分级微/纳结构ZnO的制备及其光催化性能

分别采用溶剂热法和草酸盐法制得具有分级微/纳结构但形貌迥异的两种ZnO材料,以亚甲基蓝溶液(MB)作为目标降解物对其光催化性能进行评价。结果表明:溶剂热法所制得的ZnO呈花状微球形貌,由纳米片自组装而成;草酸盐法所制得的ZnO为微米棒状形貌,以纳米颗粒为基本单元发展而来。草酸盐法ZnO材料具有更为优异的光催化性能,其对亚甲基蓝溶液的降解反应速率常数是溶剂热法ZnO材料的7.65倍。活性自由基物种鉴定结果证实,两种ZnO材料在受到紫外光激发时均能产生·OH和·O₂^-活性自由基。两种ZnO样品光催化性能的差别源于能带结构不同所引起的活性自由基生成数量上的差异。较之溶剂热法ZnO,草酸盐法ZnO在受紫外光激发时产生的·OH和·O₂^-数量更多,且以强氧化能力的·OH为主,因而表现出更为优异的光催化性能。     

电火花加工制备铜基微纳层次结构及其疏水性能

利用电火花成型加工技术制备铜基微纳层次结构疏水表面,该微纳层次结构主要由微纳孔洞、熔珠、重熔区和热应力裂纹等微观结构组成,考察了不同脉宽参数对微纳层次结构疏水性的影响。结果表明:随着脉宽的增大,微纳层次结构中微纳孔洞数量增加,各种微观结构的层次分布程度增强,增大“气垫”效应区域,可存储更多的空气在其表面,提高了微纳层次结构的疏水性。固-液界面所占面积分数(f sl)减小,水滴和表面孔洞中的“气垫”接触面积增大,使得微纳层次结构对水滴的物理吸附作用减弱。微纳层次结构接触角可增至(144.7±2.1)°,接触角滞后性范围为(8.46±3.3)°^14.10±1.2°。     

Development of a calibration methodology to improve the on-site non-destructive evaluation of concrete durability indicators

This paper addresses the use of non-destructive testing (NDT) methods to assess indicators for both the concrete durability (porosity, degree of saturation) and mechanical properties (elasticity modulus, compressive strength) of reinforced concrete structures. NDT results, called “observables”, are obtained by means of ultrasonic or electromagnetic methods and then correlated with these mechanical and durability indicators. The conversion model used to transform observables into indicators depends on the actual concrete mix design. If this conversion model is unavailable for the reinforced structure under study, then the evaluation may be inadequate due to high uncertainty on the results. This paper proposes a calibration methodology to derive a conversion model appropriate for the structure by use of a minimum number of cores in order to improve the on-site evaluation. A motorway bridge is tested and characterized by NDT, after which some cores are extracted for calibration and others for validation. The cores are subsequently non-destructively characterized in the laboratory and/or used to determine indicators by means of standardized destructive methods. The non-destructive calibration protocol on cores is presented first. Next, NDT results recorded in situ and on the corresponding core are compared. Also, durability indicators deduced from on-site NDT measurements in addition to calibration are compared with reference durability indicators that have been independently determined by standard destructive methods. Results obtained by analyzing more than 1600 data fully validate the tested calibration methodology.     

A design concept with the use of RUHTCC beam to improve crack control and durability of concrete structures

Aiming at design issues of strictly anti-cracking structures or aseismic design in crucial locations of structures when using ultra high toughness cementitious composite (UHTCC), investigations on flexural behavior of reinforced ultra high toughness cementitious composite (RUHTCC) members are carried out due to excellent crack dispersion and strain energy absorption abilities of UHTCC. According to elastic theory, a calculation model of strain-hardening composites flexural members including theoretical calculation of moment, deflection and curvature, as well as critical reinforcement ratio is proposed in detail. Then experiment on RUHTCC beams without web reinforcement is performed to verify theoretical equations. For RUHTCC beams, there is a good agreement between test results and theoretical calculation. The safe calculated ductility indices can be used to predict ductility of structures. Compared with reinforced concrete beams, UHTCC delays yielding of reinforcements and improves load bearing capacity and ductility of structures, then steel reinforcement is saved; low reinforcement ratio is propitious to exert advantages of UHTCC. Under service load conditions, crack width in RUHTCC beams is limited to 0.05 mm and can be considered without negative influence on durability. Durability of structures will be significantly improved by using UHTCC instead of concrete.     

