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Terahertz wave tomographic imaging with a Fresnel lens

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chinese Optics Letters 2003年第1期1卷 53-55页

作者： S.Wang x.-c.zhang center for Terahertz Research Rensselaer Polytechnic Institute.TroyNY 12180-3590USACenter for Terahertz ResearchRensselaer Polytechnic Institute.TroyNY 12180-3590USA

We demonstrate three-dimensional tomographic imaging vising a Fresnel lens with broadband terahertz pulses. Objects at various locations along the beam propagation path are uniquely imaged on the same imaging plane using a Fresnel lens with different frequencies of the imaging beam. This procedure allows the reconstruction of an object's tomographic contrast image by assembling the frequency-dependent images.

关键词： wave in is it THz Terahertz wave tomographic imaging with a Fresnel lens with

A quasi-in-situ EBSD study of the thermal stability and grain growth mechanisms of cocrNi medium entropy alloy with gradient-nanograined structure

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Journal of Materials Science & Technology 2022年第14期109卷 54-63页

作者： P.-c.Zhao B.Guan Y.-G.Tong R.-Z.Wang x.Li x.-c.zhang S.-T.Tu Key Laboratory of Pressure Systems and Safety Ministry of EducationSchool of Mechanical and Power EngineeringEast China University of Science and TechnologyShanghai 200237China college of Materials Science and Engineering Chongqing UniversityChongqing 400044China college of Automobile and Mechanical Engineering Changsha University of Science and TechnologyChangshaChina

The thermal stability and mechanical properties of a gradient-nanograined structure(GNS)cocrNi medium entropy alloy(MEA)processed by ultrasonic surface rolling were studied by using isothermal/isochronal annealing tests combined with quasi-in-situ electron backscatter diffraction(EBSD)characterization and Vickers micro-hardness(HV)measurements.A layer by layer high-throughput investigation method was used to quantitatively study the grain growth kinetics and grain boundary evolution with different initial grain sizes,which could effectively save specimen and time *** grain nucleation and growth,as well as shrink and disappearance process throughΣ3 coincidence site lattice boundary migration with slightly lattice rotation during annealing were directly *** layer by layer grain growth kinetics and calculated activation energy indicate that the thermal stability of nanograined top surface layer is relatively higher than that of nano-twined subsurface layer for the gradient cocrNi MEA processed by ultrasonic surface *** analysis show that the grain boundary relax.tion and dynamic recrystallization of the topmost nano-grains led to the decrease of grain boundary energy,thus improving their thermal *** present work provided theoretical basis for the application of cocrNi MEA at high ***,the high-throughput method on the investigation of grain stability by using gradient structure can be easily ex.ended to other materials and it is of great significance for understanding the microstructural evolution of gradient materials.

关键词： Medium entropy alloy Grain growth Gradient materials Nanostructured materials Annealing High throughput

Broadband THz Sources from Gases to Liquids

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Ultrafast Science 2021年第1期1卷 80-96页

作者： Yiwen E Liangliang zhang Anton Tcypkin Sergey Kozlov cunlin zhang x.-c.zhang The Institute of Optics University of RochesterNY 14627USA Department of Physics Capital Normal UniversityBeijing 100048China ITMO University St.Petersburg 199034Russia

Matters are generally classified within four states:solid,liquid,gas,and *** of the four states of matter(solid,gas,and plasma)have been used for THz wave generation with short laser pulse ex.itation for decades,including the recent vigorous development of THz photonics in gases(air plasma).However,the demonstration of THz generation from liquids was conspicuously *** is well known that water,the most common liquid,is a strong absorber in the far infrared ***,liquid water has historically been sworn off as a source for THz ***,broadband THz wave generation from a flowing liquid target has been ex.erimentally demonstrated through laser-induced *** liquid target as the THz source presents unique ***,liquids have the comparable material density to that of solids,meaning that laser pulses over a certain area will interact with three orders more molecules than an equivalent cross-section of *** contrast with solid targets,the fluidity of liquid allows every laser pulse to interact with a fresh area on the target,meaning that material damage or degradation is not an issue with the high-repetition rate intense laser *** make liquids very promising candidates for the investigation of high-energy-density plasma,as well as the possibility of being the nex. generation of THz sources.

