Showing papers by "DECHEMA published in 2009"

Oxidation Behaviour of TBC Systems on γ-TiAl Based Alloy Ti–45Al–8Nb

Abstract: The lifetime of thermal barrier coating (TBC) systems on gamma titanium aluminides was determined in the temperature range between 850 °C and 950 °C under cyclic oxidation conditions in air. Coupons of the alloy Ti–45Al–8Nb (at.%) were coated by pack aluminizing. A subset of samples was subsequently annealed at 910 °C for 312 h in argon. During this heat treatment, the two-phase (Nb,Ti)Al3 plus TiAl2 microstructure of the coating transformed into single phase γ-TiAl. On pre-oxidised aluminized, annealed and bare samples, TBCs of yttria partially stabilized zirconia were deposited using electron-beam physical vapour deposition (EB-PVD). No spallation of the TBCs was observed in cyclic oxidation tests at 850 °C for up to 3,000 cycles of 1 h dwell time at high temperature. The two-phase aluminide coating provided effective oxidation protection due to the formation of a continuous alumina scale. The lifetime of this TBC system exceeded 1,400 cycles at 950 °C, whereas an aluminized and annealed sample failed after approximately 500 cycles. The TBC on bare substrate failed when thermally cycled at 900 °C. In contrast, no spallation occurred with an aluminized and annealed specimen at this temperature during the maximum exposure length of 1,000 cycles, probably related to an increased aluminium concentration in the subsurface region. EB-PVD zirconia top coats were well adherent to the alumina scale and the thermally grown mixed oxides. Failure of the TBC systems observed with bare and annealed samples was associated with spalled oxide scales formed on γ-TiAl.

Metabolite profiling uncovers plasmid-induced cobalt limitation under methylotrophic growth conditions.

Abstract: Background The introduction and maintenance of plasmids in cells is often associated with a reduction of growth rate. The reason for this growth reduction is unclear in many cases. Methodology/Principal Findings We observed a surprisingly large reduction in growth rate of about 50% of Methylobacterium extorquens AM1 during methylotrophic growth in the presence of a plasmid, pCM80 expressing the tetA gene, relative to the wild-type. A less pronounced growth delay during growth under non-methylotrophic growth conditions was observed; this suggested an inhibition of one-carbon metabolism rather than a general growth inhibition or metabolic burden. Metabolome analyses revealed an increase in pool sizes of ethylmalonyl-CoA and methylmalonyl-CoA of more than 6- and 35-fold, respectively, relative to wild type, suggesting a strongly reduced conversion of these central intermediates, which are essential for glyoxylate regeneration in this model methylotroph. Similar results were found for M. extorquens AM1 pCM160 which confers kanamycin resistance. These intermediates of the ethylmalonyl-CoA pathway have in common their conversion by coenzyme B12-dependent mutases, which have cobalt as a central ligand. The one-carbon metabolism-related growth delay was restored by providing higher cobalt concentrations, by heterologous expression of isocitrate lyase as an alternative path for glyoxylate regeneration, or by identification and overproduction of proteins involved in cobalt import. Conclusions/Significance This study demonstrates that the introduction of the plasmids leads to an apparent inhibition of the cobalt-dependent enzymes of the ethylmalonyl-CoA pathway. Possible explanations are presented and point to a limited cobalt concentration in the cell as a consequence of the antibiotic stress.

