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Showing papers by "DECHEMA published in 2012"


Journal ArticleDOI
TL;DR: This work critically reviews the current state-of-art of immobilized redox mediators for electrochemical NAD(P)+ regeneration and various surface modification techniques, such as adsorption polymerization and covalent linkage, as well as the corresponding NAD( P)+ regeneration rates and the operational stability of the immobilized mediator films are discussed.
Abstract: The applicability of dissolved redox mediators for NAD(P)+ regeneration has been demonstrated several times. Nevertheless, the use of mediators in solutions for sensor applications is not a very convenient strategy since the analysis is not reagentless and long stabilization times occur. The most important drawbacks of dissolved mediators in biocatalytic applications are interferences during product purification, limited reusability of the mediators, and their cost-intensive elimination from wastewater. Therefore, the use of immobilized mediators has both economic and ecological advantages. This work critically reviews the current stateof-art of immobilized redox mediators for electrochemical NAD(P)+ regeneration. Various surface modification techniques, such as adsorption polymerization and covalent linkage, as well as the corresponding NAD(P)+ regeneration rates and the operational stability of the immobilized mediator films, will be discussed. By comparison with other existing regeneration systems, the technical potential and future perspectives of biocatalytic redox reactions based on electrochemically fed immobilized mediators will be assessed.

74 citations


Journal ArticleDOI
TL;DR: Alcohol dehydrogenases can be used to oxidize aldehydes, and this reaction can occur with high selectivity in the presence of a suitable cofactor regeneration system.
Abstract: Teaching old dogs new tricks: Alcohol dehydrogenases (ADHs) may be established redox biocatalysts but they still are good for a few surprises. ADHs can be used to oxidize aldehydes, and this was demonstrated by the oxidative dynamic kinetic resolution of profens. In the presence of a suitable cofactor regeneration system, this reaction can occur with high selectivity.

68 citations


Journal ArticleDOI
TL;DR: Carboxylate-based ionic liquids were identified as the most promising lead towards a high dissolution property as discussed by the authors, and three homologous series of all 27 combination of the three cations: 1-ethyl-3-methylimidazolium, 1,3-dimethylammonium, and N,N-N-diethyl-N,N,dimethyammonium with nine carboxylates as anions were synthesised.
Abstract: The dissolution of cellulose allows easier processing of this important biogenic feedstock For this, ionic liquids have been proposed Carboxylate-based ionic liquids were identified as the most promising lead towards a high dissolution property Three homologous series of all 27 combination of the three cations: 1-ethyl-3-methylimidazolium, 1,3-dimethylimidazolium, and N,N-diethyl-N,N-dimethylammonium with nine carboxylates as anions were synthesised The cellulose solubilities of the 17 ionic liquid compounds (liquid below 373 K) were measured Up to 18 wt% for 1-ethyl-3-methyl-imidazolium propionate was achieved, slightly higher than when using acetate as the anion Generally, the solubilities determined for carboxylate-based ionic liquids with imidazolium cations were found to be in the same range, whereas those with quaternary ammonium cations were found to be poor solvents for cellulose Dicarboxylates gave higher solubilities compared to monocarboxylates Regenerated ionic liquids had no apparent difference to fresh ones

62 citations


Journal ArticleDOI
TL;DR: In this paper, azeotropic distillation of EtOH/H2O was used to extract triterpene betulin from biomass with significantly improved extraction yield and purity.