关键词： absorber repetition intense

Homotopy analysis solutions for the asymmetric laminar flow in a porous channel with ex.anding or contracting walls

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Acta Mechanica Sinica 2011年第2期27卷 208-214页

作者： x.-H. Si L.-c. Zheng x.-x. zhang Y. chao Applied Science School University of Science and Technology Beijing 100083 Beijing China Department of Mechanical Engineering University of Science and Technology Beijing100083 Beijing China Research Institute of chemical Defense of the EL.A 102205 Beijing China

In this paper, the asymmetric laminar flow in a porous channel with ex.anding or contracting walls is investigated. The governing equations are reduced to ordinary ones by using suitable similar transformations. Homotopy analysis method （HAM） is employed to obtain the ex.res- sions for velocity fields. Graphs are sketched for values of parameters and associated dynamic characteristics, especially the ex.ansion ratio, are analyzed in detail.

关键词： Homotopy analysis method · Ex.anding or contracting wall · Asymmetric laminar flow · Porous channel · Ex.ansion ratio

Diffusion behavior at void tip and its contributions to void shrinkage during solid-state bonding

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Journal of Materials Science & Technology 2018年第8期34卷 1449-1454页

作者： c.zhang M.Q.Li H.Li School of Materials Science and Engineering Northwestern Polytechnical University State Key Laboratory of Solidification Processing Northwestern Polytechnical University Department of Mechanical Engineering University de Lyon

Solid-state diffusion bonding is an advanced joining technique, which has been widely used to join similar or dissimilar materials. Generally, it is easy to observe the diffusion behavior during dissimilar bonding, but for similar bonding the diffusion behavior has yet been observed via ex.eriments. In this study, the diffusion behavior at void tip was firstly observed during similar bonding of stainless steel. Scanning electron microscopy with energy dispersive spectroscopy was used to ex.mine the interface charac- teristic and diffusion behavior. The results showed that a diffusion region was discovered at void tip. Element concentrations of diffusion region were more than those of void region, but less than those of bonded region. This behavior indicated that the diffusion was ongoing at void tip, but the perfect bond has yet formed. The diffusion region was attributed to the interface diffusion from adjacent region to void tip due to the stress gradient along bonding interface. The mass accumulation at void tip transformed the sharp void tip into smooth one at the beginning of void shrinkage, and then resulted in shorter voids.

关键词： Stainless steel Micro-void morphology Solid-state bonding Void tip Element diffusion

A route for large-scale preparation of multifunctional superhydrophobic coating with electrochemically-modified kaolin for efficient corrosion protection of magnesium alloys

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Journal of Magnesium and Alloys 2022年第11期10卷 3082-3099页

作者： x.ang Liu Tian c.zhang Yux.n zhang Jinsong Rao Shaojun Yuan Low-carbon Technology&chemical Reaction Engineering Lab College of Chemical EngineeringSichuan UniversityChengdu 610065China civil&Environmental Engineering Department University of Nebraska-LincolnOmahaNE 68182-0178USA State Key Laboratory of Mechanical Transmissions College of Materials Science and EngineeringChongqing UniversityChongqing 400044China

Superhydrophobic coating has been widely studied for its great applicational potential, such as for corrosion protection of magnesium alloys while it has been restrained by ex.ensive materials, sophisticated preparation process and infirm rough structures. In this study, the electrochemical method was adopted by using a two-electrode system for rapid hydrophobic modification to obtain superhydrophobic *** mix.ng the modified superhydrophobic kaolin with commercial epox. resin and polydimethylsilox.ne glue, a paint can be formed and easily used on various substrates for preparation of superhydrophobic coating via spraying method. The influence factors on wettability of the modified kaolin and the mix.ng ratio of each component of the coating were ex.lored. Also, the wettability, durability and anticorrosion of the prepared coating were evaluated comprehensively. The coating was able to maintain superhydrophobic after immersed in Hcl solution at pH 1, the NaOH solution at pH 14, and 3.5 wt.% Nacl solution for 16, 21, 30 days, respectively. In addition, the coating ex.ibited 4A grade adhesion, high hydrophobicity after abraded for 200 cycles on a 600-mesh sandpaper with 100 g weight, and 99.86% anticorrosion efficiency after soaked in 3.5 wt.% Nacl solution for 20 days, demonstrating a good robustness and anti-corrosion property. Furthermore, the coating showed good transparency, flex.bility and was easy to make in a large scale by the spraying method, which is of great significance to promote the practical application of superhydrophobic coatings and the anticorrosion Mg alloys.

