Do ‘Functional Barriers’ Function?

The direct recycling of plastics (food grade plastic to food grade plastic) obviously gives rise to possible health hazards. Contaminants, picked up by the material during first usage, may migrate into food during second use. ‘Functional barrier’ layers have been used for a long time (e.g. aluminium, silica and silicates), but there is now considerable research and development on ‘barrier’ layers of plastics for the purpose. For technological and regulatory reasons, use of the same plastic in virgin form as the recyclate is favoured. A theoretical study shows that such a layer, in general, must function more as a sponge than a barrier. Moreover, in general, migration into and through the barrier must start at manufacture of the package, and not at containment of the food (as assumed in all legislation). Although in some instances there may be adequate delay and reduction of migration to ensure safety, this is not so in general and certainly cannot be guaranteed. Hence the concept needs reconsideration in the interest of public safety.     

“蒸汽相转化”法制备球形多级Y沸石

本文采用“蒸汽相转化”法合成了球形多级Y沸石。采用X射线衍射(XRD), 扫描电镜(SEM), 透射电子显微镜(TEM), N₂吸附-脱附, 固态核磁共振(NMR)谱和傅里叶变换红外(IR)光谱等表征手段对制备材料的结构性能进行了表征。SEM观察结果表明合成的Y型沸石是由尺寸为50~300 nm的初级晶粒组成的球形多晶聚集体, 透射电镜观察结果表明多晶聚集体为空心Y型沸石。通过分析FT-IR, ²⁹Si NMR, SEM和TEM等表征结果, 提出了空心球形Y沸石的形成机理。     

Sind die genormten Prüfverfahren für zügige und schlagartige Beanspruchung noch zeitgemäß? – Neue Wege zur Dimensionierung –

Are the Standardized Methods of Testing Tensile and Impact Loads still up to Date? – New Ways of Dimensioning – Test specifications for polymer materials are derived from proven and standardized mechanical test methods used for determining the properties of metal materials. Having established that, apart from long-term testing methods, it is impossible to derive any dimensioning characteristic data from most test methods, the picture is very unsatisfactory indeed. Added to this is the fact that, in order to determine long-term properties, extremely time-consuming test methods (some-times lasting for more than one year) must be applied and that, in order to measure stresses in the short-term and impact loading range, it is impossible to do without experiments on practical building components involving complex technical measurements. This paper takes a critical look at these two groups of problems and puts forward fresh possibilities.

• dimensioning under impact load
• calculation of the long-term behaviour from short-term tensile tests.

For amorphous plastics, we get, with decreasing time under load (< 1 s) and decreasing temperatures, a transition from semi-tough to brittle material behaviour. For PMMA, an elongation at break threshold appears to exist at 2.2% and a threshold loadability at 135 N/mm² in the region of impact loads. These values can be taken as a basis for dimensioning against impact. For most other thermoplastics examined here, the tendencies are the same, although exact thresholds cannot be given yet. It is also possible, from the curve of the shear modulus and mechanical loss factor as a function of temperature, to estimate a Young's modulus threshold, which shows good conformity with data measured in actual practice. For PMMA, the value is approx. 6,500 N/mm². Form shear modulus and attenuation curves, it is also possible to estimate how dependent on velocity and temperature the mechanical properties of a material are (tough/brittle transition). Finally, it can be shown that it even seems possible, using the test method presented here, to draw conclusions from very short-term tests (< 17 min.) about the long-term strength. The reason why the standardized short-term tensile test does not provide any characteristic material data suitable for the dimensioning is, in our opinion, that the major test condition, the strain rate, is not constant. Tests with constant strain rates, on the other hand, provide a readily describable deformation behaviour with which it is even possible to predict the long-term behaviour. In addition, scattering of the measurements is reduced in a remarkable manner. On varying the testing temperature, we get material data with which the time-temperature shifting principle leads to excellent agreement with results of earlier tests. In this way, we geht from short-term tests - at present, because of the fundamental nature of the tests, times of approx. 100 h are needed, though there are plans for a maximum testing time of 10 h in future - at various temperatures a picture of the material behaviour, which corresponds very well with the longterm behaviour. It even seems to be possible to predict the creep behaviour and obtain information about the load-bearing capacity, e.g. of weld seams, in the required dimensioning time of many thousands of hours.     

