Showing papers by "DECHEMA published in 1975"

The scaling of iron in oxygen and sulfur-containing gases

Abstract: The following possible conditions for the simultaneous formation of oxide and sulfide on iron in oxygen and sulfur-containing gases are considered: (7) simultaneous thermodynamic stability of oxide and sulfide; (2) temporal changes in gas composition; (3) intermediary cracking of the oxide film; (4) solubility and diffusion of sulfur in the oxide (lattice diffusion); (5) kinetic conditions for simultaneous oxide and sulfide formation at the scale-gas interface.

Comparative investigations of packed and fluidized bed electrodes with non-conducting and conducting particles

Abstract: Current density-potential curves and the dependency of current density on flow velocity were measured for reaction systems which are controlled by diffusion in packed and fluidized bed electrodes with conducting and non-conducting particles. Analogous measurements were carried out with plane electrodes, and the corresponding dependencies of the current density factorib/ipl were determined. For bed electrodes with conducting particles, the current density factor can be approximately described as the product of a surface scale-up factor and a diffusion-controlled factor of the order of 5. Parallel to the current flow direction, the effectiveness of a bed electrode with conductive particles covers only a layer thickness of less than 1 cm. Maximum current densities are found with both conducting and non-conducting particles at flow velocities above the fluidization point.

Elektrochemische Untersuchungen zur Hochtemperaturkorrosion hochlegierter Werkstoffe in Alkalisulfatschmelzen

Abstract: Die Untersuchungen wurden bei 625 und 800°C an Eisen, Chrom, 4 ferritischen CrStahlen, 2 austenitischen CrNi-Stahlen, je einer Ni-und Co-Basislegierung sowie an 3 Chromlegierungen unter Luft in Alkalisulfatschmelzen durchgefuhrt. Eindeutige Aussagen uber die Potentialabhangigkeit des Korrosionsverhaltens lassen nur Massenverlust-Potential-Kurven zu. Aus ihnen ergibt sich, das bei allen untersuchten Werkstoffen zwei Potentialbereiche mit unterschiedlichen Korrosionsverhalten auftreten. Bei relative negativen Potentialen bildet sich eine Schutzschicht auf der Werkstoffoberflache und die Korrosionsrate ist klein und nahezu potentialunabhangig. Oberhalb eines vom System. Werkstoff/Schmelze abhangigen Durchbruchpotentials bilden sich porose Deckschichten. In diesem Potentialbereich steigt die Korrosionsrate mit dem Potential steil an. Das Durchbruchpotential wird mit steigendem Cr-Gehalt der Werkstoffe zu positiveren Potentialen verschoben, jedoch haben Cr-Gehalt > 20% keinen wesentlichen Einflus mehr auf das Durchbruchpotential. Auch die Temperature hat keinen wesentlichen Einflus auf die Lage des Durchbruchoptentials. Potentiodynamische Summenstrom-Potential-Kurven sind mit grosem Vorbehalt zu interpretieren. Ihre Lage ist abhangig von der zeitlichen Anderung des Potentials. Die ungefahre Lage des Durchbruchpotentials ist oft nur bei sehr langsamer Potentialanderung zu erkennen. Bei groserer zeitlicher Potentialanderung wird das Durchbruchpotential in der Regel scheinbar zu negative gefunden. Das hangt wahrscheinlich mit potentialabhangigen Wachstumsvorgangen der Passivschicht zusammen. Electrochemical investigation into the high temperature corrosion of high alloy materials in alkali sulafte metals The investigations have been carried out in alkali sulfate melts under air at 625 and 800°C with iron, chromium, four ferritic chromium steels, two austenitic chromium nickel steels, one each nickel and cobalt base alloy and three chromium alloys. Clear statements concerning the potential dependence of the corrosion behaviour are feasible only on the basis of mass loss/potential curves. It results from these curves that the behaviour of all the materials studied is characterized by two potential regions with different corrosion behaviour. At relatively negative potentials a protective layer is formed on the material surface and the corrosion rate is low and almost independent from potential. Above a rupture potential (which depends from the system material/melt) porous surface layers are formed. In this potential range the corrosion rate shows a steep increase as potential increases. With increasing chromium contents of the materials the rupture potential is displaced towards more positive potentials, but chromium contents exceeding 20% have no markable influence on the rupture potential. Temperature, too, does not noticeably affect the position of the rupture potential. The interpretation of potentiodynamic accumulated current/potential curves requires great care; the shape of such curves depends from the variation of potential with time. The approximate position of the rupture potential can frequently be recognized at very low potential variations only. At larger potential variations in time the values of the rupture potential appear as a rule to be too negative; this phenomenon may probably attributed to potential dependence growth processes in the passive layer.

