EPX ‐ die Ein‐Pumpen‐Lösung

A single dry pump mechanism capable of reaching high vacuum and itself exhausting to atmospheric pressure is considered as a ’?vacuum technology panacea’. The development and deployment of a single‐shaft, high‐speed EPX dry pump has gone some considerable way to achieving this goal. This article describes the stages in its development history and applications.     

Selbsttrocknende Membran‐ Vakuumpumpen für feuchte Gase

Diaphragm vacuum pumps have proved their superiority as dry‐running systems over other types of vacuum pumps in many applications, and in particular in the medical, analysis, and process engineering sectors, as well as in the chemical industry. These pumps deliver the media without any contamination of content, have a high gas tightness, and can be designed as chemically resistant with regard to those parts which come in contact with the media. Although they are in principle relatively insensitive towards condensates which may be formed or conveyed with the media, liquids in the vapor or gas flow may be the cause for the prolongation of a vacuum process, which can be considerable and is certainly undesirable. This applies in particular to applications involving multi‐user vacuum systems in chemical laboratories, which under certain circumstances may contain very substantial volumes of condensates, and to the use of pumps in steam sterilizers (autoclaves) and vacuum drying cabinets. These examples of applications will be considered in greater detail hereinafter. The condensates which occur in the pump head of a diaphragm vacuum pump cause interference in that — due to re‐evaporation during the suction cycle — they incur a substantial reduction in the usable suction capacity of the pump. This problem can be resolved by means of a drying system for diaphragm vac uum pump heads. The drying system makes use in this case of the pressure differential which pertains between the pump chamber and the atmosphere outside the pump. The function of the drying system can be described as follows: A solenoid valve vents the pump head in a cyclic manner, with the result that liquid in the pump head will be blown out, while the process vacuum in the process engineering system will continue to be maintained. Diaphragm vacuum pumps equipped with this drying system have provided excellent results, for example in the chem ical laboratory, both in individual diaphragm vacuum pumps as well as in multi‐user vacuum systems. Extremely good experience has also been gained in the evacuation of sterilizer autoclaves and vacuum drying cabinets with the use of diaphragm vacuum pumps fitted with the drying system. When using the drying system on steam sterilizer autoclaves, another favorable effect is also encountered: The vapor fraction in the pumping medium is cooled in the diaphragm pump head to below the evaporation or boiling temperature, with the result that the vapour condenses. This reduces its volume to a fraction of the initial value, which is the equivalent of an additional suction capacity, in the same manner as with a condenser. The condensate which occurs with this process is blown out of the pump heads by the drying system, and, as a result, can no longer cause interference due to re‐evaporation.     

Vacuum effects on fatigue crack growth in submicrometre‐thick freestanding copper films

To clarify vacuum effects on fatigue crack growth in freestanding metallic thin films, experiments were conducted on approximately 500‐nm‐thick copper films inside a field emission scanning electron microscope. Fatigue crack growth accompanied by intrusion/extrusion formation occurred in vacuum, and da/dN was smaller than in air in the middle‐ΔK region (ΔK ≈ 1.7‐3.1 MPam^1/2). Conversely, in the low‐ΔK region (ΔK ? 1.7 MPam^1/2), da/dN was larger in vacuum than in air. Further, fatigue crack growth in vacuum occurred below the fatigue threshold in air (ΔK_th,air). A nonpropagating crack after reaching ΔK_th,air continued to propagate in vacuum when the environment changed from air to vacuum. This indicates that fatigue crack growth resistance is smaller in vacuum than in air under the same effective driving force. The fatigue damage area near the crack paths in vacuum in the low‐ΔK region became wider, suggesting that the nucleation of fatigue damage was enhanced in vacuum.     

Reinigung von Vakuumbauteilen für UHV‐ und UCV‐Anwendungen

Cleaning of vacuum components for UHV and UCV applications Ultra‐clean vacuum components and assemblies are fundamental to some cutting edge high‐tech sectors like semiconductor industry, particle accelerators, and surface analytics. Exceptionally critical for these applications are particles that stick at the vacuum facing surfaces as well as desorption of water and hydrocarbons from the surfaces into the system, because this may interfere with the sensitive ultra‐high vacuum (UHV) and ultra‐clean vacuum (UCV) processes. In this contribution, some established cleaning methods and surface treatments are discussed with respect to their effect on reducing particle contamination and outgassing of water and organic compounds from stainless steel surfaces. It is clarified that the resulting cleanliness severely depends on the detailed steps during the surface treatment and subsequent cleaning. As a consequence, the discussed methods should be chosen and adapted with great care according to the specific demands of the final application area.     

