Graphene nanosheets（GNSs） strengthened AgCuTi composite filler（AgCuTiG） was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTiG filler on the C/C composite surface and the ...Graphene nanosheets（GNSs） strengthened AgCuTi composite filler（AgCuTiG） was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTiG filler on the C/C composite surface and the interfacial microstructure and mechanical properties of brazed joints were investigated. The results indicate that the addition of GNSs reduced the wettability of AgCuTiG. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti3Cu4 and TiCu4 were converted to TiCu and the thickness of the reaction layer adjacent to the base material decreased. The maximum shear strength of joints brazed at 0.3 wt% GNSs was 23.3 MPa（880℃/10 min）. Further adding GNSs deteriorated the shear strength of the joints. Fracture of the joints occurred in the C/C composite substrate and the TiC layer adjacent to C/C composite.展开更多
Nano-Al2O3 particles modified Ag Cu Ni filler was adopted to braze the SiO2 ceramic and TC4.The effects of filler size as well as the brazing temperature on the interfacial microstructure and mechanical property of th...Nano-Al2O3 particles modified Ag Cu Ni filler was adopted to braze the SiO2 ceramic and TC4.The effects of filler size as well as the brazing temperature on the interfacial microstructure and mechanical property of the joints were investigated.Nanoscale filler reduced the phases dimension and promoted the homogeneous distribution of microstructure,obtaining a higher joint strength when compared to microscale filler.The increase of brazing temperature made the accelerating dissolution and diffusion of Ti,which promoted the increase of thickness of Ti4O7+TiSi2 layer adjacent to SiO2 ceramic and diffusion layer zone nearby TC4 alloy.The hypoeutectic structure was produced in the brazing seam due to the high Ti content.The maximum shear strength of^40 MPa was obtained at 950°C for 10 min.展开更多
A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interracial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmiss...A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interracial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmission electron microscope. The effects of graphene addition on the microstructure evolu-tion and mechanical properties of brazed joints were investigated, and the strengthening mechanism of graphene was analyzed. The results revealed that due to the addition of graphene, M23（C,B）6 compounds were synthesized in the y solid solution and brittle boride precipitates near the brazing seam decreased. Graphene was effective in retarding solute atoms diffusion thus impeding the precipitation of borides. Furthermore, the low coefficient of thermal expansion （CTE） of graphene was conducive to relieve stress concentration of the brazed joints during the cooling process. The shear strengths of brazed joints were significantly improved by exerting the strengthening effect of graphene. The maximum shear strengths of the brazed joints were 410.4 MPa and 329.7 MPa at room temperature and 800 ℃, respectively.展开更多
多年冻土区泥炭沼泽土壤孔隙水甲烷关联微生物及底物的研究有助于深入理解气候变化背景下寒区湿地生态系统甲烷循环过程。选取大兴安岭连续多年冻土区柴桦-泥炭藓和狭叶杜香-泥炭藓两种典型植被群落泥炭沼泽,设置开顶箱(Open Top Chambe...多年冻土区泥炭沼泽土壤孔隙水甲烷关联微生物及底物的研究有助于深入理解气候变化背景下寒区湿地生态系统甲烷循环过程。选取大兴安岭连续多年冻土区柴桦-泥炭藓和狭叶杜香-泥炭藓两种典型植被群落泥炭沼泽,设置开顶箱(Open Top Chamber,OTC)增温实验。于生长季(6月、7月、8月和9月)采集土壤孔隙水样品,对比分析OTC内外土壤孔隙水中产甲烷菌数量、甲烷氧化菌数量及溶解性有机碳(Dissolved Organic Carbon,DOC)浓度的动态变化特征,并探究土壤孔隙水甲烷关联微生物与DOC浓度的关系。结果表明:增温提高了生长季大兴安岭多年冻土区土壤孔隙水中产甲烷菌数量和DOC浓度,而对甲烷氧化菌数量的影响因月份而异。生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量的平均增加幅度分别为54.52%和44.97%,DOC浓度的平均增加幅度分别为34.16%和28.33%。增温使得生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中甲烷氧化菌平均数量分别降低了46.20%和31.42%。一元线性回归分析结果表明,土壤孔隙水中DOC浓度可分别解释柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量变化的29.00%和24.10%(P<0.01),而对两种植被群落下土壤孔隙水中甲烷氧化菌数量的影响并不显著(P>0.05)。展开更多
