Showing papers by "DECHEMA published in 2004"

Applied biocatalysis for the synthesis of natural flavour compounds--current industrial processes and future prospects.

Abstract: The industrial application of biocatalysis for the production of natural flavour compounds is illustrated by a discussion of the production of vanillin, γ-decalactone, carboxylic acids, C6 aldehydes and alcohols (`green notes'), esters, and 2-phenylethanol Modern techniques of molecular biology and process engineering, such as heterologous expression of genes, site-directed mutagenesis, whole-cell biocatalysis in biphasic systems, and cofactor regeneration for in vitro oxygenation, may result in more biocatalytic processes for the production of flavour compounds in the future

A Review of Catalytic Membrane Layers for Gas/Liquid Reactions

Abstract: This paper summarises the main ideas of how to use membranes with built-in catalytic function for performing catalysed gas/liquid reactions. Mass transfer effects on catalyst performance and other decisive factors for the design of industrial gas/liquid and gas/liquid/solid reactors are briefly reviewed. Various concepts for applying catalytic membrane layers in multiphase reactors are introduced and the motivation behind their use is explained. What follows is an assessment of the present achievements in using such concepts for gas/liquid reactions. The results available in literature are critically evaluated, focussing mainly on the field of liquid-phase hydrogenations and oxidations, which constitute the major areas where catalytic membranes have been applied to date to gas/liquid systems. The aim of such treatment is to point out the targets, to elaborate on how far the whole field has developed and what challenges remain, rather than to cover a multitude of specific aspects of the many different studies reported in literature.

Medium optimization for the production of the aroma compound 2-phenylethanol using a genetic algorithm

Abstract: Using a genetic algorithm, 13 medium constituents and the temperature were varied to improve the bioconversion of l -phenylalanine ( l -phe) to 2-phenylethanol (2-PE) with Kluyveromyces marxianus CBS 600. Within four generations plus an additional temperature screening, corresponding to 98 parallel experiments altogether, a maximum 2-PE concentration of 5.6 g/l, equivalent to an increase of 87% compared to the non-optimized medium was obtained. The vitamin content of the medium had to be raised significantly.

The role of alloy composition, environment and stresses for the oxidation resistance of modern 9% Cr steels for fossil power stations

Abstract: In recent years a new group of ferritic-martensitic chromium steels for the use in fossil power stations has been developed with chromium contents between 9 and 12%. Typical representatives of these steels are P91, E911 and Nf616, which are nowadays widely used in the more advanced power plants. In the development phase the focus was on the mechanical properties of these steels but when taking them to practical operation conditions it turned out that much of the life-time of the materials and components is determined by their oxidation properties. Oxidation resistance is first of all a function of alloy composition. For the steels of this group it is chromium, silicon, manganese and molybdenum that decide their oxidation performance and since the contents especially of the four elements can be significantly different for the different steels there can be clear differences in oxidation behaviour. One of the most important issues from this point of view is how the concentrations of these elements change in the metal subsurface zone during operation/oxidation since if their level drops below a critical level oxidation resistance of the steels will be lost. In the work to be reported the influence of alloy composition and metal subsurface zone concentration as a function of oxidation time up to 10000 h was investigated in dry air and air up to 10% water vapour at 650 °C. The investigations comprised several of the advanced commercial 9% Cr steels including P91, E911, Nf616 and six laboratory melts of Nf616 with different amounts of silicon. As the results of the investigations show humidity, which is omnipresent in combustion environments, can dramatically accelerate oxidation. Silicon as an alloying element reduces the detrimental effect of water vapour significantly while molybdenum has a negative effect. The effects of the key alloying elements in these steels was quantified for conditions with and without water vapour in the environment including the role of mechanical load and recommendations were developed on how to guarantee the optimum oxidation resistance of these steels.

Preparation and Properties of Composite Polypyrrole/Pt Catalyst Systems

Abstract: Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques).

