−1%Zn−1%Si alloy by SIMA process was also studied.
文摘Novel Bi_(2)MoO_(6) nanocrystals with tunable oxygen vacancies have been developed via a facile low-cost approach with the assistance of a glyoxal reductant under solvothermal conditions.With the introduction of oxygen vacancies,the optical absorption of Bi_(2)MoO_(6) is extended and its bandgap narrowed.Oxygen vacancies not only lead to the appearance of a defect band level in the forbidden band but can also result in a minor up-shift of the valence band maximum,promoting the mobility of photogenerated holes.Moreover,oxygen vacancies can act as electron acceptors,temporarily capturing electrons excited by light and reducing the recombination of electrons and holes.At the same time,oxygen vacancies help to capture oxygen,which reacts with the captured photogenerated electrons to generate more superoxide radicals(·O_(2)-)to participate in the reaction,thereby significantly promoting the redox performance of the photocatalyst.From Bi_(2)MoO_(6) containing these oxygen vacancies(OVBMO),excellent photocatalytic performance has been obtained for the oxidation of 1,2,3,4-tetrahydroquinoline to produce quinoline and cause antibiotic degradation.The reaction mechanism of the oxidation of 1,2,3,4-tetrahydroquinoline to quinoline over the OVBMO materials is elucidated in terms of heterogeneous Catal.via a radical pathway.
基金supported by the National Natural Science Foundation of China(No.21673285 and No.21973022)the Guangdong Basic and Applied Basic Research Foundation(No.2019A1515012117)the Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme 2019(No.GDUPS2019)。
文摘Two non-ionic hydro-fluorocarbon hybrid surfactants with and without hydroxyl groups were synthesized and compared.They exhibited good thermal stability and superior surface activity.It was observed that the hydroxyl group had a profound effect on modifying the surface tension of their solutions and the morphology of the formed micelles.This effect may be attributed to the rearranging of the alkane group from above the air/aqueous surface to below it and the disrupting of the interfacial water structure induced by the hydroxyl groups.This work provides a strategy to weaken the immiscibility between hydrocarbon and fluorocarbon chains by modifying their orientational structure at the interface,thus it is helpful for the design of surfactants with varied interfacial properties.
基金financial supports from the National Natural Science Foundation of China(No.51831007)the National Key Research&Development Program of China(No.2017YFB0702901)。
文摘Isothermal sections of the Co−Al−Re ternary system at 1100 and 1300℃ were determined experimentally by electron probe microanalysis and X-ray diffraction.The results show that there are seven three-phase regions in the 1100℃ isothermal section and five three-phase regions in the 1300℃ isothermal section.The solid solubilities ofαCo,εRe and CoAl increase a little with temperature increasing from 1100 to 1300℃.The solubility of Co in compounds AlRe2,Al11Re4 and Al4Re is negligible,<1.5 at.%.And no ternary compounds are found.
文摘As social and economic dynamics continue to evolve and the demand for companionship increases,pet ownership has become an increasingly popular lifestyle choice.Pet parks,as a new form of urban public space,are gaining significant attention.This study,grounded in the theory of spatial justice,employs a combination of questionnaires and semi-structured interviews to evaluate four representative pet parks in Hong Kong,China.It explores how pet parks,as inclusive green infrastructure in high-density environments,contribute to urban community well-being and broader spatial justice.The study reveals the conflicts between pet owners and non-pet owners regarding the rights to use public spaces,examining how to guarantee the spatial rights of specific groups while avoiding harm to others.The findings indicate that green space availability,sociability and participation,walkability,safety,and flexibility in pet parks play a positive role in achieving urban spatial justice.However,pet parks also face challenges related to social exclusion and safety,requiring a balance between promoting community integration and ensuring public safety.This study offers valuable insights for the development of pet parks,the creation of vibrant and diverse public spaces,and the promotion of harmonious human-animal environments in cities across China and other Asian countries.
