超声波在纳米材料合成中的应用

论述了超声波作为一种新型手段在纳米材料合成领域中的应用，并报告了作者在使用超声波由ＳｉＯ２进行纳米材料合成的初步结果。     

超声波技术在高分子合成中的应用研究进展

对近十年来超声波技术在高分子合成中的应用进行了综述;详细介绍了超声波技术在诸如嵌段共聚物的合成、高分子的改性、乳液聚合及本体聚合的引发、溶液聚合、微/纳米粒子的制备、高分子反应过程监测、高分子反应机理研究等等方面的应用情况;认为随着相关配套技术的发展,超声波技术今后在高分子科学各方面的应用将会不断开拓并深入,尤其因超声波引发本体聚合反应可以获得高纯聚合物材料,这一特点在某些领域必然产生独特应用。     

超声优化水解胶原蛋白粒径对合成施胶剂性能影响

利用超声波细胞粉碎机对水解胶原蛋白进行预处理,通过FT-IR、XRD、TG等手段测定超声波处理前后胶原蛋白结构的变化,结果表明,超声波处理并不改变胶原蛋白的结构。利用纳米粒度仪测定超声波处理时间和处理功率对胶原蛋白粒径的影响,以及超声波处理前后胶原蛋白的粒径分布,实验结果表明,超声波处理时间和功率在一定的范围内的确可以改变胶原蛋白的粒径,超过范围后则影响较小;超声波处理过程中,胶原蛋白大分子逐渐变为小分子,小分子通过氢键与大分子结合。利用处理过的胶原蛋白合成施胶剂,然后对瓦楞原纸进行表面施胶,通过考察施胶后纸张的性能,得到合成施胶剂的粒径与施胶后纸张的性能呈现相关性。     

声酶法合成生物柴油的比较研究

以玉米油、乙醇和Lipozyme TL IM脂肪酶为主要原料,研究了声酶法合成生物柴油不同因素的影响,并与静态、摇床作用下酶法合成生物柴油进行了比较,结果表明,随着乙醇量、反应温度或溶剂石油醚加入量的增大,生物柴油的产率均先增大后降低,随着酶添加量增大、反应时间的延长,生物柴油产率相应增大。适宜的反应条件为:油醇摩尔比1:1、反应温度60℃、酶添加量10%、溶剂加入量(mL)与玉米油质量(g)比为1:1、声酶法合成反应时间3h。超声波辐射显著提高了生物柴油的产率,在相同反应温度下,超声波辐射使生物柴油产率比静态条件下的产率提高了27%-33%,比摇床作用下的产率提高了6%-15%。超声波作用没有改变酶的最适反应温度。     

超声辐照合成Salen金属配合物的初步研究

将超声应用于Salen配体与金属配合的过程中,在超声辐照条件下分别合成了手性及非手性的Salen金属配合物:N,N'-双水杨醛缩乙二胺钴、N,N'-双水杨醛缩乙二胺锰和(S,S)-N,N'-双(水杨醛)-1,2二苯基乙二胺钴,通过元素分析、红外光谱、核磁进行了表征。讨论了反应时间、温度、以及超声波声强对产率的影响,并与常规的合成方法进行了比较。研究结果表明:在合成过程中采用变幅杆式超声波发生器,以乙醇做溶剂,Schiff base与醋酸盐在60℃下超声波声强为1.35W.cm-2左右时反应较短时间内即可完成,其配位时间大大减少,其中配体和醋酸锰的配位时间由原来的12h缩短到2.5h,反应温度的也由80℃降低到60℃,并且获得95%的产率。     

超声相转移催化氧化环己醇合成己二酸的实验研究

研究了用30%的硝酸氧化环己醇合成己二酸.实验结果表明,用聚乙二醇作相转移催化剂,在功率为50W的超声波作用下,30%浓度的硝酸氧化环己醇,己二酸的产率可达到46%.研究发现,氧化过程中尾气中NO2的浓度明显减小,相转移催化剂和超声波辐射作用对反应有重要作用.     

超声波低温快速合成球形4A分子筛

在表面活性荆存在、低温条件下用超声波快速合成了性能优良的球形4A分子筛,并用xRD、IR、SEM和粒度分布等手段对合成的产物进行了表征.结果表明,所合成的分子筛的白度为95%,钙离子交换容量为318mgCaCO3/g干沸石,产物的平均粒径为1.64μm,粒度小于4μm的含量可达100%.此外,所合成的分子筛呈球形,更适合用作洗涤助剂.     

