关键词： 方镁石   镁铝尖晶石   氧化铈   氧化钐   烧结致密化  

摘要： 为了研究稀土氧化物掺杂方镁石-尖晶石复相材料的烧结性能及显微结构,以富镁尖晶石细粉与烧结镁砂细粉为主要原料,分别外加质量分数为1%、2%和3%的CeO_2和Sm_2O_3,于1 600、1 650、1 700和1 750℃保温3 h烧成分别测定烧后试样的线收缩率、体积密度、显气孔率,并通过XRD、SEM、EDS等对其物相组成及显微结构进行分析。结果表明:1)引入稀土氧化物CeO_2与Sm_2O_3均有利于镁砂与尖晶石烧结致密化,引入CeO_2未参与反应,呈孤立形态分布于晶粒间;引入Sm_2O_3与原料中杂质反应形成稀土硅酸盐相分布于晶粒间。2)材料的体积密度和线收缩率随稀土氧化物加入量的增加而增加。在加入量相同的情况下,引入CeO_2的材料致密化程度相对较高。添加3%(w) CeO_2的材料体积密度达到3. 29 g·cm-3,显气孔率为10. 3%,烧后线收缩率为7. 79%。3)引入CeO_2和Sm_2O_3都有部分固溶于尖晶石与方镁石晶体内,活化晶格,促进晶粒发育。

关键词： Ag2CO3   形貌调控   异质结   抗光腐蚀性   电子空穴对  

摘要： Ag_2CO_3是近年来发现的一种新型的可见光响应光催化剂,对甲基橙(MO)、罗丹明B(RhB)和亚甲基蓝(MB)等染料和苯酚等有机物都具有较高的光催化降解能力.然而,在光催化反应过程中,Ag_2CO_3晶体中的Ag+会被自身的光生电子(e-)还原形成金属Ag单质,随着反应的进行,样品的稳定性和光催化效果迅速降低.贵金属沉积、非金属掺杂和形成异质结等方法,可以使Ag_2CO_3的光吸收得到扩展,同时促进光生电子空穴对的分离,从而提升Ag_2CO_3的抗光腐蚀性能和对污染物的降解效率.通过不同的物理和化学方法调控Ag_2CO_3催化材料的形貌、晶粒尺寸和晶体缺陷等,可以提升其比表面积和光生电子空穴的传输效率,进而提高其光催化活性.文中归纳了近年来Ag_2CO_3光催化材料的研究进展,分析了Ag_2CO_3光催化的特点,阐述了一系列提升Ag_2CO_3光催化性能的方法,并对Ag_2CO_3光催化材料的研究进行了总结与展望.

关键词： 生物材料   超快激光   微纳结构   细胞行为  

摘要： 提高医疗植入材料的生物相容性,对提升植入医疗器械的安全性有重要意义。通过超快激光制造出微纳米级别尺寸的材料结构以改善材料的生物相容性,近年来已被广泛应用于生物医学领域。本文简单介绍了细胞与生物材料相互作用原理,从生物材料表面微结构对其生物相容性能的影响出发,综述了超快激光加工不同材料表面形貌特征对细胞粘附、迁移、增殖、分化的影响,并进一步指出超快激光制备微纳结构在生物材料领域的局限和发展趋势。

关键词： Al   Mg   Ti   microstructure   simulation  

摘要： We highlight the current understanding of mechanisms of phase transformation, strengthening, and the role of alloying elements in aluminum, magnesium, and titanium alloys, including nucleation and growth of precipitates, precipitate- dislocation interactions, solute segregation at precipitate- matrix interfaces and planar defects, and the development of strengthening models that account for the real particle shape. Future directions such as atomic- scale elemental mapping and computation, and the influence of particle shape on mechanical properties are discussed. With the combination of advanced characterization and computational tools, it is anticipated that much less time will be needed to develop the next generation of light alloys.

关键词： Microstructure   Pozzolanic activity   Hydration   Cement composite   Compressive strength   Strength activity index   Crystallinity index   Strength gain  

摘要： This paper presents the investigation of the strength characteristics and microstructural analysis of cement composite mortar developed using nontraditional cement replacement materials. Three types of materials, namely palm oil fuel ash (POFA), treated palm oil fuel ash (TPOFA), and bottom ash (BA) were used as partial cement replacement materials at replacement levels of 0%, 10%, 20%, and 30% by weight. The water to binder ratio (w/b) of 0.32 was used for all mortars. The chemical composition and morphology of binder materials were examined by X-ray florescence (XRF) and scanning electron microscope (SEM) techniques. The fresh and hardened properties of mortar were determined in accordance with ASTM standards and the microstructure of mortar was investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). The results showed pozzolanic activity through formation of C-S-H and CH as confirmed by XRD, TGA, and FTIR. Partial replacement of cement with 10%, 20%, and 30% of TPOFA produced higher compressive strengths of 101.4, 88.4, and 83.6 MPa, respectively, which is slightly closer to 110.0 MPa obtained for control specimen at 90 days. Moreover, higher strength activity index for TPOFA and BA specimens showed better pozzolanic activity as compared to POFA-based mortar. Overall, the use of 10% of POFA, TPOFA, and BA is recommended as a cement replacement in the development of high-strength mortar of strength range of 60 to 100 MPa. (c) 2019 American Society of Civil Engineers.

