采用 5 k W连续 CO2 激光器对经等离子喷涂的 Ni Co Cr Al Y结合层和 Zr O2 陶瓷层进行二次重熔处理 ,并利用金相显微镜、扫描电镜和电子探针对激光熔敷涂层进行了显微结构和元素分布观察与测试。结果表明 :激光熔敷涂层中基体对 Ni Co ...采用 5 k W连续 CO2 激光器对经等离子喷涂的 Ni Co Cr Al Y结合层和 Zr O2 陶瓷层进行二次重熔处理 ,并利用金相显微镜、扫描电镜和电子探针对激光熔敷涂层进行了显微结构和元素分布观察与测试。结果表明 :激光熔敷涂层中基体对 Ni Co Cr Al Y合金层产生稀释 ,形成成分和组织偏析。加入了 Ti O2 - Al- Ti添加剂的 Zr O2 陶瓷层激光重熔后得到了无裂纹的定向生长柱状晶 ,并且呈现一次枝晶平均间距为 2 .3μm的表层和平均间距为 3.展开更多
A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepa...A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepared by common gas atomization and dual-phase flow atomization under similar conditions were compared. The experimental results show that the dual-phase flow-atomized powders have average particle sizes that are one-half that of the common gas-atomized particles;additionally, they possess a finer microstructure and higher cooling rate under the same atomization gas pressure and the same gas flow. The Weber number in the crash criteria of liquid atomization is adopted to measure the crash ability of the atomization media. The Weber number of the dual-phase flow atomization medium is the sum of that of the gas and the solid particles. Furthermore, the critical equation of the crash model in dual-phase flow atomization is established, and the main regularities associated with this process were analyzed.展开更多
Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)d...Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.展开更多
A facile and user friendly technique to immobilize the late-transition metal complexes on spherical MgCl2/SiO2/THF support has been developed. The spherical MgCl2/SiO2/THF-supported late-transition metal catalysts 2,6...A facile and user friendly technique to immobilize the late-transition metal complexes on spherical MgCl2/SiO2/THF support has been developed. The spherical MgCl2/SiO2/THF-supported late-transition metal catalysts 2,6-bis-[1-(2,6-dimethylphenylimino)ethyl]pyridine iron(II) dichloride(SC-A) and 1,4-bis(2,6-dimethylphenyl)- acenaphthene diimine nickel(II) dibromide(SC-B) for ethylene polymerization has been prepared by spray-drying technique using tetrahydrofuran suspension containing MgCl2, SiO2 and late-transition metal complexes. The catalysts were characterized by BET, XRD, SEM and the polymers were analyzed using GPC, DSC and 13C-NMR. The test results show that spray-drying is a very effective method for immobilizing late-transition metal catalysts for ethylene polymerization. Among six kinds of cocatalysts for olefin polymerization, TMA and TEA were confirmed to be more effective than other compounds for the ethylene polymerization system using the catalyst SC-A. For the case of the catalyst SC-B, DEAC showed the best performance as cocatalysts in ethylene polymerization. The replication of the catalyst morphology was found in the resultant polyethylene.展开更多
In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low ...In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low haze, high transmission, superhydrophobicity, oleophobicity, and high mechanical resistance. Nanostructures have been fabricated on a glass surface by reactive ion etching through a nanomask, which is formed by dewetting ultrathin metal films （〈 10 nm thickness） subjected to rapid thermal annealing （RTA）. The nanostructures strongly reduce the initial surface reflectivity （-4%）, to less than 0.4% in the 390--800 nm wavelength range while keeping the haze at low values （〈 0.9%）. The corresponding water contact angle （0c） is -24.5~, while that on a flat surface is -43.5~. The hydrophilic wetting nanostructure can be changed into a superhydrophobic and oleophobic surface by applying a fluorosilane coating, which achieves contact angles for water and oil of -156.3~ and -116.2~, respectively. The multicomponent composition of the substrate （Coming~ glass） enables ion exchange through the surface, so that the nanopillars＇ mechanical robustness increases, as is demonstrated by the negligible changes in surface morphology and optical performance after 5,000-run wipe test. The geometry of the nanoparticles forming the nanomask depends on the metal material, initial metal thickness and RTA parameters. In particular we show that by simply changing the initial thickness of continuous Cu films we can tailor the metal nanoparticles＇ surface density and size. The developed surface nanostructuring does not require expensive lithography, thus it can be controlled and implemented on an industrial scale, which is crucial for applications.展开更多
