Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting.Herein,we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes,serving as bifunctional electrocatalysts for overall water splitting.Notably,Mo doping could effectively modulate the electronic structure of NiCoP,leading to the increased electroactive site and improved intrinsic activity of each site.Furthermore,an electrochemical activation strategy is proposed to form Mo-doped(Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction.Benefiting from the unique freestanding structure and Mo doping,Mo-doped NiCoP and(Ni,Co)OOH show the remarkable electrochemical performances,which are competitive among current researches.In addition,an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm?2.Therefore,this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation.

Diffusion Bonding of Ti-6Al-4V to QAl 10-3-1.5 with Ni/Cu Interlayers

Ti-6Al-4V 并且 QAI 10-3-1.5 散开结合与 Ni/Cuinterlayers 被执行了。结合散开的关节被扫描电子显微镜学(SEM ) 评估，精力散光谱学(版本) 和微硬度试验。在接口地区的金属间化合的混合物被 X 光检查衍射(XRD ) 检测。在 Ni/Ti-6AI-4V 转变地区和 Cu 的 TiNi+CuTi_3+alpha-Ti 形式的界面的微观结构(ss。Ni ) 在 Ni/Cu 夹层之间的稳固的答案形式。反应层(TrNi ) 的厚度由抛物线的 law:y 与结合的时间增加“ ~ 2=K_0exp (-150000/RT)t, 和 K_0=2.9Xl0^(-7) m~@/s 从实验数据被弄明白。

Microstructure and Strength of Brazed Joints of Ti_(3)Al Base Alloy with Cu-P Filler Metal

Brazing of Ti3Al alloys with the filler metal Cu-P was carried out at 1173～1273 K for 60～1800 s. When products are brazed, the optimum brazing parameters are as follows: brazing temperature is 1215～1225 K; brazing time is 250～300 s. Four kinds of reaction products were observed during the brazing of Ti3Al alloys with the filler metal Cu-P, i.e., Ti3Al phase with a small quantity of Cu (Ti3Al(Cu)) formed close to the Ti3Al alloy; the TiCu intermetallic compounds layer and the Cu3P intermetallic compounds layer formed between Ti3Al(Cu) and the filler metal, and a Cu-base solid solution formed with the dispersed Cu3P in the middle of the joint. The interfacial structure of brazed Ti3Al alloys joints with the filler metal Cu-P is Ti3Al/Ti3Al(Cu)/TiCu/Cu3P/Cu solid solution (Cu3P)/Cu3P/TiCu/Ti3Al(Cu)/Ti3Al, and this structure will not change with brazing time once it forms. The thickness of TiCu+Cu3P intermetallic compounds increases with brazing time according to a parabolic law. The activation energy Q and the growth velocity K0 of reaction layer TiCu+Cu3P in the brazed joints of Ti3Al alloys with the filler metal Cu-P are 286 k J/mol and 0.0821 m2/s, respectively, and growth formula was y2=0.0821exp(-34421.59/T)t.Careful control of the growth for the reaction layer TiCu+Cu3P can influence the final joint strength. The formation of the intermetallic compounds TiCu+Cu3P results in embrittlement of the joint and poor joint properties. The Cu-P filler metal is not fit for obtaining a high-quality joint of Ti3Al brazed.

Cu-Cu low-temperature diffusion bonding by spark plasma sintering:Void closure mechanism and mechanical properties

In this study,combining the single point diamond turning(SPDT)and spark plasma sintering(SPS),we achieved high-strength diffusion bonding of copper at an ultra-low temperature of 202℃(0.35 T_(m),T_(m):absolute temperature of the melting point).Additionally,the closure mechanism of interfacial micro-and nano-voids during the Cu-Cu SPS diffusion bonding is systematically revealed for the first time.For micro-voids,the pulsed current is found to induce additional diffusion flux and plastic deformation,thereby facilitating the void closure.Molecular dynamics(MD)simulation revealed that at the atomic scale,high-energy Cu atoms induced by the pulsed current can significantly promote the diffusion of low-energy atoms in their vicinity and accelerate the void closure.This study also proposes a novel“evaporation-deposition”nano-void closure mechanism for the previously unstudied nano-void closure process.The results show that the synergistic effect of the pulsed current and nanoscale surface rough-ness can significantly improve joint strength.At a low temperature of 405℃(0.5 T_(m)),on combining the computerized numerical control(CNC)turning and SPS diffusion bonding,the joint strength can reach 212 MPa,while that for the joint obtained by traditional hot pressing diffusion bonding at the same tem-perature is only 47 MPa.We obtained an ultra-high joint strength of 271 MPa using the combined process of SPDT and SPS diffusion bonding at an ultra-low temperature of 202℃(0.35 T_(m)),which is approximately 600℃ lower than the traditional diffusion bonding process temperature of 800℃(0.79 T_(m)).To sum up,this study provides a novel method and theoretical support for realizing low-temperature high-strength diffusion bonding.

