纳米粒子在气体流动中的团聚过程研究

采用气相合成法制备纳米微粉时，由反应合成区生成的纳米微粒在随气流流向收集装置的过程中，因相互碰撞，粘附而发生聚现象，形成较大的颗粒，本论述了团聚现象发生的原因，借用气体分子动力学理论，计算了纳米粒子在气体流动中的团聚过程，得到了粒子直径，质量，体积，微观热运动速度及空间密度的沿程分布函数。     

聚氨酯/纳米碳酸钙复合材料及性能的研究

以PTM G、TD I、M OCA为原料,采用预聚法合成聚氨酯弹性体,并选用纳米碳酸钙对聚氨酯弹性体进一步增强,通过对纳米碳酸钙进行表面改性及采用超声波促进纳米粒子在基体中更好地分散,并考察了纳米碳酸钙的含量和合成温度对聚氨酯弹性体力学性能的影响。结果表明,纳米碳酸钙对聚氨酯弹性体的力学性能有一定的提高,并且在纳米碳酸钙含量为4%时综合力学性能最好,通过扫描电镜观察纳米碳酸钙在基体中发生了团聚或附聚现象。     

油酸包覆针状氢氧化镁纳米粉体的制备

采用一种新工艺来合成油酸包覆的氢氧化镁针状纳米粒子,其合成过程是在一种常温下具有特殊结构、能产生复合剪切力的反应器内进行,出料后经过特殊的搅拌、陈化、水洗、干燥工艺,可以大量合成短轴为3～4nm、长轴为50～60nm的油酸包覆的针状氢氧化镁纳米粉体,并提出可能的反应机理。用透射电镜、X射线衍射、红外光谱和热重分析等方法进行检测。结果表明:油酸包覆的氢氧化镁纳米粒子结晶度、包覆效果、分散效果、热稳定性能优异,可有效地防止纳米粒子在干燥过程中的团聚现象。     

室温合成团聚AuPd纳米粒子及其电催化性质(英文)

室温下以水合肼为还原剂,在N,N-二甲基甲酰胺中合成了团聚态的AuPd双金属纳米粒子。X射线衍射(XRD)表征结果证明,所合成的AuPd纳米粒子具有面心立方结构。高分辨透射电子显微镜表征表明,AuPd纳米粒子表面存在大量孪晶结构和晶面层错等表面缺陷。活性评价结果表明,具有高密度晶面缺陷的双团聚态AuPd纳米粒子对甲醇氧化表现出较好的催化活性。     

溶胶-凝胶法制备环氧树脂／纳米SiO2复合材料中纳米粒子的分散性研究

用溶胶-凝胶法制备环氧树脂／纳米SiO2复合材料，研究了在脱除溶剂以及反应副产物过程中温度、表面改性剂对纳米SiO2粒子的分散性、固化后样品力学性能的影响。研究表明：纳米SiO2的引入对环氧树脂的力学性能有一定的提高；随着体系溶剂脱除温度的升高纳米粒子的团聚明显；加入表面改性剂能够阻止纳米粒子的团聚，硅烷偶联剂KH550比表面活性PEG剂能够更好地阻止纳米粒子的团聚；但是表面活性剂PEG的加入会使纳米复合材料的力学性能有一定程度的下降。     

亲油性金纳米粒子的合成

利用相转移法成功地合成了粒径在2～7nm的硫醇表面修饰Au纳米粒子.采用透射电子显微镜、纳米粒度分布仪、红外光谱分析仪等现代测试技术对所合成的Au纳米粒子进行了表征.结果表明,表面为硫醇所修饰的Au纳米粒子,在有机溶剂中具有很好的分散性,表面修饰层的存在不仅有效地阻止Au纳米粒子的团聚,而且使得纳米粒子粒径分布窄,粒径可控.     

前驱体对纳米AlOOH水热制备过程中团聚的影响

为了提高水热产物的分散性,消除水热合成过程中纳米AlOOH颗粒的软团聚和硬团聚,采用振动搅拌的方式制备了前躯体,在水热合成之前进行了离心处理,制备了分散性良好的纳米AlOOH晶粒。用高分辨透射电镜观察了样品形貌,用衍射仪分析了纳米AlOOH晶体点阵结构,用亚微米粒度及电位分析仪检测产物颗粒的表观团聚平均粒径及其分布,以此评价颗粒的团聚行为。通过分析研究探讨了前躯体制备方式对水热产物形貌的影响机理,揭示了化学位差和纳米粒子具有的较高的表面能是导致软团聚的根本原因,指出了杂质离子在结晶过程中的极性配位是导致硬团聚的实质所在。     

硬脂酸对CeO2纳米粒子的表面修饰研究

利用表面修饰法合成了硬脂酸修饰的 CeO2 纳米粒子,采用透射电子显微镜(TEM)观察了经表面修饰的CeO2 纳米粒子的形貌及分散性,并采用红外光谱(IR)、紫外可见分光光度计等对修饰的CeO2 纳米粒子进行了表征。结果表明:表面修饰剂硬脂酸与 CeO2 纳米粒子表面之间发生了化学键合作用;修饰后的CeO2 纳米粒子表面存在疏水有机基团,阻隔了 CeO2 纳米粒子的团聚,起到了分散作用;同时,修饰后的CeO2 纳米粒子在苯乙烯中的稳定性得到了提高。并且获得了硬脂酸的修饰量与CeO2 纳米粒子的最佳配比。     