SysBioMed report: Advancing systems biology for medical applications

Abstract: The following report selects and summarises some of the conclusions and recommendations generated throughout a series of workshops and discussions that have lead to the publication of the Science Policy Briefing (SPB) Nr. 35, published by the European Science Foundation. (Large parts of the present text are directly based on the ESF SPB. Detailed recommendations with regard to specific application areas are not given here but can be found in the SPB. Issues related to mathematical modelling, including training and the need for an infrastructure supporting modelling are discussed in greater detail in the present text.)The numerous reports and publications about the advances within the rapidly growing field of systems biology have led to a plethora of alternative definitions for key concepts. Here, with ‘mathematical modelling’ the authors refer to the modelling and simulation of subcellular, cellular and macro-scale phenomena, using primarily methods from dynamical systems theory. The aim of such models is encoding and testing hypotheses about mechanisms underlying the functioning of cells. Typical examples are models for molecular networks, where the behaviour of cells is expressed in terms of quantitative changes in the levels of transcripts and gene products. Bioinformatics provides essential complementary tools, including procedures for pattern recognition, machine learning, statistical modelling (testing for differences, searching for associations and correlations) and secondary data extracted from databases.Dynamical systems theory is the natural language to investigate complex biological systems demonstrating nonlinear spatio-temporal behaviour. However, the generation of experimental data suitable to parameterise, calibrate and validate such models is often time consuming and expensive or not even possible with the technology available today. In our report, we use the term ‘computational model’ when mathematical models are complemented with information generated from bioinformatics resources. Hence, ‘the model’ is, in reality, an integrated collection of data and models from various (possibly heterogeneous) sources. The present report focuses on a selection of topics, which were identified as appropriate case studies for medical systems biology, and adopts a particular perspective which the authors consider important. We strongly believe that mathematical modelling represents a natural language with which to integrate data at various levels and, in doing so, to provide insight into complex diseases: 1. Modelling necessitates the statement of explicit hypotheses, a process which often enhances comprehension of the biological system and can uncover critical points where understanding is lacking. 2. Simulations can reveal hidden patterns and/or counter-intuitive mechanisms in complex systems. 3. Theoretical thinking and mathematical modelling constitute powerful tools to integrate and make sense of the biological and clinical information being generated and, more importantly, to generate new hypotheses that can then be tested in the laboratory.Medical Systems Biology projects carried out recently across Europe have revealed a need for action: 4. While the need for mathematical modelling and interdisciplinary collaborations is becoming widely recognised in the biological sciences, with substantial implications for the training and research funding mechanisms within this area, the medical sciences have yet to follow this lead. 5. To achieve major breakthroughs in Medical Systems Biology, existing academic funding schemes for large-scale projects need to be reconsidered. 6. The hesitant stance of the pharmaceutical industry towards major investment in systems biology research has to be addressed. 7. Leading medical journals should be encouraged to promote mathematical modelling.

Guidance on Safety/Health for Process Intensification including MS Design; Part I: Reaction Hazards

Abstract: The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space-time yields, higher temperatures, and a confined reaction volume comprises new risks, such as runaway reactions, decomposition, and incomplete conversion of reactants. Simplified spreadsheet calculations enable an estimation of the expected temperature profiles, conversion rates, and consequences of potential malfunction based on the reaction kinetics. The analysis illustrates that the range of optimal reaction conditions is almost congruent with the danger of an uncontrolled reaction. The risk of a spontaneous reaction with hot spots can be presumed if strong exothermic reactions are carried out in micro-designed reactors. At worst, decomposition follows the runaway reaction with the release of noncondensable gases. Calculations prove that a microreactor is not at risk in terms of overpressure as long as at least one end of the reactor is not blocked.

Improved monoterpene biotransformation with Penicillium sp. by use of a closed gas loop bioreactor

Abstract: A closed gas loop bioprocess was developed to improve fungal biotransformation of monoterpenes. By circulating monoterpene-saturated process gas, the evaporative loss of the volatile precursor from the medium during the biotransformation was avoided. Penicillium solitum, isolated from kiwi, turned out to be highly tolerant towards monoterpenes and to convert alpha-pinene to a range of products including verbenone, a valuable aroma compound. The gas loop was mandatory to reproduce the production of 35 mg L(-1) verbenone obtained in shake flasks and also in the bioreactor. Penicillium digitatum DSM 62840 regioselectively converted (+)-limonene to the aroma compound alpha-terpineol, but shake flask cultures revealed a pronounced growth inhibition when initial concentrations exceeded 1.9 mM. In the bioreactor, toxic effects on P. digitatum during biotransformation were alleviated by starting a sequential feeding of non-toxic limonene portions after a preceding growth phase. Closing the precursor-saturated gas loop during the biotransformation allowed for an additional replenishment of limonene via the gas phase. The gas loop system led to a maximum alpha-terpineol concentration of 1,009 mg L(-1) and an average productivity of 8-9 mg L(-1) h(-1) which represents a doubling of the respective values previously reported. Furthermore, a molar conversion yield of up to 63% was achieved.

