Showing papers by "DECHEMA published in 1999"

Numerical Investigations of Optimal Heat Conductivity in Micro Heat Exchangers

Abstract: The aim of this work is to determine the order of magnitude of the optimal heat conductivity by simulation. Furthermore, the question of whether and, if so, how operational and geometrical parameters influence the optimal heat conductivity is addressed. Finally, an assessment is made of the need for similar investigations, i.e. taking into account axial heat conductivity processes within the wall materail, for the design of conventional heat exchangers

Improvement of the high temperature oxidation resistance of Ti50Al via ion-implantation

Abstract: The TiAl intermetallic compound is very promising for high temperature applications, because of its good high temperature strength and its low density. At temperatures exceeding 800°C, the low oxidation resistance is a limiting factor. It is known, that Cl doping reduces the oxidation strongly even in very low concentrations of about 500 ppm (`microalloy'). In the present investigation ion beam implantation is used to dope the material close to the surface quantitatively. The well-defined depth profile obtained after implantation provided a means to monitor the diffusion of additives during oxidation. Implantation of Cl + ions (1 MeV, 10 15 –10 17 cm −2 ) results in a systematic reduction of the oxidation at 900°C in air for doses ⩾10 16 cm −2 . AES measurements were performed to investigate the diffusion process during oxidation. A microscopic model will be proposed for the enhanced oxidation resistance. For beneficial effects of Silicon a higher concentration is required (`macroalloy'). Therefore high-dose implantations were carried out (upto 8 × 10 17 cm −2 ). The change in phase composition, microstructure and the oxidation behaviour will be discussed.

Electrochemically-regeneratable ion-exchanger for use in water purification comprises a conductive electrode coated with a conductive polymer

Abstract: An electrochemically regeneratable ion-exchanger consists of an electroconductive electrode material on which is placed an electroconductive polymer.

Dynamic Modeling of Chemical Reaction Systems with Neural Networks and Hybrid Models

Abstract: A common problem in kinetic modeling of complex chemical reactions is that a rigorous description of the reaction system, e.g., based on elementary reactions, is not possible. This is because either the reaction involves too many reactions and intermediates or the reaction mechanism is not known in sufficient detail. Alternative data-driven modeling, e.g., using neural networks, normally demands large amounts of experimental data and has poor generalization capability. In such situations a combined physical and data-driven (i.e. hybrid) model may be attractive, that utilizes the specific advantages of both approaches while avoiding their disadvantages. This paper explains the procedure of hybrid modeling of integral (i.e. time-dependent) data by using examples from chemical kinetics. The benefits of the hybrid models are described in comparison to the limiting cases of purely physical and purely data-driven models. In general, the hybrid model surpasses the purely physical and neural network models in terms of a combined interpolation- and extrapolation-range criterion.

Damage of a heat‐treatment retort by metal dusting attack

Abstract: The damage of a heat-treatment retort which was made of cast Fe36Ni21Cr steel and used under a carburizing atmosphere at about 900 °C has been investigated. Strong corrosion attack had occurred, leading locally to pitting on the surface or even to hole formation in the retort walls. An oxide layer rich in chromium had formed on the outside of the metal followed by a precipitation zone of carbides. These carbides decomposed near the surface into graphite and the corresponding metal, similar to “metal dusting”. The strong corrosion attack was often correlated with preexisting imperfections in the cast material like shrinkage cavites or microporosity. Schaden an einer Warmebehandlungsretorte durch Metal Dusting Angriff Ein Schadensfall an einer aus Fe36Ni21Cr im Schleudergusverfahren hergestellten Warmebehandlungsretorte wurde untersucht. Die Retorte wurde unter aufkohlender Atmosphare bei etwa 900 °C betrieben und zeigte einen starken lokalen Korrosionsangriff in Form von Grubchenbildung bis hin zu Lochbildung. Die Untersuchungen zeigten, das sich an der Oberflache eine chromreiche Oxidschicht ausgebildet hat. In der darunter liegenden Metallrandzone fand eine starke innere Karbidbildung durch Aufkohlung statt. Vergleichbar dem „metal dusting“-Prozes zerfallen die Karbide in der Nahe der Oberflache in Kohlenststoff und das entsprechende Metall. Der verstarkte Korrosionsangriff war haufig mit herstellungsbedingten Fehlern im Guswerkstuck wie Lunker und Mikroporositat verbunden.

