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.

Electro-enzymatic hydroxylation of ethylbenzene by the evolved unspecific peroxygenase of Agrocybe aegerita

Abstract: The unspecific peroxygenase from the fungus Agrocybe aegerita (AaeUPO) is an up-and-coming biocatalyst that is able to perform specific oxyfunctionalizations of various substrates. Due to inactivation at excess concentrations of its co-substrate H2O2, AaeUPO’s technical application is still limited. This study aims to promote catalyst efficiency via electrochemical in situ supply of H2O2, using an evolved variant of AaeUPO on the example of ethylbenzene hydroxylation. Total turnover numbers of up to 400,000 molproduct molAaeUPO−1 and space-time-yields of up to 25 g L−1 d−1 were achieved in the electro-enzymatic system. These numbers are in the upper range of published data. The presented system stands out by its very high atom economy. Thus, combining electrochemistry and biocatalysis is one step closer towards the first application of peroxygenases in an industrial process.

The Influence of Hydrodynamics on Erosion-Corrosion in Two-Phase Liquid-Particle Flow

Abstract: Erosion-corrosion measurements on ferrous materials in CO2 and sand-containing formation water are correlated with hydrodynamic measurements applying laser Doppler anemometry. It is shown ...

Cracking in and around the thermally grown oxide in thermal barrier coatings: A comparison of isothermal and cyclic oxidation

Abstract: In the present paper the time and temperature dependent evolution of the microstructure of TBC systems and especially of post-experimentally determined physical defects in and around the TGO for both isothermal and cyclic exposure conditions are investigated. Specimens with APS- as well as with PVD-topcoats have been oxidised between 950 and 1100°C up to a maximum duration of 5000 h followed by extensive scanning electron microscopy and subsequent interactive image analysis to measure the maximum crack lengths in and around the TGO. These cracks are additionally classified with respect to their local orientation in the TGO or its vicinity. The results of isothermal and cyclic test conditions show a number of similarities in results e.g. an unsystematic occurrence of inwardly growing, “cauliflower like” oxide or the most frequently occurring type of cracks in APS systems. Nevertheless substantial differences concerning the final failure, microstructure, crack growth behaviour and finally life time of the component between isothermal and cyclic test conditions exist. Some indications were found, that for this particular bond coat occurance of inwardly growing oxide intrusions increases the adherence of the TGO.

Oxidation Behaviour of TBC Systems on γ-TiAl Based Alloy Ti–45Al–8Nb

Abstract: The lifetime of thermal barrier coating (TBC) systems on gamma titanium aluminides was determined in the temperature range between 850 °C and 950 °C under cyclic oxidation conditions in air. Coupons of the alloy Ti–45Al–8Nb (at.%) were coated by pack aluminizing. A subset of samples was subsequently annealed at 910 °C for 312 h in argon. During this heat treatment, the two-phase (Nb,Ti)Al3 plus TiAl2 microstructure of the coating transformed into single phase γ-TiAl. On pre-oxidised aluminized, annealed and bare samples, TBCs of yttria partially stabilized zirconia were deposited using electron-beam physical vapour deposition (EB-PVD). No spallation of the TBCs was observed in cyclic oxidation tests at 850 °C for up to 3,000 cycles of 1 h dwell time at high temperature. The two-phase aluminide coating provided effective oxidation protection due to the formation of a continuous alumina scale. The lifetime of this TBC system exceeded 1,400 cycles at 950 °C, whereas an aluminized and annealed sample failed after approximately 500 cycles. The TBC on bare substrate failed when thermally cycled at 900 °C. In contrast, no spallation occurred with an aluminized and annealed specimen at this temperature during the maximum exposure length of 1,000 cycles, probably related to an increased aluminium concentration in the subsurface region. EB-PVD zirconia top coats were well adherent to the alumina scale and the thermally grown mixed oxides. Failure of the TBC systems observed with bare and annealed samples was associated with spalled oxide scales formed on γ-TiAl.

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.