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Showing papers by "DECHEMA published in 2008"


Journal ArticleDOI
TL;DR: In this article, an overview of the important properties and design characteristics of electrolyte used in thermally activated (thermal) batteries is given. But, the authors do not discuss the physical properties of the electrolytes used in thermal batteries.

217 citations


Journal ArticleDOI
TL;DR: An overview of the pyrite FeS 2 used as cathode material in thermally activated (thermal) batteries is given in this paper, where a large emphasis is placed on physicochemical properties and electrochemical performance.

148 citations


Journal ArticleDOI
TL;DR: Microparticle-enhanced cultivation was applied as a novel method for improved biomass and product formation during cultivation of filamentous microorganisms and showed a positive effect on growth characteristics of other filamentousmicroorganisms proven by the stimulation of single hyphae/cell formation.
Abstract: Microparticle-enhanced cultivation (MPEC) was applied as a novel method for improved biomass and product formation during cultivation of filamentous microorganisms. Exemplarily, chloroperoxidase (CPO) formation by Caldariomyces fumago was analyzed in the presence and absence of microparticles of different size. Particles of approximately 500 microm in diameter had no effect on growth morphology or productivity of CPO formation by C. fumago. In contrast particles of < or =42 microm in diameter led to the dispersion of the C. fumago mycelia up to the level of single hyphae. Under these conditions the maximum specific productivity of CPO formation was enhanced about fivefold and an accumulated CPO activity in the culture supernatant of more than 1,000 U mL(-1) was achieved after 10-12 days of cultivation. In addition, the novel cultivation method also showed a positive effect on growth characteristics of other filamentous microorganisms proven by the stimulation of single hyphae/cell formation.

127 citations


Journal ArticleDOI
TL;DR: In this paper, an overview of cathode materials used or envisaged in thermally activated (thermal) batteries is presented, and physicochemical properties and electrochemical performance of different cathode families (oxides, sulfides) are reviewed.

113 citations


Journal ArticleDOI
TL;DR: In this paper, the history of anode materials developed for use in thermally activated (thermal) batteries is presented, along with the chemistries (phases) and electrochemical characteristics (discharge mechanisms) of these materials.

97 citations


Journal ArticleDOI
TL;DR: In this paper, the suitability of extracellular polymeric substances (EPS) produced by bacteria for corrosion inhibition was investigated, and a system for simulation of microbially influenced corrosion (MIC) was established.

71 citations


Journal ArticleDOI
TL;DR: The physiological functioning of the heterologous cofactor regeneration system was illustrated by a sevenfold increased α-pinene oxide yield in the presence of glucose compared to glucose-free conditions.
Abstract: Escherichia coli BL21, expressing a quintuple mutant of P450BM-3, oxyfunctionalizes α-pinene in an NADPH-dependent reaction to α-pinene oxide, verbenol, and myrtenol. We optimized the whole-cell biocatalyst by integrating a recombinant intracellular NADPH regeneration system through co-expression of a glucose facilitator from Zymomonas mobilis for uptake of unphosphorylated glucose and a NADP+-dependent glucose dehydrogenase from Bacillus megaterium that oxidizes glucose to gluconolactone. The engineered strain showed a nine times higher initial α-pinene oxide formation rate corresponding to a sixfold higher yield of 20 mg g−1 cell dry weight after 1.5 h. The initial total product formation rate was 1,000 μmol h−1 μmol−1 P450 leading to a total of 32 mg oxidized products per gram cell of dry weight after 1.5 h. The physiological functioning of the heterologous cofactor regeneration system was illustrated by a sevenfold increased α-pinene oxide yield in the presence of glucose compared to glucose-free conditions.

