为研究真空等离子喷涂Si/Yb2Si2O7/Yb2SiO5环境障涂层试样在涂层受压、涂层受拉时的室温弯曲强度及失效原因,采用超景深三维显微镜、SEM(Scanning Electron Microscope)等方法对喷涂后的试样进行了表征,并测量了涂层孔隙...为研究真空等离子喷涂Si/Yb2Si2O7/Yb2SiO5环境障涂层试样在涂层受压、涂层受拉时的室温弯曲强度及失效原因,采用超景深三维显微镜、SEM(Scanning Electron Microscope)等方法对喷涂后的试样进行了表征,并测量了涂层孔隙率;采用拉伸法测试了涂层的结合强度,并采用三点弯曲试验测试了裸材、涂层受压和涂层受拉时的室温弯曲强度。结果表明:Si/Yb2Si2O7/Yb2SiO5涂层与SiCf/SiC复合材料的结合强度为10.13 MPa,拉伸断裂主要在复材表层发生。计算涂层厚度时,涂层受压样的弯曲强度(503.21 MPa)与裸材(506.79 MPa)基本一致;不计算涂层厚度时,涂层受拉样的弯曲强度(499.77 MPa)与裸材一致;EBC涂层整体具有一定的压缩强度,其整体抗拉强度比复材自身抗拉强度小很多。压涂层时,在载荷增加至接近最大载荷时,复材层间发生破坏,并逐步失效,随后涂层发生飞崩,载荷迅速下降,试验停止;拉涂层时,在载荷很小时(约64 N)涂层就被拉开,随着载荷增加,直至接近最大载荷时,层间发生破坏并逐步失效。弯曲试验时复材的主要失效模式是SiC纤维断裂、复材的SiC基体开裂和复材层间撕裂,复材受拉面产生复材厚度方向的纵向裂纹;复材表层沉积的SiC膜层失效模式主要是开裂和剥落;EBC涂层在受压时的主要失效模式是整体飞崩和开裂,在受拉时,涂层在最大应力处断裂为2部分。本研究对含EBC涂层的SiCf/SiC复材的最大弯曲载荷设计具有参考意义.展开更多
Single-pass and double-pass high-temperature deformation experiments were conducted on 40Cr10Si2Mo steel using a Gleeble-3500 thermal simulator.The static recrystallization(SRX)behavior and recrystallization mechanism...Single-pass and double-pass high-temperature deformation experiments were conducted on 40Cr10Si2Mo steel using a Gleeble-3500 thermal simulator.The static recrystallization(SRX)behavior and recrystallization mechanisms of 40Cr10Si2Mo steel were investigated under deformation temperatures of 900-1100℃,deformation strains of 10%,20%,and 30%,and inter-pass times of 1-120 s.A static recrystallization fraction model was developed.The results showed that the SRX volume fraction increased with higher deformation temperature,larger deformation amount,and longer inter-pass time,with the deformation temperature having the most significant effect on SRX.During the deformation process,different process parameters led to different internal deformation mechanisms of the material.Static recovery and continuous static recrystallization(CSRX)dominated deformation at lower temperatures through progressive lattice rotation.In comparison,at higher temperatures,the deformation mechanism was dominated by CSRX and discontinuous static recrystallization(DSRX).The nucleation mechanisms of the SRX process were grain boundary bulging nucleation and subgrain merging nucleation,with grain boundary bulging present under all conditions.Subgrain merging nucleation could provide an additional nucleation mode at lower deformation temperatures or lower deformation amounts.Based on the traditional Avarmi equation,a modified model coefficient was used to establish the SRX kinetic model for 40Cr10Si2Mo steel.The linear correlation coefficient R2 between the predicted and experimental static recrystallization volume fraction was 0.96702,indicating high prediction accuracy.展开更多
Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH2/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreat...Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH2/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreatments,an inert environment,and long hours of physical ball milling for high homogeneity and synergistic effects.CaH2also inhibits the hydrolysis reaction by forming its products on the Al/Si surface,which hinders the direct utilization of composites.This work represents the first investigation of NaH-CaH2(Al/Si)fuel composites,which greatly overcome these limitations and can be directly used for on-site hydrogen generation and proton exchange membrane(PEM)fuel cells.The NaH-CaH2(Al/Si)fuel composites were prepared by using a straightforward mixing method with variable composition ratios,showing high H2yield and fuel cell(FC)performance.NaH addition provides the bridge effect,which opens up a new way to enable efficient hydrolysis and greatly enhances the hydrolysis activity of CaH2/(Al/Si)composites.The novel fuel composites(NaH-CaH2/Al)have extraordinary FC performance and a 0.42 W/cm2 peak power density greater than commercial hydrogen generators.It provides high H2yield 84.4%for NaH-CaH2/Al and 82%for NaH-CaH2/Si compared to NaOH-CaH2(Al/Si),NaCl-CaH2(Al/Si),and KCl-CaH2(Al/Si)composites.The NaH bridge effect hinders the direct water contact and stops the formation of Ca(OH)2 around Al/Si,which provides adequate pathways for the CaH2(Al/Si)hydrolysis.The impressive capabilities of novel fuel composites are anticipated to offer practical uses in fuel cells,automobile applications,and portable/on-board H2generation.展开更多