Superalloy thin-walled structures are achieved mainly by brazing,but the deformation process of brazed joints is non-uniform,making it a challenging research task.This paper records a thorough investigation of the eff...Superalloy thin-walled structures are achieved mainly by brazing,but the deformation process of brazed joints is non-uniform,making it a challenging research task.This paper records a thorough investigation of the effect of brazing parameters on the microstructure of joints and its mechanical properties,which mainly inquires into the deformation and fracture mechanisms in the shearing process of GH99/BNi-5a/GH99 joints.The macroscopic-microscopic deformation mechanism of the brazing interface during shearing was studied by Crystal Plasticity(CP)and Molecular Dynamics(MD)on the basis of the optimal brazing parameters.The experimental results show that the brazing interface is mainly formed by(Ni,Cr,Co)(s,s)and possesses a shear strength of approximately 546 MPa.The shearing fracture of the brazed joint occurs along the brazing seam,displaying the characteristics of intergranular fracture.MD simulations show that dislocations disassociate and transform into fine twinning with increased strain.CP simulated the shear deformation process of the brazed joint.The multiscale simulation results are consistent with the experimental results.The mechanical properties of thin-walled materials for brazing are predicted using MD and CP methods.展开更多
A bonding approach based on laser surface modification was developed to address the poor bonding be-tween Si_(3)N_(4) ceramic and Cu.The bonding mechanism in Si_(3)N_(4)/Cu heterogeneous composite structure fabricated...A bonding approach based on laser surface modification was developed to address the poor bonding be-tween Si_(3)N_(4) ceramic and Cu.The bonding mechanism in Si_(3)N_(4)/Cu heterogeneous composite structure fabricated by laser modification-assisted bonding is examined by means of scanning/transmission elec-tron microscopy and thermodynamic analysis.In the bonding process under laser modification,atomic intermixing at the interface is confirmed,as a result of the enhanced diffusion assisted by the dissocia-tion of Si_(3)N_(4) ceramic by laser.The dissociating Si precipitations on the surface,as well as the formation of micro-pores interfacial structure,would be the key concept of the bonding,by which the seamless and robust heterointerfaces were created.By controlling the laser-modifying conditions,we can obtain a reli-able heterostructure via the optimization of the trade-off of the surface structure and bonding strength,as determined by the laser-modified surface prior to bonding.The maximum structure depth and S ratio at the Si_(3)N_(4) surface were produced at a laser power of 56 W,corresponding to the maximal shear strength of 15.26 MPa.It is believed that the further development of this bonding technology will advance power electronic substrate fabrication applied in high-power devices.展开更多
A novel carbon quantum dots decorated C-doped a-Bi_(2)O_(3)photocatalyst(CBO/CQDs)was synthesized by solvothermal method.The synergistic effect of adsorption and photocatalysis highly improved contaminants removal eff...A novel carbon quantum dots decorated C-doped a-Bi_(2)O_(3)photocatalyst(CBO/CQDs)was synthesized by solvothermal method.The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies.The ceftriaxone sodium degradation rate constant(k)of CBO/CQDs was 11.4 and 3.2 times that of pure a-Bi2O3 and C-doped a-Bi_(2)O_(3),respectively.The interstitial carbon doping generated localized states above the valence band,which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes;the loading of CQDs improved the charge carrier separation and extended the visible light response;the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers.The·O2-and ht were identified as the dominant reactive species in ceftriaxone sodium degradation,and the key role of·O2-was further investigated by NBT transformation experiments.The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack,and intermediates analysis was conducted to explore the possible degradation pathways.The toxicity evaluation revealed that some degradation intermediates possessed high toxicity,thus the contaminants require sufficient mineralization to ensure safe discharge.The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of a-Bi2O3,which provides references for future studies.展开更多