63 citations


Journal ArticleDOI
TL;DR: In this paper, the top coat lifetime of thermal barrier coating (TBC) systems is described as being limited by both bond coat depletion of Al and mechanical failure of the topcoat.
Abstract: Bond coat oxidation as well as bond coat depletion of Al are still believed to be a major degradation mechanism with respect to the lifetime of thermal barrier coating (TBC) systems. In this study the top coat lifetime is described as being limited by both bond coat depletion of Al and mechanical failure of the top coat. The empirical results are introduced by considering three spallation cases, namely, Al depletion failure, thermal fatigue failure, and thermal aging failure. Al depletion failure occurs when the Al content within the bond coat reaches a critical value. In this paper bond coat depletion of Al is modeled by considering the diffusion of Al into both the thermally grown oxide (TGO) and substrate. The diffusion model results are compared to Al concentration profiles measured with an electron beam microprobe. These measured results are from oxidized air plasma sprayed TBC systems (APS-TBC) with vacuum plasma sprayed (VPS) bond coats for exposures up to 5000 h in the temperature range of 950-1100 °C. This paper focuses on the Al depletion failure and how it relates to top coat spallation.

59 citations



Journal ArticleDOI
TL;DR: In this article, the technical TiAl-alloy γ-MET (Ti 46.5Al-4(Cr, Nb, Ta, B)) was oxidised thermocyclically (24-h-cycle-test) at 900°C in wet and dry air.

42 citations


Journal ArticleDOI
TL;DR: Corynespora cassiicola DSM 62485 was identified as a novel highly stereoselective linalool transforming biocatalyst showing the highest productivity reported so far.
Abstract: The biotransformation of (±)-linalool was investigated by screening 19 fungi. Product accumulation was enhanced by substrate feeding and, for the first time, lilac aldehydes and lilac alcohols were identified as fungal biotransformation byproduct using SPME-GC-MS headspace analysis. Aspergillus niger DSM 821, Botrytis cinerea 5901/02, and B. cinerea 02/FBII/2.1 produced different isomers of lilac aldehyde and lilac alcohol from linalool via 8-hydroxylinalool as postulated intermediate. Linalool oxides and 8-hydroxylinalool were the major products of fungal (±)-linalool biotransformations. Furanoid trans-(2R,5R)- and cis-(2S,5R)-linalool oxide as well as pyranoid trans-(2R,5S)- and cis-(2S, 5S)-linalool oxide were identified as the main stereoisomers with (3S,6S)-6,7-epoxylinalool and (3R,6S)-6,7-epoxylinalool as postulated key intermediates of fungal (±)-linalool oxyfunctionalization, respectively. With a conversion yield close to 100% and a productivity of 120 mg/L·day linalool oxides, Corynespora cassii...

Reference EntryDOI
15 Mar 2008
TL;DR: In this article, the authors present a model for estimating the influence of heat and mass transfer on the effective reaction rate of an HZSM-5 Catalyst by modeling the effect of shape selectivity effects.
Abstract: The sections in this article are Introduction Mathematical Description Single Reactions (Conversion Problem) Pore Diffusion in an Isothermal Pellet Film and Pore Diffusion in an Isothermal Pellet Film and Pore Diffusion Together with Interphase Heat Transfer Film and Pore Diffusion Together with Interphase and Intraparticle Heat Transfer External Heat and Mass Transfer Use of Complex Rate Expressions Simple Reversible Reactions Simple Irreversible Reactions with Langmuir–Hinshelwood-Type Kinetics Simple Reversible Reactions with Langmuir–Hinshelwood-Type Kinetics Temperature Dependence and Reaction Order of Transport-Limited Reactions Intraparticle Diffusion Interphase Mass Transfer Diagnostic Criteria and Experimental Methods for Estimating the Influence of Heat and Mass Transfer on the Effective Reaction Rate Experimental Criteria Theoretical Criteria Experimental Methods for Estimating the Influence of Heat and Mass Transfer Effects Multiple Reactions (Selectivity Problem) Type I Selectivity Type II Selectivity Type III Selectivity Mathematical Description of the Diffusional Transport Fick's Law with Constant Effective Diffusivities Bulk Diffusion and Knudsen Diffusion Pressure-Driven Viscous Flow and Surface Diffusion Maxwell–Stefan Equations and Related Models Bulk Diffusion, Knudsen Diffusion and Pressure-Driven Viscous Flow Surface Diffusion Control of Selectivity in the Disproportionation of Ethylbenzene to Benzene and Diethylbenzenes on an HZSM-5 Catalyst by Utilizing Diffusion Effects Shape-Selective Catalysis Microkinetics Macrokinetics Modeling of Shape Selectivity Effects Simplifying Assumptions Model Equations Simulation Results Product Shape Selectivity (Unaffected by Other Factors) Product Shape Selectivity and Reactant Diffusion Limitation (Combined Effect) Product Shape Selectivity and Selective Adsorption (Combined Effect) Product Shape Selectivity and Restricted Transition State Shape Selectivity (Combined Effect) Controlled Modification of the Pore Structure Concluding Remarks Keywords: heat transfer; mass transfer; chemical reaction; reaction rate; mathematical solutions; transport effects; selectivity; macroscopic models; diffusional transport

