DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Characterization of the long time oxidation protection of fluorine implanted technical TiAl-alloys using ion beam methods

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.

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.

Modeling and simulation-based design of electroenzymatic batch processes catalyzed by unspecific peroxygenase from A. aegerita.

Abstract: Unspecific peroxygenases have attracted interest due to their ability to catalyze the oxygenation of various types of C-H bonds using only hydrogen peroxide as a cosubstrate. Due to the instability of these enzymes at even low hydrogen peroxide concentrations, careful fed-batch addition of the cosubstrate or ideally in situ production is required. While various approaches for hydrogen peroxide addition have been qualitatively assessed, only limited kinetic data concerning enzyme inactivation and peroxide accumulation has been reported so far. To obtain quantitative insights into the kinetics of such a process, a detailed data set for a peroxygenase-catalyzed benzylic hydroxylation coupled with electrochemical hydrogen peroxide production is presented. Based on this data set, we set out to model such an electroenzymatic process. For this, initial velocity data for the benzylic hydroxylation is collected and an extended Ping-Pong-Bi-Bi type rate equation is established, which sufficiently describes the enzyme kinetic. Moreover, we propose an empirical inactivation term based on the collected data set. Finally, we show that the full model does not only describe the process with sufficient accuracy, but can also be used predictively to control hydrogen peroxide feeding rates To limit the concentration of this critical cosubstrate in the system.

Elektrochemische Untersuchungen zur Hochtemperaturkorrosion hochlegierter Werkstoffe in Alkalisulfatschmelzen

Abstract: Die Untersuchungen wurden bei 625 und 800°C an Eisen, Chrom, 4 ferritischen CrStahlen, 2 austenitischen CrNi-Stahlen, je einer Ni-und Co-Basislegierung sowie an 3 Chromlegierungen unter Luft in Alkalisulfatschmelzen durchgefuhrt. Eindeutige Aussagen uber die Potentialabhangigkeit des Korrosionsverhaltens lassen nur Massenverlust-Potential-Kurven zu. Aus ihnen ergibt sich, das bei allen untersuchten Werkstoffen zwei Potentialbereiche mit unterschiedlichen Korrosionsverhalten auftreten. Bei relative negativen Potentialen bildet sich eine Schutzschicht auf der Werkstoffoberflache und die Korrosionsrate ist klein und nahezu potentialunabhangig. Oberhalb eines vom System. Werkstoff/Schmelze abhangigen Durchbruchpotentials bilden sich porose Deckschichten. In diesem Potentialbereich steigt die Korrosionsrate mit dem Potential steil an. Das Durchbruchpotential wird mit steigendem Cr-Gehalt der Werkstoffe zu positiveren Potentialen verschoben, jedoch haben Cr-Gehalt > 20% keinen wesentlichen Einflus mehr auf das Durchbruchpotential. Auch die Temperature hat keinen wesentlichen Einflus auf die Lage des Durchbruchoptentials. Potentiodynamische Summenstrom-Potential-Kurven sind mit grosem Vorbehalt zu interpretieren. Ihre Lage ist abhangig von der zeitlichen Anderung des Potentials. Die ungefahre Lage des Durchbruchpotentials ist oft nur bei sehr langsamer Potentialanderung zu erkennen. Bei groserer zeitlicher Potentialanderung wird das Durchbruchpotential in der Regel scheinbar zu negative gefunden. Das hangt wahrscheinlich mit potentialabhangigen Wachstumsvorgangen der Passivschicht zusammen. Electrochemical investigation into the high temperature corrosion of high alloy materials in alkali sulafte metals The investigations have been carried out in alkali sulfate melts under air at 625 and 800°C with iron, chromium, four ferritic chromium steels, two austenitic chromium nickel steels, one each nickel and cobalt base alloy and three chromium alloys. Clear statements concerning the potential dependence of the corrosion behaviour are feasible only on the basis of mass loss/potential curves. It results from these curves that the behaviour of all the materials studied is characterized by two potential regions with different corrosion behaviour. At relatively negative potentials a protective layer is formed on the material surface and the corrosion rate is low and almost independent from potential. Above a rupture potential (which depends from the system material/melt) porous surface layers are formed. In this potential range the corrosion rate shows a steep increase as potential increases. With increasing chromium contents of the materials the rupture potential is displaced towards more positive potentials, but chromium contents exceeding 20% have no markable influence on the rupture potential. Temperature, too, does not noticeably affect the position of the rupture potential. The interpretation of potentiodynamic accumulated current/potential curves requires great care; the shape of such curves depends from the variation of potential with time. The approximate position of the rupture potential can frequently be recognized at very low potential variations only. At larger potential variations in time the values of the rupture potential appear as a rule to be too negative; this phenomenon may probably attributed to potential dependence growth processes in the passive layer.

Impact of Deposits and Their Morphology on the Active Corrosion of Iron in Chlorine- and Sulfur-Containing Atmospheres in the Temperature Range of 350–500 °C

Abstract: Iron-based alloys have shown high corrosion rates under ash deposits typical for waste-to-energy plants. The ashes on superheater tubes in waste incineration are multicomponent systems including alkali and alkali–earth chlorides and sulfates. Under and within such salts, the corrosive effect on the alloy is induced by a complicated interplay of such ash products. On the one hand, in chlorine-containing atmospheres iron-based alloys are believed to be attacked by the so-called active corrosion, including the formation of volatile corrosion products and their transformation into stable iron oxides. At the same time, they form complex scales, involving among other compounds iron sulfides, chlorides, and oxides. Thus, in order to directly investigate the influence of a deposit on the corrosion in waste-to-energy plants and to reproduce the scales observed on field tested superheaters, this work compares the scale formation and metal wastage under different chemically inert alumina deposits with different grain sizes to a synthetic salt as well as to an actual deposit taken from a superheater tube in a plant.