“蒸汽相转化”法制备纳米多级Beta沸石催化材料

由于多级孔沸石具有实际及潜在的应用价值, 合成具有微孔-介孔孔道体系的多孔沸石引起了广泛关注。本研究在不添加二次模板剂的基础上, 采用“蒸汽相转化”法制备了多级孔Beta沸石催化材料, 对影响多级孔Beta沸石形成因素, 如凝胶碱度、模板剂用量、硅铝比、蒸汽压力和晶化时间等进行了讨论。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅立叶变换红外(FT-IR)光谱、拉曼(Raman)光谱、N₂吸附-脱附以及NH₃-TPD等表征手段对制备材料的结构性能进行了表征。在借助红外光谱、拉曼光谱及扫描电镜等表征手段的基础上, 对多级孔Beta沸石的形成机制进行了探索。结果表明: 通过“蒸汽相转化”法所制备的Beta沸石为纳米多晶聚集体, 这些多晶聚集体由粒径为10~40 nm的初级晶粒构成, 在初级纳米粒子之间形成了2~30 nm的介孔结构; 干胶制备过程中生成的初级和次级结构单元有利于快速形成大量的Beta沸石核, 较高的成核速率有利于Beta沸石纳米晶粒形成, 这些纳米晶粒相互聚集最终形成纳米多晶Beta沸石聚集体。     

羟基磷灰石超长纳米线/植物纤维纳米复合“宣纸”及其防霉性能

宣纸是中国书画作品必不可少的载体, 具有优良的耐久性和防霉性能, 因此赢得了“纸中之王”的美誉。2009年, 宣纸被联合国教科文组织列入《人类非物质文化遗产代表作名录》。羟基磷灰石具有优良的生物相容性, 环境友好, 白度高, 是一种具有良好应用前景的生物材料。羟基磷灰石超长纳米线具有高柔韧性, 可用于构建具有不同功能的新型耐火纸。本研究发展了一种新型纳米复合“宣纸”, 由羟基磷灰石超长纳米线和植物纤维复合制成。所制备的纳米复合“宣纸”的白度随着羟基磷灰石超长纳米线含量增加而得到提高, 当羟基磷灰石超长纳米线重量比为25%时, 其白度为76.1%, 高于商品生宣纸(71.9%)或商品熟宣纸(70.3%)。采用三种霉菌(球毛壳霉菌、长枝木霉菌、黑曲霉菌)研究了新型纳米复合“宣纸”的抗霉菌性能。实验结果显示, 与传统宣纸相比, 所制备的纳米复合“宣纸”的防霉性能得到显著改善, 与空白样品和商品宣纸相比, 纳米复合“宣纸”对霉菌的生长具有更好的抑制能力, 在其表面三种霉菌的生长速率明显较低, 并且随着羟基磷灰石超长纳米线含量的增加而降低。在恒温恒湿箱内培养过程中, 商品宣纸表面生长出霉菌, 但是纳米复合“宣纸”表面上没有观察到明显的霉菌生长。预期所制备的纳米复合“宣纸”有助于书画艺术品的长久安全保存, 在书法和绘画艺术中具有良好的应用前景。     

“What's to keep you from dropping out?” Student Immigration into and within Engineering

Nearly one‐half of the industrial engineering undergraduate interviewees in an investigation of their degree program indicated they previously had been enrolled in another major. Understanding why these students chose to remain in or enter a science, technology, engineering and math (STEM) major when their previous choice lost its appeal is an important piece of the STEM participation puzzle. Our data indicate effective formal and informal recruiting, contact with dynamic individuals who conveyed commitment to and excitement about the department and program, and a department that welcomed immigrants and promoted a clear, relevant image of its discipline's identity, influenced student decisions to relocate within STEM rather than attrite. The high proportion of females within the immigrant students is one factor contributing to the department's attainment of sex parity. Our students' stories offer lessons to other departments for attracting and retaining students who enter the higher education STEM pipeline.     