53 citations


Journal ArticleDOI
TL;DR: The whole cell catalyst containing LOX and HPL enzyme activity described here can be a promising approach towards a highly efficient microbial green note synthesis process.
Abstract: Green notes are substances that characterize the aroma of freshly cut grass, cucumbers, green apples, and foliage. In plants, they are synthesized by conversion of linolenic or linoleic acid via the enzymes lipoxygenase (LOX) and hydroperoxide lyase (HPL) to short-chained aldehydes. Current processes for production of natural green notes rely on plant homogenates as enzyme sources but are limited by low enzyme concentration and low specificity. In an alternative approach, soybean LOX2 and watermelon HPL were overexpressed in Saccharomyces cerevisiae. After optimization of the expression constructs, a yeast strain coexpressing LOX and HPL was applied in whole cell biotransformation experiments. Whereas addition of linolenic acid to growing cultures of this strain yielded no products, we were able to identify high green note concentrations when resting cells were used. The primary biotransformation product was 3(Z)-hexenal, a small amount of which isomerized to 2(E)-hexenal. Furthermore, both aldehydes were reduced to the corresponding green note alcohols by endogenous yeast alcohol dehydrogenase to some extent. As the cosolvent ethanol was the source of reducing equivalents for green note alcohol formation, the hexenal/hexenol ratio could be influenced by the use of alternative cosolvents. Further investigations to identify the underlying mechanism of the rather low biocatalyst stability revealed a high toxicity of linolenic acid to yeast cells. The whole cell catalyst containing LOX and HPL enzyme activity described here can be a promising approach towards a highly efficient microbial green note synthesis process.

48 citations


Journal ArticleDOI
TL;DR: A one-pot multi-step approach comprising enzymatic oxidation-hydroxymethylation-reduction enables the synthesis of optically active α-aryl vicinal diols with high yields and enantioselectivities.

48 citations


Journal ArticleDOI
TL;DR: Recent findings on the use of microparticles in the cultivation of filamentous bacteria and fungi are highlighted, with the aim of enabling a more precise control of their morphology towards better production performance.
Abstract: Filamentous microorganisms are important work horses in industrial biotechnology and supply enzymes, antibiotics, pharmaceuticals, bulk and fine chemicals. Here we highlight recent findings on the use of microparticles in the cultivation of filamentous bacteria and fungi, with the aim of enabling a more precise control of their morphology towards better production performance. First examples reveal a broad application range of microparticle based processes, since multiple filamentous organisms are controllable in their growth characteristics and respond by enhanced product formation.

43 citations


Journal ArticleDOI
TL;DR: In this paper, trathin films of various compounds were prepared on galvanized steel coated with both phytic acid (PA) and diethylene triamine pentamethane phosphonic acid (DETPMPS) self-assembled monolayers (SAM), and in the presence of small amounts of special salt (MnSO4 or Cr(NO3)3).

43 citations


Journal ArticleDOI
TL;DR: In this paper, the Ni/CG40-cermet anodes with two different ratios of nickel and ceria-gadolinia-oxide were exposed to seven different reduction temperatures between 555 and 1140°C.

42 citations


Journal ArticleDOI
TL;DR: The described process permits generation of high-value flavor and fragrance compounds bearing the desired label “natural” according to US and European food and safety regulations and demonstrates the potential of CCD enzymes for selective oxidative cleavage of carotenoids.
Abstract: A biotechnological process concept for generation and in situ separation of natural β-ionone from β-carotene is presented. The process employs carotenoid cleavage dioxygenases (CCDs), a plant-derived iron-containing nonheme enzyme family requiring only dissolved oxygen as cosubstrate and no additional cofactors. Organophilic pervaporation was found to be very well suited for continuous in situ separation of β-ionone. Its application led to a highly pure product despite the complexity of the reaction solution containing cell homogenates. Among three different pervaporation membrane types tested, a polyoctylmethylsiloxane active layer on a porous polyetherimide support led to the best results. A laboratory-scale demonstration plant was set up, and a highly pure aqueous–ethanolic solution of β-ionone was produced from β-carotene. The described process permits generation of high-value flavor and fragrance compounds bearing the desired label “natural” according to US and European food and safety regulations and demonstrates the potential of CCD enzymes for selective oxidative cleavage of carotenoids.

