关键词： 反应熔渗   C/C-SiC复合材料   氧乙炔烧蚀   微结构  

摘要： 以无纬布/网胎0°/90°叠层穿刺三维四向预制体为增强体,采用化学气相渗透(chemical vapor infiltration,CVI)、树脂浸渍碳化(polymer infiltration carbonization,PIC)与反应熔渗(reactive melt infiltration,RMI)复合工艺制备穿刺C/C-SiC复合材料,研究其微观组织及在C2H2-O2焰中的烧蚀行为.结果 表明:无纬布、穿刺纤维束由CVI+PIC制备的碳基体填充而形成致密C/C区域,RMI生成的SiC主要位于网胎层中,其含量为37.3％(质量分数).复合材料表面因过量硅化而形成了SiC富集层.当烧蚀距离为20 mm、O2∶C2H2=2∶1时,烧蚀600 s后材料X-Y、Z向线烧蚀率分别为0.8×10-4、3.6× 10-4 mm/s,比先驱体浸渍裂解(polymer infiltration pyrolysis,PIP)工艺制备C/C-SiC材料烧蚀率小1个数量级.烧蚀面SiC富集层保护及被动氧化作用是材料具有优异抗氧化烧蚀性能的主要原因.随烧蚀距离由20 mm向10 mm减小,复合材料烧蚀率先缓慢变化后快速增大,烧蚀率快速增长阶段复合材料发生主动氧化烧蚀.

关键词： Electrodes  

摘要： Fast discharge capability of automotive batteries not only affects the acceleration and climbing performance of electric vehicles, but also the accessible driving range under complex driving cycles. Understanding the intricate physical and chemical processes across multiple length-scales is critical to assist the strategic design of electrodes for improved rate performance. Here, we correlate the discharge rate performance of Ni-rich LiNi1-x-yCoxMnyO2 (NMC) cathodes to the electrode architectures, ranging from the crystallographic orientations, surface morphology and cracks at single particle level, to the factors that affect the dominance of the solid and liquid-state transport (SST and LST) at electrode level. A random orientation of the primary particles is found to incur an increase of the SST resistance by a factor of 2.35 at 5C and a heterogeneous intra-particle lithiation. Internal cracks significantly restrict the accessibility to the active material. Double-layered particles are proved to be a more promising candidate than single-crystal particles. At electrode level, the SST-dominance depth is quantified for the first time to guide the microstructural tuning and rational operating windows are proposed for electrodes of various architectures. The reaction front is observed to shuttle across the electrode depth to mitigate the polarization, which can provide valuable insights into the battery management development. Finally, by comparing the performance of single crystal and polycrystalline NMC811 electrodes, it is suggested that electrode thickness and porosity are more critical in the former for enhanced discharge rate performance, in contrast to polycrystalline electrodes, in which a gradient particle fraction and size distribution are recommended.

关键词： 微结构可控材料   跨尺度   增材制造   生物医学  

摘要： 微结构可控材料是一类利用微观结构调控整体性能的新材料.在不改变材料本身物理化学性质的条件下,通过控制微结构组成单元的尺寸、几何构型、排列方式提升宏观材料的力学、热学、表界面等性质.在微结构可控材料的研究中,性能调控的关键在于跨尺度分级结构的精准构筑.本文从制备工艺出发概述了微结构可控材料的最新研究进展,着重介绍了聚合物、金属及无机材料的跨尺度微纳加工方法对于整体性能的提升作用,并总结了微结构可控材料在生物医学领域中低密度材料、微液滴操控、微型机器人等方面的应用,展望了其未来的发展方向.