The electrospray behaviors of saturated, substituted, and lacunary polyoxometalates （POMs） with classic Keggin and Dawson structures were investigated systematically by electrospray mass spectrometry （ESI-MS）. The...The electrospray behaviors of saturated, substituted, and lacunary polyoxometalates （POMs） with classic Keggin and Dawson structures were investigated systematically by electrospray mass spectrometry （ESI-MS）. The anions included Keggin [SiW12O40]4-, [SiW11O39]8-, [SiW10O36]8 , [SiW9O34]10-, Dawson [P2W18O62]6-, [P2W17O61]10-, and metal-substituted Keggin derivatives such as [PW11MnO40]7-, [SiW10V2O40]6-, and [GeWgCu3O37]10-. Common species observed in the mass spectra arose from the protonation or cationization of either intact or dehydrated precursor ions. Compared to saturated and substituted POMs, lacunary POMs exhibited distinguished MS behaviors such as a much higher degree of cationization and dehydration of the bare polyoxoanions present in the mass spectra. In addition, some of these lacunary POMs were found to undergo subtle speciation change in solution. Freshly prepared solutions are suggested for synthetics for which lacunary POMs are starting materials. The advantages of the cation-exchange process which are prior to MS analysis are illustrated by an example.展开更多
文摘采用 5 k W连续 CO2 激光器对经等离子喷涂的 Ni Co Cr Al Y结合层和 Zr O2 陶瓷层进行二次重熔处理 ,并利用金相显微镜、扫描电镜和电子探针对激光熔敷涂层进行了显微结构和元素分布观察与测试。结果表明 :激光熔敷涂层中基体对 Ni Co Cr Al Y合金层产生稀释 ,形成成分和组织偏析。加入了 Ti O2 - Al- Ti添加剂的 Zr O2 陶瓷层激光重熔后得到了无裂纹的定向生长柱状晶 ,并且呈现一次枝晶平均间距为 2 .3μm的表层和平均间距为 3.
文摘A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepared by common gas atomization and dual-phase flow atomization under similar conditions were compared. The experimental results show that the dual-phase flow-atomized powders have average particle sizes that are one-half that of the common gas-atomized particles;additionally, they possess a finer microstructure and higher cooling rate under the same atomization gas pressure and the same gas flow. The Weber number in the crash criteria of liquid atomization is adopted to measure the crash ability of the atomization media. The Weber number of the dual-phase flow atomization medium is the sum of that of the gas and the solid particles. Furthermore, the critical equation of the crash model in dual-phase flow atomization is established, and the main regularities associated with this process were analyzed.
基金the National Natural Science Foundation of China(No.52074157)Shenzhen Science and Technology Innovation Com-mission,China(Nos.JSGG20180508152608855,KQTD20170328154443162)Shenzhen Key Laboratory for Additive Manufacturing of High-performance Materials,China(No.ZDSYS201703031748354).
文摘Based on volume of fluid(VoF)interface capturing method and shear-stress transport(SST)k-ω turbulence model,numerical simulation was performed to reveal the flow mechanism of metal melts in melt delivery nozzle(MDN)during gas atomization(GA)process.The experimental validation indicated that the numerical models could give a reasonable prediction on the melt flow process in the MDN.With the decrease of the MDN inner-diameter,the melt flow resistance increased for both molten aluminum and iron,especially achieving an order of 10^(2) kPa in the case of the MDN inner-diameter≤1 mm.Based on the conventional GA process,the positive pressure was imposed on the viscous aluminum alloy melt to overcome its flow resistance in the MDN,thus producing powders under different MDN inner-diameters.When the MDN inner-diameter was reduced from 4 to 2 mm,the yield of fine powder(<150μm)soared from 54.7%to 94.2%.The surface quality of powders has also been improved when using a smaller inner-diameter MDN.