无机纳米粒子表面修饰

在讨论无机纳米粒子团聚机理的基础上综述了纳米粒子表面修饰研究进展。表面修饰包括物理和化学修饰,重点综述了表面聚合物修饰最新研究进展。介绍了以化学键在纳米粒子表面接枝聚合物,其主要方法包括在无机纳米粒子表面引入可聚合碳-碳双键合成大分子单体、此大分子单体与相应乙烯基单体共聚在表面生成聚合物;将引发剂"固定"在纳米粒子表面合成大分子引发剂,以此引发剂引发单体聚合物生成表面接枝聚合物;反应型聚合物链与粒子表面活性基团反应将聚合物链接枝到纳米粒子表面。     

纳米技术解水玻璃老化百年之谜

通过对水玻璃贮存过程中纳米粒子尺寸的变化 ,提出了水玻璃的老化机理是由于水玻璃中纳米尺寸的多硅酸粒子缩聚成不能再水解的团聚体。团聚体用超声波处理能被打散而又产生纳米粒子     

Reinforcement in Al Matrix Composites: A Review of Strengthening Behavior of Nano‐Sized Particles

Aluminum matrix composites (AMCs) reinforced with the nano‐sized particles are very important materials for the applications in industrial fields. These aluminum matrix composites consist of an aluminum matrix and nano‐sized particles, which own very different physical and mechanical properties from those of the matrix. Nano‐sized particles show a more obvious strengthening effect on the matrix than the micro‐sized particles do, because of the high specific surface area which is positive for the pinning effect during the deformation process. Thus, the nano‐sized particle‐reinforced AMCs usually exhibit a good ductility. The main issues of the fabrication methods are the low wettability between the nano‐sized particles and the molten aluminum alloys, which is fatal to the conventional casting methods, and the agglomeration of nano‐sized particles which happened easier than the larger particles. Several alternative processes have been presented in literature for the production of the nano‐sized particle‐reinforced aluminum composites. This paper is aimed at reviewing the feasible manufacturing techniques used for the fabrication of nano‐sized particle‐reinforced aluminum composites. More importantly, the strengthening mechanisms and models which are responsible for the improvement of mechanical properties of the nano‐sized particle‐reinforced aluminum composites have been reviewed.

     

氧化锌在纸张装裱小麦浆糊中防霉作用的研究

在小麦浆糊(浆糊)里加入氧化锌超细粉(氧化锌),采用培养皿观察法评价防霉效果.讨论了6种商品氧化锌的防霉效果与其微粒大小、形貌之间的关系;考察了氧化锌加入方法、加入量及湿度条件的影响,比较了海泰纳米氧化锌、纳米氧化锌悬浮液及明矾的防霉效果.结果表明:原级粒子为纳米级且分散良好的氧化锌才能表现出很好的防霉作用;先期加入法优于后期加入法;氧化锌加入量越多、粒径越小,防霉效果则越好;在霉菌易于生长条件下,明矾几乎没有防霉效果,而纳米氧化锌悬浮液防霉效果显著.     

Influence of reinforcing particles on microstructure and mechanical properties of friction stir processed aluminium alloy AA7075-T651

This paper emphasis the improvement of mechanical properties of AA7075-T651 using friction stir processing through localized surface modification by adding nano boron carbide particles. The reinforcement techniques such as the groove and blind hole methods were used by changing reinforcements of nano boron carbide and a matrix of AA7075-T651 surface composites volume percentages (2 %, 4 %, and 6 %) along with tool rotational speed and processing speeds. Optical microscopy, scanning electron microscope and x-ray diffraction analysis were used to examine the particle dispersion for the surface composites and to correlate with the enhanced mechanical properties. Results revealed that high input parameters have given grain coarsening and precipitate agglomeration and low input parameters provide poor nugget metal consolidation and no vertical material flow. The L9 orthogonal Array designed and optimized the process parameters for enhancing the surface properties of processed samples. Mechanical properties like ultimate tensile strength, yield strength, hardness, percentage of elongation and impact strength were evaluated for the groove friction stir processing method and blind-hole friction stir processing methods. From the results, it has been observed that the blind-hole technique resulted in higher hardness and the homogenous dispersion of nano boron carbide particles in the stir zone than the groove method. Consequently, for blind-hole friction stir processing, grey relational analysis (GRA) and particle swarm optimization (PSO) approaches were proposed to optimise process parameters. From the compared optimization results between grey relational analysis and particle swarm optimization, particle swarm optimization approach was shown the best optimization results. Successively, the optimum condition in the respective experimentation is accomplished. Based on these observation and results, final validation tests were carried by changing the volume percentages of reinforcement keeping tool rotation speed and tool processing speed as constant. It is apparent that dynamic recrystallization in aluminium alloy at the processed zone due to presence of heterogeneous nucleation sites with nano boron carbide particles.     

