Institution
DECHEMA
Nonprofit•Frankfurt am Main, Germany•
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.
Papers published on a yearly basis
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TL;DR: In this article, the ozone decomposition rates of different commercial titanium dioxide based photocatalysts grafted with copper, manganese or iron ions were studied both under UVA illumination and under dark conditions.
20 citations
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TL;DR: In this article, 9% chromium steel specimens were exposed to angular silica sand particles in a fluidized-bed erosion-oxidation rig for 200h at speeds of 7.0-9.2m/s−1.
20 citations
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TL;DR: In this article, an experimental investigation on the disturbing influence of the solutal Marangoni convection during diffusion measurements is presented, and the results are compared with the results of the FOTON M2-satellite mission with similar μg-experiments.
20 citations
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TL;DR: In this paper, the carburization behavior in CO-CO2-Gemischen with ac = 1 and in feuchtem Erdgas with ac > zwischen 1000 and 1200° C durchgefuhrt was investigated.
Abstract: Es wurden Aufkohlungsversuche an den Guswerkstoffen 1.4848, 1.4857, 2.4813 und einer 25/20/5-CrNiSi-Versuchsschmelze sowie an den Knetlegierungen 1.4301 und 1.4848 in CO-CO2-Gemischen mit ac = 1 und in feuchtem Erdgas mit ac > zwischen 1000 und 1200° C durchgefuhrt. Bei T < etwa 1050° C bilden sich gleichartige oxidische Deckschichten wie an Luft (Werkstoff/Cr2O3/(Mn, Fe)Cr2O4), die eine Aufkohlung verhindern. Eine Aufkohlung tritt erst nach Zerstorung der oxidischen Schutzschichten ein. Dabei mussen mehrere Zerstorungsmechanismen betrachtet werden, (a) durch chemische Reaktion (Umwandlung von Oxid in Carbid; Reduktion von Oxid), (b) durch mechanische Beanspruchung (Temperaturwechsel, Wachsen von Graphitschichten, Kriechverformung).
Reduktionsvorgange treten nur bei Fe-reichen Oxidschichten auf. Chromoxidreiche Deckschichten werden, abhangig vom CO-Partialdruck, in Gasen mit ac = 1 oberhalb etwa 1050° C in Carbid umgewandelt. Die Geschwindigkeit dieser Umwandlung ist stark von der Kohlenstoffaktivitat der Gasphase abhangig. Wird Graphit auf der Oberflache abgeschieden, so lauft die Umwandlung schnell ab, ohne Graphitabscheidung lauft sie selbst bei ac = 1 recht langsam an.
Abgeschiedener Graphit kann auch mechanisch zerstorend wirken, da er in Risse und Poren der Oxidschicht eindringt und so Teile der Oxidschicht abreist. Bei Vorliegen der porigen Gusoberflache konnen sogar Teile des Werkstoffs abgesprengt werden. Das erklart das schleche Verhalten von Rohren mit Gusoberflachen in Crackanlagen.
Die positive Wirkung des Siliziums beruht auf der Bildung von SiO2-Schutzschichten zwischen Metall und Cr2O3 bzw. zwischen Metall und auserer Carbidschicht. Zur Ausbildung geschlossener SiO2-Schichten darf der Werkstoff einen kritischen Si-Gehalt nicht unterschreiten.
Oxidation and Carburization of High Alloyed Materials for Cracking Tubes – Part 2: The Carburization Behaviour in Oxygen and Carbon Containing Atmospheres with High Carbon Activity
Carburization tests have been carried out with the casting materials (German Designation) Werkstoff-Nr. 1.4848, 1.4857, 2.4813 and an experimental 25/20/5-CrNiSi melt, and with the wrought materials Werkstoff Nr. 1.4301 and 1.4848 in CO-CO2 mixtures with ac = 1, and in humid natural gas with ac > 1 between 1000 and 1200° C. At temperatures below appr. 1050° C oxide layers formed are analogous to those formed in air (substrate/Cr2O3/(Mn, Fe)Cr2O4) which prevent carburization. Carburization takes place only after the protective oxide layer has been destroyed. In this context several mechanisms of destruction must be considered, i.e. (a) by chemical reaction (transformation of oxide into carbide, reduction of oxide), (b) by mechanical stresses (temperature fluctuation, growth of graphite layers, creep deformation).
Reduction processes are encountered with Fe-rich oxide layers only. Scale layers rich in chromium oxide are transformed into carbide above appr. 1050° C in gases with ac = 1, depending on the CO partial pressure. The rate of this transformation strongly depends on carbon activity in the gas phase. When graphite is deposited on the surface the transformation occurs at a high rate, while it is rather slow even at ac = 1 when no graphite is deposited.
Deposited graphite may have a mechanically destructive effect, too, because it penetrates into cracks and pores in the oxide layer and thus produces spalling of oxide particles. When the surface of the cast material is porous particles of the substrate may become detached, too. This goes to explain the poor behaviour of tubes with as cast surfaces in cracking reactors.
The positive effect of silicon is due to the formation of protective silica layers between metal and Cr2O3 and metal and external carbide layer respectively. In order to form a continuous silica layer the Si content in the material must not be below a cricital value.
20 citations
Authors
Showing all 760 results
Name | H-index | Papers | Citations |
---|---|---|---|
Wolf B. Frommer | 105 | 345 | 30918 |
Michael W. Anderson | 101 | 808 | 63603 |
João Rocha | 93 | 1521 | 49472 |
Martin Muhler | 77 | 606 | 25850 |
Michael Hunger | 60 | 295 | 11370 |
Ivars Neretnieks | 44 | 224 | 7159 |
Michael Schütze | 40 | 343 | 6311 |
Jens Schrader | 38 | 129 | 4239 |
Roland Dittmeyer | 31 | 206 | 3762 |
Lei Li | 29 | 198 | 4003 |
Dirk Holtmann | 29 | 107 | 3033 |
Lasse Greiner | 26 | 74 | 1994 |
Klaus-Michael Mangold | 23 | 57 | 1590 |
A. Rahmel | 23 | 59 | 1967 |
Gerhard Kreysa | 22 | 78 | 1305 |