Progress in life time modeling of APS-TBC Part I: residual, thermal and growth stresses including the role of thermal fatigue

Abstract: For about the last two decades there has been an effort to produce a reasonable life time model for the thermal barrier coating systems (TBC) that are used in the gas turbine industry. However, recent advances in testing technology, namely acoustic emission (AE) analysis and Raman spectroscopy, have provided many new insights into the life of TBCs. This new technology used in conjunction with more traditional testing, such as the four point bend mechanical test, has provided much needed data for the development of a life time model.Part I of this paper is devoted to the stress situation that exists in isothermally and cyclically oxidized TBC systems. The focus of the current TBC research is on the air plasma sprayed (APS) systems. However, some results for the electron beam physical vapor deposited systems (EB–PVD) are presented for the purpose of providing insight into the role of interface roughness and the stresses in the thermally grown oxide (TGO). AE analysis of isothermally and cyclically o...

Diffusion coatings for heat exchanger materials

Abstract: There is a need to develop cleaner electric power systems, with reduced emission of pollutants. This implies an increase in the maximum temperature of heat exchanger tubes, which is now, 600°C in modern power plants. For conventionally used ferritic steels, this increase is limited by the steels' mechanical properties and their corrosion resistance in coal, waste or biomass fired environments. Austenitic steels and nickel based alloys are potential candidates for increasing performance at higher temperature (700°C. Nonetheless, the corrosion resistance of these materials could be improved even further by applying a coating. Pack cementation is one of the easiest and cheapest coating processes. However, it requires a heating step which is presently performed at a minimum temperature of 750–800°C. The microstructure of the material may be significantly changed at these temperatures during the coating process, especially for ferritic–martensitic steels. Since the microstructure dictates the mechanica...

Mechanical behaviour of as sprayed and sintered air plasma sprayed partially stabilised zirconia

Abstract: The mechanical behaviour of free standing air plasma sprayed (APS) partially yttria stabilised zirconia (P-YSZ) thermal barrier coatings (TBC) at room temperature and at elevated temperatures up to 1050°C have been investigated. Creep tests under constant compressive load have been conducted as well as cyclic measurements of compressive stress – strain hysteresis loops with increasing maximum load, yielding Young's moduli of the porous partially yttria stabilised zirconia. Both mechanical parameters are needed for accurate modelling of the local stress fields of, for example, airfoils to identify critical regions where damage or even failure of the component may occur. Specimens in the as sprayed and sintered state were tested. The microstructural changes caused by sintering and mechanical loading at high temperature of the thermal barrier coatings have been characterised by porosity measurements made from metallographic cross-sections.

Progress in life time modeling of APS-TBC Part II: critical strains, macro-cracking, and thermal fatigue

Abstract: Here TBC top coat failure and life time are considered as a two-step process, where step 1 is time to delamination macro-cracking and step 2 is time to through macro-cracking. This two-step failure...

The Quantitative Role of Surface Doped Fluorine for the Improvement of Oxidation Resistance of TiAl in Air

Abstract: The oxidation resistance of TiAl at elevated temperatures (> 750°C) can be improved by the addition of small amounts of fluorine. The fluorine was applied either by ion implantation or by wetting with diluted HF. The behaviour of fluorine was studied during heating up 1000°C at 1h/air. Using non-destructive Ion Beam Analysis (PIGE) the fluorine depth concentration profiles in the near surface region were determined before and after oxidation. Both types of fluorine application show similar results. The temperature dependence of the fluorine depth profiles shows a distinct loss of fluorine between 400° and 500°C after oxidation for 1 hour. In contrast to this the fluorine amount decreases slowly above 500°C up to 1000°C. The high fluorine loss is due to the formation of TiF4. The remaining fluorine content offers the possibility for a technical application of the fluorine microalloying effect to improve the oxidation resistance of TiAl-alloys above 750°C.

