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.

Selection of Materials for Use at Temperatures above 1500°C in Oxidizing Atmospheres

Abstract: The purpose of this work was to select materials for applications in oxidizing atmospheres at temperatures of a minimum of 1500°C. Several requirements had to be fulfilled, e.g. long-term oxidation resistance, low vapour pressure, high creep resistance and low gas permeability. Another important point was to avoid reactions and sintering in material combinations with silica forming materials. The investigation was based on a detailed literature screening, followed by compatibility tests at 1600°C in air with potential materials (Al2O3, ZrO2, CeO2, La2O3, Y2O3, HfO2, MgO·Al2O3) and Mosi2 as an example of a silica-forming material. The result of these experiments was, that only Y2O3 and HfO2 did not show severe reactions in contact with MoSi2. Since most of the materials available did not fulfill all the requirements, some new materials were investigated: CIPed MoSi2 with different additives (SiC, ZrB2) and recrystallized SiC (RSiC) with a polymer (polysiloxane) derived MoSi2-filled coating. The oxidation behaviour of these materials was evaluated by continuous thermogravimetric measurements at 1500°C over a period of 100 h in air and by detailed postexperimental investigations.

Preparation and Properties of Composite Polypyrrole/Pt Catalyst Systems

Abstract: Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques).

Untersuchung von Transportvorgängen bei der Korrosion

Abstract: In vielen Korrosionsfallen spielt der Antransport des angreifenden Agens oder der Abtransport der Korrosionsprodukte eine bedeutende Rolle. Nach einer Erorterung der fur den Stofftransport wichtigen Grundlagen werden eine Reihe von Untersuchungsmethoden besprochen. Es sind dies Versuche mit Hilfe der rotierenden Scheibe, dem durchstromten Rohr und dem rotierenden Zylinder. Auch wird gezeigt, das Dauertauchversuche durch naturliche Konvektion beeinflust sein konnen. Am Beispiel der Korrosion von Nickel in Salzsaurelosungen bei definiertem Sauerstoffpartialdruck wird der Einflus der Stromung untersucht. Dabei kommt die Methode der rotierenden Scheibe in einer modifizierten Form zur Anwendung, die den speziellen Forderungen bei Korrosionsuntersuchungen Rechnung tragt. Die erhaltenen Ergebnisse lassen darauf schliesen, das die untersuchte Korrosionsreaktion sowohl vom Transport als auch von der Phasengrenzreaktion abhangt. Im letzten Teil der Arbeit wird die Transportgeschwindigkeit bei den in der Praxis verwendeten Umlaufapparaturen einerseits mit der an rotierenden Scheiben und Zylindern andererseits verglichen. Das Ergebnis ist, das sich Umlaufapparaturen durch die in ihrem apparativen Aufbau wesentlich einfacheren rotierenden Scheiben und Zylinder ersetzen lassen. Investigations on transport processes during corrosion In many cases of corrosion, the transport of the corroding agent or the removal of the corrosion products play an important part. After a discussion of the basic principles governing the transport of matter, a number of investigation methods are outlined. They include tests with rotating discs, flow tubes, and rotating cylinders. It is also shown that long-term immersion tests may be influenced by natural convection. The influence of the flow is examined on the strength of the example of the corrosion of nickel in hydrochloric acid solutions at a given partial pressure of oxygen. This investigation is carried out with a modified version of the rotating disc method, which takes into account the special requirements with corrosion tests. The results permit the conclusion that the investigated corrosion reaction depends on the transport as well as on the phase boundary reaction. In the last part of the paper, the transport rate with the circulation equipment used in practice is compared with that encountered with rotating discs and cylinders. It was found that it is possible to replace the conventional equipment by rotating discs and cylinders where the apparatus is considerably simpler.

Guidance on Safety/Health for Process Intensification including MS Design; Part I: Reaction Hazards

Abstract: The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space-time yields, higher temperatures, and a confined reaction volume comprises new risks, such as runaway reactions, decomposition, and incomplete conversion of reactants. Simplified spreadsheet calculations enable an estimation of the expected temperature profiles, conversion rates, and consequences of potential malfunction based on the reaction kinetics. The analysis illustrates that the range of optimal reaction conditions is almost congruent with the danger of an uncontrolled reaction. The risk of a spontaneous reaction with hot spots can be presumed if strong exothermic reactions are carried out in micro-designed reactors. At worst, decomposition follows the runaway reaction with the release of noncondensable gases. Calculations prove that a microreactor is not at risk in terms of overpressure as long as at least one end of the reactor is not blocked.