Nanoscale thin-film composite(TFC)polyamide membranes are highly desirable for desalination owing to their excellent separation performance.It is a permanent pursuit to further improve the water flux of membrane witho...Nanoscale thin-film composite(TFC)polyamide membranes are highly desirable for desalination owing to their excellent separation performance.It is a permanent pursuit to further improve the water flux of membrane without deteriorating the salt rejection.Herein,we fabricated a high-performance polyamide membrane with nanoscale structures through introducing multifunctional crown ether interlayer on the porous substrate impregnated with m-phenylenediamine.The crown ether interlayer can reduce the diffusion of amine monomers to reaction interface influenced by its interaction with m-phenylenediamine and the spatial shielding effect,leading to a controlled interfacial polymerization(IP)reaction.Besides,crown ether with intrinsic cavity is also favorable to adjust the IP process and the microstructure of polyamide layer.Since the outer surface of the nanocavity is lipophilic,crown ether has good solvency with the organic phase,thus attracting more trimesoyl chloride molecules to the interlayer and promoting the IP reaction in the confined space.As a result,a nanoscale polyamide membrane with an ultrathin selective layer of around 50 nm is obtained.The optimal TFC polyamide membrane at crown ether concentration of 0.25 wt.%exhibits a water flux of 61.2 L·m^(−2)·h^(−1),which is 364%of the pristine TFC membrane,while maintaining a rejection of above 97%to NaCl.The development of the tailor-made nanoscale polyamide membrane via constructing multifunctional crown ether interlayer provides a straightforward route to fabricate competitive membranes for highly efficient desalination.展开更多
基金supports to this study from the National Natural Science Foundation of China–China (Nos.51505105 and 51775138)the Natural Science Foundation of Shandong Province–China (No.ZR2014EEQ001)the International Science & Technology Cooperation Program of China–China (No.2015DFA50470)
文摘Graphene nanosheets（GNSs） strengthened AgCuTi composite filler（AgCuTiG） was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTiG filler on the C/C composite surface and the interfacial microstructure and mechanical properties of brazed joints were investigated. The results indicate that the addition of GNSs reduced the wettability of AgCuTiG. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti3Cu4 and TiCu4 were converted to TiCu and the thickness of the reaction layer adjacent to the base material decreased. The maximum shear strength of joints brazed at 0.3 wt% GNSs was 23.3 MPa（880℃/10 min）. Further adding GNSs deteriorated the shear strength of the joints. Fracture of the joints occurred in the C/C composite substrate and the TiC layer adjacent to C/C composite.
基金supported by National Natural Science Foundation of China(Grant Nos.51505105,51875130 and 51775138)the Key Research&Development Program of Shandong Province(No.2017GGX40103).
文摘Nano-Al2O3 particles modified Ag Cu Ni filler was adopted to braze the SiO2 ceramic and TC4.The effects of filler size as well as the brazing temperature on the interfacial microstructure and mechanical property of the joints were investigated.Nanoscale filler reduced the phases dimension and promoted the homogeneous distribution of microstructure,obtaining a higher joint strength when compared to microscale filler.The increase of brazing temperature made the accelerating dissolution and diffusion of Ti,which promoted the increase of thickness of Ti4O7+TiSi2 layer adjacent to SiO2 ceramic and diffusion layer zone nearby TC4 alloy.The hypoeutectic structure was produced in the brazing seam due to the high Ti content.The maximum shear strength of^40 MPa was obtained at 950°C for 10 min.