New Turbomolecular Pump with Central Opening for Free Axial Access. Eine neue Turbomolekularpumpe mit zentraler Öffnung für freien axialen Zugang

Standard turbomolecular pumps show typically one annular active intake area on the high vacuum flange side (single‐flow pumps). The central circular part of the inlet of the compressor turbine is blind for pumping. The new design proposes a central opening of a turbomolecular pump all along the axis. This central bore can be used e.g. for mounting of feed throughs, manipulators, windows or for coupling to further vacuum devices, in particular also for enclosing tube‐like vacuum systems. This design allows a multi‐use of a pumping port at a vacuum vessel without reducing there the pumping speed. Moreover, the new design is ideal for axial or radial differential pumping arrangements as e.g. needed for all gas jet like set‐ups or other pressure reduction stages.     

Entwicklung eines Ionisationsmanometers mit Feldemitterkathode

Development of an ion gauge with field emissionin cryogenic vacuum environments cathode for pressure measurements The measurement of UHV or even XHV pressures in low‐temperature vacuum systems has always been considered as a metrological problem. In principle, conventional hot‐cathode ion gauges can be used for pressure measurement in cryogenic vacuum environments. However, as a consequence of their high heat generation several disadvantages must be taken into account. With the development of an ion gauge of extractor‐type whose heat‐generating thermionic cathode is replaced by a non‐thermal field emission cathode, a promising approach to realize a reliable pressure gauge for cryogenic vacuum applications can be presented in this paper. The gauge equipped with a CNT cathode was investigated both experimentally and by numerical simulations in terms of their operating characteristics. It has been successfully demonstrated that the modified extractor gauge works reliably under low temperature conditions and provides meaningful pressure readings.     

Fatigue as a process of cyclic brittle microfracture

While fatigue crack growth in vacuum may occur by slip alone, environmental fatigue including crack growth in air is strongly influenced by crack‐tip surface chemistry that adversely affects ductility. Cumulative diffusion, combined with adsorption and chemisorption in the loading half‐cycle may promote instantaneous crack extension by brittle microfracture (BMF). Unlike slip, the BMF component will be sensitive to parameters that affect near‐tip stresses, such as load history and constraint. BMF dominates near‐threshold environmental fatigue. Being a surface phenomenon, it loses its significance with increasing growth rate, as slip‐driven crack extension gains momentum and growth becomes less sensitive to environment. The BMF model provides for the first time, a scientific rationale for the residual stress effect as well as the related connection between stress–strain hysteresis and load‐sequence sensitivity of metal fatigue including notch response. Experimental evidence obtained on a variety of materials under different loading conditions in air and vacuum appears to support the proposed model and its implications.     

Herstellung funktionaler organischer Dünnschichten durch Vakuumverdampfung

Depositing of functional organic thin films by vacuum evaporation Material evaporation under high or ultra‐high vacuum conditions has been a well known method of thin film coating since nearly a hundred years. Since discovery of semiconducting organics in the 1970s and 1980s, this technology has been increasingly applied to deposit organic molecular compounds. At the moment especially materials for organic LEDs (OLEDs) and for thin‐film solar cells are in the focus of interest. While organics evaporation makes use of advantages of high‐vacuum coating (purity, compatible processing, masking etc.) there are also dedicated demands on process control coming up. The article describes basic requirements, capabilities of present temperature‐controlled evaporation sources, material‐related features, as well as typical applications.     