关键词： 石墨  

ISBN: (纸本)9787122332677

摘要： 本书介绍了电子衍射、高分辨透射电子显微术、扫描透射电子显微术、能谱分析、原位透射电子显微术、扫描电子显微术、低能电子显微术、扫描探针显微术在石墨烯、氮化硼、过渡金属硫族化合物等二维材料显微结构表征方面的应用。

关键词： Fibrous materials   Realistic modeling   Filter media simulation   Capillarity  

摘要： A physics-based nonwoven structure generation model is presented in this work. The model is capable of incorporating the mechanical properties of the fibers in the simulations by treating each fiber as an array of beads connected to one another via springs and dampers. Our algorithm can realistically simulate the bending of the fibers at fiber-fiber crossovers or when external forces are applied to the fibers during fiber deposition process. In fact, a unique attribute of the modeling approach presented in this work is that it can be modified to emulate, to some extent, the manufacturing process by which the nonwoven media have been produced. Unlike most previous structure generation models, our mass-spring-damper algorithm does not require the thickness or porosity of the media to be fed to the model as an input, and it is also capable of avoiding fiber-fiber overlaps. For demonstration purposes, virtual media with bimodal fiber diameter or contact angle distributions were produced and used to estimate the pressure required for water to penetrate through a hydrophobic fibrous membrane, i.e., the so-called liquid entry pressure (LEP). The LEP calculations here are based on a simplifying assumption that the air-water interface remains intact across the width of the simulation domain as it travels throughout the media. Effects of fiber diameter(s), fiber orientations, or fiber contact angle(s) on LEP are simulated and discussed in detail.

关键词： X ray diffraction analysis  

摘要： A metal-organic framework is employed for the preparation of an interconnected network porous structure of Mn2O3/carbon for supercapacitor applications. X-ray diffraction patterns indicate the crystal structure of the Mn2O3/carbon composites. Morphological studies reveal the formation of a carbon interconnected network porous structure of the prepared samples. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirm the carbon coating on the Mn2O3 particles. Three-electrode measurements showed that the prepared Mn2O3/C composite is suitable for asymmetric supercapacitor device fabrication, since the negative electrode exhibits a highest specific capacitance of 776 F g(-1) at a specific current of 1 A g(-1). The symmetric device yields a specific cell capacitance of 122 F g(-1) at a specific current of 2.5 A g(-1). The asymmetric device yields a maximum specific energy capacity of 54.9 W h kg(-1) at a power capacity of 2245 W kg(-1).

关键词： plastic connection   Lattice defects   disclinations   Crystalline materials   Elastoplasticity   Plastics  

摘要： This paper deals with continuous description of elasto-plastic materials with lattice defects such as dislocations and disclinations, and grain boundaries. The behaviour of crystalline solids containing defects is described by non-local fields that are smooth over an interatomic length scale and at times of micro-seconds. The dislocation and disclination densities are appropriate measures of incompatibilities of the plastic distortion and of the plastic connection relative to plastic distortion, respectively. The grain boundaries will be simulated in terms of an array of disclination dipoles. The heterogeneous initial disclinations are a source of dislocations. These lattice defects, stress, strain and the displacement vector will be provided by solving initial and boundary value problems in elasto-plastic bodies, which involve dissipative evolution equations for plastic distortion and disclination tensor. The numerical procedure and corresponding algorithms to solve the variational formulation of the initial and boundary value problems are provided. The results of numerical simulations are analyzed and a number of graphs illustrate the elasto-plastic behaviour of the sheet when a shear stress is applied on one of its edge.

关键词： target metallography   magnetic pulse field   static atomic displacements  

摘要： Changes in metallic and nonmetallic materials under the influence of a pulsed magnetic field are studied, using the method of target metallography. It is shown that the structural changes are at the minimum detectable level of the microscopic method with peak gains. It is established that local variation in structure and degradation in the sharpness of separate surface areas of the samples independent of errors in focusing is a general structure change in the action of a magnetic field. The stresses of the third kind are considered to be possible reasons for the change in structure.