基金supported financially by the National Natural Science Foundation of China(Nos.51505105,51775138 and U1537206)the International Science&Technology Cooperation Program of China(No.2015DFA50470)the Key Research&Development program of Shandong Province(No.2017GGX40103)
文摘A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interracial microstructure of brazed joints was analyzed by field emission scanning electron microscope and a transmission electron microscope. The effects of graphene addition on the microstructure evolu-tion and mechanical properties of brazed joints were investigated, and the strengthening mechanism of graphene was analyzed. The results revealed that due to the addition of graphene, M23（C,B）6 compounds were synthesized in the y solid solution and brittle boride precipitates near the brazing seam decreased. Graphene was effective in retarding solute atoms diffusion thus impeding the precipitation of borides. Furthermore, the low coefficient of thermal expansion （CTE） of graphene was conducive to relieve stress concentration of the brazed joints during the cooling process. The shear strengths of brazed joints were significantly improved by exerting the strengthening effect of graphene. The maximum shear strengths of the brazed joints were 410.4 MPa and 329.7 MPa at room temperature and 800 ℃, respectively.
文摘多年冻土区泥炭沼泽土壤孔隙水甲烷关联微生物及底物的研究有助于深入理解气候变化背景下寒区湿地生态系统甲烷循环过程。选取大兴安岭连续多年冻土区柴桦-泥炭藓和狭叶杜香-泥炭藓两种典型植被群落泥炭沼泽,设置开顶箱(Open Top Chamber,OTC)增温实验。于生长季(6月、7月、8月和9月)采集土壤孔隙水样品,对比分析OTC内外土壤孔隙水中产甲烷菌数量、甲烷氧化菌数量及溶解性有机碳(Dissolved Organic Carbon,DOC)浓度的动态变化特征,并探究土壤孔隙水甲烷关联微生物与DOC浓度的关系。结果表明:增温提高了生长季大兴安岭多年冻土区土壤孔隙水中产甲烷菌数量和DOC浓度,而对甲烷氧化菌数量的影响因月份而异。生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量的平均增加幅度分别为54.52%和44.97%,DOC浓度的平均增加幅度分别为34.16%和28.33%。增温使得生长季柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中甲烷氧化菌平均数量分别降低了46.20%和31.42%。一元线性回归分析结果表明,土壤孔隙水中DOC浓度可分别解释柴桦-泥炭藓和狭叶杜香-泥炭藓泥炭沼泽土壤孔隙水中产甲烷菌数量变化的29.00%和24.10%(P<0.01),而对两种植被群落下土壤孔隙水中甲烷氧化菌数量的影响并不显著(P>0.05)。
基金support from the National Natural Science Foundation of China(Grant Nos.52175307)the Taishan Scholars Foundation of Shandong Province(No.tsqn201812128)+1 种基金the Natural Science Foundation of Shandong Province(No.ZR2023JQ021No.ZR2020QE175).
文摘Superalloy thin-walled structures are achieved mainly by brazing,but the deformation process of brazed joints is non-uniform,making it a challenging research task.This paper records a thorough investigation of the effect of brazing parameters on the microstructure of joints and its mechanical properties,which mainly inquires into the deformation and fracture mechanisms in the shearing process of GH99/BNi-5a/GH99 joints.The macroscopic-microscopic deformation mechanism of the brazing interface during shearing was studied by Crystal Plasticity(CP)and Molecular Dynamics(MD)on the basis of the optimal brazing parameters.The experimental results show that the brazing interface is mainly formed by(Ni,Cr,Co)(s,s)and possesses a shear strength of approximately 546 MPa.The shearing fracture of the brazed joint occurs along the brazing seam,displaying the characteristics of intergranular fracture.MD simulations show that dislocations disassociate and transform into fine twinning with increased strain.CP simulated the shear deformation process of the brazed joint.The multiscale simulation results are consistent with the experimental results.The mechanical properties of thin-walled materials for brazing are predicted using MD and CP methods.
基金supported by the National Natural Science Foun-dation of China(grant Nos.52275318 and 52175307)Taishan Scholars Foundation of Shandong Province(No.tsqn201812128)+1 种基金Shandong Natural Science Foundation(Nos.ZR2023JQ021 and ZR2023QE221)China Academy of Space Technology Innovation Foundation(No.CAST2022).