Zur Oligomerenbildung bei der thermischen Copolymerisation des Systems Styrol/Acrylnitril

Abstract: dehydrogenated to about 50%. Furthel~ore, the adsorption of the cyclic hydrocarbons methylcyclopentane and cyclopentane leads to a shift of the CH2 frequency by 40 wave numbers. The band at 2965 cm1, characteristic of the strained Cs ring, is shifted to 2925 cm-1, the normal, unstrained CH2 frequency. This loss of strain in the adsorbed species can be interpreted as at least partial opening of the Cs ring. The frequency shift is not reversed after admission of hydrogen to the sample. This shows that under these conditions hydrogenation of the initially adsorbed species can hardly proceed beyond a diadsorbed state, or, more generally speaking, that multiadsorbed surface species are indeed stable under 760 torr of hydrogen. In spite of this \"r ing opening\" and the high degree of dehydrogenation the basic skeletal structure must be preserved, since up to 150 ~ chemisorbed methylcyclopentane can be desorbed from this catalyst in flowing hydrogen unreacted to about 98% of total coverage. With adsorbed 3-methylpentane the intensity ratios of CH2 to CHs bands can best be interpreted by a 1,5-adsorbed species, corresponding to a cyclic surface complex. This interpretation is supported by the fact that thermal desorption in this case yields 80% of methylcyclopentane. Although we do not want to question the possibility that under special conditions and for particular types of metal surfaces any one of the mechanisms previously postulated may play an important rofe and that two or more different reaction pathways may occur simultaneously on a given sample, several definite conclusions can be drawn, based on the nature of surface species formed in chemisorption of Ca hydrocarbons on highly dispersed platinum: ~-olefin or 7r-allyl mechanism for C-C bond rupture in the ring opening of methylcyclopentane, postulated in analogy to organometallic chemistry, is not predominant, while hydrogenolysis occurring through 1,2-diadsorbed states is fully supported by our experimental data. All the spectroscopic evidence is in agreement with the assumption that a cyclic surface species as postulated for the hydrogenolysis of methylcyclopentane with at least two (r-bonds to the metal is also formed upon adsorption of the hexanes and is essential in their isomerization and their ring-closure reaction to methylcyclopentane. Natur des Startschrittes der thermischen Polymerisation [ I 3] erhalten sollte. Die Oligolneren wurden tells nur massenspektrometrisch, tells zus~itzlich durch kernmagnetische Resonanzmessungen als

Untersuchungen zum Bruchverhalten von Kunststoffen bei Schlagbeanspruchung

Abstract: In Zugversuchen an durchsichtigen Thermoplasten kann fur verschiedene Abzugsgeschwindigkeiten der Verlauf einer optisch wahrnehmbaren Schadigungsgrenze nachgewiesen werden. Fur Abzugsgeschwindigkeiten > 200 mm/min fallt diese Grenzdehnung mit der Bruchdehnung zusammen. Der untersuchte Geschwindigkeitsbereich wird erweitert durch Schlagzugversuche an gleichartigen Proben mit Schlaggeschwindigkeiten bis ca. 5 m/s, bei denen Kraft-Verlangerungs-Diagramme aufgenommen werden konnen. So last sich der Verlauf von Spannung und Dehnung in der Probe fur den gesamten Geschwindigkeitsbereich verfolgen und fur verschiedene Werkstoffe (hier PMMA und EP-Harz) vergleichen. Durch fotografische Hochgeschwindigkeitsaufnahmen wird der Bruchverlauf beobachtet. Investigation on Fracture Behavior of Plastics at High Rates of Loading. A visible damage limit may be indicated at several rates of loading by tensile tests with transparent thermoplastics. For loading rates greater than 200 mm/min this strain limit coincides with strain at rupture. The range of loading rates investigated is enlarged by impact tensile tests up to 5 m/sec using the same specimens. As stress-strain-diagrams may be registered with both test methods it is possible to find the stress strain behaviour for several materials (here for instance PMMA and EP resin were investigated) over the whole range. Run of fracture during impact test is observed by high speed cinematographic records.