26 citations


Journal ArticleDOI
TL;DR: In this article, yttria partially stabilized zirconia (YSZ) coatings were deposited on two recently developed γ-TiAl alloys, two-phase TNB-V5 and β-stabilized TNM-B1, using electron-beam physical vapor deposition (EB-PVD).
Abstract: Establishing the formation of a thin alumina scale, fluorine-treatment of the surface of γ-TiAl alloys can function as a bond coat in thermal barrier coating (TBC) systems, eliminating problems associated with thickness and chemical compatibility of conventional bond coat types. In the present work, yttria partially stabilized zirconia (YSZ) coatings were deposited on two recently developed γ-TiAl alloys, two-phase TNB-V5 and β-stabilized TNM-B1, using electron-beam physical vapor deposition (EB-PVD). The deposition temperature was 900 °C and 1000 °C. Prior to TBC deposition, the substrate materials were treated with fluorine by dipping in dilute hydrofluoric acid or spraying of an organic fluorine-containing compound, followed, in general, by a pre-oxidation step at 900 °C for 24 h in air. With some of the samples, the latter pre-oxidation step was omitted. As revealed by scanning electron microscopy, the as-deposited zirconia topcoats were tightly adherent to both fluorine treated alloys, regardless of the fluorination technique, the TBC deposition temperature and the pre-oxidation treatment. The oxidation behavior of the coated specimens was determined under cyclic oxidation conditions at 900 °C in air. Cyclic short-term oxidation tests revealed that the pre-oxidation step was crucial to maintain the oxidation protection by the halogen effect after EB-PVD TBC application. Whereas a continuous alumina layer was found beneath the zirconia topcoat on pre-oxidized samples, a mixed layered oxide scale of TiO 2 and Al 2 O 3 formed on specimens without pre-oxidation. When thermally cycled at 900 °C, the TBC system on substrates fluorine-treated by hydrofluoric acid exhibited lifetimes exceeding 500 cycles of 1 h dwell time at high temperature. No spallation of the zirconia topcoat was observed for both TNB-V5 and TNM-B1 alloys. Therefore, YSZ TBCs offer a promising concept to thermally protect γ-TiAl based alloys in combination with the fluorine effect.

Journal ArticleDOI
TL;DR: In this article, an oxygen barrier coating was created to prevent oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures.
Abstract: Experiments have been undertaken to explore the possibility of creating an oxygen barrier coating, which is effective in preventing oxidation and oxygen embrittlement of Ti and several low-Al content Ti-base alloys during exposure to oxidizing environments at elevated temperatures. The fabrication process has involved three steps, namely co-deposition of Ti and Al by magnetron sputtering onto a substrate material to be protected, followed by vacuum annealing and plasma immersion ion implantation of fluorine. The first two steps produce an overlay of γ-TiAl while the last step provides the necessary conditions for bringing about the halogen effect upon subsequent high-temperature oxidation. Analysis techniques such as cross-sectional transmission electron microscopy (XTEM) in conjunction with electron energy loss spectroscopy (EELS), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and elastic recoil detection (ERD) have been used to study the microstructure, phase formation and depth distribution of the elements in the coating material. Following oxidation in air at 600 °C for 100 h, specimens have been prepared for metallographic analysis, and their cross sections have been characterized by scanning electron microscopy (SEM) in combination with EDX, and electron probe microanalysis (EPMA). The results obtained show that during oxidation exposure the coating is capable of forming a protective alumina-containing scale which serves as an oxygen barrier, thereby preventing oxygen embrittlement. In addition, since the only constituents of the coating are Ti and Al, it exhibits excellent chemical substrate compatibility.


Journal ArticleDOI
TL;DR: In this paper, it was shown that the corrosion resistance of 9% Cr-steels in water vapour containing combustion environments is inferior to that in dry atmospheres, due to the formation of a volatile Cr-species of the type CrO2(OH)2.
Abstract: Ferritic – martensitic steels are of high interest as superheater materials or as materials for interconnectors in solid oxide fuel cells. In comparison to austenitic steels and nickel base alloys they offer much better heat transfer behaviour and a lower coefficient of thermal expansion, as well as lower costs. Modern 9% Cr-steels have sufficient creep strength however their corrosion resistance particularly in H2O containing oxidising environments (e.g. up to 25% H2O in the combustion of biomass or the oxyfuel process) needs further improvement.A large number of studies have shown that the corrosion resistance of 9% Cr-steels in water vapour containing combustion environments is inferior to that in dry atmospheres, due to the formation of a volatile Cr-species of the type CrO2(OH)2. This investigation starts from the idea of a shift of partial pressure of CrO2(OH)2 to lower values if the solid oxide phase on the alloy surface is a manganese –chromium – spinel scale, so that at 630°C the formatio...

