Controlled interconversion of semiconducting and metallic forms of polyaniline nanofibers

Self-assembled polyaniline nanofibers doped with 2-acrylamido-2-methyl-1-propanesulfonic acid were prepared by oxidative polymerization of aniline in the presence of a nonionic surfactant. These nanofibers were dedoped to the semiconducting emeraldine base and then redoped to the metallic emeraldine hydrochloride. It was possible to introduce a different dopant anion from that used in the initial synthesis with no significant changes in fiber morphology or diameter, as observed by scanning electron microscopy (SEM). The method of sample preparation for SEM significantly affected the observed morphology. Deposition from aqueous dispersions resulted primarily in nanofibers that ranged in diameter from 28 to 82 nm (average: 56 nm), whereas drying to solid powder resulted in a less fibrous material. UV–vis–NIR absorbance spectroscopy indicated that the electronic structure of the emeraldine base nanofibers was identical to bulk emeraldine base obtained by conventional synthesis. Estimates from X-ray diffraction data suggested that the fractional crystallinity of emeraldine hydrochloride nanofibers did not differ significantly from the bulk powder.     

基于有限体积模拟的模锻优化设计

在锻造等金属大变形的工艺设计中,相关参数的确定很大程度上依赖于经验公式,而有限元法在金属大变形过程数值模拟中有明显的局限性,且模拟结果难以验证。本文基于有限体积法模拟了一典型开式模锻过程,并在通用经验值允许的范围内,根据模拟结果调整工艺设计中的参数设置,有效避免了一种锻件常见缺陷。通过分析变形过程特定时段的变形区形状、分流面的变化及变形力分布曲线,结合相关塑性理论验证了模拟结果的正确性,实现了工艺优化设计。研究证明理论预测与数值模拟相“拟合”的方法可以代替实验用于指导生产实践。     

Manurite 900钢高温制氢炉管服役后的焊接修复

通过金相组织观察、常温力学性能、常温冲击功测试等方法,分析了Manurite 900钢高温制氢炉管长期服役后的性能变化及对焊接性的影响,通过固溶处理改善了服役炉管的性能。判定了服役制氢炉管焊接裂纹的性质,研究了服役Manurite 900钢高温制氢炉管的抗液化裂纹能力及开裂倾向。分析了液化裂纹的成因及产生机理,提出了焊接修复的工艺方法和工艺原则。     

封面

在高强管线钢的工程应用过程中,较高的焊接残余应力会导致焊缝产生应力腐蚀和疲劳裂纹以至失效。简要介绍了高强度管线钢的焊接方法,对比了传统电弧焊与先进焊接方法的工艺特点,以及不同焊接方法的残余应力分布,概述了通过无损检测手段进行残余应力分析的相关研究结果,并通过数值模拟进行了焊接残余应力的对比和分析。指出,通过不同的数值模型及有限元分析等手段,可快速获得不同焊接方法的接头残余应力分布,以便于对焊接工艺进行调整。     

Development and testing of an innovative two-arm focal-plane thermal strap (TAFTS)

Temperature control of optical focal planes comes with the intrinsic challenge of creating a pathway that is both extremely flexible mechanically and highly conductive thermally. The task is further complicated because science-caliber optical focal planes are extremely delicate, yet time, cost, and their unique nature means that their mechanical resiliency is rarely tested and documented. The mechanical engineer tasked with the thermo-mechanical design must then create a highly conductive thermal link that minimizes the tensile and shear stresses transmitted to the focal plane without design parameters on an acceptable stiffness and without data on the stiffness of previously implemented thermal links.This paper describes the development and testing of the thermal link developed for the Portable Remote Imaging Spectrometer (PRISM) instrument. It will provide experimentally determined mechanical stiffness plots in the three axes of interest. Analytical and experimental thermal conductance results for the two-arm focal-plane thermal strap (TAFTS), from cryogenic to room temperatures, are also presented. The paper also briefly describes some elements of the fabrication process followed in developing a novel design solution, which provides high conductance and symmetrical mechanical loading, while providing enhanced flexibility in all three dimensions.     