Reference EntryDOI
15 Mar 2008
TL;DR: In this article, the authors discuss different types of Membrane Reactor Reactors with Hydrogen-Selective Membranes (HMSMs) and their role in the selective removal of oxygen from the air.
Abstract: The sections in this article are Introduction Types of Membrane Reactor Catalytic Reactors with Hydrogen-Selective Membranes Membrane Types Organic Polymers Solid Polymer Electrolytes Metals Microporous Membranes Ceramic Proton Conductors and Cermets Final Remarks Selective Removal of Hydrogen Dehydrogenation Hydrocarbons Alcohols Water Gas Shift Reaction Reforming Packed-Bed Membrane Reformers Fluidized-Bed Membrane Reformers Microstructured Membrane Reformers Techno-Economic Evaluation Selective Supply of Hydrogen Hydrogenation Hydroxylation by In-Situ H2O2 Formation Perspectives Reactors with Oxygen-Selective Membranes Membrane Types Mixed Oxygen-Ion- and Electron-Conducting Membranes Solid Electrolytes for Electrochemical Operation Membranes for Selective Removal of Oxygenates Pore Membranes for Non-Selective Oxygen Feeding Selective Supply of Oxygen Production of Pure Oxygen and of Oxygen-Enriched Air Partial Oxidation of Methane to Synthesis Gas Oxidative Dehydrogenation of Light Alkanes to Olefins Oxidative Coupling of Methane to C2-Hydrocarbons Solid Electrolyte Membrane Reactors Perspectives Catalytic Reactors with Non-Selective Membranes Distributed Feeding through Membranes Catalytic Membrane Contactors Gas–Liquid Applications Liquid–Liquid Applications Gas–Gas Applications Perspectives Design of Catalytic Membrane Modules Novel Inorganic Membrane Supports High-Temperature Membrane Reactor Design Concluding Remarks Keywords: membrane reactors; hydrogen-selective membranes; microporous membranes; dehydrogenation; water gas shift reaction; reforming; catalytic membrane modules

Journal ArticleDOI
TL;DR: In this article, the results of high temperature oxidation and creep tests will be presented and discussed The treatment with halogens improves the oxidation resistance of these alloys up to 1050°C A thin protective Al 2 O 3 -layer is formed after treatment with the halogens instead of the mixed TiO 2 /Al 2 O3 /TiN scale typically grown on these alloy alloys This alumina layer protects the component under isothermal and thermocyclic conditions.
Abstract: Intermetallic alloys based on TiAl are candidates for several structural high temperature applications but their oxidation resistance is limited to temperatures below 800°C In this paper the results of high temperature oxidation and creep tests will be presented and discussed The treatment with halogens improves the oxidation resistance of these alloys up to 1050°C A thin protective Al 2 O 3 -layer is formed after treatment with halogens instead of the mixed TiO 2 /Al 2 O 3 /TiN scale typically grown on these alloys This alumina layer protects the component under isothermal and thermocyclic conditions The protective effect is stable up to at least 8760 h Creep tests of halogen treated materials at high temperatures showed no effect on the creep behaviour Automotive turbocharger rotors were exposed at 1050 °C in air with and without fluorine-treatment for demonstration of real parts

Journal ArticleDOI
TL;DR: In this article, a theoretical assessment of the Al concentration range where a positive effect is expected is provided, where the authors aim to provide a theoretical analysis of the halogen effect on the surface of intermetallic TiAl base alloys.
Abstract: By applying a well defined amount of halogen to the surface of intermetallic TiAl base alloys, their high temperature oxidation resistance can be improved significantly. The socalled halogen effect consists in the preferential reaction of aluminium in the alloy with halogen, which gives rise to the formation of an almost pure alumina layer. The present study aims to provide a theoretical assessment of the Al concentration range where a positive effect is expected.

