Showing papers by "DECHEMA published in 2003"

Screening of yeasts for the production of the aroma compound 2-phenylethanol in a molasses-based medium.

Abstract: Fourteen yeast strains were screened for production of 2-phenylethanol from l-phenylalanine with molasses as carbon source Up to 1 g 2-phenylethanol l−1 was obtained Using oleyl alcohol as a second phase for in situ product removal to enhance the production of 2-phenylethanol increased the yield to about 3 g 2-phenylethanol l−1 at 35 °C The most productive strains were Kluyveromyces marxianus CBS 600 and CBS 397

Oxidation-resistant aluminide coatings on γ-TiAl

Abstract: The long-term application of TiAl alloys based on the γ-phase at temperatures above 750–800°C requires suitable surface coatings to provide the needed oxidation resistance. Without a coating, these alloys, containing large amounts of titanium, suffer from rapid oxidation attack at elevated temperatures. The pack-cementation coating process was used to aluminize the surface region of a Ti–50 at.% Al alloy to TiAl3, the most promising, oxidation-resistant phase in the Ti–Al system. The isothermal oxidation behavior of the coated alloy was studied in the temperature range 800–1000°C in air for up to 300 hr. The aluminide coating greatly improves the oxidation resistance of γ-TiAl, forming a protective alumina scale. The rapid aluminum interdiffusion between the TiAl3 coating and the γ-TiAl substrate determined the effective life of the coating. In addition, the oxidation behavior of the TiAl2 phase formed by interdiffusion of the coating system was studied by oxidation of cross sections.

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing-chloridizing atmospheres. Part I: Literature evaluation and thermodynamic calculations on phase stabilities

Abstract: In several high temperature processing environments the presence of chlorine may significantly reduce the life-time of the components. Although metallic materials have been widely used under such conditions there is still a need for data on the role of the different alloying elements in commercial alloys. In the present work this role was investigated in detail at temperatures between 650 and 1000°C in synthetic air containing up to 2 vol.% Cl2. Before starting the experimental investigation a detailed literature evaluation on chlorine high temperature corrosion was performed followed by a thermodynamic assessment of the stability and the partial pressures of the phases formed by the reaction between alloy and environment. The results of this “theoretical approach” are presented in the following first part of the publication while the experimental work will be reported in the second part appearing in a later issue of this journal. Already the results of the “theoretical approach” yield a clear picture of which alloying elements play a detrimental role and which elements are beneficial. These results can be used as a tool for a general assessment of metallic alloys with regard to their performance in oxidizing/chloridizing high temperature environments. In the second part of this work the results from this “theoretical approach” will be compared with the behavior of 14 commercial materials, where the content of the major alloying elements was varied in a systematic manner. Die Rolle der Legierungselemente in kommerziellen Werkstoffen fur die Korrosionsbestandigkeit in oxidierend-chlorierend wirkenden Atmospharen. Teil I: Literaturauswertung und thermodynamische Berechnungen zur Stabilitat der Phasen In einer Reihe von Hochtemperatur-Prozesumgebungen fuhrt die Anwesenheit von chlorhaltigen Verbindungen zu einer deutlichen Verkurzung der Lebensdauer der Anlagenbauteile. Obwohl in diesen Anlagen metallische Legierungen bereits in grosem Umfang eingesetzt werden, besteht immer noch ein ausgepragter Bedarf an Daten zur Rolle des Verhaltens der verschiedenen Legierungselemente unter diesen Bedingungen. In der vorliegenden Arbeit wurde diese Rolle im Detail bei Temperaturen von 650 bis 1000°C in Luft mit Chlorgehalten bis zu 2% vol. untersucht. Vor der Durchfuhrung des experimentellen Teils der Untersuchungen wurde eine umfangreiche Literaturauswertung vorgenommen, gefolgt von thermodynamischen Rechnungen zur Stabilitat und zum Partialdruck der Phasen, die durch die Reaktion der Legierungen mit der Prozesumgebung gebildet werden konnen. Die Ergebnisse dieses “theoretischen Ansatzes” werden im ersten Teil einer zweiteiligen Veroffentlichung vorgestellt, wahrend uber die Ergebnisse der experimentellen Untersuchungen im zweiten Teil berichtet wird, der in einer spateren Ausgabe dieser Zeitschrift erscheint. Bereits die Ergebnisse des “theoretischen Ansatzes” erlauben eine klare Einschatzung, welche Legierungselemente eine positive und welche eine negative Rolle bezuglich der Korrosionsbestandigkeit von metallischen Legierungen in diesen Umgebungen spielen. Diese Ergebnisse konnen als Werkzeug fur die Bewertung des Verhaltens kommerzieller Werkstoffe in oxidierend/chlorierend wirkenden Atmospharen eingesetzt werden. Im zweiten Teil dieser Arbeit werden die Ergebnisse des “theoretischen Ansatzes” mit dem Korrosionsverhalten von 14 kommerziellen Werkstoffen verglichen, bei denen der Gehalt der wichtigsten Legierungselemente in systematischer Weise variiert wurde.