Journal ArticleDOI
TL;DR: In this article, the microstructural evolution of slurry-derived coatings manufactured on CM 247 in inert atmosphere as well as in air was investigated, and it was demonstrated that iridium has a high influence on the diffusion behavior and especially the distribution of platinum in the coatings.
Abstract: Slurry-derived coatings are an interesting alternative method to pack aluminization of nickel-base superalloys, which provide similar properties and protection at high temperatures. For highest performance, these aluminide coatings are modified by the addition of Pt or, as recent research suggests, with Pt/Ir. While the combination of Pt and Pt/Ir with an out-of-pack process is state of the art, slurry coatings are of special interest as a repair method for turbine blades. In this study, the microstructural evolution of slurry-derived coatings manufactured on CM 247 in inert atmosphere as well as in air was investigated. Layers of Ni, Pt, and Pt/Ir mixtures were electrodeposited. After annealing, a diffusion heat-treatment with a slurry containing aluminum or aluminum–silicon powder was applied on the samples. The addition of silicon is well known to be beneficial for hot corrosion environments. The reaction and interdiffusion behavior of aluminum/aluminum–silicon determines the microstructural evolution of the coatings. Depending on the initial electroplated layer on the surface, different microstructures can be obtained, such as the Pt/Ir-modified beta phase (Ni,Pt)Al or two-phase layers of PtAl2 and NiAl. Additionally, the reactivity between the elements at the surface and those from the slurry was shown to determine homogeneity and surface roughness of the diffusion coating, also depending on the atmosphere used during slurry aluminization. Finally, it was demonstrated that iridium has a high influence on the diffusion behavior and especially the distribution of platinum in the coatings. Such new coatings have the potential to overcome some disadvantages of conventionally manufactured high-activity aluminide coatings, as the combination of Pt/Ir-electroplating with the slurry process results in less detrimental substrate elements like molybdenum or tungsten close to the surface.

Journal ArticleDOI
TL;DR: In this article, the authors provide a comprehensive summary of the oxidation mechanisms and the parameters influencing oxide scale formation, including the role of metallic alloying elements, the halogen effect, and recent results concerning the prevention of oxidationinduced room temperature embrittlement of TiAl alloys.
Abstract: Above 750-800°C oxidation becomes a serious life time issue for the new group of intermetallic light-weight high temperature alloys based on titanium aluminides (TiAl). Fast growing titanium oxide competes with protective alumina as a surface scale in the oxidation reaction by which the formation of a slow-growing protective oxide scale is prevented. The key to the development of alloys with sufficient oxidation resistance is the understanding of the thermodynamic and kinetic situation during the oxidation process. The latter is influenced by the type of alloying elements, the Al- and Ti-activities in the alloy, the oxidation temperature and the environment (e.g. dry or humid air, etc.). This paper provides a comprehensive summary of the oxidation mechanisms and the parameters influencing oxide scale formation. Besides the role of metallic alloying elements, the halogen effect will also be discussed. The paper finishes with recent results concerning the prevention of oxidation-induced room temperature embrittlement of TiAl alloys.

