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.

Potential‐Controlled Chromatography of Short‐Chain Carboxylic Acids

Abstract: A chromatographic column was constructed which could be operated with an electrically conductive stationary phase of graphite particles. This column allowed chromatographic experiments at variable electric potentials of the column material. The chromatographic behavior of selected carboxylic acids was significantly influenced at positive column potentials. An equimolar mixture of three different carboxylic acids were separated at a potential of +600 mV (versus. Ag/AgCl). Surprisingly, the stereoisomers maleic and fumaric acid, which are identical in molecular mass and charge, could also be separated. Further improvements to the chromatographic performance were achieved by applying potential drops and linear potential gradients.

Failure of oxide scales on advanced materials due to the presence of stresses

Abstract: Stresses in protective oxide scales often receive too little attention although loss of the protective effect in very many cases can be attributed to scale failure due to mechanical stresses. These stresses may be the result of externally applied deformation of the scale/substrate composite, of temperature changes and of the oxide growth process itself, and have to be expected under most practical conditions. In the paper an approach is described based on model considerations and on materials data which allow a quantitative characterization of the role of stresses and strains respectively for failure of the protective oxide scales. The data used for discussion are relevant for scales on advanced materials.

Strömungsabhängigkeit der Lochkorrosion eines Cr-Ni-Stahles in NaCl-Lösung. Teil I: Versuche mit der rotierenden Scheibe

Abstract: Die Lochkorrosion des Chrom-Nickel-Stahles X 5 CrNi 18 9, Werkstoff Nr. 1.4301, in NaCl-Losungen (1 und 3 n) bei 25 °C wurde mit Hilfe der rotierenden Scheibe in Abhangigkeit von der Drehzahl bzw. von der Diffusionsschichtdicke untersucht. Potentiokinetische und potentiostatische Versuche zeigten, das das Lochfraspotential fur stabile Lochkorrosion wesentlich mehr durch Stromung beeinflust wird als das Lochfraspotential fur repassivierbare Lochkorrosion. Mit zunehmender Drehzahl bzw. mit abnehmender Diffusionsschichtdicke nehmen die Lochdichte zu und die Korrosionsgrenzstromdichte sowie die durchschnittlichen und maximalen Lochradien ab. Das besagt, das die Lochfrasstellen oberhalb einer kritischen Grose repassiviert werden, die mit steigender Drehzahl abnimmt. Im Gegensatz zu den Verhaltnissen in ruhenden Losungen, in denen die Lochdichte zeitlich nahezu konstant bleibt, werden bei Stromung neben der Repassivierung standig neue Lochfrasstellen erzeugt. Die Lochdichte nimmt hier also mit der Zeit scheinbar zu. Flow dependence of the pitting of a CrNi steel in NaCl solution. Pt. I: Experiments with the rotating disc The pitting of the CrNi steel (German designation X 5 CrNi 18 9, Werkstoff Nr. 1.4301) in NaCl solution (1 and 3 N) at 25 °C has been investigated with the aid of the rotating disc, with a view to its dependence from the number of revolutions and the thickness of the diffusion layer. Potentiokinetic and potentiostatic experiments have shown, that the pitting potential for stable pitting is a function of flow in a more pronounced way than the potential for repassivating pitting corrosion. The pitting density increases as the number of revolutions increases and the thickness of the diffusion layer decreases, while the corrosion limiting current density and the average and maximum pit radii decreases in the same conditions. This goes to show that the sit locations are repassivated when exceeding a critical size which decreases with increasing number of revolutions. Contrary to the conditions prevailing in stagnant solutions where the pit density is almost independent from time, new pits are generated permanently despite repassivation under conditions of flow. Consequently, there is a apparent increase of pit density with time.