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.

Continuous free-radical polymerization of styrene in the stirred tank reactor: Effect of retarders†

Abstract: The influence of different retarders on the conversion and the molecular weight distribution of initiated styrene polymerization in a continuous stirred tank reactor (CSTR) was investigated. The retarders used were nitrobenzene, tert-butylpyrocatechol (tBC) and tert-butyl-o-quinone. The inhibition constant of the nitrocompound was taken from literature to test the mathematical model. For the other two substances the inhibition constant was determined experimentally. The effectiveness of tBC increases in the presence of oxygen. Our results indicate that oxygen transforms the normal alkyl radicals of the polymerization into peroxy radicals having a higher reactivity towards the retarder thus leading to an overall increase in efficiency. Der Einflus von verschiedenen Verzogeren auf den Umsatz und die Molekulargewichtsverteilung der initiierten Styrolpolymerisation in einem kontinuierlichen Ruhrkesselreaktor (CSTR) wurde untersucht. Die Verzogerer waren Nitrobenzol, tert-Butylbrenzcatechin (tBC) und tert-Butyl-o-benzochinon. Die Inhibitionskonstante der Nitroverbindung wurde der Literatur entnommen, um das mathematische Modell zu prufen. Fur die anderen zwei Substanzen wurde die Inhibitionskonstante experimentell bestimmt. Die Wirksamkeit von tBC ist in Gegenwart von Sauerstoff verstarkt. Unsere Ergebnisse deuten darauf hin, das Sauerstoff die normalen Alkylradikale der Polymerisation in Peroxyradikale uberfuhrt, die eine hohere Reaktivitat hinsichtlich des Verzogerers besitzen und so insgesamt zu einer hoheren Effektivitat fuhren.

Diffusion coatings for aggressive high temperature process environments

Abstract: Diffusion coatings can provide an excellent corrosion protection in aggressive high temperature environments due to the enrichment of thermodynamically stable oxide formers at the alloy surface. Besides conventional monoelement diffusion coatings (e.g. al diffusion), multielement coatings can be produced in a single process step. The production of al diffusion and Al–Si, Al–Ti and Al–Si–Ti codiffusion coatings on ferritic and austenitic steels and Ni base alloys, and their performance under high temperature chloridising, sulfidising and metal dusting environments are described.

Untersuchungen zum Einfluß der Flüssigkeit bei der Naßmahlung in Kugelmühlen

Abstract: Studies on the influence of liquid in wet grinding in ball mills Etude de l'influence du liquide lors du broyage humide dans les broyeurs a boulets

Oxidation protection of several intermetallic TixAly alloys by fluorine

Abstract: The oxidation resistance of γ-TiAl alloys can be dramatically improved by the fluorine effect. The Al content is a critical factor. It has to be above at least 40 at.% to get the fluorine effect to operate. Alloys with an Al content near this value or below have to be enriched with Al in advance. For this purpose, aluminisation is one possibility. The Al content within the diffusion layers can be determined by variation of the pack parameters, i.e. Al activity, time and temperature. These Al-rich diffusion layers form a protective alumina layer during high-temperature exposure in oxidising environments, but they have to be treated subsequently with fluorine to stabilise their protective effect. Results of high-temperature exposure tests of several untreated and treated alloys will be presented in this paper. Post experimental metallographic investigations reveal the formed oxide scales so that the effects can be rated. Finally, the results will be discussed in view of the known fluorine effect for...

Economic Surface Treatment of Ti-Alloys to Improve their Resistance against Environmental High Temperature Attack

Abstract: High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Al-enrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.