Progress in corrosion protection as a requirement for technical progress

Abstract: In many of the more recent technologies, corrosion plays a crucial role in determining their successful application. The present paper identifies such important corrosion issues in a number of technologies, which are currently under development or have been recently discussed. In this sense, CO2 sequestration, fuel cells, offshore wind energy and other offshore technologies, geothermalenergy,advancedcoalconversion technologies,nuclearenergy,light weight construction in transport, ionic liquids as well as medical technologies are discussed with respect to corrosion problems and existing research needs. In this way, this paper intends to show the complexity and the variety of corrosion topics of today and at the same time, point at the economic aspects and the impact on daily life. In the end, this leads to an introduction of the World Corrosion Organization and its study on future needs for research and development in materials degradation and corrosion control.

Thermogravimetric study of the dehydration reaction of LiCl·H2O

Abstract: The dehydration of LiCl·H2O was studied under inert helium atmosphere by DTA/TG for different heating rates. The dehydration of LiCl·H2O proceeds through a two step reaction between 99–110 and 160–186°C, respectively. It leads to the formation of LiCl·0.5H2O as intermediate compound. The proposed mechanism is: Open image in new window and Open image in new window Based on the temperature peak of the DTA signals the activation energies of the two reactions were determined to be 240 kJ mol−1 (step 1) and 137 kJ mol−1 (step 2), respectively.

Development of Corrosion Assessment Diagrams for High Temperature Chlorine Corrosion. Part I: State of the Art and Development of the Basis for a New Extended Approach

Abstract: As in many other areas of material science there is an increasing need for computational tools predicting materials behaviour, also in high temperature corrosion. In many cases stability diagrams have been developed for the assessment of high temperature corrosion resistance of metallic materials where the potentially formed corrosion products are plotted as fields of stability as a function of the activities or partial pressures of the species in the reaction environment. One major drawback of these diagrams is that they only contain solid or liquid phases as reaction products, but in halogen induced high temperature corrosion volatile metal halides are also formed. In order to overcome this drawback, the present paper deals with the development of a new type of diagram for high temperature halogen corrosion which will be developed and discussed for the example of oxygen/chlorine environments and which will be named “dynamic” quasi-stability diagram. In part I of the paper, the basis for this new approach to the corrosion resistance assessment of metals under chlorine environments is established using the present understanding described in the literature. A comparison is made between the concept of the conventional stability diagram and the recently developed “static” quasi-stability diagram, where in the latter case the evaporation of the gaseous metal chloride phases is taken into account through the use of a critical metal chloride partial pressure of 10−4 bar, as a criterion distinguishing critical and non-critical corrosion conditions. Concluding from the existing knowledge, the fundamentals for the new improved approach are developed in the form of a “dynamic” quasi-stability diagram. This new type of diagram is based not only on thermodynamic considerations (as for the diagrams existing so far) but also on the products and reactants flow through a gas boundary layer formed on the material surface. As a consequence, in this approach the criterion for corrosion resistance is given in terms of a metal recession rate for dynamic conditions as encountered in most industrial applications. In part II diagrams of the new type will be established for the most common alloying elements, i.e. Fe, Ni, Mo, Cr, Si and Al, and a comparison with experimental data will be performed.

