Showing papers by "DECHEMA published in 1985"

Deformation and cracking behavior of protective oxide scales on heat-resistant steels under tensile strain

Abstract: The deformation and cracking behavior of oxide scales formed in air on four heat-resistant steels and on nickel 99.6 have been studied in constant-extension-rate tests at 800°C. The strain rates in the experiments ranged between 10−6 and 10−9 s−1. Acoustic emission (AE) was used as an instrument for detecting the beginning of scale cracking. Additionally, metallographic, SEM, and micro-probe investigations were performed which supported the results from the AE measurements. The strain-to-cracking of the scales did not exceed 0.5% except when lateral growth effects in the oxide scales occurred, leading to critical strains of up to nearly 2.5%. Also the crack distribution in the scales was measured. The deformation and cracking behavior of the scales investigated could be explained by model like considerations.

Modelling of gas evolving electrolysis cells. I: The gas voidage problem

Abstract: A critical review of experimental gas voidage data for gas—liquid mixtures available in the literature yields the result that these data cannot be explained by known theories of the gas hold-up. Based on the empirical experience that bubble coalescence is hindered in electrolyte solutions, new equations are derived for the calculation of the gas voidage as a function of the superficial gas velocity by introducing a coalescence barrier model. Experimental investigations confirm the theoretical prediction of the existence of a limiting gas voidage which is a characteristic quantity of each gas—electrolyte combination.

Fundamental studies on a new concept of flue gas desulphurization

Abstract: A new process for removal of sulphur dioxide from waste gases is proposed consisting of both electrochemical and catalytic sulphur dioxide oxidation. In the catalytic step a part of the sulphur dioxide is oxidized by oxygen on copper producing sulphuric acid and copper sulphate. The other part is oxidized electrochemically on graphite. The cathodic reaction of this electrolysis is used for recovering the copper dissolved in the catalytic step. The basic reactions of this process have been studied experimentally in detail. It has been shown that sulphur dioxide can be electrochemically oxidized on carbon electrodes to sulphuric acid with high current efficiency. The reaction rate of the electrochemical copper deposition is increased by dissolved sulphur dioxide in the electrolyte. The catalytic oxidation of sulphur dioxide on copper has been investigated for different sulphur dioxide concentrations and temperatures. The ratio of the reaction products, sulphuric acid and copper sulphate, varies over a wide range depending on the experimental conditions.

Kinetic Investigations of the Primary Step of Electrochemical Coal Oxidation

Abstract: The stress corrosion cracking of sensitized stainless steels due to thiosulfate and tetrathionate has been associated with an increased rate of anodic dissolution in the active-passive region of voltammetric scans, via the mutual sensitivity of both phenomena to a series of anionic inhibitors. The increased anodic dissolution is caused by the adsorption of the sulfur compound and its catalysis of metal oxidation. The inhibitors function, not by competitivel desorbing the corrodent, but by aiding the passivation process.

Performance criteria and nomenclature in electrochemical engineering

Abstract: This paper is a recommendation of the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineering. It was prepared by a sub-committee composed of: G. Kreysa (Frankfurt am Main) Chairman F. Coeuret (Rennes) A. Storck (Nancy) H. Wendt (Darmstadt) The helpful discussions and comments of colleagues in the Working Party are gratefully acknowledged.

Indirect electrochemical degradation and dissolution of coal by means of persulphate

Abstract: The idea of electrochemical coal conversion has recently been revived1–7. The mechanism of anodic coal oxidation has been shown to be indirect and that the electron transfer is mediated by Fe3+/Fe2+ leached out of the coal. Although the application of various mediator systems has been discussed in detail, all these systems suffer from either comparatively low reaction rates or high CO2– current efficiencies. Caro's acid (H2SO5), obtained as a hydrolysis product during anodic persulphate formation is a powerful redox mediater system for the degradation of the macromolecular coal structure in mild conditions, providing a nearly complete dissolution of coal in sulphuric acid. We propose here that the high current efficiencies accompanied by low CO2 evolution might open a route of potential interest for the electrochemical production of aromatic carboxylic acids from coal.

