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.

Korrosionsbedingte Veränderungen von Festigkeitseigenschaften metallischer Werkstoffe

Abstract: Korrosion bewirkt Veranderungen im Festigkeitsverhalten von Metallen, die sich durch mechanisch-physikalische Werkstoffprufung erfassen lassen. Die nach der Korrosionsbeanspruchung verbliebene Restfestigkeit ist z. B. bei Kupfer im Falle eines flachigen Werkstoffabtrages dem Gewichtsverlust proportional, wenn man die Proben im Zerreisversuch pruft. Die Bruchdehnungen gehen indessen schon bei geringem Angriff unerwartet stark zuruck. Bei Korngrenzenkorrosion wird das Festigkeitsverhalten nicht nur durch eine Verminderung des tragenden Querschnittes, sondern zusatzlich durch die Kerbwirkung der korrodierten Korngrenzen bestimmt. Dies wird an potentiostatisch vorkorrodierten Proben eines 18/9 CrNi Stahles gezeigt. Bei transpassiven Potentialen wird dieser Werkstoff auch im losungsgegluhten Zustand interkristallin angegriffen. Wegen der auserdem noch geringen Intensitat der Korngrenzenkorrosion in diesem Potentialbereich ergeben sich hier keine signifikanten Unterschiede im Festigkeitsverhalten fur verschieden sensibilisierten Stahl. Das Dauerschwingverhalten des CrNi Stahles verschlechtert sich in dem Mase, wie die interkristalline Korrosion in die Tiefe des Gefuges fortschreitet. Gunstig wirken Chromcarbidausscheidungen, die die Gleitebenen blockieren und somit die Schwingfestigkeit verbessern. Changes in the strength properties of metallic materials due to corrosion Corrosion produces changes in the strength properties of metals and such changes can be assessed by mechanicophysical testing of materials. The residual strength after corosion is proportional to the weight loss, e.g. for uniformly corroded copper and when the specimens are tested in the tensile ruptured. The elongation at break, however, shows an unexpectedly strong decrease already at low corrosion levels. In the case of intercrystalline corrosion the strength properties depend not only from the reduction of the load-bearing cross section, but, additionally, are determined by the notch effect of corroded grain boundaries. This fact is shown on potentiostatically precorroded specimens of a CrNi steel 18/9. At transpassive potentials this material is attached by intercrystalline corrosion even after solution annealing. Because oft he low intensity of the intercrystalline attack in this range of potentials there are, however, no significant differences in the strength behaviour of the steel after different sensibilization treatments. The fatigue resistance of the CrNi steel is becoming worse as intercrystalline corrosion is advancing into the depth of the metal structure. Chromium carbide precipitation have a favourable effect because they block slip planes and thus improve fatigue resistance.

Depletion sensor for protective high temperature coatings

Abstract: In order to minimise corrosion at high temperatures metallic or intermetallic Al-and/or Cr-rich protective coatings are applied to metallic alloys. Protection against corrosion is achieved by the formation of a continuous Al(2)O(3) and/or Cr(2)O(3) layer. Progressive scale formation, as well as interdiffusion between the coating and the substrate during long operating stages depletes the scale-forming elements, Al and Cr. The decrease of their concentration below a critical value is followed by accelerated corrosion and rapid breakdown of the component. Non-destructive depletion measurement is not possible, because of the absence of suitable materials that serve simultaneously as depletion sensors and reservoir phases. In a novel development, protective high temperature coatings containing a magnetic phase which at the same time acts as a reservoir phase are used as a depletion sensor. The alloy surface is coated with the magnetic substance either by reactive magnetron co-sputtering or by using pack cementation. In the course of operation, the formation of a protective oxide scale depletes the reservoir and the measured magnetic signal decreases. Measurement of the change of the coating's magnetic signal enables in situ assessment and non-destructive detection of depletion. In order to avoid perturbances in the magnetic signal coming from the coating the metallic substrate must be non-magnetic. Therefore this concept is restricted to Cr/Ni-austenitic steels and Ni-base alloys. Doping of AlN with transition metals (Al(1 - x)Me(x)N, Me = Cr, Co, Mn, x = 2-7 at) makes it a suitable magnetic reservoir phase, i.e. Al- and/or Cr-containing. Furthermore, it is ferromagnetic, has a high Curie temperature and is magnetically soft. Samples of Alloy 800 and Alloy 602 CA were coated with Al(1 - x)Cr(x)N (x = 2 and 3 at) using both pack cementation and PVD. Measurements of the magnetic moments of the coatings at temperatures up to 300 degrees C show very soft ferromagnetic behaviour. Coatings on different substrates with Al(1 - x)Mn(x)N, Al(1 - x)Co(x)N (x = 2-7 at) and Al(1 - x)Cr(x)N with higher Cr contents (x = 4-7) are underway. Investigations of the magnetic properties of the coatings at temperatures up to the Curie point are also in progress.

Isolation and use of chromosome 1 probes for linkage studies on Charcot-Marie-Tooth disease.

Abstract: Nine probes were isolated from a human chromosome 1 enriched library and mapped to regions of chromosome 1 using somatic cell hybrid lines. One clone, LR67, which mapped to 1q12----q23 detected a BglI RFLP. This probe, as well as 4 other known chromosome 1 markers, alpha-spectrin, Factor XIIIB, DR10 and DR78, were used for linkage studies in 15 Charcot-Marie-Tooth disease (CMT1) families. Close linkage of CMT1 to any of the 5 markers was not indicated. Total lod scores excluded linkage of CMT1 to LR67 and to DR10 at 5 cM or less, to DR78 at 10 cM or less, alpha-spectrin at 15 cM or less and Factor XIIIB at 20 cM or less. Possible linkage, however, was shown between LR67 and CMT1 at a distance of 30 cM. Also linkage at a distance of 5 cM was detected between this probe and alpha-spectrin.

Werkstoff- und Korrosionsprobleme bei der Süßwassergewinnung†

Abstract: Neben verfahrenstechnischen Problemen sind bei der Suswassergewinnung aus Meerwasser vor allem Werkstoff- und Korrosionsprobleme zu losen, uber die dieser Beitrag einen kurzen Uberblick gibt. Die aufgezeigten Werkstoff-Fragen werden dabei unter den extremen Bedingungen thermischer Verfahren gesehen, die nach dem heutigen Stand der Technik am wirtschaftlichsten sind.