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.

Influence of alloy compositions on the halogen effect in TiAl alloys

Abstract: F-implantation concentration profile simulations were carried out and the influence of the ion fluence, implantation energy as well as the alloy composition were investigated. For alloys with Al contents between 40 and 50 at% the conditions to get the halogen effect were assessed by thermodynamic calculations. According to the thermodynamic predictions the implantation parameters were kept constant in this composition range. The implanted alloys were exposed in laboratory air over 4000 h. With the implantation parameters used (20 keV and 1 x 10 17 F/cm 2 ), the halogen effect was found to be efficient over 4000 h. The oxide growth kinetic constants were measured and vary between 1.2 and 2.7 x 10 -13 g 2 / cm 4 /s.

Elektrochemische Untersuchungen über die Stimulation der kathodischen Teilreaktion und der freien Korrosion von Silber und Chromstählen in Alkalisulfatschmelzen

Abstract: Es wird uber den Einflus von V2O5, NaVO3, Na3 VO4, MoO3, WO3 und K2CrO4 auf die kathodische Summenstromdichte-Potential-Kurve an Platin und auf die freie Korrosion von Silber und die ferritischen Chromstahle Werkstoff-Nr. 1.4713 und 1.4742 in Alkalisulfatschmelzen bei Temperaturen zwischen 625 und 800 °C berichtet. Alle genannten Substanzen auser WO3 stimulieren die kathodische Teilreaktion erheblich. Gehalte um 2 Mol-% lassen den Summenstrom um rd. zwei Grosenordnungen ansteigen. In allen Fallen treten Diffusionsgrenzstrome auf. V2O5 wird zu V2O4 und K2CrO4 zu Cr2O3 reduziert. WO3 hat nur einen relativ kleinen Einflus, da es in Alkalisulfatschmelzen nahezu unloslich ist. Ein Zusatz von Sauren (V2O5, NaVO3, MoO3) verschiebt das Redoxpotential der Schmelze um mehrere hundert Millivolt zu positiveren Potentialen. Ein Zusatz von Salzen (Na3 VO4, K2 CrO4) hat dagegen einen relativ geringen Einflus auf die Lage des Redoxpotentials. Die Korrosion von Silber wird besonders durch Sauren (V2O5, MoO3) beschleunigt, weil in diesen Fallen das freie Korrosionspotential besonders stark zu positiveren Potentialen verschoben wird. Im System K, Li2 SO4-V2O5 steigt z. B. bei 750 °C die Korrosionsrate des Silbers um rd. 6 Zehnerpotenzen an. Die ferritischen Chromstahle bilden unterhalb eines kritischen Potentials (Durchbruchspotential) passivitatsahnliche oxidische Deckschichten. Hier tritt starke Korrosion unter Bildung poroser sulfidhaltiger Deckschichten nur dann auf, wenn das freie Korrosionspotential uber dem Durchbruchspotential liegt. Das wird z. B. durch Zusatz von V2O5 und beim Werkstoff-Nr. 1.4713 auch durch Zusatz von NaVO3 zur Alkalisulfatschmelze erreicht. Hohere Gehalte der Schmelze an Na3 VO4 konnen aber auch die anodische Teilstromdichte-Potential-Kurve der Metallauflosung stimulieren. Electrochemical investigations into the stimulation of the cathodic partial reaction and free corrosion of silver and chromium steels in alkali sulfate melts Information is presented concerning the influence of vanadium pentoxide, sodium metavanadate, sodium vanadate, molybdenum trioxide, tungsten trioxide and potassium chromate on the cathodic accumulated corrosion density potential curve on platinum and on the free corrosion of silver and ferritic chromium steels (Werkstoff- No. 1.4713 and 1.4742) in alkali sulfate melts at temperatures between 625 and 800 °C. All the compounds mentioned, except WO3, produce a considerable stimulation of the cathodic partial reaction. Contents amounting to about 2 mole-% give rise to an increase of the accumulated current by appr. two orders of magnitude. In all the cases studied limiting diffusion currents are observed. V2O5 is reduced to V2O4 and potassium chromate to Cr2O3. The influence of WO3 is relatively small because of its insolubility in alkali sulfate melts. Addition of acidic compounds (V2O5, NaVO3, MoO3) shifts the redox potential of the melt by several hundres millivolts toward more positive potentials, while the addition of salts (Na3VO4, K2CrO4) has but little influence on the position of the redox potential. The corrosion of silver is accelerated, in particular by acidic compounds (V2O5, MoO3), which shift the free corrosion potential to much more positive values: in the system (K, Li)2SO4V2O5 the corrosion rate of silver at 750 °C increases by six orders of magnitude. Below critical potential (rupture potential) the ferritic chromium steels form oxidic surface layers resembling passivation layers. This effect is connected with the formation of porous, sulfide containing layers only in those cases where the free corrosion potential is above the rupture potential. This effect is attained e.g. by addition of V2O5, and in the case of material No. 1.4713 also by addition of NaVO3 to the sulfate melt. Higher contents of Na3VO4 in the melt, however, may give rise to a stimulation of the anodic partial reaction of metal dissolution.

Macrokinetics and mathematical modelling of quinone reduction by cyanobacteria

Abstract: The kinetics of the reduction of externally added 2-hydroxy-1,4-naphthoquinone by blue-green algae of the strains Anabaena PCC 7120 and Anacystis nidulans PCC 6301 were studied in aqueous cell suspensions by electrochemical monitoring of the concentration of the formed hydroquinone. This reaction is of potential interest for bioelectrochemical fuel cells. The experimental curves obtained could be interpreted by a model that takes into account that both substrate and product have to be transported through the microbial cell walls and that the conversion reaction takes place with firstorder kinetics within the microbial cells. No clear evidence was found for the involvement of photosynthesis. It is suggested that the reduction of the quinone probably occurs via the enzyme-catalyzed oxidation of endogenous storage product(s), presumably glycogen.

Methanol Utilisation Technologies

Abstract: Oil and gas are raw materials—the availability of which is prognosticated to run short in the near future. The peak oil discussion is an example generally perceived as proof of this development to come.