关键词： 水凝胶   水泥基复合材料   冻融循环   微结构  

摘要： 借助纤维素/聚乙烯醇(PVA)水凝胶对温度变化的响应特性,可缓解由正负温变化导致的水泥基材料损伤破坏。在分析纤维素/PVA对水泥基材料流动性、冻融循环前后力学性能影响基础上,研究了水凝胶复合水泥基材料水化产物、孔、裂缝等微结构特征。结果表明:纤维素/PVA溶液提高了水泥浆体的流动度;经冻融循环的纤维素/PVA溶液形成了交联网络状结构,提高了水泥基复合材料的总孔隙率,但有效缓解由于冻融循环作用而导致的强度下降和损伤。

关键词： 激光熔覆   纳米微结构   表面粗糙度   温度场分布   流体力学  

摘要： 采用一种操作简单且成本低的激光熔覆方法将氧化铝涂层一步熔覆到柔性铜网表面,在铜网表面上形成不同粗糙度的纳米级颗粒状结构修饰层,调控表面润湿特性。引入瞬态热分析法探索由扫描路径间距减小引起的温度场变化情况。研究发现,当激光熔覆过程的扫描路径间距为10μm时,分离网表面铝涂层呈现α-Al_(2)O_(3)晶型,耐久性良好,在空气中水的接触角接近0°,水下油的接触角大于160°,经循环测试后分离效率仍超95%。针对微流体管道应用中的油水分离需求,对分离膜柔性基底卷曲成型的管道进行油水分离测试和流体行为仿真研究,利用计算流体力学法分析如何通过调控表面纳米颗粒的分布来调节管道内部压强场和速度场的分布,从而促进管道内流体平稳流动而增强油水分离性能。

关键词： Hydroxyapatite   Ca/P ratio   Phase decomposition   Sintering   Mechanical properties   In-vitro bioactivity   Tetracalcium phosphate   Particle size-density relationship   Calcium phosphates  

摘要： The sintering behaviour and microstructural evolution of two batches of a commercial calcium-deficient hydroxyapatite powder were investigated. First, the sintered density as a function of the starting particle size distribution was studied, and the minimum particle size to get the desired target density was determined. Then, as the two batches were characterized by a slight difference in Ca/P ratio, the role of such ratio on phase and microstructural evolutions during sintering, as well as on mechanical and biological properties was investigated. It was observed that the powder with lower Ca/P ratio underwent significant hydroxyapatite (HA) to beta-tricalcium phosphate (beta-TCP) decomposition, with a simultaneous formation of tetracalcium phosphate (TTCP). The microstructure of sintered gelcast samples evolved during isothermal sintering at 1300 degrees C, moving from a starting homogeneous and narrow grain size distribution to a bimodal distribution after 3 h sintering. In fact, over time, large grains decomposed into smaller ones, finally providing a microstructure composed of coarse grains surrounded by plenty of ultra-fine grains. On the contrary, the powder with the higher Ca/P ratio provided a limited HA to beta-TCP transformation, and normal grain growth by increasing the sintering time. Such differences lead to different mechanical properties for gelcast samples produced by the two powder batches, as the material with the lower Ca/P ratio affected by lower mechanical strength. Finally, sintered samples from both powders showed in-vitro bioactivity, with a larger surface coverage observed for the lower Ca/P ratio material. The morphology of the apatite layer seemed to be affected by the material composition, too, showing flake-like and needle-like morphologies depending on the Ca/P ratio of the starting powder.

关键词： Resin-based composits   Flexural strength   Fracture toughness   Dynamic-mechanical analysis  