超声波辅助纤维素系高吸水树脂的合成及表征

选用可生物降解的纤维素为基本骨架,利用硝酸铈铵作为引发剂处理纤维素,采用超声波辅助方法使其与丙烯酸发生接枝共聚反应,合成高吸水树脂.研究超声波功率、引发剂用量、丙烯酸与微晶纤维素的质量比、中和度、交联剂用量对树脂吸水倍率的影响,并对纤维素系高吸水树脂进行红外光谱和扫描电镜分析.结果表明,最佳工艺条件:超声波功率为500 W,引发剂用量为1.8 mL,丙烯酸与微晶纤维素的质量比为3.0:2.0,中和度为50％,交联剂质量分数为0.10％.此条件下制得的吸水树脂的吸蒸馏水倍率为486倍,吸自来水倍率为173倍.经红外光谱和扫描电子显微镜综合分析,证明超声波处理可以使得微晶纤维素表面发生变化,促进微晶纤维素与丙烯酸的固相接枝共聚,合成的纤维素系高吸水树脂保留了微晶纤维素分子骨架和聚丙烯酸各自的特性,在纤维素大分子表面和无定型区引发了接枝聚合.     

金属有机骨架材料合成方法对氮氧化物吸附性能的影响

金属有机骨架材料(Metal-organic frameworks,MOFs)因具有高的比表面积和孔隙率,使得其拥有良好的气体吸附性能.与传统的NOx吸附材料相比,MOFs材料拥有超高的比表面积和孔隙率,结构丰富多样且具有周期性,良好的热稳定性和化学稳定性.国内外学者采用不同的合成方法合成MOFs材料,以达到对NOx高效吸附的目的.MOFs材料的合成方法主要有水热法、溶剂热法、超声波合成法和微波合成法.水热法操作步骤简单,合成的晶体质量高,但是晶粒较大,孔体积小;溶剂热法和水热法原理相同,通过加入不同官能团的有机溶剂,合成的材料结构更为丰富,比表面积和孔容更大,对NOx的吸附效果比水热法好,也是使用最广泛的方法;超声波合成法合成的MOFs材料粒径较小且尺寸均一,比表面积和孔容较大,对NOx的吸附效果好,但是成本较高;微波合成法可加快反应速率,形成更小的晶粒,比表面积和孔容较大,对NOx的吸附量很高,但是同样也具有经济成本高的劣势.为此,本文对MOFs材料的合成方法、改性技术进行了总结,同时分析了不同方法合成的MOFs对氮氧化吸附效果的影响,并对MOFs材料吸附氮氧化物的发展趋势作了展望.     

纳米石墨的制备方法(英文)

简要概述了现有的纳米石墨制备方法,这些方法从材料来源上可以分为2类,一类由鳞片石墨来制备,另一类由富碳材料合成.由鳞片石墨制备纳米石墨的方法主要有球磨法、超声波粉碎法、爆轰裂解法和电化学插层法;由富碳材料合成纳米石墨的方法主要包括爆轰合成法、化学气相沉积法、激光脉冲沉积法和化学合成法.     

The mechanical behaviour of aluminium foam structures in different loading conditions

The use of foam has the potential for energy absorption enhancement. Many types of materials can be produced in the form of foams, including metals and polymers. Of the metallic based foams, aluminium based are among the most advanced. Aluminium foams couple good specific mechanical properties with high thermal stability. Among the various aspects still to be investigated regarding their mechanical behaviour is the influence of a hydrostatic state of stress on yield strength. Unlike metals, the hydrostatic component affects yields. Therefore, different loading conditions have to be considered to fully identify the material behaviour. Another important issue in foam structure design is the analysis of composite structures. The mechanical behaviour of an aluminium foam has been examined. The foam was subjected to uniaxial, hydrostatic stress, pure deviatoric stress, and combinations thereof. Results obtained will be presented as quasi-static and dynamic uniaxial compression and quasi-static bending and shear loading. Moreover, composite structures were made by assembling the foam into aluminium cold extruded closed section 6060 aluminium tubes. The results show that the energy absorption capability of the composite structures is much greater than the sum of the energy absorbed by the two components, the foam and the tube.     

Acoustic and vibrational damping in porous solids

A porous solid may be characterized as an elastic-viscoelastic and acoustic-viscoacoustic medium. For a flexible, open cell porous foam, the transport of energy is carried both through the sound pressure waves propagating through the fluid in the pores, and through the elastic stress waves carried through the solid frame of the material. For a given situation, the balance between energy dissipated through vibration of the solid frame, changes in the acoustic pressure and the coupling between the waves varies with the topological arrangement, choice of material properties, interfacial conditions, etc.Engineering of foams, i.e. designs built on systematic and continuous relationships between polymer chemistry, processing, micro-structure, is still a vision for the future. However, using state-of-the-art simulation techniques, multiple layer arrangements of foams may be tuned to provide acoustic and vibrational damping at a low-weight penalty.In this paper, Biot's modelling of porous foams is briefly reviewed from an acoustics and vibrations perspective with a focus on the energy dissipation mechanisms. Engineered foams will be discussed in terms of results from simulations performed using finite element solutions. A layered vehicle-type structure is used as an example.     

Lightweight Cellular Plastics

Plastic foams have found a number of applications in the energy absorption, thermal, and acoustic markets. Here advances that have been made with extruded polystyrene, polyolefin, and polyurethane foams, and their uses, particularly in the automotive industry, are highlighted. The Figure shows a 65 % compressed foam.     