Protective behaviour of newly developed coatings against metal dusting

Abstract: Publisher Summary This chapter presents that whether a material is resistant to Metal Dusting (MD) depends on the ability of the material to develop a protective oxide scale. Most of the conventional low-cost steels widely used in plant technology do not possess a sufficient potential for protective oxide scale formation. However, to prevent corrosion of the materials, protective coatings rich in Al, Cr, Ti, and Si can be applied, which can form protective oxide scales and thus protect the underlying substrate from corrosive attack. In the chapter, Al, Cr, Si, and Ti have been chosen to produce diffusion and overlay coatings for reasons of their ability to form very stable protective oxide layers. The chapter presents several newly developed coatings and discusses the influence of temperature on oxide formation and behavior of the different coatings. The first type of coatings was applied by the pack cementation method leading to a diffusion coating on the base material. These coatings are based on stable oxide formers, such as Al, Ti, Si, and Cr.

Mechanical Properties of Oxide Scales on Mild Steel at 800 to 1000°C

Abstract: In the hot-rolling process of steels the oxide scales play a key role with regard to surface quality of the sheet. Therefore, a quantitative knowledge of the mechanical properties of oxide scales at rolling temperature can provide a significant improvement of sheet quality. In the present paper the mechanical properties of the oxide scales formed on mild steel were investigated in 4-point bend tests at 800, 900, and 1000°C in dry air, humid air (7–19.5 vol.% H2O) and laboratory air at different deformation rates. It turns out that the environment has a significant influence on scale thickness and structure as well as on adhesion of the oxide scales. The mechanical measurements show plastic-creep deformation of the oxide scales. Water vapor did not have any significant effect on the creep properties of the oxide scales. In the measurements the secondary-creep-stress values of the oxide were determined as a function of the strain rate and plotted into an Ashby map for FeO. This plot can serve for an extrapolation of the data for even higher strain rates as relevant for the hot-rolling process.

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing‐chloridizing atmospheres. Part II: Experimental investigations

Abstract: In an extensive study the role of the alloying elements in commercial alloys for corrosion resistance was studied in air without and with 0.1 and 2 vol.% Cl2, respectively. In the first part of this paper [1] the thermodynamic fundamentals were discussed on the basis of the new concept of the quasi-stability diagrams. The second part which is presented here reports the results from investigations at 650, 800 and 1000°C and testing times up to 1000 hrs where 14 commercial alloys were tested with regard to their corrosion behavior. The materials were selected so that the role of the alloying elements Mo, C, Si, Al, N, Fe, Ni and Cr would be evident from the results. The exposure tests were followed by extensive microstructural analyses of the corrosion scales and the metal subsurface zones so that type, mechanism and extent of corrosion could be characterized in great detail. At the end a ranking was possible of the different materials and with regard to the detrimental or beneficial role of the different alloying elements. The present results thus provide a much deeper insight into materials resistance in oxidizing-chloridizing environments at high temperatures. Die Rolle der Legierungselemente in kommerziellen Werkstoffen fur die Korrosionsbestandigkeit in oxidierend-chlorierend wirkenden Atmospharen. Teil II: Experimentelle Untersuchungen In einer umfangreichen Forschungsarbeit wurde die Rolle von Legierungselementen in kommerziellen Legierungen bezuglich deren Hochtemperaturkorrosionsbestandigkeit in Luft ohne und mit 0,1 bzw. 2 vol.% Chlor untersucht. Im ersten Teil des Berichts [1] werden die thermodynamischen Grundlagen auf der Basis des neuen Konzepts des “Quasi-Stabilitatsdiagramms” diskutiert. Der vorliegende zweite Teil berichtet uber die Ergebnisse aus den Korrosionsversuchen bei 650, 800 und 1000°C, in denen 14 kommerzielle Legierungen untersucht wurden und die bis zu 1000 h liefen. Die Werkstoffe waren nach einem System zusammengestellt worden, bei dem die Rolle der Legierungselemente Mo, C, Si, Al, N, Fe, Ni und Cr deutlich werden sollte. An die Korrosionsversuche schlossen sich umfangreiche mikroanalytische Untersuchungen an, in denen sehr detailliert Erscheinungsform, Mechanismen und Ausmas der Korrosion charakterisiert wurden. Am Ende konnte eine Einordnung der verschiedenen Werkstoffe bezuglich ihrer Korrosionsbestandigkeit und der Legierungselemente bezuglich ihrer positiven oder negativen Wirkung vorgenommen werden. Die Ergebnisse konnen einen wesentlichen Beitrag zum besseren Verstandnis der Korrosionseigenschaften technischer Legierungen in oxidierend-chlorierend wirkenden Umgebungen bei hohen Temperaturen liefern.