Journal ArticleDOI
TL;DR: In this article, the partial hydrogenation of 1,5-cyclooctadiene was performed in a pore-flow-through membrane reactor at 50°C and 1 MPa hydrogen pressure with single capillary membranes and a bundle of 27 capillaries for scale-up studies.
Abstract: The partial hydrogenation of 1,5-cyclooctadiene was performed in a pore-flow-through membrane reactor at 50°C and 1 MPa hydrogen pressure with single capillary membranes and a bundle of 27 capillaries for scale-up studies. A preparation method for the catalytically active membranes and their characterization are described. Compared to millimeter-sized spherical catalyst pellets in fixed-bed or slurry reactors, mass transfer limitations could be successfully reduced in the membrane reactor. The conversion rate of 1,5-cyclooctadiene in the membrane reactor was mainly affected by the Pd amount and the mass flow rate of the reaction mixture through the membrane. Under optimum conditions a selectivity of 95% for cyclooctene at complete conversion of 1,5-cyclooctadiene was obtained. This value corresponds to the selectivity obtained with a powder catalyst with a particle size of approx. 25 μm in a slurry reactor for which microkinetic control of the reaction is expected to result in the highest possible selectivity. © 2007 American Institute of Chemical Engineers AIChE J, 2008

Journal ArticleDOI
TL;DR: Inorganic nanoparticle-based coatings for magnesium alloys were developed and tested for their performance in corrosion protection as mentioned in this paper, and they were applied by dip or brush coating to form layers on AZ31 and AZ91.
Abstract: Inorganic nanoparticle based coatings for magnesium alloys were developed and tested for their performance in corrosion protection. Nanoparticles are characterised by a high sintering activity. This allows to obtain inorganic coatings by a sintering process at rather low temperatures which is suitable for magnesium alloys. Coating sols are based on silicon dioxide and sintering additives such as boron or sodium oxide. One technique is based on aqueous, commercial nanosols which can be applied by dip or brush coating to form layers on AZ31 and AZ91. Another technique is based on the electrophoretic deposition of silicon dioxide nanoparticles which also contain boron and phosphorus oxide. Crack free layers with a thickness of up to several micrometres could be obtained by a two step process including a bimodal particle distribution and polydiethoxysiloxane as adhesion promoter. The composition and surface structure of these novel coatings are characterised by modern analytical methods including SEM and atomic force microscopy and their applicability as protective coatings is investigated by using electrochemical impedance spectroscopy.

Journal ArticleDOI
TL;DR: In this article, the same authors showed that (Fe,Ni)Al and NiAl coatings on the austenitic steels and the Inconel 617 alloy were significantly corroded via intergranular and internal chloridation-sulphidation-oxidation.
Abstract: P91 ferritic-martensitic steel, 17Cr-13Ni and alloy 800 austenitic stainless steels and Inconel 617 alloy have been aluminised to form Fe 2 Al 5 , (Fe,Ni)Al and N1 2 A1 3 aluminide coatings. These alloys and their corresponding coatings were subjected to corrosion in air by 50:50 mol/mol K 2 SO 4 /KCl deposits at 650 °C for 300 h. With the exception of the Inconel 617 alloy, significant metal losses (>180 (Ji m) were recorded. These losses were planar for P91 alloy but involved internal corrosion for the two austenitic steels. The (Fe,Ni)Al and NiAl coatings on the austenitic steels and the Inconel 617 alloy were significantly corroded via intergranular and internal chloridation-sulphidation-oxidation. In contrast, the Fe 2 Al 5 coating on the P91 alloy coating was virtually unattacked. For the alloys, the relative extents of corrosion damage can be explained in terms of the stability and volatility of metal chlorides formed. For the coatings, STEM/EDS analyses enable clear linkages to be made between the presence and number of Cr-rich particles on coating grain boundaries and the corrosion damage observed for the coatings.