摘要： Objective: The aim of the study was to determine the influence of the microstructure on the mechanical behavior of resin-based composites (RBC) with little variation in chemical composition, and to verify a possible mutual dependency. Methods: Four RBCs with similar chemical composition of fillers (Ba-Al-B-F-Si-glass, SiO2), but with different mean (0.7 mu m to 1.8 mu m) and maximum particle size values (5 mu m to 20 mu m) were selected. Fracture toughness/K-IC was evaluated in an NTP (Notchless Triangular Prism) test. Flexural strength/FS and modulus/E were measured in a 3-point-bending test. A fractographic analysis determined the fracture mode and origin. Quasistatic and viscoelastic parameters were assessed by a depth-sensing indentation test equipped with a DMAmodule. One and multiple-way analysis of variance (ANOVA), Tukey honestly significant difference (HSD) post-hoc tests (alpha = 0.05), and Weibull statistics were applied. Results: The influence of the microstructure and the chemical composition of the organic matrix is weighted differently in the measured properties. The inorganic filler amount influences highest K-IC (eta(2)(P) = 0.813), followed by FS (eta(2)(P) = 0.768) and E (eta(2)(P) = 0.611). An optimized filler distribution with a high proportion of larger fillers up to 20 mu m contributes to high FS and E data. The reliability of the material (Weibull parameter m) did not depend on the origin of fracture. Smaller inorganic fillers and the addition of 1% larger pre-polymer fillers improve the fracture toughness. Analysed RBCs were well adapted to chewing frequencies. Conclusions: The properties of RBCs can be tuned by little variation in microstructure and monomer matrix. Clinical significance: Reverse engineering of clinically successful materials can be used to better design future RBCs.

关键词： 人体器官  

ISBN: (纸本)9787118124330

摘要： 本书简要概述活性人体组织与器官的临床需求、现有的主要制造方法, 以及活性组织打印的现状、特点和优势, 介绍人体组织与器官微观结构系统的建模与仿生设计方法 ; 介绍了生物3D打印技术在典型人体组织可降解支架骨组织、骨/韧带/软骨梯度结构、肌肉、肝组织、气管、乳腺等方面的研究状况、主要工艺方法及临床应用情况 ; 介绍了细胞打印与器官打印的主要工艺方法, 以及其在组织病理模型、药物模型及器官芯片等领域的最新研究成果 ; 介绍了人体组织与器官的原位/体内打印新技术 ; 最后分析与讨论人体组织与器官3D打印技术未来发展的主要技术挑战, 以及可能的解决思路。

关键词： nanocomposites   carbon nanotube   graphene   percolation   electrical conductivity   synergy   hybrid   microstructure property relationships  

摘要： The electrical conductivity and percolation onset of graphene-based nanocomposites are studied by varying both planar and transversal aspect ratios of graphene nanoplatelets (GNP) fillers using a three-dimensional stochastic percolation-based model. The graphene nanoplatelets are modeled as elliptical fillers to enable planar aspect ratio variations. We find that decreasing the graphite's thickness results in an exponential performance improvement of the nanocomposites, in contrast to a linear improvement obtained when the planar aspect ratio is increased, for the same filler volume. Furthermore, we show that hybrid nanocomposites fabricated with partial replacement of GNP by carbon nanotube (CNT) may improve the electrical performance of the GNP monofiller composites. Improvement or deterioration of the electrical properties is mainly based on the morphology and content of the fillers mixed in the hybrids. Nonetheless, using a minimal amount of CNT for substitution always leads to the highest improvement in conductivity in the hybrids, while additional CNTs only lead to smaller improvement at best or even deterioration. The results are validated against experimental works and offer useful insights for the fabrication of highly conductive nanocomposites.

关键词： 耐火材料   MgO-Al-C材料   造粒氧化铝微粉   氧化铝空心微珠   六铝酸钙   抗热震性   高温性能   滑动水口  

摘要： 以烧结镁砂骨料、电熔镁砂细粉、Al粉、N220炭黑为原料,酚醛树脂为结合剂,制备MgO-Al-C材料,研究了三种铝基原料(造粒氧化铝微粉、氧化铝空心微珠、六铝酸钙)对其常温抗折强度、高温抗折强度、抗热震性及抗氧化性的影响,并借助XRD和SEM对其物相组成及显微结构进行分析。结果表明,造粒氧化铝微粉是多孔结构,可吸收热应力,加入量为1%(质量分数,下同)时,可提高材料的常温抗折强度和抗热震性,明显改善材料的抗氧化性。氧化铝空心微珠是中空结构,可缓冲热应力,加入量为3%时,可明显提高材料的常温抗折强度,并具有较高的抗热震性和抗氧化性。六铝酸钙的热膨胀系数较低,可赋予材料较好的韧性,加入量不超过5%时,样品具有较好的抗热震性。