Investigation of the Fluorine Microalloying Effect in the Oxidation of TiAl at 900°C in Air

Abstract: High-temperature oxidation resistance of gamma titanium aluminides can be achieved by the formation of a continuous scale of slowly growing Al2O3. The formation of such a scale was favored by the addition of small amounts of fluorine. It is shown that fluorine can have a beneficial effect on oxidation resistance in a certain F-range which is quantified by thermodynamic calculations and by experimental investigations. It is assumed that the F-effect offers a significant potential for improvement of the oxidation resistance of technological TiAl alloys.

Influence of surface inhomogeneities of boron doped CVD-diamond electrodes on reversible charge transfer reactions

Abstract: The electrochemical behaviour of reversible charge transfer reactions on boron doped diamond (BDD) was studied by cyclic voltammetry and electrochemical impedance spectroscopy using rotating disc electrodes under defined convection. Diamond films of 5 μm thickness with doping levels of 200, 3000 and 6000 ppm were prepared by hot filament chemical vapour deposition on niobium substrate. The electrochemical measurements were carried out on BDD electrodes in deaerated 0.5 M Na2SO4 + 5 mM K3[Fe(CN)6]/K4[Fe(CN)6] solution at rotation frequencies 0 < frot < 4000 rpm. Comparative measurements were carried out on an active Pt electrode. The BDD electrodes exhibit distinct irreversibilities indicated by a larger peak potential difference in the cyclic voltammograms, lower diffusion limiting current densities and an additional impedance element at high frequencies. Mechanical polishing with carbon fleece and SiC paper strongly affects the irreversible behaviour of the BDD electrodes. The experimental results are explained by a partial blocking of the diamond surface with reversible charge transfer at active sites. The impedance spectra are analysed quantitatively using a transport impedance model for reversible reactions on partially blocked electrode surfaces.

Naphthalene and Hydronaphthalenes

Abstract: The article contains sections titled: 1. Physical and Chemical Properties 2. Production 3. Uses 4. Alkylnaphthalenes 5. Hydronaphthalenes 6. Economic Aspects 7. Toxicology

Potential‐Controlled Chromatography of Short‐Chain Carboxylic Acids

Abstract: A chromatographic column was constructed which could be operated with an electrically conductive stationary phase of graphite particles. This column allowed chromatographic experiments at variable electric potentials of the column material. The chromatographic behavior of selected carboxylic acids was significantly influenced at positive column potentials. An equimolar mixture of three different carboxylic acids were separated at a potential of +600 mV (versus. Ag/AgCl). Surprisingly, the stereoisomers maleic and fumaric acid, which are identical in molecular mass and charge, could also be separated. Further improvements to the chromatographic performance were achieved by applying potential drops and linear potential gradients.

Production of enclosed zeolite layers for use in e.g. catalysis or separation membranes, comprises first seed crystallization on carrier followed by further crystallization using different synthesis solution or gel

Abstract: Production of enclosed zeolite layers involves: (1) single-stage crystallization of zeolite seed crystals directly on a carrier; and (2) treating the seeded carrier with a synthesis solution or gel under suitable conditions to grow an enclosed layer in a second crystallization step, the synthesis solution or gel in this second crystallization cycle having a composition different to that in the seeding layer process.