Process of treatment of an Al alloy surface, particularly a piece of TiAl alloy,and application of organic halocarbon compounds or halogenides bound in an organic matrix

Abstract: Articles of aluminum alloy are shaped at normal temperatures and then have an organic halogen-carbon compound, or a matrix containing such a compound, applied to the surface. The article is then heated up to at least 700[deg]C so that the halogen combines with the aluminum and the organic components evaporate. Heating can take place when the article is in use for the first time. An independent claim is also included for the use of this process to improve the oxidation resistance of aluminum alloys, especially titanium-aluminum alloys. Application of organic halogen compounds can be by brush, spraying or dipping to produce between 3.5X10->12 and 6.5X10->4 mol fluorine/cm2>.

The Role that Interacting Failure Mechanisms Have on the Lifetime of APS-TBC under Oxidizing Conditions

Abstract: Bond coat (BC) oxidation as well as bond coat depletion of Al are still believed to be the major degradation mechanisms with respect to the lifetime of thermal barrier coating (TBC) systems. For more than one decade the influence of oxidation behaviour on the service life of components was described by simply the thermally grown oxide (TGO) thickness. However, it has recently been shown that the adherence of the top coat is also an important parameter for the durability of the system. Fracture mechanics in conjunction with finite element modelling (FEM) has also provided valuable insight with regards to the mechanical breakdown and failure of the thermal barrier coating systems. In this study the top coat lifetime is described as being limited by both “mechanical” failure of the top coat and bond coat depletion of Al. The empirical results are introduced by considering three spallation cases, namely, thermal fatigue failure, thermal ageing failure and Al depletion failure. Top coat and TGO degradation due to thermal fatigue is characterized by in-situ acoustic emission analysis, where the data were acquired during cyclic oxidation testing. Degradation due to thermal aging and TGO growth is characterized by four-point bend testing of isothermally preoxidized samples. This four-point bend test also uses acoustic emission analysis for the purpose of determining the critical strains of the top coat and TGO, where the critical strains for the onset of delamination and the onset of through cracking are found. Bond coat depletion of Al is modelled by considering the diffusion of Al into both the TGO and substrate. The diffusion model results are compared to the measured TGO growth kinetics and the Al concentration profile measured with an electron beam micro probe. Top coat spallation occurs when the Al content within the bond coat reaches a critical value. The three mechanisms and the measured results are embedded into a lifetime prediction model. This model is applied to both isothermal and cyclic oxidation samples. The results are compared to measured life times up to 5000 hr in the temperature range of 950°C through 1150°C. Introduction Spallation Cases Here the spallation of the APS-TBC top coat is classified into three cases, namely, Case 1 thermal fatigue failure, Case 2 thermal ageing failure and Case 3 Al depletion failure, which are depicted in Fig. 1. Cases 1 and 2 are considered to be, more or less, “mechanical” failures, where case 3 is considered to be a type of “chemical” failure. This classification produces a conceptual framework that separates “mechanical” and “chemical” spallation mechanisms, which can in turn be modeled separately when the appropriate measurement data is available. In all three cases bond coat oxidation and TGO growth are considered part of the top coat spallation mechanisms. The three mechanisms and the measured results are embedded into a lifetime prediction model. This model is applied to both isothermal and cyclic oxidation samples, where the preliminary modelling equation for “mechanical” failure can be found in reference [1]. The preliminary modelling equations for Al depletion are provided below. Materials Science Forum Online: 2004-08-15 ISSN: 1662-9752, Vols. 461-464, pp 729-736 doi:10.4028/www.scientific.net/MSF.461-464.729 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:01:57) Case 1 Thermal Fatigue Failure Case 2 Thermal Ageing Failure Case 3 Al Depletion Failure top coat top coat TGO TGO TGO top coat Fig. 1. Spallation Cases: Case 1) Thermal Fatigue Failure; Case 2) Thermal Ageing Failure and Case 3) Al Depletion Failure. Case 1 Thermal Fatigue Failure (cyclic oxidation). The sample on the left of Fig. 1 failed during thermal cyclic oxidation. The oxidation test was at 1100°C and during each cycle the sample experienced one hour at temperature, also during each cycle the sample was cooled to room temperature and remained at room temperature for at least 30 minutes. This type of cycle will produce the maximum thermal expansion mismatch strains (ε=∆α∆T). The macroscopic delamination crack seen in the figure, which plays a critical role with regard to top coat spallation of the smaller oxidation sample, lies mostly within the yttria stabilised zirconia (YSZ) top coat with some of the cracking extending into the TGO. The sample spalled after 277cy, which is 277hr at temperature. Here it is proposed that this sample failed due to a thermal cyclic fatigue mechanism, where the details will be made more clear below. Additionally, bear in mind that the TGO thickness is about 6.7μm and is mostly Al2O3, which indicates that the bond coat is not critically depleted of Al. Case 2 Thermal Ageing Failure (isothermal oxidation). The sample in the middle of Fig. 1 failed after isothermal oxidation. It was tested at 1100°C for 1000hr and experienced only one cooling step. The macroscopic delamination crack seen in this photo again passes through the YSZ top coat with some of the cracking extending into the TGO. In contrast to the case 1 sample, the case 2 sample lived three times longer. The life time of cycled TBC ́s in many cases is shorter than that of isothermally exposed specimens, which is viewed as thermal cycling produces a thermal cyclic fatigue mechanism that can dominate the life time of the sample. The degradation of the top coat under isothermal condition is likely to be caused by sintering of the YSZ and TGO growth. The TGO in the case 2 sample is about 9.3μm, which is about 38% thicker than the case 1 sample. The composition of the TGO is again mostly Al2O3, which is again an indication that the bond coat is not critically depleted of Al. Case 3 Al Depletion Failure (isothermal or cyclic oxidation). The samples of case 1 and case 2 show the crack path passing through the top coat, consequently, the mechanical properties of the YSZ and how the mechanical reliability of the top coat degrades with the respective thermal exposure are suspected to be of crucial importance. The sample on the right side of Fig. 1 (spallation case 3) is showing something completely different when compared to cases 1 and 2. The case 3 sample was isothermally oxidized at 1050°C for 5000hr, where it spalled after cooling. The crack face passes only through the TGO. The TGO is >30μm thick and is composed of Al2O3 with a large amount of Ni (Co,Cr)-spinels. The formation of the spinels and the TGO thickness, which should be 13.1μm thick when calculated from the Al2O3 oxidation kinetics data, is a strong indication that the bond coat is depleted of Al. Consequently, case 3 is classified as Al depletion failure. 730 High Temperature Corrosion and Protection of Materials 6