基金supported by the National Natural Science Foundation of China (Grant No.U1162114)the Science Foundation of Tianjin University of Science & Technology (20090420)
文摘A facile and user friendly technique to immobilize the late-transition metal complexes on spherical MgCl2/SiO2/THF support has been developed. The spherical MgCl2/SiO2/THF-supported late-transition metal catalysts 2,6-bis-[1-(2,6-dimethylphenylimino)ethyl]pyridine iron(II) dichloride(SC-A) and 1,4-bis(2,6-dimethylphenyl)- acenaphthene diimine nickel(II) dibromide(SC-B) for ethylene polymerization has been prepared by spray-drying technique using tetrahydrofuran suspension containing MgCl2, SiO2 and late-transition metal complexes. The catalysts were characterized by BET, XRD, SEM and the polymers were analyzed using GPC, DSC and 13C-NMR. The test results show that spray-drying is a very effective method for immobilizing late-transition metal catalysts for ethylene polymerization. Among six kinds of cocatalysts for olefin polymerization, TMA and TEA were confirmed to be more effective than other compounds for the ethylene polymerization system using the catalyst SC-A. For the case of the catalyst SC-B, DEAC showed the best performance as cocatalysts in ethylene polymerization. The replication of the catalyst morphology was found in the resultant polyethylene.
文摘In this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low haze, high transmission, superhydrophobicity, oleophobicity, and high mechanical resistance. Nanostructures have been fabricated on a glass surface by reactive ion etching through a nanomask, which is formed by dewetting ultrathin metal films （〈 10 nm thickness） subjected to rapid thermal annealing （RTA）. The nanostructures strongly reduce the initial surface reflectivity （-4%）, to less than 0.4% in the 390--800 nm wavelength range while keeping the haze at low values （〈 0.9%）. The corresponding water contact angle （0c） is -24.5~, while that on a flat surface is -43.5~. The hydrophilic wetting nanostructure can be changed into a superhydrophobic and oleophobic surface by applying a fluorosilane coating, which achieves contact angles for water and oil of -156.3~ and -116.2~, respectively. The multicomponent composition of the substrate （Coming~ glass） enables ion exchange through the surface, so that the nanopillars＇ mechanical robustness increases, as is demonstrated by the negligible changes in surface morphology and optical performance after 5,000-run wipe test. The geometry of the nanoparticles forming the nanomask depends on the metal material, initial metal thickness and RTA parameters. In particular we show that by simply changing the initial thickness of continuous Cu films we can tailor the metal nanoparticles＇ surface density and size. The developed surface nanostructuring does not require expensive lithography, thus it can be controlled and implemented on an industrial scale, which is crucial for applications.
基金financially supported by the National Natural Science Foundation of China(21371025)the 111 Project(B07012)a Fundamental Research Grant(20121942006)by the Beijing Institute of Technology
文摘The electrospray behaviors of saturated, substituted, and lacunary polyoxometalates （POMs） with classic Keggin and Dawson structures were investigated systematically by electrospray mass spectrometry （ESI-MS）. The anions included Keggin [SiW12O40]4-, [SiW11O39]8-, [SiW10O36]8 , [SiW9O34]10-, Dawson [P2W18O62]6-, [P2W17O61]10-, and metal-substituted Keggin derivatives such as [PW11MnO40]7-, [SiW10V2O40]6-, and [GeWgCu3O37]10-. Common species observed in the mass spectra arose from the protonation or cationization of either intact or dehydrated precursor ions. Compared to saturated and substituted POMs, lacunary POMs exhibited distinguished MS behaviors such as a much higher degree of cationization and dehydration of the bare polyoxoanions present in the mass spectra. In addition, some of these lacunary POMs were found to undergo subtle speciation change in solution. Freshly prepared solutions are suggested for synthetics for which lacunary POMs are starting materials. The advantages of the cation-exchange process which are prior to MS analysis are illustrated by an example.