燃煤细微颗粒物声波团聚的机理研究

采用数值模拟的方式,对声波团聚中的同向团聚机理、流体力学作用机理以及布朗作用团聚机理等分别做了深入研究.模拟中选取四组具有代表性的颗粒粒径,分别从声波频率、声场强度、颗粒粒径、颗粒间距以及温度五个方面模拟计算.计算结果表明:同向团聚机理下存在一个最优团聚频率带,随着声压级的升高团聚效果也增强;较大的团聚颗粒存在一个粒径比其小的最佳团聚颗粒粒径;相同条件下,同向团聚机理所产生的团聚效果最明显,其次是声波尾流效应,其他的团聚机理相比前者影响较小.研究发现在某些特定因素影响下,声波尾流效应会强于同向团聚,说明了其在声波团聚过程中的重要性.     

Plastic Deformation of Nano-TiO2 Ceramics Prepared by Different Methods

1.IlltroductionThestudyofthesuperplasticdeformationofsub-micrograinceramicshasgotgreatprogress,buttheoperatingtemperatureswerestiIltoohigh(atleastabove1loo'C)forpracticalapplication[1].Inordertolowerthetemperatureofsuperplasticdeformationofceramics,onepossiblestepisusingthenanometerparticlesasstartingmaterialstomakenanograince-ramics.Soinrecentyearsthestudyofsuperplasticdeformationofnanograinceramicshasattractedmoreandmoreattention.Karcheta1.firstreportedtheductilityofunsillterednano-ceramics…     

Crystal agglomeration of europium oxalate in reaction crystallization using double-jet semi-batch reactor

The particle agglomeration of europium oxalate was investigated in a double-jet semi-batch reactor over a wide range of operating variables, including the agitation speed, reactant feed rate, and reactant concentration. The size of the agglomerates was directly dictated by the particle collision and supersaturation promoting agglomeration and the fluid shear force inhibiting agglomeration. Thus, with a longer feeding time and higher feed concentration for the reaction crystallization, the mean particle size increased, while the corresponding total particle population decreased due to the enhanced chance of particle agglomeration, resulting from a longer residence time and higher supersaturation in the reactor. Agitation was found to exhibit a rather complicated influence on particle agglomeration. Although both particle collision and turbulent fluid shear were promoted by an increase in the mixing intensity, the crystal agglomeration of europium oxalate was maximized at around 500 rpm of agitation speed due to an optimized balance between particle aggregation and breakage.     

化学氧化聚合制备微/纳米结构聚苯胺研究进展

近年来多种见诸报道的新颖聚苯胺(PANI)微/纳米结构及其制备途径,可大体归为:主要控制了苯胺化学氧化聚合中聚合产物成核、生长过程或对聚合反应施加了影响.主要从聚合产物的生长和团聚、苯胺化学氧化聚合所用氧化剂和掺杂剂三方面归纳了制备微/纳米结构PANI的反应条件及其影响因素.     

Al-Si/SiC nanoparticles composites synthesized by double stir casting

The present invention provides Al-Si/SiC nanoparticles composites with the composition of 7%Si, 15%SiC with average particle size (APS) of SiC, 20, 30, 40 nm and 65μm using a novel double stir casting method. The inventive nano-composites by double stir casting show a nearly uniform distribution and good dispersion of the nano-particles within the Al matrix, although small agglomeration was found in the matrix of the micro-composite. The enhancement in values of impact strength and tensile strength observed in this study is due to small particle size and good distribution of the nano particles, which were confirmed by SEM spectrum. Patents WO 2010135848 and WO2011/011601 have some relevant information about the topic developed in this study, because the principle in both cases relies on the interactions between metal matrix and the nano-particles. Hence, novel double stir casting method can be used to improve the properties of nano-composites.     

Effect of turbulent flow field properties on improving the removal of coal-fired fine particles in chemical-turbulent agglomeration

Chemical-turbulent agglomeration is a promising coupling agglomeration method to improve the removal of fine particles, in which the turbulent flow field plays an important role on the collision of chemical droplets and fine particles. However, there is no specific study about the effect of turbulent flow field properties on the agglomeration and removal of fine particles. In this work, three kinds of turbulent vortex sheets with different structures were designed to generate vortexes with different scales and generation dimensions, the particle agglomeration effect and characteristics, as well as the particle removal effect by ESP with different turbulence generators were investigated. The results demonstrated that the turbulence generator with large-scale and two-dimensional vortexes in flow field had the best effect on improving the agglomeration and removal of fine particle. Besides, the motion trajectories and the turbulent agglomeration kernel of chemical droplets and fine particles were calculated to further explore the interaction mechanism of particle agglomeration and flow field properties. The results proved that the turbulent flow field containing large-scale and two-dimensional vortexes can effectively enlarge the capture area of fine particles by chemical droplets and promote the collision probability of them, thus improving the agglomeration and removal of fine particles.