Flow-dependent corrosion – II. Ferrous materials in pure and particulate chloride solutions

Abstract: The corrosion behaviour of non alloyed steel, cast iron, and 13% chromium steel has been investigated in chloride containing media without and with sand (one-phase and two-phase flow) at various flow velocities. In one-phase flow mass transfer determined corrosion prevails with the structure and composition of surface layer being the dominating factor. In two-phase flow mainly erosion corrosion is observed together with a strong influence of hydrodynamic parameters. Particular emphasis is given to the experimental techniques required for the investigation of flow dependent corrosion. Stromungsabhangige Korrosion – II. Verhalten von Eisenwerkstoffen in Chloridlosungen mit und ohne Feststoffpartikel Das Korrosionsverhalten von unlegiertem Stahl, Graugus und 13% Chromstahl wird in chloridhaltigen Medien ohne und mit Sandgehalt (ein- und zweiphasige Stromungen) bei unterschiedlichen Stromungsgeschwindigkeiten untersucht. In einphasigen Stromungen dominiert die stofftransportbestimmte Korrosion, wobei Struktur und Zusammensetzung der Deckschicht masgebend sind. In zweiphasigen Stromungen wird hauptsachlich Erosionskorrosion und in Verbindung hiermit eine starke Beeinflussung durch hydromechanische Parameter beobachtet. Die fur die Untersuchung der stromungsabhangigen Korrosion geeigneten Untersuchungsverfahren werden eingehend beschrieben.

Use of coarse granules of layered silicates as adsorbents for proteins

Abstract: 1. The use of coarse-grain layer silicates - prepared by dropwise addition of a suspension of a layer silicate to an aqueous polymer solution, dropwise addition of the resulting suspension to an electrolyte solution and recovery of the grains or beads formed - as adsorbents for proteins.

Process for the oxidative conversion of coal.

Abstract: The macromolecular coal structure is broken down by oxidative attack by means of peroxoacids or peroxoanions to form low-molecular products. The oxidising agent is dissolved in an aqueous electrolyte, and the reaction takes place below the boiling point. The peroxo compounds used are preferably regenerated electrochemically in the process. This can be carried out either in the reactor containing the coal or in an external reactor. Apart from the production of low-molecular compounds from coal, this process can also be used for breaking down coal underground and thus converting it into an easily extractable form.

Simulating plant conditions in the laboratory – Principles and limitations†

Abstract: Before corrosion tests are carried out, one must realise the scale to be selected. As in chemical engineering the problem of “scaling down” and “scaling up” arises if plant conditions are to be simulated on a laboratory scale. As a consequence of the multiplicity of corrosion phenomena, parameters and mechanisms the number of corrosion testing methods is large and test procedures have carefully to be adjusted to the particular practical problem. Simulation principles are illustrated by a number of examples.

Verhalten von thermoplastischen Kunststoffen gegenüber aggressiven Medien – Einfluß der Morphologie am Beispiel von Polyethylen hoher Dichte

Abstract: Durch unterschiedliche Herstellungsverfahren (Pressen, Extrudieren) bzw. unterschiedliche Abkuhlbedingungen bei einem bestimmten Verfahren kann die Morphologie von Halbzeugen in bestimmten Grenzen variiert werden. Derart unterschiedlich hergestellte Platten und Rohrabschnitte aus unpigmentiertem PE-HD Granulat einer Charge wurden einem physikalisch aktiven Medium (p-Xylol), einem chemisch aktiven Medium (50%ige Chromsaure) und einem oberflachenaktiven Medium (2%ige Netzmittellosung) ausgesetzt. Neben Einlagerungsversuchen bei unterschiedlichen Temperaturen wurden an den Platten Kriechversuche unter konstanter Last durchgefuhrt. Die sich ergebenden Unterschiede hinsichtlich Sorption, Kriechnachgiebigkeit, Risbildung u. a. werden im Zusammenhang mit der morphologischen Struktur (z. B. Kristallinitat) diskutiert. Behaviour of thermoplastic materials in aggressive Media – Influence of morphology on the example of high density polyethylene To a certain degree the morphology of thermoplastic intermediate products can be influenced either by using different fabrication techniques (molding, extrusion) or in case of a special technique e.g. by varying the cooling conditions. Plates and pipes produced from unpigmented PE-HD granule of a certain batch, differing in morphology only were exposed to a physically active medium (p-xylene), a chemically active medium (50% chromic acid) and a surface-active medium (2% wetting-agent). Apart from immersion-tests at varying temperatures creep-experiments on plates under constant load were carried out. The registered differences in sorption, creep-compliance, cracking etc. are discussed in context with the different morphological structures (e.g. crystalline phase).