关键词： 水泥混凝土   微结构   耐久性   纳米硅灰   有机硅乳液  

摘要： 为增强水泥混凝土材料耐久性,研究基于混凝土材料多孔特点,通过在混凝土拌制过程中掺加纳米硅灰和有机硅乳液的方法,提高混凝土材料的密实度和抗渗性能。通过测试改造前后混凝土的早期抗裂性能、氯离子渗透性能、碳化性能、抗硫酸盐侵蚀性能以及抗冻性能,来评价改造前后混凝土耐久性变化情况,并通过压汞试验绘制孔径分布曲线,从微观孔结构角度解释混凝土宏观耐久性变化的原因。研究结果表明,通过掺加纳米硅灰和有机硅乳液的方法,可以比较全面的改善混凝土材料的宏观耐久性。微观孔结构测试结果表明,由于混凝土的孔径分布曲线得到了优化,经过改造后的混凝土100 nm以下的小孔数量明显增多。研究成果为混凝土材料的应用提供参考。

关键词： 激光技术   激光选区熔化   TiN颗粒   钛基复合材料   耐磨性能  

摘要： 采用激光选区熔化技术成功制备了TiN增强钛基复合材料,并研究了TiN含量对钛基复合材料微观结构、显微硬度和摩擦磨损行为的影响。结果表明:随着TiN含量的增加,α-Ti相衍射峰发生偏移,TiN衍射峰强度逐渐增强,复合材料的显微硬度从纯钛的(228±13) HV逐渐增大到(403±20) HV;当添加TiN的质量分数为7.5%时,复合材料的磨损性能比纯钛提高了29.2%。TiN颗粒的加入使钛基复合材料的硬度与磨损性能显著提升。

关键词： 碳纳米管   五氯苯酚   吸附   微波   再生  

摘要： 制备了5种典型不同微结构特性碳纳米管(CNTs),比较研究了其对水中难降解有机物五氯苯酚(PCP)的吸附特性,和微波法再生后吸附的PCP效果。实验结果表明,5种CNTs对PCP吸附平衡快,60 min内达到平衡,平衡时间差异不大,吸附动力学均遵循准2级反应动力学方程;吸附等温线均符合Freundlich模型,且比表面积大的CNTs吸附量大。主要影响因素中,酸性有利于吸附;温度升高,不利于吸附。对于吸附PCP饱和的CNTs微波辐照3min得以高效再生,吸附、微波再生循环6次,再生率均达90%以上。

关键词： 光学设计   透光性能   LightTools仿真   注塑成型  

摘要： 基于LightTools软件分析了光在光盘纹(CD纹)微结构扩散板中的传输过程,采用注塑成型制备工艺进行实测验证,研究扩散板表面的CD纹微结构对光提取效率的影响。通过理论研究、模拟仿真和实验对比,对扩散板表面微结构进行建模和大规模分布式光线追迹。结果表明:在80mm×80mm照明面积范围内,相对于无微结构扩散板,CD纹微结构扩散板的光流明效率有明显提高;当线宽为200μm时,光流明效率提升最多,提高了13.52%。根据最优模拟尺寸制备出由若干同心圆环组成的CD纹微结构扩散板,以LED筒灯为实验灯具,用积分球测量使用微结构扩散板、一般扩散板和不使用扩散板的灯具的总流明输出,得到CD纹微结构扩散板的透光率达90.6%,比一般扩散板的透光率提高了8.8%的结论。

关键词： High entropy alloy   Deformation   Annealing   TEM   EBSD   Tensile properties  

摘要： The influence of severe warm-rolling and subsequent annealing on the microstructure and mechanical properties in an AlCoCrFeNi2.1 high entropy alloy consisting of a lamellar arrangement of ordered L1(2) and B2 phases was studied. For this purpose, the as-cast EHEA was severely warm-rolled up to 90% reduction in thickness at selected temperatures of 400 degrees C, 600 degrees C, and 750 degrees C. The severely warm-rolled EHEAs were further annealed at temperatures ranging from 800 degrees C to 1200 degrees C for 1 h. Warm-rolling resulted in a unique disordering behavior of the L1(2) depending on the temperature of warm-rolling. However, the B2 phase maintained the ordered structure irrespective of the warm-rolling temperature. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed a predominantly lamellar microstructure, while the EHEA warm-rolled at 750 degrees C showed a novel heterogeneous microstructure featured by a mixture of lamellar and non-lamellar regions. Annealing of the 90% warm-rolled materials resulted in the formation of predominantly duplex microstructures consisting of disordered FCC and B2 phases. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed high strength but rather limited ductility, which could be improved upon annealing. Remarkably, the EHEA warm-rolled at 750 degrees C showed the most outstanding properties featured by exceptional strength-ductility combination owing to the novel heterogeneous microstructure. Annealing of the heterogeneous EHEA resulted in the deterioration of the strength-ductility balance owing to the annihilation of the heterogeneous microstructure, being replaced by a microduplex structure.