锈蚀对钢筋混凝土结构耐久性的影响研究

钢筋混凝土结构在工程建设中得到广泛的应用,然而结构中的钢筋锈蚀是影响钢筋混凝土结构耐久性的主要因素。文章阐述了混凝土结构的耐久性理论,锈蚀影响混凝土耐久性的因素以及预防锈蚀的措施等。     

微纳米结构硫酸钡的仿生合成与表征

以天然棉花和棉布作为生物模板成功制备了具有棉花和棉布纤维形貌的微纳米BaSO4晶体.研究了反应物浓度、反应温度、超声时问等因素对所得产物形貌的影响,确定了最佳反应条件.并用SEM、IR、XRD对最佳反应条件所得产物进行了表征.     

Adding limestone fines as cementitious paste replacement to improve tensile strength,stiffness and durability of concrete

The addition of a filler such as limestone fines (LF) to fill into the voids between aggregate particles can reduce the cementitious paste volume needed to produce concrete. In previous studies, it has been found that the addition of LF to reduce the cementitious paste volume would substantially increase the cube strength, and reduce the heat generation and shrinkage of the concrete produced. In this study, the authors aimed to evaluate the effects of adding LF as cementitious paste replacement on the tensile strength, stiffness and durability of concrete. For the evaluation, a series of concrete mixes with LF added to replace an equal volume of cementitious paste were tested for their workability, cube strength, tensile splitting strength, modulus of elasticity, water penetration depth and chloride permeability. The results showed that the addition of LF as cementitious paste replacement would at the same water/cement ratio, and even at the same cube strength, improve the tensile strength, stiffness and durability of concrete.     

Thermal conductivity of polymer composites with close-packed structure of nano and micro fillers

Thermal conductivity of polymer composites with nano and micro fillers has been investigated numerically and experimentally. The nano fillers used were multi-walled carbon nanotubes (MWNTs) and alumina nanoparticles, and the spherical alumina particles were selected as the micro fillers. A periodic unit cell with a random close-packed structure was created using a packing algorithm that treat the micro filler as spheres. Finite element analyses were also performed to predict the potential of nano fillers to enhance thermal conductivity of the composites and to analyze the effect of microstructure of micro fillers. Additionally, the polymer composites with nano and micro fillers were made and the thermal conductivity of the composites were measured. The results showed that the addition of MWNTs to the matrix lead to a large increase in thermal conductivity of the composites. The proposed thermal model predicted a thermal conductivity in good agreement with experiment.     

生物模板法制备微纳米二氧化锡

以SnCl4.5H2O为起始原料,采用不同的生物模板(定量滤纸、鸡蛋内膜),通过浸渍和煅烧,在常压空气气氛中成功地制备出具有不同生物形态的微纳米SnO2。采用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征样品的相组成和微观结构。结果表明:两种模板所制得的产物纯度很高,且很好地复制了原模板的形貌。同时,研究了制备条件诸如煅烧温度和反应物浓度对产物结构、形貌和尺度的影响,并初步探讨了不同生物形态的微纳米SnO2形成的机理。     

Foreword to the special issue on micro/nano biosensors

正Micro/nano biosensors had rapidly progressed and enabled a verity of applications that were otherwise impossible/challenging with traditional methods. The three key components in micro/nano biosensors consist of (1) the analyte preparation (living cells or biomarker molecules),(2) signal transduction (from bio-signal/event to more readable electronic/optical signal), and (3) signal readout (preferably by integrated instrumentation). A verity of work has been dedicated to each     

Dependence of thermal conductivity in micro to nano silica

This work presents the measurement of thermal conductivity of nano-silica particles using needle probe method. The validation test of thermal probe was conducted on ice and THF hydrates using our experimental set up and the results are satisfactory when compared with the literature data. The nano silica used in this study is with particle sizes in the range 50–1000 nm. The sand powders sieved in different sizes ?<75 and 75  μ m ?>? d ?>? 250  μ m were also studied to probe the particle size dependence on thermal conductivity. Thermal conductivity decreased by about 70% in silica nano powders.     