Journal ArticleDOI
TL;DR: In this article, the effects of moderate temperatures (550-700°C), dwelling times and Al particle size on the final characteristics of the coatings were investigated. But the results showed that the increase of dwelling time did not provide any significant thickness increase as the Al particles got practically emptied after 2h.
Abstract: Novel, unconventional type of high temperature coating systems can be elaborated by depositing Al micro-particles on nickel base substrates, using an appropriate binder, and converting them into a thermal barrier type coating by a two-step heat treatment under argon. Final result is a coating structure consisting of a quasi-foam top coat, constituted by spherical hollow alumina particles, surmounting a β-NiAl diffusion layer able to form during high-temperature oxidation a protective alumina scale. In this work, pure nickel was employed as a model material to evaluate the effects of moderate temperatures (550-700°C), dwelling times and Al particle size on the final characteristics of the coatings. Almost no diffusion occurred below 600°C. In contrast, a Ni2Al3 layer very quickly formed at 650 or 700°C. The rapidity of coating formation was attributed to the appearance of a liquid phase at the coating/substrate interface. The increase of dwelling time did not provide any significant thickness increase as the Al particles got practically emptied after 2h. In addition, the use of different micro-sized particles resulted in similar Al diffusion coatings under the investigated conditions.

Journal ArticleDOI
TL;DR: Comparative investigations with racemic linalool suggest that predominantly (2S)- configuration derivatives can be expected by using (S)-(+)-configured substrate, and this work established a substrate feeding product removal (SFPR) system based on hydrophobic adsorbers.
Abstract: Linalool oxides are of interest to the flavour industry because of their lavender notes. Corynespora cassiicola DSM 62475 has been identified recently as a production organism because of high stereoselectivity and promising productivities [Mirata et al. (2008) J Agric Food Chem 56(9):3287–3296]. In this work, the stereochemistry of this biotransformation was further investigated. Predominantly (2R)-configured linalool oxide enantiomers were produced from (R)-(−)-linalool. Comparative investigations with racemic linalool suggest that predominantly (2S)-configured derivatives can be expected by using (S)-(+)-configured substrate. Substrate and product inhibited growth even at low concentrations (200 mg l−1). To avoid toxic effects and supply sufficient substrates, a substrate feeding product removal (SFPR) system based on hydrophobic adsorbers was established. Applying SFPR, productivity on the shake flask scale was increased from 80 to 490 mg l−1 day−1. Process optimisation increased productivity to 920 mg l−1 day−1 in a bioreactor with an overall product concentration of 4.600 mg l−1 linalool oxides.

Journal ArticleDOI
Christoph Nacke1, Jens Schrader1
TL;DR: Micelle based delivery of water-insoluble hydrophobic substrates was investigated with regard to qualitative and kinetic effects of vesicle properties on the enzymatic reaction to complement recent studies on the properties of liposomes and micelles as substrate delivery vesicles.
Abstract: Substrate delivery vesicles such as micelles or liposomes can permit the conversion of strongly hydrophobic substrates in aqueous media if the enzyme used is not adaptable to organic media. Micelle based delivery of water-insoluble hydrophobic substrates was investigated with regard to qualitative and kinetic effects of vesicle properties on the enzymatic reaction. The oxidative 9′,10′ cleavage of structurally related carotenoids by Arabidopsis thaliana carotenoid cleavage dioxygenase 1 (AtCCD1) was applied as model reaction. Unlike commonly assumed, non-ionic surfactants differed significantly in their ability to deliver the strongly hydrophobic carotenoid substrates to the enzyme. Even small structural differences in the carotenoid substrates led to different non-ionic surfactants being required for efficient micellar delivery to the enzyme. The reaction velocities using the same substrate but different non-ionic surfactants varied by up to the 19-fold of the lowest value. The kinetic activation of micelle based enzymatic carotenoid cleavage by organic cosolvents was investigated in order to complement published data on this recently discovered effect [1] . The length and saturation of the surfactant aliphatic side chain determined the concentration of water-soluble organic cosolvent at which maximum kinetic activation was achieved. The required cosolvent concentrations were between 6 and 15% (v/v) and led to up to 3.8-fold increased reaction velocities. For specific combinations of enzymes and non-ionic surfactants, kinetic lag phases were observed. Factors of influence on occurrence and duration were investigated and a hypothesis for the underlying mechanism was formulated. The results complement recent studies on the properties of liposomes and micelles as substrate delivery vesicles [1] , [2] , [3] . The systematic study of delivery systems for hydrophobic substrates will in the long run permit their rational design for enzymatic conversions requiring to be conducted in aqueous media.

