Showing papers by "DECHEMA published in 1983"

Elektrochemie mit dreidimensionalen Elektroden

Abstract: Electrochemistry with three-dimensional electrodes. Three-dimensional electrodes such as are used in fixed-bed and fluidized bed electrolysis are suitable for purifying waste water containing heavy metals and for metal recovery from dilute solutions, and also open up new possibilities for electrochemical purification of waste gases. An account of the theoretical principles of the macrokinetics of these systems is followed by descriptions of a waste-water purification process by fixed bed electrolysis, which is already in industrial use, of the rotating fixed-bed electrode, and of the state of the art of fluidized bed electrolysis for production of metals. An electrochemical absorption tower permits removal of chlorine and sulphur dioxide from waste gases.

Acidic and basic fluxing of Ni-base superalloys in a 90Na2SO4-10K2SO4 melt at 1173 K

Abstract: The influence of the electrode potential on the corrosion behavior of a series of Ni-base superalloys has been investigated in a (mole %) 90Na2SO4-10K2SO4 melt at 1173 K. Acidic fluxing occurs at positive potentials and basic fluxing at negative potentials. A protective scale is formed in an intermediate (neutral) potential range on high chromium-containing alloys such as IN-738LC, IN-939, IN-597, and IN-657. The breakthrough potentials for acidic and basic fluxing depend on the composition of the alloy. Alloys with low chromium contents such as IN-100 and IN-713LC do not form stable protective scales at any potential. Numerous sulfide phases have been identified in the scale and subscale, depending on potential, severity of attack, and material composition. NaCrS2 only forms under basic fluxing conditions. Its presence can therefore be considered as an indication that basic fluxing conditions have existed.

Flow-dependent corrosion. I. Current understanding of the mechanisms involved†

Abstract: Wall geometry, flow and corrosion patterns are interrelated and lead to corrosion types caused predominantly by either mass transport or wear, according to the nature and intensity of the flow. The relationships between flow rate and corrosion rate can be evaluated as diagnostic criteria. In addition to a synopsis of the information available on the basic processes for copper, aluminium and steel, an attempt is made to classify the various types of flow-dependent corrosion in relation to existing standards for corrosion and wear. Stromungsabhangige Korrosion. I. Gegenwartiger Kenntnisstand bezuglich des Mechanismus Wand-, Stromungs- und Korrosionsgeometrie sind miteinander verknupft und fuhren je nach Art und Intensitat der Stromung zu den vorwiegend stofftransport- oder verschleisbedingten Korrosionserscheinungen. Die Zusammenhange zwischen Stromungsgeschwindigkeit und Korrosionsrate lassen sich als mechanistisches Unterscheidungskriterium auswerten. Neben einer Zusammenstellung der Kenntnisse uber die Grundvorgange an Kupfer-, Aluminium- und Eisenwerkstoffen wird eine Einordnung der verschiedenen Arten stromungsabhangiger Korrosion in bestehende Korrosions- und Verschleisnormen vorgenommen.

Thermal polymerization of styrene — the formation of oligomers and intermediates, 1. Discontinuous polymerization up to high conversions

Abstract: During the thermal polymerization of styrene small quantities of dimeric and trimeric styrenes are formed which affect essential properties of the polymer. The kinetics of the oligomer formation are investigated under industrially important reaction conditions and the concentrations of the intermediates formed during the initiation reaction are determined by UV-spectroscopy. The results show that no gel effect occurs in the reactions investigated. Using the kinetic fomulae and reaction rate constants obtained it is possible to describe the formation of oligomers and intermediates at temperatures of 137°C and 180°C up to 97% monomer conversion. Bei der thermischen Polymerisation von Styrol entstehen in geringen Mengen dimere und trimere Styrole, welche wesentliche Eigenschaften des Polymeren beeinflussen. Die Kinetik der Oligomerenbildung wird bei technisch interessierenden Reaktionsbedingungen untersucht, und die Konzentrationen der bei der Startreaktion gebildeten Zwischenprodukte werden UV-spektroskopisch bestimmt. Die Ergebnisse zeigen, das bei den untersuchten Reaktionen kein Geleffekt auftritt. Mit den erhaltenen kinetischen Gleichungen und Reaktionsgeschwindigkeitskonstanten kann die Bildung der Oligomeren und der Zwischenprodukte bei Temperaturen von 137°C und 180°C bis zu Monomerumsatzen von 97% beschrieben werden.

Aktuelle Entwicklungslinien der elektrochemischen Prozeßtechnik

Abstract: Development trends in electrochemical process engineering. Important electrochemical production processes have recently been crucially modified or newly developed and this opened new horizons for the future of industrial electrochemistry. The thrust of this development is discussed in three selected areas: alkali chloride electrolysis, water electrolysis, and organic electrosynthesis. Important past steps are the invention of the dimensionally stable anodes, the development of the cation exchange membrane and membrane electrolysis, the successful testing of zero gap cells, SPE electrolysis and the economic use of two phase electrolytes. These successes have arisen mainly from an improved knowledge and understanding of the fundamental principles of electrochemical engineering.

Möglichkeiten der elektrochemischen Kohleumwandlung

Abstract: Possibilities of electrochemical conversion of coal. Coal as a macromolecular organic substance can principally undergo electrochemical conversions. Presently three main directions are under investigation: electrochemical gasification with the formation of hydrogen and carbon dioxide; modification of the chemical composition of coal; and degradation to low-molecular substances. A historical survey as well as the present state of the art is given and the electrochemical reactions of the coal and their mechanisms are discussed in detail.

Untersuchungen zum Mechanismus und zur Katalyse der elektrochemischen Salpetersäurereduktion

Abstract: Electrochemical nitric acid reduction has been investigated on graphite and titanium electrodes obtaining current-potential-curves, current-time-curves and applying electrochemical mass spectrometry for product analysis. Integral current efficiencies and selectivities for the various products has been determined. On graphite at low reduction potentials only NO is formed. At potentials where thermodynamically hydrogen evolution is possible the main products are H2, NO, N2O, and NH. Under these conditions the reduction is catalysed by Cu2+, Ag+, and Pb2+-ions which were deposited at the base electrode. These metals strongly influence the product distribution. A general reaction scheme is proposed, and the various electrocatalytic effects are discussed.