Comprehensive experimental and theoretical investigations on microstructure and mechanical properties were conducted to explore the refinement of Mg2Si in Mg-Al-Si alloys through the addition of Ca and Y.Alloys of ...Comprehensive experimental and theoretical investigations on microstructure and mechanical properties were conducted to explore the refinement of Mg2Si in Mg-Al-Si alloys through the addition of Ca and Y.Alloys of Mg-Al5.5-Si9.5-Cax(x=0,0.05,0.1,0.15,wt.%)and Mg-Al5.5-Si9.5-Yx(x=0,0.3,0.6,0.9,wt.%)were designed based on the CALPHAD(CALculations of PHAse Diagram)calculations and literature data.With the experimentally determined optimal individual addition of 0.1 wt.%Ca and 0.9 wt.%Y respectively,a crossexperiment involving simultaneous addition of Ca and Y for the refinement of Mg2Si was carried out.The alloy composition with the optimal refinement effect and mechanical properties was identified as Mg-Al5.5-Si9.5-Ca0.1-Y0.6(wt.%).In Y-containing alloys,a novel coreshell structure evolution mechanism of MgSi2Y2//Al4MgY//Mg2Si was proposed based on experimental observation and first principles calculations,revealing MgSi2Y2as the core for the heterogeneous nucleation of Mg2Si.展开更多
With the rapid advancement of optoelectronic technology,high-performance photodetectors are increasingly in demand in fields such as environmental monitoring,optical communication,and defense systems,where ultraviolet...With the rapid advancement of optoelectronic technology,high-performance photodetectors are increasingly in demand in fields such as environmental monitoring,optical communication,and defense systems,where ultraviolet detection is critical.However,conventional semiconductor materials suffer from limited UV-visible detection capabilities owing to their narrow bandgaps and high dark currents.To address these challenges,wide-bandgap semiconductors have emerged as promising alternatives.Here,we fabricated a horizontally structured n–n heterojunction photodetector by growingβ-Ga2O3 on Si–GaN via plasma-enhanced chemical vapor deposition.The device exhibits a self-powered photocurrent of 3.5 nA at zero bias,enabled by the photovoltaic effect of the space charge region.Under 254-nm and 365-nm illumination,it exhibits rectification behavior,achieving a responsivity of 0.475 m A/W(0 V,220??W/cm~2 at 254 nm)and 257.6 mA/W(-5 V),respectively.Notably,the photodetector demonstrates a high photocurrent-to-dark current ratio of 10~5 under-5-V bias,highlighting its potential for self-powered and high-performance UV detection applications.展开更多
A series of Co-based molecular sieve catalysts with different Si/Al ratios was prepared by the impregnation method.The microstructure properties of Co active sites were finely characterized by means of XRD,TEM,Raman,H...A series of Co-based molecular sieve catalysts with different Si/Al ratios was prepared by the impregnation method.The microstructure properties of Co active sites were finely characterized by means of XRD,TEM,Raman,H2-TPR,Py-FTIR and XPS technology.The results show that the surface Co species mainly exist in the form of CoOx nanoclusters and isolated Co2+,and the latter exhibits better N2O decomposition activity.Decreasing the Si/Al ratio of the MFI zeolite promotes the generation of isolated Co2+active sites,thereby enhancing the catalytic activity.Compared with the Co/S-1 catalyst with pure silicon S-1 carrier,the Co/HZ60 with a low Si/Al ratio of ZSM-5 carrier reduces the temperature required for complete N2O decomposition by 80℃,and it shows excellent resistance to O2 and NO.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52174371)the National Key Research and Development Program of China(Grant No.2021YFB3501003)the Shaanxi Provincial Science and Technology Department Enterprise Joint Fund(Grant No.2021JLM-33).