Journal ArticleDOI
TL;DR: In this article, the authors report on materials development work involving coated heat exchange alloys and the effect of welding of the coated alloys, simulating fabrication, on subsequent corrosion performance under laboratory conditions.
Abstract: In recent years there has been a steadily increasing focus on energy efficiency as a means to reduce the negative impact of human activity on climate, and in particular the effect that industrial emissions have on changes in the climate, specifically global warming. As far as power generation is concerned, emissions can be limited by maximizing energy efficiency while ensuring high levels of plant reliability. This paper reports on materials development work involving coated heat exchange alloys and the effect of welding of the coated alloys, simulating fabrication, on subsequent corrosion performance under laboratory conditions. Samples of the common boiler steels P91 (9% Cr) and HCM12A (12% Cr) were treated by chemical vapour deposition (CVD) in a pack cementation process to produce Al-rich coatings up to 100 μm thick. The samples were machined to give bevelled edges for welding. Welding was carried out using commonly available alloy 625 filler metal. It was found that sound weldments could readily be produced provided that care was taken to limit the heat input during the welding process. Excessive heat input could lead to cracking, but more importantly to dilution of Al in the coating adjacent to the weldment and in segregation of elements (Mo and Nb) in the weldment itself. Both dilution and segregation effects led to decreased corrosion resistance.

Journal ArticleDOI
TL;DR: Results indicate that fluctuating polarization at a rate of once per minute inhibits the physiological processes during biofilm formation during one week, and investigations are in process to determine further details of this effect.

Journal ArticleDOI
TL;DR: In this paper, a failure mechanism based on hydrogen embrittlement is supported by acoustic emission measurements, and it is shown that a few drops of distilled water leads to a significant increase in acoustic emission.

Journal ArticleDOI
TL;DR: In this article, a thermal conductivity detector was used to measure the residence time distribution of microstructures with gas flow with sufficient accuracy, and a relatively large dispersion within the microstructure was found, which could be the result of unequally distributed flow through the microreactor channels.

Journal ArticleDOI
TL;DR: In this paper, the influence of the ion fluence, implantation energy as well as alloy composition were investigated for alloys with Al contents between 40 and 50 at% and the conditions to get the halogen effect were assessed by thermodynamic calculations.
Abstract: F-implantation concentration profile simulations were carried out and the influence of the ion fluence, implantation energy as well as the alloy composition were investigated. For alloys with Al contents between 40 and 50 at% the conditions to get the halogen effect were assessed by thermodynamic calculations. According to the thermodynamic predictions the implantation parameters were kept constant in this composition range. The implanted alloys were exposed in laboratory air over 4000 h. With the implantation parameters used (20 keV and 1 x 10 17 F/cm 2 ), the halogen effect was found to be efficient over 4000 h. The oxide growth kinetic constants were measured and vary between 1.2 and 2.7 x 10 -13 g 2 / cm 4 /s.

Journal ArticleDOI
TL;DR: Unmodified AtCCD1 showed a 45% increased maximum rate in the Tween 20 system compared to Triton X-100 based reference system, emphasizing the importance of engineering the interface for the in vitro application of this enzyme family.
Abstract: The effect of various surfactants on both the solubilization of the carotenoid cleavage dioxygenase, AtCCD1, from cell lysates and the enzymatic activity in an aqueous micellar system was investigated. Solubilization with sodium cholate more than doubled the specific activity. Lag phases were observed when Tween surfactants were used for substrate delivery and were dependent on the surfactant and enzyme modification. In contrast to His6- and GST-tagged AtCCD1, unmodified AtCCD1 showed a 45% increased maximum rate in the Tween 20 system compared to Triton X-100 based reference system. The results emphasize the importance of engineering the interface for the in vitro application of this enzyme family.