Three-dimensional Ni(OH)2 nanoflakes/graphene/nickel foam electrode with high rate capability for supercapacitor applications

Supercapacitor, known as an important energy storage device, is also a critical component for next generation of hydrogen fuel cell vehicles. In this study, we report a novel route for synthesis of three-dimensional Ni(OH)₂/graphene/nickel foam electrode by electrochemical depositing Ni(OH)₂ nanoflakes on graphene network grown on nickel foam current collector and explore its applications in supercapacitors. The resulting binder-free Ni(OH)₂/graphene/nickel foam electrode exhibits excellent supercapacitor performance with a specific capacitance of 2161 F/g at a current density of 3 A/g. Even as the current density reaches up to 60 A/g, it still remains a high capacitance of 1520 F/g, which is much higher than that of Ni(OH)₂/nickel foam electrode. The enhanced rate capability performance of Ni(OH)₂/graphene/nickel foam electrode is closely related to the presence of highly conductive graphene layer on nickel foam, which can remarkably boost the charge-transfer process at electrolyte–electrode interface. The three-dimensional graphene/nickel foam substrate also significantly improves the electrochemical cycling stability of the electrodeposited Ni(OH)₂ film because of the strong adhesion between graphene film and electrodeposited Ni(OH)₂ nanoflakes. Results of this study provide an alternative pathway to improve the rate capability and cycling stability of Ni(OH)₂ nanostructure electrode and offer a great promise for its applications in supercapacitors.     

铝/钢电弧辅助激光对接熔钎焊铺展特性

采用小功率TIG电弧辅助激光热源进行5A06铝合金和热镀锌ST04Z钢的预置粉末对接熔钎焊工艺试验,通过SEM,Photoshop来研究预留间隙、背面填涂钎剂、激光热输入、辅助电弧电流、热源中心间距、填加焊丝对熔钎焊接头铺展宽度的影响. 结果表明,预留小于0.5 mm的间隙与背面填涂钎剂均可增大铺展宽度;在未焊穿的前提下,随激光热输入和辅助电弧电流的增加,铺展宽度增大;随热源中心间距的增大,铺展宽度先增加后减小. 焊接熔池中填加Al-Si焊丝较未填加焊丝的铺展性更好,获得连续、美观的焊缝表面形貌.     

Fe基非晶涂层厚度与其爆炸喷涂沉积特性及性能

目的 评估沉积厚度对Fe基非晶涂层在殷瓦钢基体上服役性能的影响。方法 利用爆炸喷涂在殷瓦钢表面沉积了4种不同厚度(d_AC1≈50μm,d_AC2≈150μm,d_AC3≈250μm,d_AC4≈500μm)的Fe基非晶涂层,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、维氏显微硬度计、纳米压痕仪、液压式万能试验机、电化学工作站等,研究了涂层的微观结构、物相组成、显微硬度、弹性模量、残余应力、结合强度和电化学腐蚀特性。结果 不同厚度Fe基非晶涂层均未出现明显的晶化现象,AC1涂层的孔隙率明显较高(2.8%～1.4%),在厚度增至AC3时涂层与基体界面出现了明显的裂纹,且裂纹随着厚度的增加继续恶化,至AC4时在截面形貌上仅观察到少量界面结合连接区域;随着涂层厚度的增加,涂层孔隙率、冷却残余拉应力和结合强度显著降低,显微硬度和弹性模量略有上升。AC1涂层因形成了电偶腐蚀,从而加剧了基体腐蚀,不具备耐腐蚀防护能力。当涂层厚度达到AC3后,涂层的腐蚀电流密度小于基体的腐蚀电流密度,其腐蚀电位和极化电阻均高于...     

ZL270LF铝合金的热变形行为与组织演变

通过热压缩实验研究了ZL270LF铝合金在变形量为70%,温度为300~550 ℃,应变速率为 0.01~10 s^-1范围的热变形行为,建立了流变应力本构方程模型,绘制出了二维热加工图,确定了最佳热加工区域,采用电子背散射衍射（EBSD）和透射电子显微镜（TEM）技术研究了该合金的组织演变规律。结果表明：ZL270LF铝合金的流变应力随变形温度的升高和应变速率的降低而降低,热变形激活能为309.05 kJ/mol,最优热加工区为温度470~530 ℃、应变速率为0.01~1 s^-1。该合金在热变形过程中存在3种不同的DRX机制,即连续动态再结晶（CDRX）、不连续动态再结晶（DDRX）和几何动态再结晶（GDRX）,其中CDRX是ZL270LF铝合金动态再结晶的主要机制。