摘要Single-pass and double-pass high-temperature deformation experiments were conducted on 40Cr10Si2Mo steel using a Gleeble-3500 thermal simulator.The static recrystallization(SRX)behavior and recrystallization mechanisms of 40Cr10Si2Mo steel were investigated under deformation temperatures of 900-1100℃,deformation strains of 10%,20%,and 30%,and inter-pass times of 1-120 s.A static recrystallization fraction model was developed.The results showed that the SRX volume fraction increased with higher deformation temperature,larger deformation amount,and longer inter-pass time,with the deformation temperature having the most significant effect on SRX.During the deformation process,different process parameters led to different internal deformation mechanisms of the material.Static recovery and continuous static recrystallization(CSRX)dominated deformation at lower temperatures through progressive lattice rotation.In comparison,at higher temperatures,the deformation mechanism was dominated by CSRX and discontinuous static recrystallization(DSRX).The nucleation mechanisms of the SRX process were grain boundary bulging nucleation and subgrain merging nucleation,with grain boundary bulging present under all conditions.Subgrain merging nucleation could provide an additional nucleation mode at lower deformation temperatures or lower deformation amounts.Based on the traditional Avarmi equation,a modified model coefficient was used to establish the SRX kinetic model for 40Cr10Si2Mo steel.The linear correlation coefficient R2 between the predicted and experimental static recrystallization volume fraction was 0.96702,indicating high prediction accuracy.
基金financial support granted by the National Natural Science Foundation of China (No. 22402225)the Gusu Innovation and Entrepreneurship Leading Talent Plan(No. ZXL2023193)+2 种基金the Sinano Talents Plan (No. 2022000175)the Guangdong Basic and Applied Basic Research Foundation (No.2023A1515111133)the ANSO Scholarship for Young Talents
摘要Inorganic materials can solve transportable and on-site hydrolytic hydrogen generation issues.CaH2/(Al/Si)composites are preferable due to their notable chemical properties.However,these composites require pretreatments,an inert environment,and long hours of physical ball milling for high homogeneity and synergistic effects.CaH2also inhibits the hydrolysis reaction by forming its products on the Al/Si surface,which hinders the direct utilization of composites.This work represents the first investigation of NaH-CaH2(Al/Si)fuel composites,which greatly overcome these limitations and can be directly used for on-site hydrogen generation and proton exchange membrane(PEM)fuel cells.The NaH-CaH2(Al/Si)fuel composites were prepared by using a straightforward mixing method with variable composition ratios,showing high H2yield and fuel cell(FC)performance.NaH addition provides the bridge effect,which opens up a new way to enable efficient hydrolysis and greatly enhances the hydrolysis activity of CaH2/(Al/Si)composites.The novel fuel composites(NaH-CaH2/Al)have extraordinary FC performance and a 0.42 W/cm2 peak power density greater than commercial hydrogen generators.It provides high H2yield 84.4%for NaH-CaH2/Al and 82%for NaH-CaH2/Si compared to NaOH-CaH2(Al/Si),NaCl-CaH2(Al/Si),and KCl-CaH2(Al/Si)composites.The NaH bridge effect hinders the direct water contact and stops the formation of Ca(OH)2 around Al/Si,which provides adequate pathways for the CaH2(Al/Si)hydrolysis.The impressive capabilities of novel fuel composites are anticipated to offer practical uses in fuel cells,automobile applications,and portable/on-board H2generation.