The deformation of brittle starch foams

There exists a theoretical model to describe the deformation of solid foams which relates the mechanical properties to the foam density and the cell-wall properties. Previous work has assumed that the wall properties are constant for a wide range of different density foams and can be characterized by the properties of the unfoamed material. In this paper we show that, when considering extruded starch foams, variation of the extrusion parameters in order to produce different bulk density foams has an effect on the cell-wall material: notably upon the crystallinity,T _g and wall density. Therefore, both the bulk foam and cell-wall mechanical properties were measured in order to test the full theory. For the relative fracture stress, excellent agreement was found between the predicted power law behaviour and the experimental results. However, the power law for the relative modulus is larger than the predicted value.     

Ultrasonic Thickness Measurement of Multilayered Aluminum Foam Precursor Material

Metallic foams are prospective materials for use in the aerospace and automotive industry for crash energy absorption safety parts or lightweight constructions. During manufacturing, artifacts in the foamable precursor material or material quality variations can influence the foam structure after the foaming process; thus, such a process requires quality control. The advantage of ultrasonic techniques is the possibility to perform noncontact and one-sided access measurements online. A three-layer system consisting of a layer of aluminum foam precursor sandwiched between two aluminum sheets has been investigated. The problems of ultrasonic nondestructive characterization of such materials are due to the very similar density and ultrasound velocity of the adjacent layers, which produce very weak reflections of ultrasonic waves, and the thin layers also give overlapped reflections in the time domain. The objective of this paper was to develop an ultrasonic technique that is suitable for measurement of the total thickness and the thickness of individual layers. The proposed technique is based on the identification of object parameters. The numerical iterative deconvolution technique was investigated, analyzed, and adapted to measure the thickness of individual layers with similar density and ultrasound velocity of the multilayered aluminum foam precursor material. Theoretical analysis and experimental investigations have shown that application of the proposed numerical iterative deconvolution enables the thickness measurement of individual layers with the expanded uncertainty of less than $pm 10 muhbox{m}$.      

Blast resistance and energy absorption of foam-core cylindrical sandwich shells under external blast

The early time, through-thickness stress wave response of a foam-core, composite sandwich cylindrical shell under external blast is examined in this paper. Solutions for the transient response of the facesheets were derived as stress waves propagated through an elastic–plastic, crushable foam core. These solutions were found to be in good agreement with results from finite element analysis. The blast response of the composite sandwich cylindrical shell was shown to be affected by the magnitude and duration of the pressure pulse. High amplitude, low duration (impulsive) pressure pulses induced the greatest energy absorption. Low amplitude, long duration pressure pulses caused minimal energy absorption. The amount of energy absorbed increased and the failure load decreased with increasing core thickness. Sandwich shells with foams of varying density, compressive modulus and crushing resistance were also examined. The sandwich shells with the foam of the highest density, compressive modulus and crushing resistance (Divinycell HCP100) were found to be the most blast resistant to failure even though no energy was absorbed by them. Per unit weight, however, the shells with a lighter, less stiff and strong, Divinycell H200 foam core were more blast resistant to failure than shells with a Divinycell HCP100 foam core.     

Hygrothermal studies on syntactic foams and compressive strength determination

Syntactic foams are commonly used as core materials in composite sandwich structures for weight sensitive applications such as aircraft and spacecraft structures and boat hulls. Moisture absorption is highly undesirable in these applications. The present study evaluates the hygrothermal properties of two types of syntactic foams. Distribution of outer diameter of cenospheres (hollow particles) incorporated in both types of syntactic foams is the same but there is variation in the internal diameter causing difference in the density of syntactic foams. Epoxy resin is used as matrix material and the volume fractions of matrix and cenospheres are kept at 0.35 and 0.65 by volume, respectively. Moisture absorption experiments are conducted at two different temperatures, 25 and 70 °C and in deionized and salt waters. Non-destructive ultrasonic imaging technique is used to find the extent of moisture penetration and damage to the specimens. Syntactic foam samples are tested for compressive strength after moisture absorption and the results are compared with the compression test results of dry syntactic foam samples.     

Characterization of close-celled cellular aluminum alloys

The deformation behaviour of two different types of aluminium alloy foam are studied under tension, compression, shear and hydrostatic pressure. Foams having closed cells are processed via batch casting, whereas foams with semi-open cells are processed by negative pressure infiltration. The influence of relative foam density, cell structure and cell orientation on the stiffness and strength of foams is studied; the deformation mechanisms are analysed by using video imaging and SEM (scanning electronic microscope). The measured dependence of stiffness and strength upon relative foam density are compared with analytical predictions. The measured stress versus strain curves along different loading paths are compared with predictions from a phenomenological constitutive model. It is found that the deformations of both types of foams are dominated by cell wall bending, attributed to various process induced imperfections in the cellualr structure. The closed cell foam is found to be isotropic, whereas the semi-open cell foam shows strong anisotropy.