Cyclic Oxidation Behaviour of Halogen Implanted Ti-46.5Al-4(Cr, Nb, Ta, B)

Abstract: Intermetallic alloys based on titanium aluminides, especially γ-TiAl (Ti-50at.%Al), are of great attraction for structural high temperature applications e.g. in aero engines because of their low specific weight (about 4g/cm3) and their good mechanical properties at elevated temperatures. However, the use of TiAl alloys is still limited to a temperature of approximately 750°C due to their poor oxidation resistance at higher temperatures. The oxidation behaviour of TiAl alloys has to be improved before these alloys can be used at temperatures of 800°C and above. The improvement of the oxidation resistance of γ-TiAl can be achieved by small amounts of halogens F, Cl, Br and I (so called halogen effect). The halogens can be incorporated in several ways e.g. by ion implantation. In this paper results of a technical TiAl alloy called γ-MET [Ti-46.5Al-4(Cr, Nb, Ta, B)] with and without implantation are presented.

Ion exchange cell for continuous electrochemical treatment with two modified ion exchange electrodes separated by an ion exchange membrane useful for removal of ions from aqueous and organic solutions, and especially for water softening

Abstract: Ion exchange cell for continuous electrochemical water treatment with at least two modified ion exchange electrodes separated by an ion exchange membrane, which can be regenerated by altering the polarization is new. An Independent claim is included for a process for treating water (water softening) in which the cell is electrochemically conditioned, brought into contact with an ion containing solution, and finally the ion laden membrane (sic) is regenerated by application of a counter-voltage.