基金support from National Key Laboratory of Science and Technology on High-strength Structural Materials are greatly acknowledgedthe Central South University Independent Innovation Project (Project No 1053320221864)+1 种基金the Central South University Study Abroad Funding Project supportthe Czech Science Foundation for the financial support (Project No 22-22187S).
摘要Comprehensive experimental and theoretical investigations on microstructure and mechanical properties were conducted to explore the refinement of Mg2Si in Mg-Al-Si alloys through the addition of Ca and Y.Alloys of Mg-Al5.5-Si9.5-Cax(x=0,0.05,0.1,0.15,wt.%)and Mg-Al5.5-Si9.5-Yx(x=0,0.3,0.6,0.9,wt.%)were designed based on the CALPHAD(CALculations of PHAse Diagram)calculations and literature data.With the experimentally determined optimal individual addition of 0.1 wt.%Ca and 0.9 wt.%Y respectively,a crossexperiment involving simultaneous addition of Ca and Y for the refinement of Mg2Si was carried out.The alloy composition with the optimal refinement effect and mechanical properties was identified as Mg-Al5.5-Si9.5-Ca0.1-Y0.6(wt.%).In Y-containing alloys,a novel coreshell structure evolution mechanism of MgSi2Y2//Al4MgY//Mg2Si was proposed based on experimental observation and first principles calculations,revealing MgSi2Y2as the core for the heterogeneous nucleation of Mg2Si.
基金Project supported by the Joints Fund of the National Natural Science Foundation of China(Grant No.U23A20349)the Young Scientists Fund of the National Natural Science Foundation of China(Grant Nos.62204126,62305171,62304113)。
摘要With the rapid advancement of optoelectronic technology,high-performance photodetectors are increasingly in demand in fields such as environmental monitoring,optical communication,and defense systems,where ultraviolet detection is critical.However,conventional semiconductor materials suffer from limited UV-visible detection capabilities owing to their narrow bandgaps and high dark currents.To address these challenges,wide-bandgap semiconductors have emerged as promising alternatives.Here,we fabricated a horizontally structured n–n heterojunction photodetector by growingβ-Ga2O3 on Si–GaN via plasma-enhanced chemical vapor deposition.The device exhibits a self-powered photocurrent of 3.5 nA at zero bias,enabled by the photovoltaic effect of the space charge region.Under 254-nm and 365-nm illumination,it exhibits rectification behavior,achieving a responsivity of 0.475 m A/W(0 V,220??W/cm~2 at 254 nm)and 257.6 mA/W(-5 V),respectively.Notably,the photodetector demonstrates a high photocurrent-to-dark current ratio of 10~5 under-5-V bias,highlighting its potential for self-powered and high-performance UV detection applications.
基金Supported by Fundamental Research Program of Shanxi Province(202403021212293)Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2024L018,2024L019)the Key Research and Development Special Project of Lüliang School-Locality Cooperation(2023XDHZ02).
摘要A series of Co-based molecular sieve catalysts with different Si/Al ratios was prepared by the impregnation method.The microstructure properties of Co active sites were finely characterized by means of XRD,TEM,Raman,H2-TPR,Py-FTIR and XPS technology.The results show that the surface Co species mainly exist in the form of CoOx nanoclusters and isolated Co2+,and the latter exhibits better N2O decomposition activity.Decreasing the Si/Al ratio of the MFI zeolite promotes the generation of isolated Co2+active sites,thereby enhancing the catalytic activity.Compared with the Co/S-1 catalyst with pure silicon S-1 carrier,the Co/HZ60 with a low Si/Al ratio of ZSM-5 carrier reduces the temperature required for complete N2O decomposition by 80℃,and it shows excellent resistance to O2 and NO.