Numerical simulation of permeation through vacuum‐coated laminate films

The material usage in the packaging market of Germany has decreased over the last few years. This trend results from the substitution of heavy packages with light‐weight, flexible materials. In this context, aluminium foil‐based multilayer films have been partly replaced by metallized laminates in food packaging technology. Other coating materials, such as Al₂O₃ or SiO_x, are used where transparent films are desired. The disadvantage of these vacuum‐coated layers is the existence of pinholes which allow diffusion processes, in contrast to aluminium foil‐based multilayer films. In this study the barrier behaviour of vacuum coated laminate films was predicted by numerical simulation. The results are presented in terms of dimensionless parameters so that they may be transferred to analogous problems. This model provides a method to calculate the oxygen permeation through coated laminates. However, it is invalid for condensable gases such as water vapour. The simulation is suited for characterizing the influence of the compound structure on the barrier properties of vacuum coated laminate films. The results are verified by comparing the calculated with measured values. Copyright © 2002 John Wiley & Sons, Ltd.     

Stabile Vakuumprozesse mit Dreh‐/Schiebedurchführungen

Stable vacuum processes despite rotary/sliding feedthroughs – Effects of motion speed and direction using the MeTraVac system as an example Components for ultra‐high (p < 1 · 10^?7 mbar) and extreme high vacuum (p < 1 · 10^?11mbar) conditions must have very clean surfaces with low outgassing rates. The determination of outgassing characteristics for static components is common practice. However, it is unusual to investigate the influence of the outgassing rates of dynamic components when they move in a vacuum. Various experiments with a self‐designed and built rotary/sliding feed‐through were carried out. The aim of these investigations was to monitor the pressure increases during movements and thereby draw conclusions on the quality of the vacuum conditions. One rotary and two translational movement types were selected exemplarily for practical vacuum applications. Each experiment was performed in an unconditioned and conditioned (in‐situ bake‐out) state. For the experiments a heatable test setup was assembled. The rotary motion does not affect the process vacuum perceivable. Two translational movements were carried out, which differed in the speed. The pressure increases during slower and faster translatory movements show that the speed of movement has no significant influence on the vacuum. Nevertheless, a significant change in pressure was observed with translational movements. By bake‐out, the amount of water released per movement will significantly be reduced. Most kind of vacuum‐sided movements do not affect the process pressure at all or only to a small extent.     

Vakuummikro‐ und Vakuumnanoelektronik mit Feldemission

Vacuum microelectronics and nanoelectronics with field emission — features of breakdown voltage in vacuum gaps lower than 10 μm Further miniaturization in vacuum electronics will be possible only with field‐emitter cathodes. However in microscale vacuum gaps in the range 10 μm field emission is a dominant process in gas breakdown process, leading to signif icant deviations from the traditional Paschen's Law. At first a significant reduction of breakdown voltage is observed. The high surface‐to‐volume ratio in microscale dimensions 3 μm and in interactions with gas desorption, outgassing and gas ionization during electron field‐emission give a ignition and stabilization of micro plasmas (glow discharges) or/and micro arcs, which exist largely independent of surrounding vacuum, atmospheric or over pressure. In this range the Paschen's Law is invalid. This is an interesting approach which opens up new dimensions for basic research, field emission‐driven micro plasmas and for novel fieldemitter applications in vacuum electronics and plasma technology.     

Moderne Vakuumelektronik

Modern Vacuum Electronics — between nostalgia and high technology Vacuum electronics is about 140 years old. The operation of vacuum electronic components and devices is based on the motion of electrons or ions in vacuum and diluted gases under the influence of electric, magnetic and electromagnetic fields. The classical radio tube has a nostalgic application in tube amplifiers for music enthusiasts. But presently, research activities are concentrated on absolutely necessary special tubes, especially travelling wave tubes, gyrotrons, klystrons, X‐ray tubes and vacuum pressure measurement gauges. The use of novel fied‐emitter cathodes also enables miniaturization and new applications in modern vacuum electronics. The ITG‐Fachausschuss 8.6 is a competent contact partner for vacuum‐electronic problems. Every two years this committee organizes a workshop in Bad Honnef, Germany.     

