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.

Elektrochemische Vorgänge bei der Elektrolyse einer eutektischen Alkalisulfat‐Schmelze

Abstract: Fur die Untersuchungen wurde eine eutektische Schmelze aus Lithium-, Natrium- und Kaliumsulfat bei 625°C benutzt. An der Anode entsteht durch Oxidation der Sulfat-Ionen Schwefeltrioxid, das teilweise von der Schmelze gelost wird und ihr einen sauren Charakter gibt. An der Kathode wird, je nach Elektrodenpotential, Sulfat zu Sulfit, Schwefel oder Sulfid reduziert. Bei sehr negativen Potentialen gelingt auch eine Abscheidung von Alkalimetallen. An Gold, Platin und Silber kommt es dabei zur Bildung von Legierungen mit den Alkalimetallen, wodurch das Abscheidungspotential der Alkalimetalle um 200 bis 600 mV in positive Richtung verschoben wird. An Platin treten in der anodischen Stromdichte/Potential-Kurve ein Maximum und ein Minimum auf, die vermutlich auf Deckschichtenbildung zuruckzufuhren sind.

Modelling of the long time stability of the fluorine effect in TiAl oxidation

Abstract: Recently the target temperature of components manufactured from γ-TiAl alloys like turbine blades, turbocharger rotors or automotive valves has been increased to 900 °C. However, there is an insufficient oxidation resistance above 750 °C. One method used to improve the γ-TiAl oxidation behaviour is the so-called fluorine microalloying effect. After application of fluorine to the TiAl surface by ion implantation or treatment with diluted HF and oxidation at 900 °C in air a dense alumina layer is formed. However, after the treatments a distinct loss of fluorine was observed during heating and within the first hours of oxidation. In this work, the long time behaviour during isothermal and cyclic oxidation up to 1500 h/900 °C/air was investigated showing a slow fluorine decrease. The alumina layer acts as a diffusion barrier for fluorine, whereas fluorine diffuses into the metal. The diffusion coefficient was calculated. The results fit the theoretical model of the fluorine effect.

Improved Corrosion Resistance of Superheater Materials in H2O Containing Environments Using Mn-Diffusion Coatings

Abstract: The oxidation resistance of ferritic-martensitic 9% chromium steels in water vapour containing atmospheres is not yet satisfactory. The chromia layer provides little protection because water vapour in the atmosphere is known to promote the formation of the volatile chromium species CrO2(OH)2. If a chromium manganese spinel is formed instead, the vapour pressure of the oxy-hydroxide is greatly reduced and evaporation can largely be avoided. Enrichment of the substrate with manganese was achieved using three different processes: using (i) a sputtering technique, (ii) electrochemical deposition both followed by a diffusion heat treatment, (iii) the pack cementation method. Uniform diffusion of manganese was obtained with all of the investigated processes. The improved oxidation behaviour of the coated samples in synthetic air with 10% water vapour at 650°C was demonstrated.