挤压铸造对Al-Cu合金显微组织及溶质分布的影响

研究了挤压铸造工艺条件下,工艺参数对Al-5Cu-0.4Mn合金显微组织及Cu元素分布的影响。结果表明,合金在25MPa压力下成形时,初生α-Al晶粒尺寸得到明显细化;浇注温度越高组织变得越粗大;升高模具预热温度,晶粒尺寸增大且分布不均匀。挤压铸造改变重力铸造条件下Cu的逆偏析现象,从铸件边缘往心部的Cu含量呈现增加的趋势,主要原因为晶间富铜液相在压力的强制补缩下,通过枝晶骨架通道被挤向铸件内侧。Cu在α-Al基体中的固溶度随着压力的增大而增加;沿径向远离铸件心部,α-Al晶内Cu含量逐渐增加。在挤压力为100MPa、浇注温度为680～730℃、模具温度为200℃的工艺条件下,可获得晶粒细小、组织致密、宏观偏析少的Al-5Cu-0.4Mn合金挤压铸件。     

Combustion characteristics of fuel droplets with addition of nano and micron-sized aluminum particles

The burning characteristics of fuel droplets containing nano and micron-sized aluminum particles were investigated. Particle size, surfactant concentration, and the type of base fluid were varied. In general, nanosuspensions can last much longer than micron suspensions, and ethanol-based fuels were found to achieve much better suspension than n-decane-based fuels. Five distinctive stages (preheating and ignition, classical combustion, microexplosion, surfactant flame, and aluminum droplet flame) were identified for an n-decane/nano-Al droplet, while only the first three stages occurred for an n-decane/micron-Al droplet. For the same solid loading rate and surfactant concentration, the disruption and microexplosion behavior of the micron suspension occurred later with much stronger intensity. The intense droplet fragmentation was accompanied by shell rupture, which caused a massive explosion of particles, and most of them were burned during this event. On the contrary, for the nanosuspension, combustion of the large agglomerate at the later stage requires a longer time and is less complete because of formation of an oxide shell on the surface. This difference is mainly due to the different structure and characteristics of particle agglomerates formed during the early stage, which is a spherical, porous, and more-uniformly distributed aggregate for the nanosuspension, but it is a densely packed and impermeable shell for the micron suspension. A theoretical analysis was then conducted to understand the effect of particle size on particle collision mechanism and aggregation rate. The results show that for nanosuspensions, particle collision and aggregation are dominated by the random Brownian motion. For micron suspensions, however, they are dominated by fluid motion such as droplet surface regression, droplet expansion resulting from bubble formation, and internal circulation. And the Brownian motion is the least important. This theoretical analysis explains the different characteristics of the particle agglomerates, which are responsible for the different microexplosion behaviors that were observed in the experiments.     

A novel synthesis of mesoporous carbon microspheres for supercapacitor electrodes

Mesoporous carbon microspheres (MCMs) with the diameters of 0.5-2.0 μm, main mesopore sizes of 2.6-4.0 nm and specific surface areas of 449-1212 m² g⁻¹ are synthesized by a novel hydrothermal emulsion-activated method. The typical MCMs as electrode materials have a specific capacitance of 157 F g⁻¹ at a high current density of 10.0 A g⁻¹ in 6 M KOH aqueous solution. The resultant MCMs electrode materials with high current charge and discharge capability in 6 M KOH aqueous solution provide important prospect for electrode materials in supercapacitors which could offer high power density for electric vehicles.     

