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.     

Vakuum‐ und Plasmagestützte Dünnschichttechnik – wohin geht die Reise?

Das Programm der V2011 – Industrieausstellung & Workshop‐Woche ?Vakuumbeschichtung und Plasmaoberflächentechnik”? liegt vor, vgl. S. 42 in diesem Heft. Das Programm ist nach Anwendungsgebieten gegliedert, eine gute Gelegenheit zu fragen, wo liegen auf diesen Gebieten die gegenwärtigen Schwerpunkte, welche davon sind möglicherweise zukunftsträchtig.     

Elektronenfeldemission mit Nanoemitter ohne Begrenzung und Restgas‐Ionisation?

Electron field emission from nano‐emitter without limitation and residual‐gas ionisation? The article is dealing with hyper giant conductivity at room temperature, as published in this journal. The novel material property was explained with a field‐emission measurement of a nano‐emitter. The apparently measured current density of 1.8 GA/cm² has been transferred to the emitter material. But the current density of electron field emission is limited in the range of kA/cm² (FN theory), and so other emission mechanism will be analysed, too. Especially the triplepoint (metal‐insulator‐vacuum) is an excellent field emitter and active over the entire length of cathode edge. Secondary electron emission is increased by the increasing of residualgas ionization and transition to gas discharge will be accelerated. Also, it must be considered that nanorods have a material‐independent quantum resistance in relation to h/e ². There are enough criteria for a metrological and scientifically reviewing.     

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%.     

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.     

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.     

Arteriovenous fistula: end‐to‐end or end‐to side anastomosis?

The purpose of the present study was to compare the end‐to‐end (ETEa) with the end‐to‐side (ETSa) anastomosis in patients starting hemodialysis by means of radio‐cephalic artero‐venous fistulae (AVF). In our experience, we compared the results, as early failure (EF), late thrombosis (LT), stenosis, steal syndrome, and primary patency (PP), in 2 groups of hemodialysis incident patients that had been placed an AVF by means of ETEa or ETSa. The observation period lasted 24 months for each of the 2 types of AVF, starting from October 2005 to September 2007 for ETEa and from October 2007 to September 2009 for ETSa. One hundred forty patients were included in the present study. We have consecutively performed 99 AVF interventions at the wrist or at the third distal of the forearm, in 70 patients by means of ETEa and 82 AVF interventions in the same anatomical places in 70 patients by means of ETSa. The patients with ETEa had a mean age of 64.4 ± 14.6 years, males were 65.8% and the age dialysis at the end of observation was 10.4 ± 5.7 months. Those with ETSa had a mean age of 65.9 ± 15.5 years and the males were 62.9%, the age dialysis at the end of observation was 9.2 ± 5.5 months. The surgical team was composed by the same nephrologists. The statistical study was performed by means of the χ chi‐square and Fisher's exact test. We have observed more late thrombosis (10% vs. 4.1%) and stenosis (21.4% vs. 2.7%) in ETEa than in ETSa. The number of early thrombosis was similar in the 2 types of anastomosis. The primary patency 1‐year rate was better though not significantly in the ETS (80% vs. 85.7%) In our experience the ETSa provides, overall better results, both regarding the complications and primary survival than ETEa. For the benefits that seem to come from it, we believe, that a broad ETSa in the distal native AVF is preferable to the ETEa.     

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.     

MOF‐Based Metal‐Doping‐Induced Synthesis of Hierarchical Porous Cu?N/C Oxygen Reduction Electrocatalysts for Zn–Air Batteries

A transition‐metal–nitrogen/carbon (TM–N/C, TM = Fe, Co, Ni, etc.) system is a popular, nonprecious‐metal oxygen reduction reaction (ORR) electrocatalyst for fuel cell and metal–air battery applications. However, there remains a lack of comprehensive understanding about the ORR electrocatalytic mechanism on these catalysts, especially the roles of different forms of metal species on electrocatalytic performance. Here, a novel Cu? N/C ORR electrocatalyst with a hybrid Cu coordination site is successfully fabricated with a simple but efficient metal–organic‐framework‐based, metal‐doping‐induced synthesis strategy. By directly pyrolyzing Cu‐doped zeolitic‐imidazolate‐framework‐8 polyhedrons, the obtained Cu? N/C catalyst can achieve a high specific surface area of 1182 m² g^?1 with a refined hierarchical porous structure and a high surface N content of 11.05 at%. Moreover, regulating the Cu loading can efficiently tune the states of Cu(II) and Cu⁰, resulting in the successful construction of a highly active hybrid coordination site of N? Cu(II)? Cu⁰ in derived Cu? N/C catalysts. As a result, the optimized 25% Cu? N/C catalyst possesses a high ORR activity and stability in 0.1 m KOH solution, as well as excellent performance and stability in a Zn–air battery.