Production of corrosion resistant coatings for metals comprises applying metallic or non-metallic inorganic nano-particulate powder in an organic matrix onto the metal surface, removing the organic matrix, and sintering

Abstract: Production of corrosion resistant coatings for metals comprises applying metallic or non-metallic inorganic nano-particulate powder in an organic matrix onto the metal surface, removing the organic matrix at 300-600 deg C, and sintering the nano-powder at 300-900 deg C to form a layer. An Independent claim is also included for the corrosion resistant coating produced. Preferred Features: The metal surface is degreased before applying the suspension. The organic matrix is made of paraffin or other high molecular material.

Electrochemical Reaction Engineering

Abstract: Electrochemical reaction engineering deals with modelling, calculation and prediction of the rate of electrochemical conversion or production in real reactors, that means the calculation of space time yields, selectivities and energy efficiencies of electrolyzers. Such predictions are based on one hand on microkinetic investigations of the relevant electrochemical reactions that means on information extracted from current voltage curves and preparative laboratory scale electrolyses and on the other hand on calculated spatial current density and potential distributions in electrolyzers along or across the electrodes or for instance in porous electrodes.

Comparative Study of the Acidic and Catalytic Properties of the Mesoporous Material H‐MCM‐41 and Zeolite H‐Y

Abstract: The objective of this work is to give a comparative characterization of aluminosilicate MCM-41 and zeolite Y, in particular with respect to acidity and catalytic properties in hydrocarbon cracking. These studies are compared to a well investigated amorphous aluminosilicate, based on the fact that the new mesoporous MCM-41 materials are a mixture of ordered material with amorphous pore walls. Characterization of differently treated MCM-41 materials and zeolite Y for comparison by N 2 sorption, XRD, TPAD (Temperature Programmed Ammonia Desorption) with in situ FTIR in combination with catalytic testing by MAT (Micro Activity Test) is discussed. Combination of the characterization data and the catalytic testing gives an interesting explanation of the surface properties especially in comparison with zeolite Y.

Production of a diffusion barrier comprises producing a ceramic particle dispersion below the surface of a metallic material

Abstract: Production of a diffusion barrier comprises producing a ceramic particle dispersion below the surface of a metallic material. Preferred Features: The particle dispersion is produced by diffusing metallic elements that form oxides, carbides or nitrides in an oxidizing, carburizing and/or nitriding atmosphere. The particle dispersion consists of ZrO2, Y2O3, Al2O3, CrO3, HfO2 or CeO2.

Application of an alloy from aluminium and titanium as well as a coating material for such an application

Abstract: An alloy of aluminum and titanium is used as a high temperature corrosion resistant coating material of heat resistant steels in installations with process gases which have a very low partial pressure of oxygen and, as consequence of carbon compounds in their composition, possess a high carbon activity. The claimed coating material has an atomic aluminum content amounts to 22-56 %.

Electrochemical Engineering of Porous Electrodes and Disperse Multiphase Electrolyte Systems

Abstract: Industrial electrochemistry has often to deal with a situation where either the electrolyte is not homogeneous but contains a second solid, liquid or gaseous dispersed phase or the electrode possesses a particulate structure comprising the electrolyte in pores, channels or holes. Considering the phase structure of such more involved multiphase systems the following classification can be given.

Mass Transfer by Fluid Flow, Convective Diffusion and Ionic Electricity Transport in Electrolytes and Cells

Abstract: The performance of electrochemical processes is not only determined by charge transfer and electrode kinetics, but a number of additional phenomena cause and rule the electrode kinetics (in the microkinetic as well as macrokinetic sense), the heat balance of the cell and the mass balances of all process streams (electrolyte, gases, solid products). Among these factors the fluid dynamic conditions, under which the electrolyte enters, passes and leaves the electrolysis cell or moves in it under free convection, is the most powerful process parameter since hydrodynamics rule mass and heat transport.

High-temperature, oxidation-suppressing thermal insulation composite, used successfully on metallic, inter-metallic and ceramic substrates, is made by pyrolyzing simple coating of zirconia in polysiloxane

Abstract: High-temperature, oxidation-suppressing thermal insulation composite is made by pyrolyzing a simple coating of zirconia particles in polysiloxane which is converted by pyrolysis into an inorganic binder phase.

