Effect of electromigration induced joule heating and strain on microstructural recrystallization in eutectic SnPb flip chip solder joints

A refinement of the lamellar microstructure was observed in eutectic SnPb solder joints in electromigration. Electromigration has both atomic flux and electron flow. The latter generated joule heating and the former caused strain. The formation of nanoscale lamellar microstructure spent a large amount of interfacial energy, and we proposed that the driving force comes from the strain induced by electromigration under a high current density. Kinetically, refinement of the lamellar microstructure required fast atomic diffusion at a high homologous temperature. The joule heating mainly from the on-chip Al interconnect lines tremendously increased the temperature of solder bumps and enabled fast atomic diffusion. The strain induced by electromigration, when combined with a high homologous temperature, could lead to recrystallization in the sample to form the nanoscale lamellae.     

Numerical study of hydrogen addition to DME/CH4 dual fuel RCCI engine

In this study, the effect of hydrogen addition to DME/CH₄ dual-fuel RCCI (Reactivity Controlled Compression Ignition) engine is investigated using three dimensional calculations coupled with chemical kinetics. A new reduced DME (Dimethyl Ether) oxidation mechanism is proposed in this study. With the addition of H₂, the ignition time is advanced and the peak cylinder pressure is increased. The addition of hydrogen has a greater effect on the beginning stage of combustion than the later stages of combustion. The CH₄ emission is reduced with the addition of H₂. However, as the flame does not propagate throughout the charge, the CH₄ emission is still high. The CO emission is reduced and most of the remaining CO is produced by the combustion of the premixed CH₄. With the addition of hydrogen, NO emission is increased. The simulation shows that the final NOx emissions are significantly determined by the injection strategy and quantity of the pilot fuel during dual fuel operation conditions.     

The controllable hydrolysis rate for LaMg12 hydride

In this work, the hydrogenation mechanism for LaMg₁₂ alloy is revealed by introducing hydrogen step by step and the hydrogenation degree is found to affect the hydrolysis properties of LaMg₁₂H_x hydrides. Because the hydrolysis performance of Mg is affected limitedly while MgH₂ is accelerated significantly by LaH₃, the hydrolysis rate is controllable through adjusting the ratio of LaH₃ to MgH₂. The synergistic effect of LaH₃ and MgH₂ leads to the complete hydrolysis of the fully hydrogenated LaMg₁₂H₂₇, yielding 9.73 wt. % (1089.55 ml g⁻¹) hydrogen.     

Fabrication and evaluation of polyamide 6 composites with electrospun polyimide nanofibers as skeletal framework

In this study, two types of polyimide (PI) nanofiber mats, including (1) the mats consisting of (almost) randomly overlaid PI nanofibers and (2) the mats consisting of highly aligned PI nanofibers, were prepared by the materials-processing technique of electrospinning. The nanofiber mats were subsequently used to develop composites with polyamide 6 (PA6) via the composites – fabrication method of polymer melt infiltration lamination (PMIL). Owing to superior mechanical properties (i.e., the tensile strength and modulus were 1.7 GPa and 37.0 GPa, respectively) and large specific surface area of electrospun PI nanofibers, the PI/PA6 composites with PI nanofiber mats as skeletal framework demonstrated excellent mechanical properties. In particular, the PI/PA6 composite containing 50 wt.% of aligned PI nanofibers had the tensile strength and modulus of 447 MPa and 3.0 GPa along the longitudinal direction, representing ～700% and ～500% improvements as compared to neat PA6.     

Design and preparation of stress-free epitaxial BaTiO3 polydomain films by RF magnetron sputtering

Domain structures of BaTiO₃ thick films grown on (100) SrTiO₃ single-crystal substrates were engineered using an RF magnetron sputtering deposition process. By tuning the sputtering power and cooling rate and using an off-axis sputtering technique to prepare conducting perovskite oxide bottom electrode with heteroepitaxial quality, we have deposited epitaxial tetragonal single-domain and polydomain BaTiO₃ films with a self-assembled three-domain architecture. The electrical properties and microstructure of the BaTiO₃ films were characterized, and a c/a₁/a₂ cellular polydomain structure was clearly observed in as-grown films by optical microscopy. Such a polydomain structure was a consequence of a complete relaxation of misfit stresses of the film. Engineering of this self-assembled microstructure has great potential in providing large, field-tunable pyroelectric and electromechanical responses in next-generation microelectronic devices and micro-electro-mechanical systems (MEMS).     

Pointwise plucking of suspended carbon nanotubes

Vibration of nanotubes/wires is significant for fundamental and applied researches. However, it remains challenging to control the vibration with point-level precision. Herein, individual suspended carbon nanotubes are plucked point by point to vibrate in scanning electron microscope with the electron beam as a nanoscale pointer. The vibration is directly imaged, and its images fit well with simulations from the plucking mechanism. This demonstrates a new way to manipulate the nanotube vibration with unprecedented precision.     

提升油料学与炼油工艺课堂教学效果的探索与实践

油料学与炼油工艺是一门理论与应用紧密结合的专业必修课程,其教学效果的好坏直接关系到我校在油气储运工程专业的定位和专业特色的体现。笔者通过对教学方法、教学手段、教学内容等方面的改革和尝试,提升了课程教学效果。     

BF填料接触氧化法处理化工综合废水试验研究

试验研究了以采用新型BF填料的生物接触氧化法处理化工综合废水的效果.结果表明其处理效果稳定、表观污泥产率低、抗冲击能力强.为检验填料的性能,提出以填料丝长负荷判断去除效果,在填料的CODCr、BOD5和NH3-N丝长负荷分别高达67.39、32.68、10.24g/(m·d)的情况下,CODCr、BOD5和NH3-N去除率仍分别达86.43%、95.55%和90.19%.     

Electrosyntheses and characterizations of novel electrochromic copolymers based on pyrene and 3,4-ethylenedioxythiophene

The copolymers based on pyrene and 3,4-ethylenedioxythiophene (EDOT) are electrochemically synthesized in acetonitrile (ACN) containing tetrabutylammonium perchlorate (TBAP) via the direct oxidation of pyrene/EDOT mixtures. FT-IR and ¹H NMR characterizations confirm that the obtained polymers contain both pyrene and EDOT units. Elemental analyses results show that the ratio of pyrene/EDOT units in polymers decreases as the feed ratio of pyrene/EDOT decreases in ACN. The effects of pyrene/EDOT feed ratio and polymerization potential on the electrochemical properties of the obtained copolymers are studied by cyclic voltammetry (CV). Compared with polypyrene, the copolymers perform reversible redox process, and their UV–vis absorption peaks exhibit obvious red-shift. It is interesting that the obtained copolymer films present a property of tunable electrochromism, smooth morphology and good thermal stability.     

Photocatalytic Degradation of Isopropanol Over PbSnO3 Nanostructures Under Visible Light Irradiation

Nanostructured PbSnO₃ photocatalysts with particulate and tubular morphologies have been synthesized from a simple hydrothermal process. As-prepared samples were characterized by X-ray diffraction, Brunauer–Emmet–Teller surface area, transmission electron microscopy, and diffraction spectroscopy. The photoactivities of the PbSnO₃ nanostructures for isopropanol (IPA) degradation under visible light irradiation were investigated systematically, and the results revealed that these nanostructures show much higher photocatalytic properties than bulk PbSnO₃ material. The possible growth mechanism of tubular PbSnO₃ catalyst was also investigated briefly.