激光冲击强化对钛合金疲劳寿命影响综述*

对提升钛合金零件的疲劳强度,已有相关技术的试验研究,但缺乏对技术的系统介绍,阻碍了该技术的产业化应用。通过整理大量试验数据及其结果,就激光冲击强化对钛合金零件的疲劳特性的影响展开分析。简要介绍激光冲击强化技术的发展状况,分别从表面形貌、残余应力、微观组织、硬度、表面粗糙度等方面进行分析总结。结果发现,当激光脉冲能量为7 J时,材料塑性变形量最大;当激光功率密度为3 GW/cm^(2),材料表面残余压应力值最高;当冲击次数达到5次以上时,材料表层的位错密度不断增大;当在工件表面覆盖一层高强度的光滑金属接触膜时,材料表面粗糙度将降低。综合数据可知激光功率密度及冲击次数对钛合金疲劳寿命的影响最大。整理了大量试验数据,可为得到最佳的激光冲击强化效果及提升疲劳寿命提供理论参考。     

射频等离子体改性PTFE表面液滴撞击接触起电对润湿性的影响∗

液滴撞击固体表面是自然界的常见现象,研究超疏水表面的液滴撞击对其润湿性的影响,对于超疏水性材料的潜在应用具有重要的科学意义。采用 3、10、20 min 氧等离子体处理（OPT）和 1 min 八氟环丁烷等离子体聚合沉积（PPD）的等离子体方法改性聚四氟乙烯（PTFE）表面,获得具有不同尺寸和间距的微 / 纳米锥的超疏水 PTFE 表面,研究射频等离子体改性 PTFE 表面的液滴静态接触角、滚动角及液滴撞击动力学行为,分析在不同个数液滴撞击后 PTFE 表面的润湿性和液滴撞击行为变化,确定 PTFE 表面液滴撞击起电效应的影响机制。结果表明：通过 1~9 个液滴撞击后,PTFE 表面的静态接触角随撞击液滴数量增加而减小,导致静态接触角低于 150°;液滴滚动角随撞击液滴数量增加而增大,造成液滴滚动角高于 10°。 撞击液滴的接触时间随撞击液滴数量增加而增大,回弹系数随撞击液滴数量增加而减小。随撞击液滴数量增加,回弹液滴的正电荷和 PTFE 表面的负电压增大,PTFE 表面的负电荷对液滴产生强吸引作用,导致低粘附超疏水性被破坏。3 min OPT 和 1 min PPD 改性 PTFE 表面的纳米锥间距小,密度大,表面负电荷量增加明显,造成 PTFE 表面的疏水性降低的程度最显著。 研究结果可为改善超疏水稳定性的表面织构设计提供理论依据。     

Bromination of [60]Fullerene. I. High-Yield Synthesis of C60Brx (x=6, 8, 24)

The systematic study of the bromination of C₆₀ was performed under various experimental conditions. Application of some chloroarenes as reaction media resulted in the high-yield (70-96%) selective synthesis of C₆₀Br₆ and C₆₀Br₈. Direct bromination of fullerene yielded either C₆₀Br₈, C₆₀Br₁₄, or C₆₀Br₂₄ depending on the reaction time. Possible pathways of bromination of C₆₀Br₈ were analyzed using semiempirical (AM1) calculations, two most probable molecular structures are conjectured for the first isolated C₆₀Br₁₄.     

Effective medium theory of the microwave and the infrared properties of composites with carbon nanotube inclusions

Carbon nanotubes (CNs) are electrically small particles at infrared and microwave frequencies. The Mossotti–Clausius formalism for estimating the effective permittivity dyadic of a dilute composite containing CN inclusions is described, and simplifications for certain orientational statistics are discussed. The polarizability dyadic of an electrically small CN is estimated from that of an infinitely long CN of the same cross-sectional diameter. A collection of randomly dispersed, aligned, nonchiral, electrically small CNs is shown to be transparent in the axial direction, but it can be either opaque or transparent in the transverse plane. Its effective electromagnetic response properties can be manipulated by a biasing magnetic field.     

Photocatalyzed oxidation in zeolite cages

A new concept of room temperature selective oxidation of olefins, alkyl substituted benzenes and alkanes by electron transfer from the hydrocarbon to the oxygen molecule induced by irradiation with visible light is shown. The hydrocarbon radical cation–O₂ charge-transfer pair is generated inside the cavities of alkali or alkaline-earth ion-exchanged zeolites, in which the large electrostatic field stabilizes the highly polar charge-transfer states of hydrocarbon–O₂ collisional pair and allows to control the pathways of further transformation. High selectivities to useful products are obtained using this approach.     

Size matters: Challenges in imprinting macromolecules

A large number of molecularly imprinted polymers (MIPs) have been investigated and reported over the last decade. Various templates have been successfully exploited and used, leading to significant advances in separation, adsorption, catalysis, sensing, and drug delivery. Among all the templates, small molecules have dominated in the synthesis of MIPs. In contrast, progress made in imprinting macromolecules has been slow, mainly due to the challenges presented by the size, structure and conformational fragility of biological macromolecules. In this review, we focus on discussing some key issues involved in the imprinting of macromolecules from recent publications. The similarity and difference between imprinting small molecules and macromolecules are highlighted. Other aspects relating to polymer design and function are also discussed.