Electrode Kinetics and Electrocatalysis

Abstract: Charge transfer between an electrode and the electrolyte proceeds by electron tunnelling between the electrode metal and a suitable electron acceptor or donor on the solution side of the electrode/electrolyte interface across very small distances of the order of fractions of nanometers. In this immediate vicinity of the electrode surface, matter is neither isotropic nor homogeneous. Considering the electrode/electrolyte interface, there is on neither side of it a well defined phase boundary. On the side of the electrode metal there is in atomar dimensions a certain change of electrical potential and charge density, that means an accumulation of negative charge at potentials negative to the potential of zero charge, E Epzc What follows on the solvent side in the direction perpendicular to the electrode surface is a relatively ordered but mobile sheet of solvent molecules and/or adsorbed species (ions or surfactive molecules) which is designated as the inner Helmholtz layer (IHL). A second less ordered sheet of solvent molecules which is called the outer Helmholtz layer (OHL) forms a smooth transition towards the fully established structure of the bulk solvent which is usually a mix of close range ordered clusters of solvent molecules being in long range statistical disorder (Fig. 4.1 a). The electronic charge on the metal side of the electrode is balanced by ionic countercharges in the vicinity of the electrode in the IHL and OHL and particularly in the so called diffuse part of the electrochemical double layer. In this diffuse part of the double layer a diffuse cloud of counter ions accumulates due to the coulombic interaction between the charged electrode and the charges of the different dissolved ions.

The Scope and History of Electrochemical Engineering

Abstract: The Scope of Electrochemical Engineering was the title of a contribution of Carl Wagner in the second volume of Advances in Electrochemistry and Electrochemical Engineering in 1962. On ten pages he described some examples of his own work on particular topics in electrochemical engineering science [1]. Typical for the situation in electrochemical engineering science at that time was that he concentrated mainly on questions of mass transfer by convective diffusion on one hand and on current-density distributions on electrodes on the other hand. Also typical for the prevailing situation at that time and even more typical for his personality was his methodical approach. Carl Wagner was — compared to other physicochemists and even more compared to average chemists of this time — obsessed by mathematics. He was never content with only formulating the problem under consideration exactly and well founded by the respective set of differential equations. He was satisfied only if — at least for some well defined borderline cases — a closed solution could be found for the problem. In that way he even treated relatively complicated problems as for instance the onset of free convection driven by small density differences of the electrolyte at copper anodes and cathodes of copper refining electrolysis cells and its influence on steady state mass transfer at these electrodes.

Electrochemical Cell and Plant Engineering

Abstract: Metallic materials — cheap steels in particular — are preferred for the construction of process equipment for the chemical industry and also for electrochemical plants. But electrolytes are always corrosive towards metals. Because of their ionic conductivity and their protonic and/or basic properties they favour corrosion by formation of local elements for instance by cathodic O2 reduction or H2 evolution combined with anodic metal dissolution. Since the metallic elements which constitute the usual steels — in particular iron — are less noble than hydrogen, steels will always tend to corrode and the tendency to corrode will even be enhanced in oxygen-containing electrolytes unless the metals are not passivated by alloy-components like Cr, Mo or Ni, to speak only of the most common passivating additives, which tend to form dense and passivating oxide layers.

Messen von Zustands-und Quantitätsgrößen

Abstract: In den Produktionsbetrieben der verfahrenstechnischen, insbesondere der chemischen Industrie haben Temperaturmessungen eine grose Bedeutung zur Fuhrung chemischer Prozesse. Fast alle verfahrenstechnischen Apparate, wie Reaktoren, Rohrleitungen und Destillationskolonnen, sind mit elektrischen Temperaturmessungen ausgerustet. Bei der Beurteilung verfahrenstechnischer Betriebsablaufe werden mit Hilfe von Temperaturmessungen Ausbeute- und Energiebilanzen erstellt. Viele Temperaturregelkreise sind fur selbsttatige Betriebsablaufe wichtig. Manche Temperaturalarme und Temperaturabschaltungen sind fur die Anlagensicherheit im Sinne der Storfallverordnung von erheblicher Wichtigkeit. In der betrieblichen Praxis werden hauptsachlich elektrische Widerstandsthermometer und Thermoelemente zur Temperaturmessung eingesetzt. Die Anwendung dieser elektrischen Thermometer in chemischen Produktionsbetrieben erfordert mehr praktische Erfahrungen mit verfahrenstechnischen, maschinenbaulichen und physikalischen Grundlagen als bei entsprechenden Temperaturmessungen im Labor. Zur umfassenden Beurteilung einer Temperaturmessung im chemischen Betrieb ist regelungstechnisches Grundlagenwissen (APC: Automatic Process Control) ebenso notwendig wie der Umgang mit der statistischen Prozeskontrolle (SPC: Statistical Process Control).

Basic Principles and Laws in Electrochemistry

Abstract: An electrochemical reaction, for example the cell reaction of copper electrowinning, $$CuS{O_4} + {H_2}O \to Cu + 1/2{O_2} + {H_2}S{O_4}$$ (2.1) represents a redox reaction and may be considered as composed of two partial reactions, an anodic oxidation and a cathodic reduction. For the process under discussion the partial reactions are: