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Institution

DECHEMA

NonprofitFrankfurt 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.
Topics: Corrosion, Oxide, Coating, Alloy, Catalysis


Papers
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Journal ArticleDOI
TL;DR: In this article, the microstructure and phase development of silicon and molybdenum-implanted γ-TiAl was investigated, and the influence of the local Si concentration on the oxidation behavior was discussed.
Abstract: Titanium aluminide alloys based on γ-TiAl have a substantial potential for high-temperature applications. However, there are still problems concerning the high-temperature oxidation behavior. Ion implantation is a promising tool for improving the oxidation resistance without disturbing the mechanical properties. A systematic investigation of the microstructure and phase development of silicon- and molybdenum-implanted γ-TiAl is presented. For Si, the fluence is varied from 2.5×10 16 to 8×10 17 cm −2 at an implantation energy of 1 MeV resulting in a local concentration of Si between 1 and 35 at.% at a projected range of 1 μm, measured by AES depth profiling. Grazing incidence XRD and transmission electron microscopy show the formation of a buried Ti 5 Si 3 enriched layer at 650°C, which acts as a diffusion barrier for oxygen. Long-term TGA oxidation tests at 900°C in air show a positive effect in the beginning of oxidation for the fluence of 8×10 17 Si cm −2 . After a few hours the oxidation kinetics is similar to unimplanted Ti50Al, but the mass gain after 100 h is still 30% smaller. The influence of the local Si concentration on the oxidation behavior is discussed. Implantation of Mo at 180 keV (2×10 16 and 1×10 17 cm −2 ) has only a minor influence on the oxidation at 900°C. After implantation, Mo precipitates are found for the high fluence.

12 citations

Journal ArticleDOI
01 Nov 1978
TL;DR: In this article, the authors describe the kinetics of the reactions of some aliphatic mercaptans with O(3P) atoms, and the experimental arrangement consists of a fastflow reactor, a supersonic molecular beam sampling system, a high resolution mass spectrometer as detector and a dosage system.
Abstract: The kinetics of the reactions of some aliphatic mercaptans with O(3P) atoms is described. The experimental arrangement consists of a fastflow reactor, a supersonic molecular beam sampling system, a high resolution mass spectrometer as detector and a dosage system. The rate constants were determined under O atomrich conditions ([O] ≈ 10−10 mol/cm3, 8 ≤ [O]/[RSH] ≤ 43) by measuring the mercaptan decay which was found to be pseudo-first order. The following Arrhenius parameters for CH3SH to C5H11SH were found; Frequency factors A: (8.5 ± 1), (5.75 ± 0.3), (8.33 ± 0.54), (5.78 ± 0.33), (6.18 ± 0.35) 1012 cm3/moles; activation energies E: (5.2 ± 0.3), (3.25 ± 0.15), (4.11 ± 0.18), (2.67 ± 0.16), (2.73 ± 0.16) in kJ/mol. With an excess of O atoms mainly SO2, CO2, HCHO, and H2S were found; for mercaptan-rich mixtures sulphides and disulphides were formed in addition, indicating the occurrence of thiyl radicals as intermediates. OH and CH3 radicals were also analysed. – As O2 is present in the atmosphere, in part II its influence on the reaction system is discussed, especially its reactions with thiyl radicals. In a CSTR, oxygen-nitrogen mixtures, containing small amounts of mercaptan (0.5 ± 10−9 – 30. mol/cm'), were irradiated with quanta of I, = 253.7 nm. The reactions of the originating thiyl radicals at different 0,concentrations were investigated. The identified reaction products were aldehyde, SO, and disulphide. Together with these results, a possible sequence of primary reaction steps in the reaction of mercaptans with 0 atoms is given. Die Kinetik der Reaktionen einiger aliphatischer Merkaptane mit O(3P)-Atomen wird beschrieben. Die Versuchsanordnung besteht im wesentlichen aus einem Stromungsreaktor, einem Uberschallmolekularstrahl-Probenahmesystem,einem hochauflosenden Massenspektrometer als Analysator und den Dosiereinrichtungen. Aus der zeitlichen Abnahme der Merkaptankonzentration bei 0-Atomuberschus ([O] ≈ 10−10 mol/cm3, 8 ≤ [O]/[RSH] ≤43) wurden die Geschwindigkeitskonstanten bestimmt; das Zeitgesetz entsprach einer Reaktion pseudo-erster Ordnung. Die folgenden Arrheniusparameter fur Methyl- bis Pentylmerkaptan wurden ermittelt; Frequenzfaktoren A: (8.5 ± 1). (5.75 ± 0,3), (8,33 ± 0,541, (5,78 ± 0.33). (6.18 ± 0,35) 10 12cm3/mol Aktivierungsenergien E: (5.2 ± 0.3). (3.25 ± 0.15 ). ( 4,11 ± 0,18), (2,67 ± 0,16), (2,73 ± 0,16) in Bei 0-Atomuberschus wurden hauptsachlich SO2, CO2 HCHO und HIS gefunden; fur hoheren Merkaptangehalt wurden daruber hinaus noch Sulfide und Disulfide gebildet. Dies kann als Hinweis auf gebildete Thiylradikale gewertet werden. OH- und CH,-Radikale wurden ebenfalls nachgewiesen. -Wegen des hohen 0,-Gehaltes der Atmosphare wird im zweiten Abschnitt dieser Arbeit der mogliche Einflus von 02, auf das Reaktionssystem diskutiert, insbesondere wird die Reaktion von Thiylradikalen mit O2 untersucht. In einem kontinuierlichen Ruhrkessel wurden Sauerstoff/Stickstoff-Mischungen, die geringe Mengen Merkaptan (0.5 · 109 bis 30 · 10−9-mol/cm) enthielten, mit Quanten der Wellenlange λ = 253,7 nm bestrahlt. Die Reaktionen der entstehenden Thiylradikale wurden in Abhangigkeit vom 02-Partialdruck verfolgt; sie fuhrten zu Aldehyd, SO2 und Disulfid. Zusammen mit diesen Ergebnissen wurde eine mogliche Folge von Primarschritten fur die Reaktion von Merkaptanen mit 0-Atomen ausgearbeitet.

12 citations

Journal ArticleDOI
TL;DR: In this paper, four-point bend testing in both tension and compression and direct tensile and compression tests are discussed, and an attempt is made to estimate errors and consider the effects of important test variables such as strain rate, temperature and dwell periods.
Abstract: Consideration is given to methods currently used for the determination of tensile and compressive fracture strains of thermally formed protective oxide layers at ambient and elevated temperatures. The methods discussed are four-point bend testing in both tension and compression and direct tensile and compression tests. Detection of failure of the oxide is usually by acoustic emission, but in some cases, where the acoustic signal is too small, direct observation of failure can be made by in situ methods using scanning electron microscopy or acoustic microscopy. Details of the tests are described together with the limitations of the different techniques. An attempt is made to estimate errors and consider the effects of important test variables such as strain rate, temperature and dwell periods.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of the superalloy composition and crystal orientation on the formation of an unconventional thermal barrier coating system (TBC) was reported, where a 6-μm-thick Pt layer was first electrodeposited onto a directionally solidified (DS) CM-247LC and a single crystal (SX) PWA-1483 substrate followed by annealing.
Abstract: The influence of the superalloy composition and crystal orientation on the formation of an unconventional thermal barrier coating system (TBC) is reported. A 6 μm-thick Pt layer was first electrodeposited onto a directionally solidified (DS) CM-247LC and a single crystal (SX) PWA-1483 substrate followed by annealing. A water-based slurry containing Al microparticles was then applied and annealed to form simultaneously a ceramic top coat and a diffusion bond coat. Irrespective of the annealing treatment (Pt, slurry), thinner diffused layers were obtained with the SX than with the DS material. Dual PtAl 2 and (Ni,Pt)Al phases formed in both diffused layers but Cr segregation at the coating/substrate interface restricted further ingress of Pt and of Al into the SX superalloy compared to the DS one. This was related to the greater Cr content in the SX than in the DS material and to the absence of grain boundaries in the former. Nevertheless, a ceramic top coat composed of hollow alumina spheres formed over the thermally grown oxide and the diffused layer on both substrates.

12 citations


Authors

Showing all 760 results

NameH-indexPapersCitations
Wolf B. Frommer10534530918
Michael W. Anderson10180863603
João Rocha93152149472
Martin Muhler7760625850
Michael Hunger6029511370
Ivars Neretnieks442247159
Michael Schütze403436311
Jens Schrader381294239
Roland Dittmeyer312063762
Lei Li291984003
Dirk Holtmann291073033
Lasse Greiner26741994
Klaus-Michael Mangold23571590
A. Rahmel23591967
Gerhard Kreysa22781305
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
20231
20227
202145
202053
201949
201844