Reference EntryDOI
15 Mar 2008
TL;DR: Shin-Etsu Group as mentioned in this paper is expanding production capacity at Shintech Inc. in the U.S. and strengthening business in the Netherlands while taking appropriate measures as a trilateral structure.
Abstract: With 60% of its material being salt and only 40% petroleum, PVC is a general-purpose resin that has many advantageous properties. It is easy to process and economical as well. Compared with other plastics, the manufacturing of PVC involves far less dependency on petroleum resources, and coupled with the progress of recycling, PVC makes major contributions to the environment from the standpoint of life cycle assessment. The superior properties of PVC have received high evaluations, marked by continuing growth in global demand of 5% annually. Demand for PVC is largely for applications in pipes and sidings in the U.S. and for pipes and window profiles in Europe and Asia. In particular, demand is growing strongly in China, mainly for construction materials and consumer goods. In addition, the use of PVC window profiles has started to spread in Japan recently. This is due to their superior insulating effects that help prevent condensation in winter and contribute to the reduction of global warming by cutting air conditioning costs in summer. In its PVC business, the Shin-Etsu Group is expanding production capacity at Shintech Inc. in the U.S. as global demand increases. Expansion construction at Shin-Etsu PVC B.V. in the Netherlands was completed in 2006, and business operations there have been expanding. The expansion of PVC production capacity in China has continued rapidly in recent years, causing concern about its effect on the global PVC market. The Shin-Etsu Group will continue as it has in the past, focusing on Shintech Inc. and strengthening business in the Netherlands while taking appropriate measures as a trilateral structure. Silicones Shin-Etsu provides more than 4,000 different silicone products for applications in broad areas such as the electric, electronics, automotive, construction, cosmetics, toiletries and chemical industries. Silicones combine organic and inorganic properties and can take different physical forms, including fluid, resin or rubber. Their numerous unique properties include electrical insulation, as well as heat, cold and weather resistance. In each market, we are striving to improve product functionality and to make production processes more efficient. Among the wide range of different applications for silicones, one that has been steadily growing in recent years is that of automotives, where high functionality is increasingly required and silicones are becoming an essential material in various applications such as electronics equipment, interior finishes, airbags and engine casings. Furthermore, in electrical and electronics uses, silicones serve application needs for an efficient heat transfer medium. In cosmetics applications, silicones have attracted a great deal of attention for their ability to help make products feel good on skin while giving them a better texture. The Shin-Etsu Group is aggressively going forward on a global basis with the expansion of production and sales of silicones in the regions where demand is growing. In addition to its production bases in Japan, the U.S., the Netherlands, Korea, Taiwan and China, the Shin-Etsu Group has been working to achieve stable operations at its integrated silicone monomer and polymer manufacturing facilities in Thailand. The Shin-Etsu Group will continue to develop new products and new applications of silicone while utilizing its features that are in demand in a wide range of fields. In addition, the Group will increase production capacity at plants in Japan, Thailand, the U.S. and other countries, and aims to expand overseas operations in tandem with those in Japan.

Book ChapterDOI
TL;DR: In this paper, defect free BEA type zeolite membranes with varying Si/Al ratio (18 to 33) were prepared on stainless-steel supports using a multiple in-situ crystallization technique.
Abstract: In this work defect free BEA type zeolite membranes with varying Si/Al ratio (18 to 33) were prepared on stainless-steel supports using a “multiple in-situ crystallization” technique. The quality of the membranes was evaluated using p-/o-xylene isomer separation, and 1,2,4-/1,3,5-trimethyl benzene isomer separation. A maximum p-xylene permeance of 1.5 × 10 −7 mol s−1 m−2 pa−1 and p-/o-xylene separation factor of 3.3 was obtained while in the trimethyl benzene separation experiments permeances were lower but the separation factor was comparatively higher (~ 4.8).

