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.

Korrosionsprüfung durch Stromdichte‐Potential‐Messungen in flüssigen Medien

Abstract: Metallauflosungsvorgange in flussigen Medien gehoren zu den heterogenen chemischen Reaktionen und verlaufen nacheinem elektrolytischen Mechanismus. Dadurch wird es moglich, neben den in der chemischen Kinetik ublichen mesbaren Grosen auch den Strom und das Potential mit einzubeziehen. Fur kinetische Untersuchungen besonders interessant ist die Stromdichte, die unter bestimmten Bedingungen ein direktes Mas fur die Korrosionsgeschwindigkeit ist. Zur Ermittlung der Korrosionsge-schwindigkeit werden folgende Metoden angewandt: 1Extrapolation der anodischen und kathodischen Teilaste der Stromdichte-Potential-Kurve, sofern sie der Tafelschen Beziehung gehorchen. 2Messung des Polarisationswirderstandes. 3Auswertung der Stromdichte-Potential-Kurve in Hinsicht auf geschwindig-keitsbestimmende Grenzstrome. 4Ermittlung der Korrosionsstromdichte aus der Stromspannungskurve passivierbarer Metalle und dem Potential eines vorgegebenen Redoxsystems. 5Messung des Korrosionsstromes im Lokalelement-Modell. 6Bestimmung der Stromverteilung im Elektrolyten bei lokaler Korrosion. Verschiedene Beispiele zeigen die allgemeine Anwendbarkeit und die Grenzen der einzelnen Methoden, wobei besonders auch auf die Probleme in der Praxis eingagangen wird.

Mechanical Properties and Adherence of Oxide Scales

Abstract: In the high temperature oxidation of metallic alloys oxide scale strains and in particular critical scale strains play a key role with regard to scale adherence. Scale spallation/exfoliation is a vital issue for not only long term alloy performance but also steel sheet production. In many cases materials selection is based on thermodynamic considerations and short term laboratory data, not taking into account changes in the oxidation mechanisms resulting from stresses induced by thermal cycles, oxide growth, specimen or component geometry, or other operational factors. This paper presents a very concise summary of the present knowledge in the form of an approach to a comprehensive scale failure model which is based on a number of microscopic and macroscopic system parameters. This failure model is part of an on-going work which aims at a computer-assisted assessment of oxide scale mechanical reliability.

Degradation mechanisms of aluminium diffusion coatings on 12% chromium steels under elevated temperature erosion – oxidation conditions

Abstract: Aluminium diffusion coatings offer one possible solution for improving the erosion–corrosion resistance of candidate steels for future power plants. However, their successful utilisation at temperatures higher than currently and under erosive load of solid particles requires an understanding of possible degradation phenomena that take place in both the short and the long term. This paper reports on the degradation resistance of aluminium diffusion coatings in the temperature range 550 – 700°C under impacts by silica sand particles at 30° and 90° for 200 h.For 90° particle impacts at 550°C and 600°C and 30° particle impacts at 650°C and 700°C, degradation of the coatings occurs rapidly by erosion, with oxidation or other diffusional processes in a minor role. For 30° particle impacts at 550°C and 600°C, the rate of erosion exceeds the rate of oxidation, with oxidation-affected erosion being the prevailing erosion – corrosion mode. Chipping and cutting wear pose the greatest challenge for long-term ...

A new concept of oxidation protection of Ni-base alloys by using the halogen effect

Abstract: The Ni-base alloys with Al-contents of less than 10 wt% are widely used in high temperature technology due to their beneficial mechanical properties. However, their oxidation resistance may be insufficient at temperatures above 1000°C. Oxidation of these Ni-base alloys does not form a pure continuous Al2O3 protective scale on the surface, but rather a complex layer structure. This structure is characterized by inward growing oxides showing a discontinuous alumina scale. A new method for the formation of a dense protective alumina scale on the surface is now presented. The method is based on the halogen effect, which was successfully applied for TiAl-alloys. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. The fluorine treatment is performed by ion implantation. The implantation parameters are defined by using Monte Carlo simulations. Following these results fluorine implantations of the Ni-base alloy IN 738 are...