Gefilterte Bogenbeschichtung – alte Probleme und neue Lösungen

Currently, the vacuum arc deposition (VAD) technique is well established in industry, primarily to deposit wear protective hard coatings such as metal nitrides and carbides onto tools and components. From the beginning of the industrial development of the vacuum arc deposition, it was obvious that the emission of macroparticles or droplets is a fundamental drawback of this coating technology. The emission is caused by the highly dynamic process of plasma generation and limits the fields of application significantly. Different methods have been proposed to minimize the macroparticle flux to the substrate surface. But the only way to hinder droplets from reaching the substrate reliable is to separate the plasma from particles by using curved magnetic fields. This filtered arc technique has proven its superiority of depositing high quality films compared to conventional arc applications in numerous laboratory tests. Current demands have stimulated new developments at the Fraunhofer IWS of more compact and higher productive filtered arc sources. One important application of ultra thin protective films is the topcoat on hard disks. In order to increase the storage density, the head‐to‐media spacing as well as the thickness of the overcoat has been reduced continuously. Until now, the thickness of the sputtered films was reduced to about 4 nm. The limit for this technology seems to be achieved. Filtered arc deposition is one of the most promising candidates for the deposition of thinner films – down to 1.3 nm with an even improved mechanical and chemical resistance. Another application area is the manufacturing of metallic lines and interconnections with high aspect ratios in the deep sub‐micron region in microelectronics. The excellent properties of this new filtered source for the deposition of conducting lines in microelectronics were been demonstrated. Actually, the technology for the subsequent deposition of barrier films and conducting wires is under development. Besides the micro technologies, there are a lot of applications requiring higher quality but not (yet) such a perfect film surface. Therefore, using a quite simple filter design – the so‐called Venetian blind filter – a filter unit was developed which can be used at the common industrial vacuum arc deposition machines. The filter does not reduce the deposition area, so the standard deposition processes can be used furthermore. With this filter, the number of droplets can reduced dramatically. A plasma transmission through the filter of approximately 20 % could be measured. Such filter module was realized and is in use now.     

Colloidally Stable Monolayer Nanosheets with Colorimetric Responses

Despite the discovery of chromogenic‐layered materials for decades of years, fabrication of colloidally stable monolayer organic 2D nanosheets in aqueous media with colorimetric responses is still challenging. Herein reported is the first solution synthesis of chromic monolayer nanosheets via the topochemical polymerization of self‐assembled amphiphilic diacetylenes in aqueous media. The polydiacetylene (PDA) nanosheets are ≈3–4 nm thick in solution and only ≈1.9 nm thick in the dried state, while the lateral size can reach several micrometers. Moreover, the aqueous stability endows PDA nanosheets with excellent processability, which can further assemble into films via vacuum filtration or act as an ink for high‐resolution inkjet printing. The filtrated films and printed patterns exhibit fully reversible blue‐to‐red thermochromism, and the film also displays an interesting reversible colorimetric transition in response to near‐infrared light, which is not reported for other PDA‐only systems. The present colloidal PDA nanosheets should represent a new kind of chromic organic 2D nanomaterials that may be applied as novel building blocks for developing intelligent hybrid materials and may also find diverse sensing, display and/or anticounterfeiting applications.     

Vakuummessung im Wandel der Zeit

Vacuum Measurement over the Course of Time — From Torricelli to bakeable digital wide‐range sensors for measurement from 10³ to 10^‐12 mbar Since the first vacuum measurement in the middle of the 17th century, various methods have been developed to measure total vacuum pressures. After establishing the kinetic theory of gases in the late 19th century, the development of different indirect measurement methods started. Hereby, the lower detection limit — located in the fine vacuum range for direct methods such as mercury tubes — has been continuously shifted down to the ultrahigh vacuum range. The combination of different measuring principles in wide‐range sensors soon allowed the measurement over extended pressure ranges — with just one device. Latest developments have yielded to the creation of a new generation of vacuum measurement: passive bakeable wide‐range sensors. Consisting of optimized ionization‐sensors and a novel integration of a digital Pirani principle, they are the first vacuum sensors for precise total pressure measurement over 15 decades — from atmosphere down to the ultra‐high vacuum (10⁺³ to 10^‐12 mbar).     