Mechanical Properties and Microstructure of 6082-T6 Aluminum Alloy Joints by Self-support Friction Stir Welding

The majority of this research has concentrated on developing the self-support friction stir welding(SSFSW) tool which consists of a big concave upper shoulder and a small convex lower shoulder, and procedures for making reliable welds in aluminum hollow extrusion. The 5-mm-thick 6082-T6 aluminum alloy was self-support friction stir welded at a constant tool rotation speed of 800 r/min. The effect of welding speed on microstructure and mechanical properties was investigated. The results of transverse tensile test indicated that the tensile strength of joints increased and the elongation decreased with increasing welding speed. The whole values of microhardness of SSFSW joints increased with increasing welding speed from 10 to 200 mm/min. The defectfree joints were obtained at lower welding speeds and the tensile fracture was located at the heat-affected zone(HAZ) adjacent to the thermo-mechanically affected zone(TMAZ) on the advancing side. The investigation of the flow pattern of the softened metal around the SSFSW tool revealed that the flow pattern of the softened metal was driven by two shoulders and the stir pin. The failure of specimens in tension presented the ductile fracture mode.

Brazing of C/C composite and Ti-6Al-4V with graphene strengthened AgCuTi filler:Effects of graphene on wettability,microstructure and mechanical properties

Graphene nanosheets(GNSs) strengthened AgCuTi composite filler(AgCuTi_G) was used to braze C/C composite and Ti-6Al-4V. The effects of GNSs on the wettability of AgCuTi_G 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 AgCuTi_G. The interfacial microstructure of brazed joints evolved with the addition of GNSs, where Ti_3Cu_4 and TiCu_4 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.

Vacuum brazing of GH99 superalloy using graphene reinforced BNi-2 composite filler

A novel graphene reinforced BNi-2 composite filler was developed for brazing GH99 superalloy. The interfacial 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 evolution 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 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?C, respectively.

有机无机杂化钙钛矿电镜表征的虚与实

近年来,由于合成价格低廉以及光电转化效率高,基于有机无机杂化钙钛矿材料的太阳能电池得到了飞速发展.然而这些材料容易分解,这极大地限制了该技术的商业化应用.基于透射电子显微镜的表征有助于解析这些材料的降解机理.然而杂化钙钛矿材料对电子束辐照十分敏感,易引起结构失稳甚至分解,进而阻碍我们获取真实结构信息.本文利用低电子束剂量成像技术系统地研究了不同实验条件下杂化钙钛矿的结构不稳定性,揭示了最优的透射电镜表征条件.我们发现,低温(-180°C)并没有减缓束损伤,反而导致了快速的非晶化;较高的加速电压有利于降低损伤;MAPbI3(100)面比(001)面更稳定.基于这些发现,我们成功地获得了MAPbI3原始的原子结构,并确定了其表征窗口非常窄.这些发现有助于指导未来对这些电子束敏感材料的电子显微表征,也有助于寻找提高钙钛矿型太阳能电池稳定性的策略.

Atomic-scale structural and chemical evolution of Li3V2(PO4)3 cathode cycled at high voltage window

Here,by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy,we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0-4.8 V).We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases.These Li-deficient phases exhibit structure distortion with superstructure stripes,likely caused by the migration of the vanadium,which can slow down the lithium ion diffusion or even block the diffusion channels.Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss.Thus,the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling.After 500 cycles,the thickness of active LVP layer decreases to be - 5-20 nm.Moreover,the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated,indicating the thick SEI film also contributes to the capacity loss.The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale,which is essential to understand the voltage fading and capacity decaying of LVP cathode.

Additive manufacturing of a high-strength ZrC-SiC and TC4 gradient structure based on a combination of laser deposition technique and brazing

A ZrC-SiC and TC4 gradient structure(ZTGS)was additively manufactured through the laser deposition technique and brazing process.The research results indicated that SiC-reinforced TC4-based gradient layers could be obtained on the TC4 surface by laser deposition.ZrC-SiC and TC4 coated with gradient layers were brazed using an AgCuTi filler to fabricate the ZTGS.The effects of the gradient structure and brazing parameters on the ZTGS strength were investigated.With an increase in Layer II and Layer III thickness,the ZTGS shear strength increased.The brazing temperature and holding time affected the ZTGS shear strength by controlling the formation and distribution of the Cu4Ti phase in the brazing zone.The strengthening mechanism of the ZTGS was revealed by analyzing the residual stress distribution in the ZTGS.Compressive residual stress was formed in ZrC-SiC adjacent to the TC4 substrate or the deposited gradient layer,which was found to negatively affect the properties of the ZTGS.The increase in gradient layer thickness reduced the maximum residual stress in ZrC-SiC,and the effect of Layer III on the residual stress was more significant than that of Layer II.The calculated residual stress evolution matched the ZTGS property values well,revealing the strengthening mechanism.