Hydrothermal synthesis and characterization of micro to nano sized carbon particles

Experiments under hydrothermal conditions were carried out to study the formation of elemental carbon through the decomposition of β-Silicon carbide (β-SiC) in the presence of organic compounds. The organic compounds were known to dissociate at low P-T conditions and produce the C–O–H supercritical fluids, which will have great influence on the decomposition of β-SiC. These hydrothermal runs under the influence of supercritical fluids will not only help in dissociating the silicon carbide into SiO₂ and free elemental carbon but also control the type of carbon phase formation. The Scanning Electron Microscopic (SEM) studies of the run products indicate the formation of the micron sized carbon particles having characteristic shapes like spherical/ovoid, scaly with metallic lustre and in some runs we find the formation of nano sized octahedral crystallites. Micro Raman study of these carbon particles reveals that bulk of the carbon formed in these runs were disordered / sp²–hybridized carbon but we also noticed the formation of black scales over the spherical particles and the octahedral crystallites which exhibits the sp³-hybridization having the characteristic sharp band at 1332 cm^-1, comparable to that of diamond powder. The octahedral crystallites are formed at the inner walls of the hollow spherical carbon particles. In any of the experimental runs we haven't used either the metal catalysts or the diamond seed with the charge material. Thus, the nucleation and formation of nano sized octahedral crystallites of diamond (sp³-hybridized carbon) in the present study at lower P-T conditions compared to that of its formation in nature is a significant breakthrough in the study of diamond synthesis.     

Influence of a fine glass powder on the durability characteristics of concrete and its comparison to fly ash

A detailed investigation carried out to ascertain the durability characteristics of fine glass powder modified concretes is reported in this paper. Tests were designed to facilitate comparisons between concretes modified with either glass powder or fly ash at the same cement replacement level. The optimal replacement level of cement by glass powder is determined from strength and hydration tests as 10%. The later age compressive strengths of glass powder and fly ash modified concretes are seen to differ by only 5%. The durability characteristics are ascertained using tests for rapid chloride permeability, alkali–silica reactivity, and moisture transport parameters. The chloride penetrability values indicate some amount of pore refinement. The potential of glass powder to reduce the expansion due to alkali–silica reaction is established from tests conducted in accordance with ASTM C 1260, but fly ash is found to perform better at similar replacement levels. Glass powder–fly ash blends that make up a 20% cement replacement level are found to be as efficient as 20% fly ash in reducing expansion. The control concrete is seen to exhibit the lowest overall moisture intake after 14 days of curing, and fly ash concrete the highest, with the glass powder concrete in between. The trend is reversed at later ages, demonstrating that both the replacement materials contribute to improved durability characteristics. The sorptivity and moisture diffusion coefficient values calculated from the moisture intake-time data also demonstrate a similar trend. These studies show that fine glass powder has the potential to improve the durability of concretes.     

酪素胶束结构及其纳米功能化的研究进展

总结了国内外关于酪素胶束微观结构及其胶束结构表征手段的研究,重点阐述了纳米粒子改性酪素胶束结构以获得功能材料的研究进展,希望对从事酪素研究的工作者有所帮助。     

Design of concrete structures for durability and strength to Eurocode 2

The Structural Eurocodes of the European Communities establish requirements for building and civil engineering works in terms of reliability, adequate performance in service conditions and durability. For the achievement of durability, several steps are necessary in the sesign process. They are the subject of Eurocode 2 and the European Standard EN 206 for concrete technology. The basic elements of the design concept are described in the present paper.

