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.

Stresses generated during oxidation sequences and high temperature fracture

Abstract: This paper deals with the stresses generated during high temperature oxidation and their relationship to scale fracture. In the first part, the objective is to differentiate growth stresses from thermal stresses and give evidence for relaxation phenomena. The results obtained for materials which develop NiO, Cr2O3 or Al2O3 scales indicate that, in most cases, growth stresses in the oxide films are negligible compared to thermal stresses, probably on account of stress relaxation at high temperature. Moreover, the stress sign in the oxide scale is inconsistent with conventional views based on the Pilling-Bedworth ratio, but closely related to the growth mechanism of the oxide: a preponderantly cationic diffusion leads to tensile stresses, whereas a preponderantly anionic diffusion leads to compressive stresses. Thermal stresses are closely related to the differences between the expansion coefficients of the scale and the substrate, but can be modified by parameters which can promote stress relaxation such a...

Kinetic Analysis of Terminal and Unactivated CH Bond Oxyfunctionalization in Fatty Acid Methyl Esters by Monooxygenase‐Based Whole‐Cell Biocatalysis

Abstract: The alkane monooxygenase AlkBGT from Pseudomonas putida GPo1 constitutes a versatile enzyme system for the ω-oxyfunctionalization of medium chain-length alkanes. In this study, recombinant Escherichia coli W3110 expressing alkBGT was investigated as whole-cell catalyst for the regioselective biooxidation of fatty acid methyl esters to terminal alcohols. The ω-functionalized products are of general economic interest, serving as building blocks for polymer synthesis. The whole-cell catalysts proved to functionalize fatty acid methyl esters with a medium length alkyl chain specifically at the ω-position. The highest specific hydroxylation activity of 104 U gCDW−1 was obtained with nonanoic acid methyl ester as substrate using resting cells of E. coli W3110 (pBT10). In an optimized set-up, maximal 9-hydroxynonanoic acid methyl ester yields of 95% were achieved. For this specific substrate, apparent whole-cell kinetic parameters were determined with a Vmax of 204±9 U gCDW−1, a substrate uptake constant (KS) of 142±17 μM, and a specificity constant Vmax/KS of 1.4 U gCDW−1 μM−1 for the formation of the terminal alcohol. The same E. coli strain carrying additional alk genes showed a different substrate selectivity. A comparison of biocatalysis with whole cells and enriched enzyme preparations showed that both substrate availability and enzyme specificity control the efficiency of the whole-cell bioconversion of the longer and more hydrophobic substrate dodecanoic acid methyl ester. The efficient coupling of redox cofactor oxidation and product formation, as determined in vitro, combined with the high in vivo activities make E. coli W3110 (pBT10) a promising biocatalyst for the preparative synthesis of terminally functionalized fatty acid methyl esters.

Role of platinum in the na2so4-induced hot corrosion-resistance of aluminum diffusion coatings

Abstract: Electrochemical corrosion measurements have been carried out with Pt-containing and Pt-free Al-diffusion coatings on IN 738 LC in a 90Na2SO4+ 10K2SO4 (mol%) melt at 1173 K. Pt improves the resistance to basic fluxing while there are no significant differences between both coating types in their resistance to acidic fluxing. The corrosion resistance of the Pt-containing coating is also higher in the passive potential region where protective scales rich in Al2O3 are formed. The reason for the different behavior of both coating types appears to be related to the high corrosion resistance of the Pt-rich surface layer of the coating and an increased Al2O3 content in the scale of the Pt-containing type.

An extensive study about influence of the carbon support morphology on Pt activity and stability for oxygen reduction reaction

Abstract: Several commercial carbons were tested with respect to their thermal stability and electrochemical activity as Pt catalyst support for oxygen reduction reaction (ORR). TGA analysis revealed that carbons with low BET surface such as graphite nanoparticles (GNP500, 100 m² g−1) are less prone to degradation than ordered mesoporous carbon (OMC, 1000 m²g−1). Moreover, high Pt loading favored considerably carbon oxidation rate in air. Best results in terms of activity for ORR and stability during electrochemical accelerated degradation tests (ADT) were yielded by Pt/GNP500 and Pt/OMC, respectively. High graphitization level and mesoporous surface structure of carbon were found to be determinant for sustainable Pt stability. Addition of certain amount of PTFE to Nafion as binder in gas diffusion electrode (GDE) catalyst layer clearly improved electrochemical surface area (ECSA) retention. Comparative identical location TEM images of electrochemically-aged Pt on Vulcan and OMC demonstrated positive influence of mesoporous carbon surface on immobilization of catalyst particles and consequently on ECSA retention. After 10,000 ADT cycles, ECSA retention was close to 30% for Pt/OMC compared to about 1% for Pt/Vulcan. This was due to dramatic increase of Pt particle size on Vulcan support up to 40 nm compared to about 15 nm for Pt on OMC.