Journal ArticleDOI
TL;DR: In this article, four supercritical fluids were investigated: carbon dioxide, fluoroform, ethane, and sulphur hexafluoride, and the results showed that water activity and enzyme preparation were the main influence parameters.
Abstract: Benzaldehyde lyase is a versatile catalyst for the organic synthesis of enantiopure α-hydroxy ketones. In view of poor solubility and stability of many substrates and products and the prospect of downstream processing, supercritical fluids are explored as an alternative solvent in view of residual stability, activity, and selectivity. Four supercritical fluids were investigated: carbon dioxide, fluoroform, ethane, and sulphur hexafluoride. Water activity and enzyme preparation (pH of lyophilisation) showed to be the main influence parameters. Activity increased with increasing water activity but stability decreased. Furthermore, non-carbon dioxide supercritical fluids give better results in view of stability, activity, and enantioselectivity. Suprisingly, the enantioselectivity is heavily influenced by the reaction from almost racemic in sulphur hexafluoride with up to 90% enantiomeric excess.

Journal ArticleDOI
TL;DR: Several white mutants were isolated that are superior strains for the production of the valuable enzyme chloroperoxidase (CPO) by mutant-colony screening of Caldariomyces fumago, which uncovers possible interactions between pigmentation and enzyme secretion.
Abstract: By mutant-colony screening of Caldariomyces fumago, several white mutants were isolated that are superior strains for the production of the valuable enzyme chloroperoxidase (CPO). Their culture supernatant lacks the contaminating dark pigment, which simplifies downstream processing. Furthermore, the CPO content increased significantly faster than the wild-type rate, which uncovers possible interactions between pigmentation and enzyme secretion.

Journal ArticleDOI
TL;DR: In this paper, the surface of the TiAl-alloys was treated with small amounts of fluorine to suppress the formation of a fast growing mixed oxide scale on untreated alloys, and a thin protective alumina scale was formed on samples after fluorine treatment.
Abstract: The oxidation resistance of TiAl-alloys can be improved drastically by treating the surface of the components with small amounts of fluorine. The oxidation mechanism is changed. Hence, the formation of a fast growing mixed oxide scale on untreated alloys is suppressed. Instead a thin protective alumina scale is formed on samples after fluorine treatment. The different methods only influence the surface region of the components so that the bulk properties are not affected. Recent results achieved with F-containing inorganic compounds showed that the fluorine effect can be improved even further. TiAl-specimens were treated only with fluorine and with F-containing compounds in several ways and their performance during high temperature oxidation tests in air was investigated. Results of isothermal and thermocyclic oxidation tests are presented. The results are discussed in terms of a later use of the fluorine effect for technical applications.

Journal ArticleDOI
TL;DR: In this article, a continuous heat balance calorimetry is used to determine mixing efficiency by measurement of effective excess enthalpy of non-reactive streams, which can be normalised to the dimensionless goodness of mixing G with the experimentally independently accessible enthpy of mixing.

Journal ArticleDOI
TL;DR: In this article, a project of computer-aided alloy development based on the CALPHAD (CALculation of PHAse Diagrams) method various alloys were melted on the Al-rich side of the ternary system Al-Cu-Er under argon atmosphere and their microstructures were characterized in the as-cast state or after long-term isothermal annealing (400°C/960 h).
Abstract: Alloying with rare earth metals improves to the mechanical properties and corrosion resistance of aluminium base alloys at high temperatures. The rare earth metal erbium may be used for grain refinement. Within a project of computer-aided alloy development based on the CALPHAD (CALculation of PHAse Diagrams) method various alloys were melted on the Al-rich side of the ternary system Al-Cu-Er under argon atmosphere and their microstructures were characterized in the as-cast state or after long-term isothermal annealing (400°C/960 h) by means of different investigation techniques. As a result, the phases fcc(Al), τ1-Al8Cu4Er, θ-CuAl2, η-CuAl, and Al3Er were identified, their compositions and fractions were quantified, and their hardnesses were determined. The experimental obtained microstructures agree very well with the calculated solidification behaviors of the cast alloys. The knowledge gained from this work about the phase compositions and microstructures can also be utilized for the fine optim...