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Résumé Les Eurocodes sur les structures de la Communauté Européenne définissent des exigences pour les batiments et les ouvrages de génie civil en terme de fiabilité, de performance dans les conditions de service et de durabilité. Afin de remplir l'exigence de durabilité, plusieurs étapes sont nécessaires dans le processus de conception. Elles sont l'objet de l'Eurocode 2 et de la norme européenne Béton EN206. Les éléments de base de la conception de plan sont décrits dans cet article.

     

Phenomenological aspect of concrete durability theory

It is shown that concrete destruction by freezing and thawing, in dry and hot climate, under sulphate and potassium aggression occurs because of high inner tensile stresses appearing as a result of bonding in concrete conglomerate the components with widely different deformations under the action of corrosion. The problem of concrete frost resistance is considered in detail. The model of concrete as a material of “conglomerate in conglomerate” type, divided into three structural levels is proposed. The measurement of damage to concrete, being characterized by the ratio of maximum total inner stresses to local strength of structure is introduced. It is shown that the developed approach makes it possible to explain from a single viewpoint the majority of experimental facts, known in the field of concrete durability.     

Limestone aggregate concrete,usefulness and durability

Inland and on sea coasts, crushed limestone aggregate has been used in France and elsewhere for structural concrete when gravel aggregates were not available. Crushed limestone fillers have, since the oil crisis, been allowed as partial constituent of cement; they are now currently used as additions in concrete mixtures, as partial replacement of Portland cement. Limestone aggregate concretes have not been considered inferior to gravel aggregate concretes, particularly in durability. However, recently some cases of alkali-silica deleterious reactivity and one case of sulphate attack, have questioned their good performance status.     

Enhanced stress durability of nano resonators with scandium doped electrodes

To explore mechanical stress durability of thin aluminum–scandium (AlSc) films, 0.86 GHz nano resonators with AlSc electrodes have been manufactured. Four different samples have been prepared altering the Sc content in the alloy between 0.0% and 2.5%. A final lift-off step accomplished manufacture procedure of the devices. The resonators have been operated with heavy load to determine power durability. The resonators with AlSc electrodes show increased power durability compared to conventional Al metallized devices. Texture and grain structure of all films have been investigated by means of electron backscatter diffraction (EBSD) and atomic force microscopy (AFM). Material fatigue of electrodes has been visualized by scanning electron microscopy (SEM). The refined grain structure of these alloys can explain the enhanced mechanical stress durability of AlSc electrodes.     

微米及纳米金刚石薄膜的制备及其组织性能研究.

采用微波等离子体化学气相沉积(MPCVD)方法在铜衬底上沉积了微米和纳米两种金刚石薄膜,过渡层均为钛一铝一钼.用场发射扫描电子显微镜(FESEM)观察薄膜的表面及断面形貌,用拉曼(Raman)光谱测量所得金刚石薄膜的质量,利用压痕法测试了所得薄膜的附着性能,研究结果表明:过渡层可有效提高微米金刚石薄膜在铜衬底上的附着力,反应气氛中Ar的存在可促使纳米金刚石薄膜的形成,改善薄膜表面的粗糙度.     

以CuCl纳米棒薄膜为前驱体制备CuS纳米/微米管和CuO纳米/微米晶薄膜

在本文中,以由氯化亚铜纳米棒组成的薄膜为前驱体,分别通过气-固相的硫化和氧化反应获得了由直径150到200纳米,长度达数微米的硫化铜管组成的薄膜和粒径为150到200纳米的氧化铜纳米/微米晶所组成的薄膜.利用XRD,SEM,TEM测试方法对薄膜的晶化度,纯度,形貌及结构特点进行了分析.制备的薄膜具有大尺寸,高比表面积,构筑单元为单晶的特点.研究表明,硫化铜纳米/微米管是通过克肯达尔效应形成的,而氧化铜纳米/微米晶是氯化亚铜与空气反应通过类似于化学气相沉积过程形成的.