Characterization,Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr_(55)Cu_(30)Ni_5Al_(10) Bulk Metallic Glass

The composition of oxide film of Zr_(55)Cu_(30)Ni_5Al_(10) bulk metallic glass was identified by X-ray photoelectron spectroscopy.In addition,the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding.The joint interfaces were observed by scanning electron microscopy and atomic force microscopy.The hardness of joints near the interface was higher than that far away from the interface,which is attributed to the difference of structural relaxation.According to the result of micro-focused X-ray diffractometry and transmission electron microscopy,the joints retained the amorphous structure when the holding time is less than 20 min.The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection.Moreover,the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength.The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.

Wettability and joining of SiC by Sn-Ti: Microstructure and mechanical properties

Reliable Si C/Sn-Ti/Si C joints were obtained by brazing(950?C/10 min)and soldering(250?C/2 min)following premetallization depend on the wettability of Sn-Ti on Si C.The microstructures of Sn-Ti/Si C interface were characterized by scanning electron microscopy,X-ray diffraction and transmission electron microscopy,and the mechanical properties of joints were evaluated by shear tests.Active Ti enhanced the wettability of Sn on Si C with the decrease of contact angle from 150?to 20?.Ti direct reacted with Si C to produce Ti C and combines with released Si forming Ti5Si3.Much lower Ti concentration per contacting area in brazing and metallization,compared to wetting,resulted in defective bonding of Sn-Ti/Si C and few amounts of interfacial products(thin Ti C layer or partial covered Ti C layer with Ti5Si3).All of the Si C/Si C joints possess a similar shear strength of 27–32 MPa and rupture through?-Sn matrix in ductile fracture.

Vacuum wetting of Ag/TA2 to develop a novel micron porous Ti with significant biocompatibility and antibacterial activity

Porous Ti with low modulus,excellent bio-corrosion resistance,biocompatibility,and antibacterial activity is highly pursued as advanced implant materials.In this work,a new approach to prepare micron porous structures on the surface layer of a grade 2 commercially-pure Ti(TA2)was proposed,which utilized a simple vacuum wetting process of pure Ag on the surface of TA2.The microstructure,corrosion resistance,biocompatibility,mechanical properties,antibacterial ability,and formation mechanism of the asfabricated porous Ti were studied.The results show that the pores(with average pore sizes of 0.5-5μm)are distributed on the surface layer of the TA2 with a depth of~10μm.In particular,a large number of silver nanoparticles(Ag NPs)form which are dispersed on the porous structures.The formation mechanisms of the porous structures and Ag NPs were elucidated,suggesting that the volatilization/sublimation of Ag in TA2 is crucial.The porous Ti possesses excellent bio-corrosion resistance,surface wettability,biocompatibility,antibacterial activity,and a relatively low elastic modulus of 40-55 GPa,which may have a promising future in the field of orthopedic implants.This work also provides a novel idea for the development of advanced porous Ti materials for orthopedic-related basic research and biomedical applications.

我国民艺保护体系的建立与未来规划——冯骥才访谈

《民艺》:您曾指出"民间文化是我们母亲的文化",在您的文学创作中蕴涵着深厚的民间文化情结。21世纪初,您发起了中国民间文化遗产抢救工程,出版了一系列有关民间文化与民间艺术的著述,研究成果颇为丰硕。请问,对于开展这项工作,您当时是如何考虑的?

Residual stress distribution as a function of depth in graphite/copper brazing joints via X-ray diffraction

The residual stress distributions as a function of depth in three different graphite/copper brazing joints:with no interlayer,with a copper interlayer and with a niobium interlayer are measured via X-ray diffraction by transmission geometry.The residual stress in all the joints is found to be generally compressive and increasing from the surface to the interface.Copper and niobium interlayers are both effective in alleviating the residual stress in the joint and the stress value in the joint with a niobium interlayer appearing to be the lowest.The strength of the joint is demonstrated to be closely related to the residual stress and the fracture position of the joint corresponds well with the highest residual stress.

绽放在千年民间生活中的靛蓝奇花

一蓝印花布是从更古老的捺印、拓印、夹缬等印花工艺中蜕变出来的。从现存的史料看,800年前开始使用的纸版刻制、漏版刮浆的药斑布,应是最早的蓝印花布。然而,当这种新兴的印花工艺甫一出现,缘其简便,灵活,便于操作,很快就被广泛地采用了。它最初的中心在上海的嘉定和苏州的昆山一带,这里水丰土沃,日照充足,极适宜栽种棉花和蓝靛。棉花纺织成布,靛蓝染花其上,一切得天独厚,蓝印花布便应运而生。

文化三题

文化责任感责任感这个词儿已被当今文学界所厌倦。以流行的看法,它像绳索——如果出于作家自身,写作就会如同自我捆绑起来,不得轻松,难以随心所欲、呼风唤雨地过把瘾;如果是来自某某人的要求呢,则是外加的束缚,更谈不上写作的自由了。于是,责任感几乎被当今文学推出门外。以致80年代初那种"为民请命"的作品,干脆被定性为非文学。