Journal ArticleDOI
TL;DR: In this article, the fluorine effect on a multi-phase TiAl-alloy in the cast and hot-isostatically pressed condition at 800°C in air was investigated.
Abstract: Intermetallic titanium aluminides are potential materials for application in high temperature components. In particular, alloys solidifying via the β-phase are of great interest because they possess a significant volume fraction of the disordered body-centered cubic β-phase at elevated temperatures ensuring good processing characteristics during hot-working. Nevertheless, their practical use at temperatures as high as 800°C requires improvements of the oxidation resistance. This paper reports on the fluorine effect on a multi-phase TiAl-alloy in the cast and hot-isostatically pressed condition at 800°C in air. The behavior of the so-called TNM material (Ti-43.5Al-4Nb-1Mo-0.1B, in at %) was compared with that of two other TiAl-alloys which are Nb-free and contain different amounts of Mo (3 and 7 at%, respectively). The oxidation resistance of the fluorine treated samples was significantly improved compared to the untreated samples. After fluorine treatment all alloys exhibit slow alumina kinetics indicating a positive fluorine effect. Results of isothermal and thermocyclic oxidation tests at 800°C in air are presented and discussed in the view of composition and microstructure of the TiAl-alloys investigated, along with the impact of the fluorine effect on the oxidation resistance of these materials.

Journal ArticleDOI
TL;DR: In this paper, the nano-particulate thin coatings obtained by the sol-gel process to improve the oxidation resistance of 22MnB5 steel were investigated and the structural properties of the coating materials were characterized using different methods like XRD and differential thermal analysis.
Abstract: The need for lighter constructional materials in automotive industries has increased the use of high-strength steel alloys. To enhance passenger's safety press hardening may be applied to steel parts. However, as the steel parts are heated up to 950 °C during this process they have to be protected by some kind of coating against the intense oxide formation usually taking place. As the coating systems used so far all have certain disadvantages in this work the ability of nano-particulate thin coatings obtained by the sol–gel process to improve the oxidation resistance of 22MnB5 steel is investigated. The coatings obtained from three sols containing lithium aluminum silicate and potassium aluminum silicate showed the best performance against oxidation. The structural properties of the coating materials were characterized using different methods like XRD and differential thermal analysis. Comparison of the oxidation rate constants proved the ability of the coatings to protect against oxidation at temperatures up to 800 °C. Press-hardening experiments in combination with investigations on the thermal shock resistance of the coated samples also showed the ability of the coatings to stay intact during press hardening with only slight spalling of the coatings in the bending areas. The absence of any secondary intermetallic phases and layer residues during laser beam welding experiments on coated samples proves the suitability of the nano-particulate coatings for further industrial processing.


Reference EntryDOI
01 Dec 2012
TL;DR: In this article, the authors proposed a method to combine copper-zinc alloys (brass) and chlorinated hydrocarbons (chloroethanes) to produce chloroethane-copper alloys.
Abstract: This article has no abstract. Keywords: chlorinated hydrocarbons - chloroethanes; copper-zinc alloys (brass)

Journal ArticleDOI
TL;DR: The illustrated literature series Asterix (and Obelix) is commonly known as entertainment and distraction, but behind that mask, case studies for chemical production in small medium enterprises and the crucial role of research and development can be discovered.
Abstract: The illustrated literature series Asterix (and Obelix) is commonly known as entertainment and distraction, but behind that mask, case studies for chemical production in small medium enterprises and the crucial role of research and development can be discovered. The series rightly puts chemistry and chemical engineering at the heart of success and prosperity. Overall, the motives exemplified are of high relevance today for chemical industry.