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.

Future Directions in the Field of High-Temperature Corrosion Research

Abstract: High-temperature corrosion research will face a significant change in the near future. Up until now, this research area was dominated by materials issues related to the use of fossil fuels in energy conversion and transportation. Recent political decisions in many of the industrialized countries resulted in a paradigm shift towards the preference of non-fossil renewable energy and CO2 neutral or CO2-free technologies. These political constraints driving the development of new energy conversion technologies in combination with new materials and new manufacturing methods lead to new challenges in high-temperature corrosion research. The availability of advanced investigation techniques as well as increased IT power provides significant potential for the improved in-depth understanding of corrosion mechanisms and the development of comprehensive and reliable lifetime models. The present overview addresses all these aspects and attempts to sketch an outlook, although incomplete, on expected future developments in high-temperature corrosion research.

A single step process to form in-situ an alumina foam/aluminide TBC system for alloys in extreme environments at high temperatures

Abstract: A new approach to manufacture a complete thermal barrier coating system in a single step is studied in the frame of the European FP7 project PARTICOAT. Spherical μm-Al particles are deposited on different substrate alloys. During the sintering process in air, the μm-Al particles are oxidized and converted into hollow alumina spheres forming a ceramic “foam” (top coat), and simultaneously an Al rich diffusion layer (bond coat) is formed in the subsurface zone of the substrate. The “green” coatings deposited by air brush on IN738, Rene80 and CM247 nickel based alloys were cured at 300 °C and then isothermally exposed at 800 and 1000 °C in air for up to 1000 h. The oxide formation and the microstructure of the coatings were studied by thermo gravimetrical analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX). The coatings were adherent for all the substrates and temperatures tested. Rene80 shows the lowest mass gain whereas IN738 and CM247 show higher mass gains at the temperatures studied. Additionally, the use of reactive element oxides in the coating was investigated, demonstrating the flexibility and viability of this low cost coating concept.

Elektrochemische Korrosionsuntersuchungen in einer eutektischen Alkalisulfatschmelze

Abstract: Es wird eine Versuchsanordnung fur elektroschemische Korrosionsuntersuchungen in Salzschmelzen beschrieben. Als „Modellschmelze” wurde das ternare Eutektikum aus Li2SO4, Na2SO4 und K2SO4 gewahlt. Als Referenzelektrode wurde eine auf dem Gleichgewicht Silber/Silberionen basierende Elektrode entwickelt. Eine Trennung der Elektrodenraume erwies sich als wichtig, da die Oxydations- und Reduktionsprodkute der Schmelze weitgehend in der Schmelze verbleiben und zusatzliche Elektrodenprozesse verursachen. Dies Trennung der Elektrodenraume erfolgt durch Glas, des bei hoher Temperature ein reiner Ionenleiter ist. Als Beispiel fur die Anwendbarkeit der Methode werden einige Stromdichte-Potential-Kurven und Strom-Zeit-Kurven gezeigt. Die Korrosionsgeschwindigkeit kann durch Messen des Polarisationswiderstandes verfolgt werden. Electrochemical corrosion investigation in an eutectic alkali sulphate melt The author describes an experimental setup for electrochemical corrosion investigation in molten salts. The ternary eutectic system formed by lithium, sodium and potassium sulphates was selected as the model melt. An electrode based on the silver/silver ion equilibrium has been developed as a reference electrode. A separation of the electrode departments is important since the oxidation and reduction products of the melt largely remain in the latter and give rise to additional electode processes. This separation of the electrode departmetns is achieved by glass which is a pure ionic conductor at igh temperatures. As an example of possible applications of this method the author shows some current density/potential and current/time curves. The corrosion rate can be observed by measuring polarisation resistance.

Zum Mechanismus der Erosionskorrosion in schnell strömenden Flüssigkeiten

Abstract: Das Korrosionsverhalten von Kupfer, Messing und Graugus wird in 3%iger luftgesattigter NaCl-Losung bzw Meerwasser untersucht Die Versuche werden in einer Apparatur mit kreisformiger Couette-Stromung durchgefuhrt Bei Kleinen und sehr grosen Stromungsgeschwindigkeiten ist die Korrosionsgeschwindigkeit stark stromungsabhangig Oberhalb bestimmter kritischer Stromungsgeschwindigkeiten kommt es zu einer Lokalisierung des Angriffes, wobei an Stellen groser Turbulenz Erosionskorrosion auftritt Mit Hilfe elektrochemischer Methoden wird die jeweilige Korrosionsgeschwindigkeit ermittelt und es wird gezeigt, das der kathodische Teilschritt der Korrosionsreaktion geschwindigkeitsbestimmend ist Bei der Entstehung der Erosionskorrosion spielen nicht nur mechanische Wechselwirkungen des Mediums mit der Metalloberflache eine Rolle, sondern auch Vorgange innerhalb der Deckschicht Demgemas sind fur die Erosionskorrosion neben Stromungszustand und Oberflachenbeschaffenheit auch die Art und Stabilitat der Deckschichten entscheidend Mechanism of erosion corrosion in fast flowing liquids The corrosion behaviour of copper, brass and gray cast iron has been studied in 3 % air-saturated NaCl solution and seawater respectively The tests have been carried out in an experimental setup enabling a circular Couette type flow to be formed At low and very high rates the corrosion rate clearly depends from the flow Above certain critical flow rates the attack is localized and erosion corrosion is found at high turbulence spots By electrochemical methods the particular corrosion rates are determined and it is shown, that the cathodic partial corrosion reaction is rate-controlling The origin of mechanical interaction between the medium and the metal surface, but also to processes occurring within the covering layer Erosion corrosion consequently depends from flow conditions and surface properties and also from type and stability of the surface layers

Enzymatic production and in situ separation of natural β-ionone from β-carotene

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.