文摘A bonding approach based on laser surface modification was developed to address the poor bonding be-tween Si_(3)N_(4) ceramic and Cu.The bonding mechanism in Si_(3)N_(4)/Cu heterogeneous composite structure fabricated by laser modification-assisted bonding is examined by means of scanning/transmission elec-tron microscopy and thermodynamic analysis.In the bonding process under laser modification,atomic intermixing at the interface is confirmed,as a result of the enhanced diffusion assisted by the dissocia-tion of Si_(3)N_(4) ceramic by laser.The dissociating Si precipitations on the surface,as well as the formation of micro-pores interfacial structure,would be the key concept of the bonding,by which the seamless and robust heterointerfaces were created.By controlling the laser-modifying conditions,we can obtain a reli-able heterostructure via the optimization of the trade-off of the surface structure and bonding strength,as determined by the laser-modified surface prior to bonding.The maximum structure depth and S ratio at the Si_(3)N_(4) surface were produced at a laser power of 56 W,corresponding to the maximal shear strength of 15.26 MPa.It is believed that the further development of this bonding technology will advance power electronic substrate fabrication applied in high-power devices.
基金supported by the National Key R&D Program(2019YFC0408200)Natural Science Foundation of Shanghai[21ZR1415600]National Natural Science Foundation of China[41807340].
文摘A novel carbon quantum dots decorated C-doped a-Bi_(2)O_(3)photocatalyst(CBO/CQDs)was synthesized by solvothermal method.The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies.The ceftriaxone sodium degradation rate constant(k)of CBO/CQDs was 11.4 and 3.2 times that of pure a-Bi2O3 and C-doped a-Bi_(2)O_(3),respectively.The interstitial carbon doping generated localized states above the valence band,which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes;the loading of CQDs improved the charge carrier separation and extended the visible light response;the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers.The·O2-and ht were identified as the dominant reactive species in ceftriaxone sodium degradation,and the key role of·O2-was further investigated by NBT transformation experiments.The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack,and intermediates analysis was conducted to explore the possible degradation pathways.The toxicity evaluation revealed that some degradation intermediates possessed high toxicity,thus the contaminants require sufficient mineralization to ensure safe discharge.The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of a-Bi2O3,which provides references for future studies.
基金the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University(IMSIU)for funding and supporting this work through Research Partnership Program(No.RP-21-09-75)。
文摘Nanoscale thin-film composite(TFC)polyamide membranes are highly desirable for desalination owing to their excellent separation performance.It is a permanent pursuit to further improve the water flux of membrane without deteriorating the salt rejection.Herein,we fabricated a high-performance polyamide membrane with nanoscale structures through introducing multifunctional crown ether interlayer on the porous substrate impregnated with m-phenylenediamine.The crown ether interlayer can reduce the diffusion of amine monomers to reaction interface influenced by its interaction with m-phenylenediamine and the spatial shielding effect,leading to a controlled interfacial polymerization(IP)reaction.Besides,crown ether with intrinsic cavity is also favorable to adjust the IP process and the microstructure of polyamide layer.Since the outer surface of the nanocavity is lipophilic,crown ether has good solvency with the organic phase,thus attracting more trimesoyl chloride molecules to the interlayer and promoting the IP reaction in the confined space.As a result,a nanoscale polyamide membrane with an ultrathin selective layer of around 50 nm is obtained.The optimal TFC polyamide membrane at crown ether concentration of 0.25 wt.%exhibits a water flux of 61.2 L·m^(−2)·h^(−1),which is 364%of the pristine TFC membrane,while maintaining a rejection of above 97%to NaCl.The development of the tailor-made nanoscale polyamide membrane via constructing multifunctional crown ether interlayer provides a straightforward route to fabricate competitive membranes for highly efficient desalination.