我国自强自立高质量发展“四个基础”面临的科学理论难题与对策建议

基础材料、基础元器件、基础软件和基础算法(简称为“四个基础”)是我国基础工业和高科技工业发展的基石, 未来十五年是我国“四个基础”突破重围、自强自立高质量发展并引领国际的关键时期。本文通过战略研究, 分析了我国“四个基础”的发展现状, 提出了“四个基础”发展面临的核心科学理论难题, 建议从五个方面系统建设有利于突破重围和超越引领的原始创新环境与体制机制。     

一维β-SiAlON材料可控合成

以Si粉、Al粉和Al₂O₃粉为原料压制成条样, 在1650~1850 K氮气和埋Si₃N₄颗粒气氛下分别合成了β-SiAlON晶须、带状和柱状晶, 并系统研究了一维β-SiAlON材料可控合成条件, 进而结合热力学分析了一维β-SiAlON材料的生长机制。结果表明: 以Si粉、Al粉和Al₂O₃为原料, 在氮气(纯度99.9%)和埋Si₃N₄颗粒气氛下在1650~1850 K保温6 h, 可以合成不同形貌的一维β-SiAlON材料。生长温度是一维β-SiAlON材料形貌控制的关键因素。生长温度为1650 K时, 合成了β-SiAlON晶须, 晶须直径200~400 nm, 长径比100~1000; 生长温度在1700~1800 K时, 可以合成β-SiAlON带状晶体, 厚度为200 nm, 宽度为1~4 μm, 长宽比在10~20之间; 生长温度升高至1800 K时, 出现大量柱状晶体。结合晶须显微结构形貌和热力学分析, β-SiAlON晶须的生长机制为气-固(VS)生长机制。     

载铂多级孔ZSM-5分子筛用于邻二甲苯的“吸附-催化燃烧”循环脱除

首先利用F127作为软模板, 采用蒸汽辅助晶化法合成出具有一定介孔结构的多级孔ZSM-5分子筛, 然后采用等体积浸渍法负载铂, 成功制备了载铂的多级孔ZSM-5分子筛催化剂。利用X射线衍射(XRD)、氮气吸附等温线(N₂ isotherm)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对制备的催化剂进行了表征, 并将催化剂用于邻二甲苯的吸附和催化燃烧反应, 最后考察了催化剂“吸附-催化燃烧”循环脱除邻二甲苯的性能。结果表明, 与传统ZSM-5分子筛相比, 多级孔ZSM-5分子筛结晶度略有下降, 但是介孔度和孔体积明显提升。介孔结构与微孔结构并存, 极大提升了多级孔ZSM-5分子筛对邻二甲苯的吸附能力, 其饱和吸附量达到了传统ZSM-5分子筛的约8倍。此外, 介孔结构的存在提高了铂的分散度, 使得载铂多级孔ZSM-5分子筛具有最佳的催化燃烧邻二甲苯性能, 三次“吸附-催化燃烧”循环使用后的吸附容量依然基本保持不变, 并且在催化燃烧过程中无二次污染物生成, 具有较高的吸附容量和循环使用稳定性。     

Nanoclusters – Building Blocks for Future Nanoelectronic Devices?

Ligand stabilized metal nanoclusters in the size range of 1–2 nanometers exhibit well pronounced quantum size behaviour, even at room temperature. This is due to the development of discrete energy levels in those metal particles which are reduced in size to quasi zero‐dimensionality. Quantum mechanically they can be considered as big atoms. Studies of the current‐voltage (I‐U) characteristics identified these clusters as single electron transistors and herewith as highly promising candidates as building blocks in future nanoelectronics. As a condition, the clusters – here it is especially Au₅₅(PPh₃)₁₂Cl₆ – have to be organized in two and one dimensions. Procedures have been developed to generate well ordered cluster monolayers by self assembling. Quasi one‐dimensional cluster wires became available by degradation of monolayers by means of modified Langmuir‐Blodgett techniques. Very first electrical investigations of short cluster wires indicate them as quantum mechanically determined units.     