Plasma‐Immersion‐Ion‐Implantation of Fluorine to Protect TiAl‐Components against High‐Temperature Oxidation

Abstract: Titanium aluminides are promising light weight materials for several high-temperature applications, e.g., in aero engines but due to their insufficient oxidation resistance at temperatures above roughly 800°C they cannot be used yet despite of their good mechanical high-temperature properties. The oxidation behavior of TiAl-alloys can be improved significantly by adding small amounts of fluorine into the subsurface zone of the components (microalloying). One possibility to apply fluorine to the surface of complex TiAl-components is the PI 3 -technique (plasma-immersion-ion-implantation). The use of an Ar/CH 2 F 2 -plasma for the F-PI 3 into small coupons led to a positive effect which was as good as the beamline implantation of elemental fluorine gas into samples of the same geometry. Turbine blades, as examples for real TiAl-components, were implanted with an optimum set of parameters. Post-exposure investigations like scanning electron microscopy revealed a thin protective alumina scale on the surface of the implanted samples in contrast to a thick mixed oxide scale (TiO 2 / A1 2 O 3 ) growing on untreated samples during high-temperature oxidation in air. The high-temperature oxidation resistance of several TiAl-alloys was improved by plasma-immersion-ion-implantation of fluorine. Small coupons showed a much lesser oxidation during high-temperature exposure after fluorine treatment than untreated samples. The performance of turbine blades for the low pressure compressor of a new generation of jet engines was also improved. Fluorine treated samples are covered with a thin, protective alumina scale after high-temperature exposure in air instead of a fast growing, nonprotective mixed oxide (TiP 2 /A1 2 O 3 ) scale which is found on untreated samples.

Climate protection by an alternative use of methane--the carbon moratorium.

Abstract: Despite a rising output, in the last few decades the known reserves of fossil energy resources have steadily increased. Additionally, there are in all likelihood tremendous reserves of methane hydrate. In view of the climate change, new means must be explored for its use as an energy source. Starting with an assessment of various options for dealing with the carbon cycle and thermodynamic considerations of methane chemistry, a new approach for the use of methane as energy source is developed in this Concept. After thermal methane cracking, only the energy content of the hydrogen is used and the carbon is stored safely and retrievably in disused coal beds. Arguments for the viability of a carbon moratorium of this kind are discussed.

Development of Corrosion Assessment Diagrams for High Temperature Chlorine Corrosion Part II: Development of “Dynamic” Quasi-stability Diagrams

Abstract: The corrosion of metals at high temperatures in halogen containing environments differs from most other types of high temperature corrosion in that in addition to solid and liquid corrosion products volatile phases are also formed. The latter are not covered by the usual thermodynamic stability diagrams, which are often used for prediction of the corrosion products formed, and indirectly on whether corrosion has to be regarded as critical or not. The present paper aims at including the situation where gas phase corrosion products determine the extent of corrosion and a new type of diagram is developed and discussed for the example of chlorine containing environments. Part I of this paper (Latreche et al. Oxid Met 2009) was dedicated to the establishment of the basis for a new extended approach to a corrosion risk assessment diagram called the “dynamic” quasi-stability diagram. The present part deals with the principles of the new type of diagram and the establishment of specific diagrams for the most common alloying elements, i.e. Fe, Ni, Mo, Cr, Si, Al. For the development of the specific diagrams, the calculation of gas viscosities and gas diffusion coefficients of all relevant volatile potential corrosion products was conducted, with methods specified in the paper. The new “dynamic” quasi-stability diagrams were then compared to experimental results from kinetics investigations of pure metals, which showed quite good agreement with the experimental observations. Furthermore, the diagrams were used to assess the behaviour of the metallic elements in alloys. Again, in this case good agreement between prediction and experimental results was observed if the specific role of the different elements in the corrosion behaviour of the alloys was taken into account.