Method for coating a substrate

Abstract: The invention relates to a method for coating a substrate with a metal or a metallic compound. According to said method, a metallo-organic parent compound and a substrate to be coated are introduced into a receptacle. Before the coating process, an organic solubilizer for the metal-organic parent compound is applied to the substrate. The receptacle containing the substrate and the metallo-organic parent compound is placed in an oven for approximately two hours at a temperature of 300° C. In this way, the desired coating is obtained.

Neue Biopharmazeutika durch Manipulation pharmakologischer Parameter

Abstract: Verbesserung der Bindungseigenschaften, Steuerung der Pharmakokinetik, Schutz vor proteolytischem Abbau: Eine ganze Reihe von Beispielen zeigt, wie mit proteinchemischen, gentechnischen und immunologischen Methoden Probleme bei der Anwendung von Proteintherapeutika in den Griff zu bekommen sind. Das rationale Design dieser makromolekularen Wirkstoffe fuhrt zu Arzneimitteln mit uberlegenen Eigenschaften.

Zur Geschichte der Eisengewinnung mit Holzkohle und Steinkohlenkoks

Abstract: Iron, which gave the impulse to the age of machines and industry, still represents the most important and mostly utilized raw material. Concerning this, a large amount of literature exists but not much about its history within human culture. For that reason, we try to demonstrate the importance of this metal for technical purposes and the life of mankind by reviewing the centuries from prehistory up to modern times. With regard to the production of iron the substitution of charcoal by coal coke was of very great importance, and the life-work of the family Darby essentially participated in this invention. Their pioneering minds and creative energy helped the iron industry to a remarkable rise, which eventually introduced the Industrial Revolution.

Silicalite-1 membranes prepared via one-step In situ seeding

Abstract: A modified seeding technique is developed for the preparation of high-integrity stainless-steel-supported MFI membranes using two hydrothermal synthesis steps. Seeding is achieved in-situ, in a single crystallization step, by applying synthesis conditions that promote nucleation and deposition of closelypacked nanocrystals on the support grains. In a second step, these nanocrystals are grown into a closed film using synthesis conditions that are suitable for crystal growth. These membranes are characterised by X-ray powder diffraction, scanning electron microscopy and H 2 /SF 6 single gas permeation measurements. The dependence of membrane characteristics on crystallisation time are studied in detail. Ideal hydrogen/sulphur hexafluoride perm-selectivities of ca. 50 at room temperature are achieved with good reproducibility after 24 h synthesis time.

Biochemie und Molekularbiologie 2003

Abstract: Hochdurchsatzmethoden fuhren zu ersten Erfolgen bei der Vorhersage der biologischen Aktivitat funktionell nicht charakterisierter Proteine anhand von Strukturhomologien. Proteintherapeutika halten Einzug in den medizinischen Alltag. Die RNA, in ihrer Bedeutung lange unterschatzt, hat mit ihren verschiedenen Formen in Grundlagen- und Pharmaforschung ein Comeback erlebt.

Process for preparation of inorganic fluorine-containing protective coatings using a coating composition obtained by hydrolysis and polycondensation silanes useful for coating metal substrates, e.g. in steel, Cu, Cr, Al or Mg

Abstract: Process for preparation of inorganic fluorine-containing protective coatings using a coating composition obtained (sic) by hydrolysis and polycondensation of one or more silanes is new. A process for preparation of inorganic fluorine-containing protective coatings using a coating composition obtained (sic) by hydrolysis and polycondensation of one or more silanes of formula (I) or an oligomer derived from the silane and one or more fluorsilanes of formula (II) or an oligomer derived from it. HnSiX4-n (I) FnSiX4-m (II) X = hydrolysable groups, n = 0, 1, or 2, m = 1 or 2.