Beyond HCF – Is there a fatigue limit?

The paper gives an overview to the present state of research on fatigue strength and failure mechanisms at very high number of cycles (N>10⁷). Testing facilities are listed. A classification of materials with typical S‐N curves and influencing factors like notches, residual stresses and environment are given. Different failure mechanisms, which occur especially in the VHCF‐region like subsurface failure, are explained. There microstructural inhomogeneities and statistical conditions play an important role. Investigated materials are different metals with body‐centred cubic lattice like low‐ or high‐strength steels and quenched and tempered steels but also materials with a face‐centred cubic lattice like aluminium alloys and copper.     

Anwendung moderner Vakuum‐ und Plasmatechnologien in der Oberflächentechnik ‐ möglich oder notwendig?

Low pressure plasma technology uses the advantages of the combination of vacuum and plasma processes. Exist ing possibilities are shown by examples. The application of the high innova tive potential of the vacuum and plasma processes is necessary for solving the growing demands on the functionality of product surfaces in accordance with economy and enviroment compatibility.     

Transparentes leitfähiges TiO2:Nb – ein TCO‐Material der Zukunft?

Transparent conductive TiO₂:Nb – a TCO material of the future? Niobium doped titania is a widely unknown TCO material. We present the results of TiO₂:Nb thin films deposited by DC and pulse DC sputtering from a ceramic titania target with a content of approximately 6 wt.‐percent Nb in a pilot scale in‐line sputtering plant. With DC sputtering on Borofloat 33 substrate a 100 nm thin film show after annealing at 450 °C a resistivity of 7.2 × 10^?4 Ωcm with a low extinction coefficient of 0.02 and a transmittance in the visible range of 74.8%.     

微波加热催化反应低温制备β-SiC粉体

以硅粉和酚醛树脂为原料, 硝酸镍为催化剂前驱体, 采用微波加热催化反应法, 在流通氩气气氛中1150℃/0.5 h反应后合成了β-SiC粉体。研究了反应温度、催化剂用量和保温时间等对合成β-SiC的影响。采用XRD、SEM和TEM对产物的物相组成及显微结构进行了表征。结果表明: 微波加热条件下, 无催化剂存在时, β-SiC的完全合成温度为1250℃; 而添加1.0wt%的Ni作催化剂时, 1150℃/0.5 h反应后即可合成纯相的β-SiC。所合成的试样中都存在着颗粒状和晶须状两种SiC, 加入催化剂后会使试样中β-SiC晶须的长径比变大。密度泛函理论(DFT)计算结果表明, Ni-Si合金纳米颗粒的形成使Si原子之间的键长拉长, 弱化了Si原子之间的结合强度, 进而促进了Si粉在低温下的碳化反应。     

Don’t Trust your Simulation ‐Computational Materials Science on its Way to Maturity?

Progress reports are a new type of article in Advanced Engineering Materials, dealing with the hottest current topics, and providing readers with a critically selected overview of important progress in these fields. It is not intended that the articles be comprehensive, but rather insightful, selective, critical, opinionated, and even visionary. We have approached scientists we believe are at the very forefront of these fields to contribute the articles, which will appear on an annual basis. The article below describes the latest advances in Computational Materials Science.     

Obsolescence or opportunity? Patent & trademark librarians in the Internet age

The effect of the Internet databases offered by IBM and by the USPTO on a US patent and trademark library is described. For example, document delivery has declined significantly. Implementation of a substantial price reduction by the library for this service has arrested the decline. A charged trademark search service has been launched on the back of an increased number of statutory trademark applications in the USA, and is proving popular. Another activity, awareness of IP issues, has also been expanded, especially on their website.The author concludes that the net result of all these changes is hard to predict. However she foresees that the collating of statistics on the number of users, the nature of their research, and their affiliation, will increasingly be needed as the Internet Intellectual Property services further impinge on the work of traditional patent information providers.