Efficient SWCNT-Based Anode for DMFC Applications

Abstract: Carbon Vulcan XC72 is still considered as the standard catalyst support in gas diffusion electrodes for low temperature polymer fuel cell applications. Because of its relatively low specific area and poor corrosion resistance, alternative materials such as carbon nanotubes (CNTs) are currently the focus of numerous investigations. This work reports on the test of single-walled carbon nanotubes (SWCNTSs) as Pt and PtRu catalyst support in the direct methanol fuel cell (DMFC) anode. After the treatment of the CNTs in air at 300°C or in a high concentrated nitric acid solution, power densities of 152 and 157 mW cm -2 have been reached under DMFC conditions at 2 bar abs , and 80°C. The anodic and cathodic Pt loadings amounted to 1 mg cm -2 . The performance of the membrane electrode assembly (MEA) with a PtRu-SWCNT anode was about 10-15% higher than that of the MEA with a conventional as-prepared PtRu-Vulcan XC72 system. This was principally ascribed to higher catalyst utilization, lower impedance, and methanol crossover of the carbon-nanotube-based electrodes compared to those of the carbon-Vulcan-based one.

A new concept of oxidation protection of Ni-base alloys by using the halogen effect

Abstract: The Ni-base alloys with Al-contents of less than 10 wt% are widely used in high temperature technology due to their beneficial mechanical properties. However, their oxidation resistance may be insufficient at temperatures above 1000°C. Oxidation of these Ni-base alloys does not form a pure continuous Al2O3 protective scale on the surface, but rather a complex layer structure. This structure is characterized by inward growing oxides showing a discontinuous alumina scale. A new method for the formation of a dense protective alumina scale on the surface is now presented. The method is based on the halogen effect, which was successfully applied for TiAl-alloys. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. The fluorine treatment is performed by ion implantation. The implantation parameters are defined by using Monte Carlo simulations. Following these results fluorine implantations of the Ni-base alloy IN 738 are...

Automated system for spectrophotometric detection of liquid phase hydrogen peroxide for concentrations up to 5% w/w

Abstract: An automated flow injection analysis system for H2O2 detection in the liquid phase, based on the photometric determination of the complex between hydrogen peroxide and a titanium (IV) reagent is presented. The system was tested for monitoring the H2O2 concentration in a lab-scale experimental setup for H2O2 direct synthesis. In its final configuration, the developed system allows a reliable and reproducible determination of H2O2 for a broad concentration interval between 1.02×10−3 mol l−1 and 1.16 mol l−1.

CO2 – und was nun? Technische Optionen für den Umgang mit CO2

Abstract: Der durch anthropogene Emissionen von CO2 und anderen klimarelevanten Gasen verursachte Klimawandel ist Gegenstand einer intensiven offentlichen Debatte Die politischen Bemuhungen, den Klimawandel zu begrenzen, wurden intensiviert, doch bei allen Bemuhungen um die Reduzierung von CO2-Emissionen fuhren die diskutierten Szenarien zum Klimawandel zu einer Erhohung der globalen Durchschnittstemperatur Selbst fur das gunstigste Szenario werden +2 °C bis 2100 erwartet Das Europaische Parlament verabschiedete eine Resolution, die die Europaische Kommission auffordert, ein umfangreiches Masnahmenpaket vorzulegen mit dem Ziel, alle Moglichkeiten zur Gewahrleistung des +2 °C-Zieles auszuschopfen

Electrochemical behaviour of iron in a third-generation ionic liquid: cyclic voltammetry and micromachining investigations.

Abstract: The electrochemical behaviour of Fe in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim](+)Ntf2(-)) and mixtures with Cl(-) is studied with the aim of investigating the applicability of ionic liquids (IL) for the electrochemical machining of iron. Whereas in pure IL iron could not be significantly dissolved, the addition of Cl(-) enables the active dissolution with anodic current densities up to several mA cm(-2). Although several anodic peaks appear in the cyclic voltammograms (CV), the distinct assignment of those electrochemical processes remain difficult. In particular no proof for the formation of FeCl(x) (2-x) complexes during Fe dissolution are deduced from the CV, although such complexes are shown to be stable in the employed electrolyte. In addition, we present electrochemical drilling experiments with short potential pulses, which demonstrate that electrochemical machining of Fe is, in principle, possible in IL based electrolytes, even though hampered by slow machining speed.