关键词： Superhydrophobic coating Large-scale application Magnesium alloys corrosion protection

Binary doping of nitrogen and phosphorus into porous carbon: A novel di-functional material for enhancing cO_(2) capture and super-capacitance

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Journal of Materials Science & Technology 2022年第4期99卷 73-81页

作者： Yuan Wang Jianfei x.ao Hanzhi Wang Tian c.zhang Shaojun Yuan Low-carbon Technology&chemical Reaction Engineering Lab College of Chemical EngineeringSichuan UniversityChengdu 610065China civil&Environmental Engineering Department University of Nebraska-LincolnOmahaNE 68182-0178USA

Designing of hetero-atomic doped carbon-based systems through pyrolysis of abundant element organic precursors is a novel approach to construct rational porous carbon ***,a highly-cross-linked triazine polymer is employed to fabricate N,P co-doped porous carbon(A-TDP-12)with tunable active nitrogen in the carbon framework for simultaneous enhancement of cO_(2) capture capability and Supercapacitance(Sc).The synthesized A-TDP-12 possesses a typical hierarchically porous framework(micro-pores and meso-pores)with a large surface area(1332 m^(2) g^(-1))and a rich content of N(7.89 at.%)and P(0.74 at.%).It delivers a cO_(2) adsorption capacity of 1.52 and 5.68 mmol g^(-1) at 1 and 5 bar,respectively,with almost no decay after successive 8 *** 6 M KOH aqueous electrolyte,A-TDP-12 ex.ibits a superior specific capacitance of 172.7 F g^(-1) at a current density of 1 A g^(-1).Even at a high current density of 10 A g^(-1),80%of its initial capacity still *** work not only offers a novel strategy for fabricating promising adsorbents and electrodes for cO_(2) uptake and Scs,but also provides new insights into design of porous carbon material for related applications.

关键词： N,P co-doping Porous carbon cO_(2)capture Super-capacitors Bi-function

The Kirkendall effect on erosion resistance of chrome-coated 25cr3Mo2WNiV and 30SiMn2MoV gun barrel steels

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Journal of Materials Science & Technology 2024年第10期177卷 246-255页

作者： c.H.Dou P.F.Jin c.Z.Wang J.J.Li c.zhang J.F.Huang c.zhang Key Laboratory for Advanced Materials Processing State State Key Laboratory for Advanced Metals and MaterialsUniversity of Science and Technology BeijingBeijing 100083China National Joint Engineering Research center for Abrasion control and Molding of Metal Materials School of Materials Science and EngineeringHenan University of Science and TechnologyLuoyang 471003China

This study aimed to investigate the erosion behavior and mechanism of a newly developed 25cr3Mo2WNiV steel with a chrome coating using promoted ignition combustion *** erosion threshold pressure and temperature of the chrome-coated 25cr3Mo2WNiV steel were determined to be 0.2 MPa and 254.3 K higher than those of traditional chrome-coated 30SiMn2MoV ***,Kirkendall voids and inter-diffusion between the cr coating and matrix.were first observed before *** improved erosion resistance of the chrome-coated 25cr3Mo2WNiV steel was attributed to the suppression of the Kirkendall effect,which minimized heat generation at the cr/matrix.interface by pre-venting ox.gen diffusion and reducing ox.gen affinity.

关键词： Erosion resistance Kirkendall effect cr coating Gun steel

Study on Melting and Recrystallization of Poly(butylene succinate) Lamellar crystals via Step Heating Differential Scanning calorimetry

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chinese Journal of Polymer Science 2017年第12期35卷 1552-1560页

作者： Zhi-yu Lv Michael c.zhang Yang zhang Bao-hua Guo 徐军 Key Laboratory of Advanced Materials (Ministry of Education) Department of Chemical Engineering Tsinghua University

Differential scanning calorimetry（DSc） has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually ex.ibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization ex.therm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly（butylene succinate）（PBS） crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not ex.ibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent meltrecrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.

关键词： DSc Step heating Poly(butylene succinate) Metastability Melting-recrystallization Melting kinetics