Plasma immersion ion implantation of TiAl using chlorine containing plasma

Abstract: In order to apply the protective effect of Cl doping for high-temperature oxidation resistance of TiAl alloys of complex-shaped parts, plasma immersion ion implantation (PI 3 ) of chlorine into technical TiAl alloys was investigated. A specialized PI 3 apparatus was optimized for the strongly etching electronegative Cl plasma. Plasma diagnostics was performed using a Langmuir probe. In order to sustain a sufficiently dense plasma, different RF antenna configurations are discussed and the resulting densities are compared. The influence of plasma pulsing on the surface interaction of Cl during the process was evaluated. Two different commercial alloys were implanted and tested. The resulting depth profiles of the modified surface layer were investigated using depth profiling with Auger electron spectroscopy (AES). After implantation, the Cl is located close to the surface. Oxidation tests at 900 °C in air for 100 h showed a strong decrease in oxidation, which is comparable to conventional beamline implantation of Cl. The effect is rather independent of the alloy composition.

Verfahren zur Behandlung der Oberfläche eines aus einer AL-Legierung, insbesondere TiAL-Legierung bestehenden Bauteiles sowie die Verwendung organischer Halogenkohlenstoffverbindungen oder in einer organischen Matrik eingebundener Halogenide

Abstract: Die Aufbringung von organischen Halogen-Kohlenstoffen, z. B. PTFE (Polytetrafluorethylen) oder PVC (Polyvinylchlorid) oder in einer organischen Matrix eingelagerte Halogenide, auf die Werkstoffoberflache kann die Oxidationsbestandigkeit von TiAl-Legierungen im Temperaturbereich von 700 bis 1100°C an Luft gegenuber unbehandelten TiAl-Legierungen deutlich erhohen. Die Halogenverbindungen konnen durch verschiedene Verfahren, z. B. Eintauchen oder Bespruhen, auf den Werkstoffen aufgebracht werden. Der Erfolg dieser Methode kann dem Diagramm der Fig. 1 entnommen werden, die zeigen, dass patentgemas behandelte Legierungen keine Massezunahme erfahren, die auf eine Oxidation hinweisen (Kurven 1 und 2). Der Vergleich zeigt die Kurve 3 fur unbehandeltes Titan.

Electron spin resonance study of electron localization and dynamics in metal?molten salt solutions: comparison of M?MX and Ln?LnX3 melts (M = alkali metal, Ln = rare earth metal, X = halogen)

Abstract: We have studied the electron spin resonance (ESR) spectra in liquid K–KCl and M–(NaCl/KCl)eut mixtures at different concentrations in salt-rich melts approaching the metal–nonmetal transition region. In both systems F-centre-like characteristics are found. Strongly exchange narrowed signals clearly indicate that fast electron exchange occurs on the picosecond timescale. In contrast, the ESR spectra of a (NdCl2)(NdCl3)–(LiCl/KCl)eut melt are characterized by a large line width of the order of 102 mT which decreases with increasing temperature. In this case, the g-factor and correlation time are consistent with the model of intervalence charge transfer, which is supported by recent conductivity and optical measurements. The different transport mechanisms will be discussed.

Aluminum-titanium diffusion layers, used for improving corrosion resistance of metallic materials used in refinery for gasifying coal, petroleum coke or other residual materials, are produced by co-diffusion

Abstract: Aluminum-titanium diffusion layers are produced by co-diffusing the diffusion elements aluminum and titanium as pure metal powder in a weight ratio of 1: (0.1-5). Preferred Features: The layer is produced using a powder packing process. Activators, preferably ammonium halides, especially aluminum or titanium halides are used to produce the diffusion layers.

Production of protective coatings on metallic surfaces, especially anti-corrosion coatings, involves hydrolysis and polycondensation of coating compositions based on hydrolyzable silane compounds

Abstract: Protective organic-inorganic coatings are produced on metallic substrates by the hydrolysis and polycondensation of coating compositions containing (a) silanes with hydrolyzable groups or hydroxyl groups and optionally with non-hydrolyzable groups and (b) other compounds. A method for the production of protective organic-inorganic coatings on metallic substrates involves using a coating composition based on the hydrolysis and polycondensation of silane(s) of formula RnSiX4-n (I) or their oligomers, plus one or more other compounds, in which X : hydrolyzable groups or hydroxyl groups; R : non-hydrolyzable groups; and n : 0, 1 or 2.