Finite Elemente Methode (FEM) Analyse in der Vakuummechanik

Finite element method analysis in vacuum mechanics In engineering sciences the finite element method (FEM) is widely accepted as standard for the simulation of solid body characteristics. Modern FEM‐Software, used with a CAD‐system, enables the optimization of mechanical systems in an early development stage. Vacuum‐mechanic engineers can use FEM to adapt vacuum vessels on specific mechanical and thermal requirements. The use of aluminum alloys for vacuum components, especially vessels for UHV / XHV, needs to consider the mechanical properties of aluminum. FEM is an easy to use method to enable this, regarding safety and low cost aspects. In the context of the new development and advancement of vacuum‐flange‐systems, FEM can be conducive to gain important insight to their functionality. Assembly parameters and operating conditions can be derived with such investigations. The following article describes the basic principles of an FEM‐analysis and presents the respective procedure using examples of vacuum mechanics.     

Optische Schnittstellen

Optical interfaces: Viewing into the vacuum The requirements concerning in‐vacuum process diagnostics are more and more challenging. On the one hand, the setup itself has to be decoupled from the process to avoid any external impact on the process. On the other hand, the process parameters have to be in‐situ characterized and controlled by an in‐vacuum monitoring system. In the vicinity of these two contradictive requirements optical fiber applications gain more and more impact, since optical fibers cover several advantages: high transmission signal, inherent immunity against external electromagnetic forces, high durability and high mechanical as well as optical flexibility. The focus of the contribution is a new in‐vacuum optical temperature sensor combined with high‐temperature fiber optical feedthroughs. The sensor based on fiber Bragg gratings (FBG) in the optical fiber, which are extremely sensitive to temperature variations. In a first case study, the application of FBG with the feedthrough as an in‐vacuum optical temperature sensor is demonstrated. Thus an optical fiber containing a bunch of several FBG becomes a compact, robust, and flexible in‐vacuum network of local temperature sensors. Each individual sensor captures temperature variations over a signal path that is several km long with a remarkable accuracy up to 0.1 K and with speed of light.     

The stress relaxation of thermoplastic elastomer–the influence of oxygen on the network structure of SBS during γ‐radiation

Abstract

Thermoplastic elastomer (TPR) of the SBS type was irradiated in a vacuum and in air with various gamma dosages of Co‐60 at room temperature, and the stress relaxation behavior of the irradiated TPR was studied in air and in a nitrogen atmosphere. It was found that TPR was crosslinking during irradiation both in air and in a vacuum, and the crosslinking density of TPR irradiated in air was found to be higher than that irradiated in a vacuum. This result may be attributed to the presence of oxygen which could participate in the radiation‐induced reaction.

A TPR sample irradiated in a vacuum showed very extensive physical stress relaxation and minor chemical stress relaxation, measured both in air and in nitrogen. The latter could be caused by oxidative chain scission along the main chain. However, the chemical stress relaxation of TPR irradiated in air was found to be different from that irradiated in vacuum. In addition to the oxidative chemical stress relaxation, the former was further caused by the scission of crosslinking site which was formed during Co‐60 irradiation.     

CXS chemical dry vacuum pump brings smart vacuum to the process industry

The chemical sector as a whole has been quick to recognise the clear advantages of dry vacuum pumps over traditional wet technologies, and dry vacuum pumps are now well established around the world as an efficient, reliable option. A new trend is now emerging: for vacuum to be seen as a ‘utility’. In response, dry vacuum technology is being developed by manufacturers to be available on demand in a ‘plug and pump’ system that requires minimum set‐up and maintenance. The most advanced chemical dry vacuum pumps, such as the new CXS pump from Edwards, deliver exceptional energy efficiency and performance, are cost‐effective to run, and are environmentally sound.     

Hydrophobic nanocellulose aerogels as floating, sustainable, reusable, and recyclable oil absorbents

Highly porous nanocellulose aerogels can be prepared by vacuum freeze-drying from microfibrillated cellulose hydrogels. Here we show that by functionalizing the native cellulose nanofibrils of the aerogel with a hydrophobic but oleophilic coating, such as titanium dioxide, a selectively oil-absorbing material capable of floating on water is achieved. Because of the low density and the ability to absorb nonpolar liquids and oils up to nearly all of its initial volume, the surface modified aerogels allow to collect organic contaminants from the water surface. The materials can be reused after washing, recycled, or incinerated with the absorbed oil. The cellulose is renewable and titanium dioxide is not environmentally hazardous, thus promoting potential in environmental applications.