同轴式套管换热器应用于家用循环式热泵热水器的特性试验研究

分析以采用普通高效换热管的同轴式套管换热器为冷凝器的热力特性,并针对其运用在家用循环式热泵热水器的特点,试验研究采用该套管换热器的家用循环式热泵热水器的特性,得到在名义制热工况及冷却水进口温度为30℃条件下,不同水流量所对应的冷凝负荷、功率等特性及性能。结果可应用于家用循环式热泵热水器的开发设计。     

基于网络粘黏的竞争力扩散效应

网络企业的扩张表现出有别于传统行业的特殊性。以腾讯公司为背景,利用网络粘黏解释网络企业的竞争力扩散效应。研究发现,腾讯借助已有的即时聊天工具QQ积累了大量粘黏度很高的网络用户,借此开展多项网络服务业务,形成良好赢利模式。研究认为网络企业只有在拥有核心业务之后,利用网络粘黏效应培养具有竞争力的多元业务,才能真正实现成功的网络多元化经营。网络粘黏下的竞争力扩散效应研究对腾讯这一类网络企业扩张提供了理论解释,并且丰富了网络行为研究,具有一定的理论与现实意义。     

Surface-induced synthesis and self-assembly of metal suprastructures

A systematic study on the synthesis of a series of self-assembled suprastructures, such as cubes, stars, belts, and microspheres, of Ag nanoparticles (AgNPs) in borosilicate glassware heavily cleaned with aqua regia is presented. These self-assembled structures are mostly formed from the crystallographically iso-oriented AgNPs, and exhibit well-defined shapes. In regular washed glassware, only Ag nanowires are synthesized. The formation mechanisms of these self-assembled Ag structures, based on monitoring of their structural evolution in glassware decorated with different molecules, are proposed. This work not only demonstrates that the surface energy of glassware can affect chemical synthesis, but also provides an interesting approach to the shape-controlled synthesis of novel self-assembled suprastructures of AgNPs, which could be potentially used as synthesis templates, drug vessels, and microreactors.     

Electrodeposition and morphology analysis of Bi-Te thermoelectric alloy nanoparticles on copper substrate

Nanoscale Bi-Te particles with thermoelectric properties on copper substrate were investigated. The substrate was prepared by electroplating copper layer on a copper zinc alloy plate in a copper sulfate solution. Electrodeposition of the Bi-Te alloy particles was then performed in a nitrate bath. The electrolyte is composed of 0.05 M bismuth nitrate and 0.01 M tellurium dioxide dissolved in 2.0 M HNO₃. Cyclic voltammetry and quartz microbalance tests associated with the electrodeposition process were conducted to show the mechanism and kinetics of the deposition. The morphology and compositional analysis of Bi-Te was obtained using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) respectively. The morphology analysis suggested that nanoscale Bi-Te particles were obtained and the EDS results indicated that the surface of the copper substrate contained Cu₂O. The atomic ratio 1:1 for Bi:Te in the alloy, which is equivalent to the weight percentage of Bi:Te = 62%:38% was confirmed from the data obtained.     

Kr ion irradiation study of the depleted-uranium alloys

Fuel development for the reduced enrichment research and test reactor (RERTR) program is tasked with the development of new low enrichment uranium nuclear fuels that can be employed to replace existing high enrichment uranium fuels currently used in some research reactors throughout the world. For dispersion type fuels, radiation stability of the fuel-cladding interaction product has a strong impact on fuel performance. Three depleted-uranium alloys are cast for the radiation stability studies of the fuel-cladding interaction product using Kr ion irradiation to investigate radiation damage from fission products. SEM analysis indicates the presence of the phases of interest: U(Al, Si)₃, (U, Mo)(Al, Si)₃, UMo₂Al₂₀, U₆Mo₄Al₄₃ and UAl₄. Irradiations of TEM disc samples were conducted with 500 keV Kr ions at 200 °C to ion doses up to 2.5 × 10¹⁹ ions/m² (∼10 dpa) with an Kr ion flux of 10¹⁶ ions/m²/s (∼4.0 × 10⁻³ dpa/s). Microstructural evolution of the phases relevant to fuel-cladding interaction products was investigated using transmission electron microscopy.     

稳健统计方法在老采空区沉降数据处理中的应用

老采空区地基沉降和变形监测是沉降研究的可靠方法。基于监测数据进行沉降规律的分析和预测预报,指出了应用最普遍的统计方法即最小二乘回归分析方法存在的问题,应用稳健估计对含有粗差的沉陷数据进行了回归分析,得到了比较好的结果。