Journal ArticleDOI
Gerhard Kreysa1
TL;DR: In this paper, a new Konzept zur energetischen Nutzung des Methans entwickelt is proposed, in der vorliegenden Arbeit ein neues KonzePT zur energy-intensive Nutzkonzept is introduced.
Abstract: Trotz steigender Forderung sind die bekannten Vorrate fossiler Energierohstoffe in den letzten Jahrzehnten stetig gestiegen. Hinzu kommen hochstwahrscheinlich riesige Vorkommen von Methanhydrat. Fur deren energetische Nutzung bedarf es vor dem Hintergrund des Klimawandels neuer Wege. Ausgehend von einer Bewertung verschiedener Optionen des Umgangs mit dem Kohlenstoff-Kreislauf und thermodynamischen Uberlegungen zur Methanchemie wird in der vorliegenden Arbeit ein neues Konzept zur energetischen Nutzung des Methans entwickelt. Nach thermischer Methanspaltung wird nur der Energiegehalt des Wasserstoffs genutzt und der Kohlenstoff in ehemaligen Kohlelagerstatten sicher und ruckholbar gelagert. Die Argumente fur die Realisierung eines solchen Kohlenstoff-Moratoriums werden diskutiert.

Journal ArticleDOI
TL;DR: In this article, single and double fluorine beam line implantation was found to improve the high temperature oxidation resistance of this class of materials with Al-contents higher than 40 at%.
Abstract: In the present work the oxidation resistance of fluorine treated technical TiAl-alloys was investigated. Single and double fluorine beam line implantation was found to improve the high temperature oxidation resistance of this class of materials with Al-contents higher than 40 at.%. Calculated and measured fluorine depth profiles were compared. It was shown that the alloying elements do not modify significantly the fluorine profile and do not disturb the halogen effect. After single and double fluorine implantation and for different oxidation stages (isothermal/thermocyclic conditions) the maximum of the fluorine profile was measured by PIGE (Proton Induced Gamma Emission). The fluorine maximum was found to be located at the metal/oxide interface. The time dependence of the fluorine profile was determined as well. Double implantation led to a slower growing alumina layer. In this case a F-reservoir is obtained and improves the long term oxidation resistance of TiAl-based alloys.

Journal ArticleDOI
H.-E. Zschau1, Michael Schütze1
TL;DR: In this article, the long time behavior during isothermal and cyclic oxidation up to 1500 h/900 ˚C/air was investigated showing a slow fluorine decrease.
Abstract: Recently the target temperature of components manufactured from γ-TiAl alloys like turbine blades, turbocharger rotors or automotive valves has been increased to 900 °C. However, there is an insufficient oxidation resistance above 750 °C. One method used to improve the γ-TiAl oxidation behaviour is the so-called fluorine microalloying effect. After application of fluorine to the TiAl surface by ion implantation or treatment with diluted HF and oxidation at 900 °C in air a dense alumina layer is formed. However, after the treatments a distinct loss of fluorine was observed during heating and within the first hours of oxidation. In this work, the long time behaviour during isothermal and cyclic oxidation up to 1500 h/900 °C/air was investigated showing a slow fluorine decrease. The alumina layer acts as a diffusion barrier for fluorine, whereas fluorine diffuses into the metal. The diffusion coefficient was calculated. The results fit the theoretical model of the fluorine effect.

Journal ArticleDOI
TL;DR: The coefficients of thermal expansion (CTEs) of Ni−Al−Hf alloys have been investigated due to their potential as corrosion resistant coatings in aggressive environments at high temperature.
Abstract: The coefficients of thermal expansion (CTEs) of Ni–Al–Hf alloys have been investigated due to their potential as corrosion resistant coatings in aggressive environments at high temperature. The CTEs of (Ni0·5Al0·5)(1–x)Hfx alloys (x=0...0·2) were measured between 473 and 1073 K (200–800°C) and range between 8 and 15×10–6 K–1 depending on temperature and alloy composition. The temperature dependence of the CTE was found to be properly described by a simple expression: (19·982–0·24016X Hf)[0·15182+1·8287×10–3(T/K)–2·12378×10–6(T/K)2+8·87011×10–10(T/K)3]. It was shown that the CTE of (Ni0·5Al0·5)(1–x)Hfx alloys varies linearly with the amount of Hf in the alloy which allows the control of the CTE. Within the (Ni0·5Al0·5)(1–x)Hfx alloy composition range (x=0...0·2) it covers the CTE range of most of the austenitic and ferritic steels and the CTE of the coatings can be adjusted to those of the substrate to be protected without inducing additional strains at the coatings/substrate interface.