Effect of preparation conditions on the characteristics of exfoliated graphite

Exfoliated graphite (EG) was prepared from graphite intercalation compounds (GICs) synthesized electrochemically with different electricity consumption from 10.83 to 40.00 A h/kg. Effects of electricity consumption on the synthesis of GICs and of exfoliation temperature on different parameters of EG, i.e. exfoliation volume, volatile content, specific surface area and pore volume measured by mercury porosimetry, length and width of worm-like particles, and distance between neighboring balloons based on the zigzag model for worm-like particles of EG, were studied. These parameters were found to depend strongly on the electricity consumption and also on exfoliation temperature. Exfoliation volume, volatile content, specific surface area and pore volume on EG prepared at 1000 °C increased with increasing electricity consumption, but the distance between neighboring balloons was found to decrease. These results reveal marked development of pores in EG samples. Raising exfoliation temperature increased exfoliation volume, specific surface area and pore volume up to 800 °C. Above this temperature these parameters tended to be stable.     

切削速度对锯齿形切屑形成的影响规律

为研究TC4切削加工过程中切削速度对锯齿形切屑破坏程度的影响,对TC4进行单因素切削试验,分析TC4的动态行为,并进行有限元仿真,进一步探究锯齿形切屑影响因素以及切屑与切削速度之间的联系。结果表明：在TC4切削过程中,随着切削速度的提高,切屑的锯齿状越来越明显;通过数值计算得出,TC4的能量势垒随着切削速度增大而降低,而绝热剪切带内部应力、应变随着切削速度提高而增大,切削速度越高越容易形成锯齿形切屑。     

Electrospun magnetic carbon composite fibers: Synthesis and electromagnetic wave absorption characteristics

Electrospun polyacrylonitrile (PAN)‐based carbon composite fibers embedded with magnetic nanoparticles have been developed as materials for electromagnetic wave absorption. The nanocomposite fibers were prepared by electrospinning from a dispersion of magnetite (Fe₃O₄) nanoparticles stabilized by L ‐glutamic acid in a solution of PAN and N, N‐dimethyl formamide. The Fe₃O₄‐embedded PAN nanofibers were stabilized at 270°C in air and carbonized at 800°C in nitrogen. The Fe₃O₄ nanoparticles were crystalline with a particle size of about 7 nm, most of which was reduced to Fe₃C with agglomerates of up to 50 nm diameter in the carbon fibers. The carbon morphology was mostly disordered, but exhibited a layered graphitic structure in the vicinity of the nanoparticles. The carbon composite fiber exhibited ferromagnetic behavior, and the induced magnetic saturation per unit mass of fibers increased with increasing Fe₃O₄ content in the precursor. The complex relative dielectric permittivity was tuned by adjusting the amount of Fe₃O₄ in the carbon fiber precursor. With increasing Fe₃O₄ content, good electromagnetic wave absorption characteristics were observed below 6 GHz, even for samples with fiber loadings as low as 5 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

纳米材料的应用及其生物安全性评价

纳米技术是21世纪科技产业革命的重要内容,而纳米材料是纳米技术研究的重点,是物理、化学、生物医学等多个学科的交汇,需要各学科的密切配合与协作。伴随着纳米技术的不断发展,各种新型纳米材料开始涌现,并在医学、生物传感、化工生产和环境等各个领域充当重要的角色。     

富水型热储层深井套管式换热器传热特性研究

基于所建立的深井套管式换热器井孔内、外非稳态传热模型,推导得到富水型热储层地下水渗流作用下深井换热器进（出）水管、固井水泥温度以及热储层过余温度的瞬态解析解。以示范工程现场监测数据与有限体积法数值计算结果为验证依据,探究热储层中渗流过程对于深井换热器传热特性的影响。计算得到,当深井换热器循环水量稳定在30 m³/h时,热储层中达西流速由0提高到5×10^-6 m/s时,平均换热量增大55 kW。然而在忽略热储层中渗流过程时,循环水量由30 m³/h提高到60 m³/h,平均换热量增大34 kW,循环水泵耗功提高20.6 kW。研究表明：随着渗流速度的增大,热储层中的传热机制发生改变,从而强化深井换热器的传热过程;同时降低了循环水流量对于深井换热器换热性能的影响程度。     

模具结构对挤压铸造Al-Cu合金热裂倾向的影响

研究了模具结构对挤压铸造Al-Cu合金热裂倾向的影响,探讨了挤压铸造模具中集渣包对铸件热节提供有效补缩的机理。试验发现当集渣包的凝固模数大于相邻热节部位的凝固模数时,集渣包可以为热节部位提供有效补缩,从而大大降低铸件的热裂倾向。试验铸件的热裂率由模具修改前的27%降低至修改后(扩大集渣包)的6%。     

A combination of hierarchical pore and buffering layer construction for ultrastable nanocluster Si/SiOx anode

Porous Si can be synthesized from diverse silica (SiO₂) via magnesiothermic reduction technology and widely employed as potential anode material in lithium ion batteries. However, concerns regarding the influence of residual silicon oxide (SiO_x) component on resulted Si anode after reduction are still lacked. In this work, we intentionally fabricate a cauliflower-like silicon/silicon oxide (CF-Si/SiO_x) particles from highly porous SiO₂ spheres through insufficient magnesiothermic reduction, where residual SiO_x component and internal space play an important role in preventing the structural deformation of secondary bulk and restraining the expansion of Si phase. Moreover, the hierarchically structured CF-Si/SiO_x exhibits uniformly-dispersed channels, which can improve ion transport and accommodate large volume expansion, simultaneously. As a result, the CF-Si/SiO_x-700 anode shows excellent electrochemical performance with a specific capacity of ~1,400 mA·h·g⁻¹ and a capacity retention of 98% after 100 cycles at the current of 0.2 A·g⁻¹.

     

应用定量荧光技术判识番禺低隆起—白云凹陷北坡残余油藏并重构烃类充注史

珠江口盆地白云凹陷油气勘探程度较低,目前尚未发现油田,已发现的天然气田和含气构造主要分布在番禺低隆起—白云凹陷北坡,天然气藏多伴生一定数量的凝析油。应用储层砂岩颗粒萃取液荧光定量分析(QGF-E)技术,测定了9口探井224个天然气产层或非产层砂岩样品萃取物的荧光发射光谱及强度。依据测定结果,结合储层流体包裹体资料、测井资料、MDT资料以及埋藏史研究结果分析认为:研究区内残余油藏主要分布在珠海组和珠江组下段,且分布较广泛,油质较轻;20~10Ma期间区内可能发生过两期石油充注,14~0Ma期间可能发生过两期天然气充注。     

应用于同步加速器时序控制的片上可编程系统的设计

同步加速器对控制信号的时闻约束要求非常严格,时序控制是加速器控制系统中十分重要的环节.在兰州重离子加速器冷却储存环(HIRFL-CSR)控制系统中,时序控制主要采用FPGA+ARM+linux+DSP的体系结构.本文介绍基于FPGA和uClinux操作系统的片上可编程系统(SOPC)的设计,可将目前ARM+LINUX的工作完全集成在FPGA内实现,省去专用ARM芯片.其最高工作频率可达185 MHz,硬件资源消耗不到4%.片上可编程系统的硬件处理器系统和操作系统都可根据具体需求重新裁剪和配置.SOPC技术在加速器物理以及其他领域有着非常广泛的应用前景.