The effect of moisture on the delayed spallation of thermal barrier coatings: VPS NiCoCrAlY bond coat+APS YSZ top coat

Abstract: A fundamental understanding of failure mechanisms for thermal barrier coatings (TBC) is important for accurate life-time prediction and hence of much interest for industry. Failure (i.e. spallation or cracking) of the TBC usually occurs immediately upon cooling the specimen. However, in some cases spallation of the TBC is observed with a delay of several hours or even days after cooling, when the specimen is at ambient temperature and exposed to laboratory air. Because laboratory air contains water vapour, one hypothesis is that water plays a role in delayed failure of TBCs. This hypothesis is strongly supported by experiments in which the application of liquid water to a pre-oxidized TBC leads to spontaneous spallation/delamination at room temperature. The aim of this work is to study the effect of moisture on TBC systems in more detail. A series of experiments including acoustic emission techniques for in situ detection of cracking within the specimen and nuclear reaction analysis to determine h...

The halogen effect for Ni-base alloys – A new method for increasing the oxidation protection at high temperatures

Abstract: A new method for oxidation protection of Ni-base alloys is presented. The method is based on the halogen effect. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. Ion implantation has been chosen for fluorine treatment. The implantation parameters are defined by using the T-DYN simulation software. Based on these results fluorine implantations of the Ni-base alloy IN 738 are performed to meet the required fluorine content near the surface. The fluorine depth profiles are analyzed by using the PIGE-technique. After oxidation at 1050 °C a dense protecting external alumina scale is formed on the surface.

Sustainable management of the global carbon cycle through geostorage of wood.

Abstract: Combustion of fossil energy sources has caused the carbon inventory of the atmosphere to increase by more than 200 Gt. It will be almost impossible to prevent it from growing by at least another 400 Gt in the present century. Theoretically, there exists only one single possibility to effect a decline of the resultant increase in atmospheric CO(2) concentration: the excess carbon has to be removed from the carbon cycle by transferring it into an environment in which it is safe from oxidation, just as is the case for the deposits of fossil fuels. Only natural photosynthesis offers the possibility of efficiently fixing carbon dioxide from the air and removing it from the carbon cycle through geostorage of the resulting biomass. The present paper shows, in the context of an initial feasibility study, that the use of forests and the geostorage of wood in an environment corresponding to lignite deposits represents the ecologically most sensible and economical variant of removal of carbon from the carbon cycle and, thereby, reclamation of the atmosphere.

Diffusion coatings for aggressive high temperature process environments

Abstract: Diffusion coatings can provide an excellent corrosion protection in aggressive high temperature environments due to the enrichment of thermodynamically stable oxide formers at the alloy surface. Besides conventional monoelement diffusion coatings (e.g. al diffusion), multielement coatings can be produced in a single process step. The production of al diffusion and Al–Si, Al–Ti and Al–Si–Ti codiffusion coatings on ferritic and austenitic steels and Ni base alloys, and their performance under high temperature chloridising, sulfidising and metal dusting environments are described.

Characterisation of the Oxide/Metal Interface of Fluorine Treated Titanium Aluminides

Abstract: Surface modifications with well defined amounts of fluorine have proven to improve significantly the oxidation resistance of titanium aluminides and to offer the potential to decrease the sensibility of TiAl-based alloys against environmental embrittlement. By means of combined EPMA and SEM analyses the formation of an oxide layer on fluorine treated specimens was characterised. The thicknesses of the external oxide layer as well as the oxygen and nitrogen-rich subsurface layer were measured. Their growth kinetics was found to follow a cubic and a parabolic law, respectively. By subtracting the mass variation due to the ingress of oxygen and nitrogen into 2-Ti3Al, underneath the alumina layer, this allowed calculating the true value of the kinetic constant for the growth of a pure alumina layer on titanium aluminides.