关键词： HVI   Microstructural material characterization   Debris cloud   Pitting damage   Dynamic recrystallization  

摘要： In a hypervelocity impact (HVI) between the micrometeoroids/orbital debris (MMOD) and multi-layered shielding mechanisms of spacecraft, the debris cloud, formed by shattered materials of the outer bumper layer and projectile, commits multitudinous pitting craters and cracks that are disorderedly scattered in the rear wall layer. Material degradation due to the pitting damage is a precursor of structural fragmentation and system failure of the space assets. In this study, microscopic material degradation of the rear wall of a typical dual-layered Whipple shield, initiated and intensified by the debris cloud-engendered pitting damage, is characterized using metallographic analysis including optical microscope (OM), laser scanning microscope (LSM), scanning electron microscope (SEM) and X-ray diffraction (XRD). Results have revealed that (1) the degree of material degradation shows difference in the central cratered area, the ring cratered area, and the spray area, respectively;(2) the dynamic recrystallization gives rise to the formation of fine grains adjacent to pitting craters;(3) the extents of recrystallization and dislocation depend on the strain rate levels during HVI;and (4) the temperature elevation, caused by the heat transformed from the adiabatic plastic deformation energy and shock heating, warrants the recrystallization. Two types of damage, namely micro-voids and micro-cracks, are identified beneath the pitting damage area;under the extremely high compressive strain rate induced by HVI, micro-voids are initiated by the nucleation of grains or deteriorate from existing material defects, and these micro-voids further expand at the grain boundaries and within the grains to form micro-cracks under a tensile-type wave converted from the HVI-induced shock wave.

关键词： Geopolymer grouting materials   Rheological properties   Microstructure   Fuller-fine sand   Drying shrinkage  

摘要： While metakaolin (MK)-based geopolymer grouting materials (MGGMs) are new type of grouting materials, the poor rheological properties and high drying shrinkage hinder their practical applications. In this work, Fullerfine sand powders (Fuller-FS) (10, 20, 30 and 40 wt%) were used as a fine inorganic admixture to investigate effects of this addition on the rheological properties, drying shrinkage and mechanical strength of MGGMs. The results indicated that pure MGGMs or MGGMs containing Fuller-FS were more consistent with the Herschel-Bulkley rheological model. Incorporating Fuller-FS into MGGMs can improve their rheological and compressive strength properties, and reduce their drying shrinkage. The initial shear stress value of geopolymer with FullerFS was 80% lower or more than that of pure metakaolin-based geopolymer at a constant shear rate (100 s(-1)) and the MGGM containing 30 wt% Fuller-FS presented satisfactory yield stress (about 1 Pa). The replacement of different content of metakaolin by Fuller-FS improved particles packing and compactness of MGGMs, thus resulting in lower 91-day drying shrinkage ( by 65 %), and higher 28-day compressive strength ( by 35 %) (curing at 20 degrees C and 50 +/- 10% RH).

关键词： Microstructure   Clustering   Multiphase materials   Voronoii tesselations  

摘要： In disperse multiphase systems, the dispersion of particles (microstructure) is regarded as a key factor affecting the processing of materials and determining their performance. Among many microstructural features, clustering, the tendency of dispersed particles phase to form clusters of various sizes, is considered to be of primary significance. The purpose of this study is to quantify clustering, and to understand its evolution with dimensionless temperature and surface fraction parameters using Monte-Carlo simulations of the Metropolis algorithm governed by Lennard-Jones potential restriction. The proof of concept of the use of Voronoii tesselation analysis was demonstrated to diagnose clustering. The scaling relationship of the clustering level with regards to the varied dimensionless temperature and surface fraction was derived. (C) 2019 Elsevier B.V. All rights reserved.

关键词： Li-rich cathode   Fluoride anion doping   Cycling performance   Crystal growth   Energy storage and conversion  

摘要： At present, the lithium-rich metal oxide Li1+zMO2 (M = Ni, Co, Mn, etc.) is one of the promising cathodes materials for high-energy lithium-ion batteries. In this work, we report the effect of different doping amounts of fluoride ions on the microstructural and electrochemical properties of Li [Li0.2Mn0.54Ni0.13Co0.13]O-2 cathode material. At low doping levels, the fluoride ions substituted the oxygen ions. When the doped fluorine was more than the theoretical limit of x = 0.15, LiF-based material was attached on the surface of the material, offering better cycling performance of battery. With the doping effect, a discharge capacity of 230 mAh/g and a capacity retention rate of 98% were found respectively, which are better than the pristine electrode. (C) 2019 Elsevier B.V. All rights reserved.