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.

Slurry coated Ni-plated Fe-base alloys: Investigation of the influence of powder and substrate composition on interdiffusional and structural degradation of aluminides

Abstract: A novel approach to apply slurry aluminides to produce a thermal barrier system based on an aluminum diffusion zone and an alumina foam layer in one step is being studied in the European FP7 project PARTICOAT. The results suggest possible coating and substrate combinations to decrease the degradation of slurry-produced aluminide coatings under high temperature exposure in heat exchangers, boilers or combustion chambers present in waste incineration and power plants. Spherical Al or Al–Si particles were deposited by air brush technique on austenitic (AISI347), ferritic (AISI446) and ferritic–martensitic (P91) steels. Isothermal exposure tests were performed at 600 °C and 800 °C for up to 1000 h to study the microstructural changes and the oxidation behavior in air. After manufacturing, the resulting diffusion coating consisted of different iron–aluminide phases with porous alumina foam on top. The diffusion layer on top of the ferritic steels contained cracks due to the large thermal expansion coefficient mismatch between the substrate and the bondcoat, but was homogenous and continuous on the austenitic alloy. These cracks are generally filled with aluminum oxide in pure oxidizing atmospheres and the recession of aluminum in the diffusion layer is lower for the austenitic than for the ferritic alloys. The advantage of using an Al–Si based compared to a pure Al-slurry is a significantly decreased aluminum interdiffusion into the ferritic steels which contain high amounts of chromium. The latter effect could be related to the formation of a Cr3Si layer, which acts as an aluminum diffusion barrier.

Sulphidation Behavior of a Non Harmful Water-Based Al and Al–Si Slurry Coating on CM247 Superalloy

Abstract: Slurry aluminide coatings are widely applied to protect metallic surfaces from oxidation and corrosion. They are frequently used in gas turbine engine nozzles because of economical advantages and a straight-forward manufacturing route. A variety of commercial slurries are available to aluminize the surfaces of nickel-based superalloys, however, they have two main disadvantages. First, the phosphates and chromates or halides used as binders and to activate the diffusion species are environmentally harmful; second, the conventional systems have to be heat-treated in an inert atmosphere. As an outcome of the PARTICOAT project the variety of slurry derived coatings has been extended by tailoring the particle size of the metallic source. By doing that, environmentally friendly water-based slurries were developed to produce in a one-step process und atmospheric conditions, a thermal barrier system based on an aluminum diffusion layer and an alumina foam layer which serves as bond coat as well as top coat (TC). CM 247 nickel base superalloy was coated and heat-treated in air using newly developed Al and Al–Si slurries. The oxidation behavior was investigated at 1,000 °C and then compared to pack-cemented aluminide coatings. The sulphidation behavior was investigated at 1,000 °C in an atmosphere of 1.5 vol% SO2 in synthetic air for Al and Al–Si slurry coated samples with and without the alumina foam TC layer. PARTICOAT Al-based slurries,, after the initial stabilization of the TC, showed similar oxidation kinetics as pack cemented aluminides when exposed to air. When the coatings were exposed to sulphide-containing atmospheres, their oxidation rates increased, producing typical type I corrosion damage. Coatings without TC produced more protective oxide scales. The weight gain and coating area affected by corrosion were slightly lower for the Al-based slurries after 1,000 h of exposure than for the Al–Si based ones. The new coating presented here offers unique advantages in comparison to state-of-the-art slurry and pack cemented coatings by opening a potential way to manufacture a complete thermal barrier coating system by a simple, inexpensive and environmentally safe deposition and heat-treatment in air.

Reference electrodes based on conducting polymers.

Abstract: Several attempts to produce conducting polymer based all-solid-state reference electrodes are presented. Open circuit potential of conducting polymers is redox sensitive and Donan equilibrium dependent. Therefore, more sophisticated constructions are necessary. Most promising were bilayers composed of conducting polymers with different ion-exchanger properties.

Der Einfluß von Kriechverformung auf die Ausbildung der Oxidschicht auf der Hochtemperaturlegierung Ni20Cr

Abstract: Die Ausbildung der Cr2O3-Schicht auf Ni20Cr ist bei 850°C in H2/H2O (p(O2) = 10−19 bar) unter gleichzeitiger Kriechverformung an Flachproben untersucht worden. Die Schadigung der schutzenden Oxidschicht durch Risse wurde in Abhangigkeit von der Verformungs-geschwindigkeit und der Dehnung des Grundwerkstoffes beobachtet. Zur Trennung des Einflusses der plastischen Verformung der Oxidschicht und der Risheilung wurden erganzend voroxidierte Proben in reiner Ar-Atmosphare verformt. Unterhalb der Kriechgeschwindigkeit von 10−9s−1 werden keine Risse mehr festgestellt. Bei < etwa 3 × 10−8s−1 treten Risse nur oberhalb Legierungskorngrenzen auf, bei hoheren liegen sie auch in Bereichen uber den Legierungskornern. Fur > etwa 3 × 10−8s−1 hangt die Risdichte nicht mehr von ab. Aus der unterschiedlichen Schadigung der Oxidschicht in den beiden Gasatmospharen kann geschlossen werden, das bei zwischen 10−9s−1 und 10−7s−1 neben einer Plastizitat der Oxidschicht insbesondere die Risheilung mesbare Einflusse bei der Summe der Risoffnungen hervorruft, mit steigendem wird der Beitrag der Plastizitat vernachlassigbar klein. Influence of creep deformation on the formation of the oxide layer on the high temperature alloy Ni20Cr The formation of the Cr2O3-layer on Ni20Cr has been investigated at 850°C in H2/H2O (p(O2) = 10−19 bar) under simultaneous creep deformation with flat samples. The damage of the protecting oxide layer by cracks has been observed in dependence on deformation rate and strain. For additional information about the influence of the plastic deformation of the oxide layer and the healing of the cracks, preoxidized samples have been deformed in pure Ar-atmosphere. At strain rates below 10−9s−1 cracks cannot be observed. When strain rates < about 3 × 10−8s−1 are applied, cracks occur only above grain boundaries of the alloy, at higher strain rates they also lie in regions above the grains of the alloy. For > about 3 × 10−8s−1 the crack density depends no more on but only on strain . The different damages of the oxide layers in the two atmospheres allow the conclusion, that at from 10−9s−1 to 10−7s−1 beside the plasticity of the oxide layer in particular the crack healing influences the sum of the crack openings measurably. With increasing strain rates the contribution of plasticity can be neglected.

Synthesis of bifunctional BaFe1−xCoxO3−y−δ(OH)y catalysts for the oxygen reduction reaction and oxygen evolution reaction

Abstract: Perovskite oxides with mixed ionic and electronic conductivities are very promising candidates for their application as energy materials related to fuel cell and metal air battery integration. In this article, we report on the systematic characterization of mixed proton and electron conducting compounds of composition BaFe1−xCoxO3−y−δ(OH)y synthesized via nebulized spray pyrolysis. Independent of the value of x, all samples BaFe1−xCoxO3−y−δ(OH)y were found to crystallize in an orthorhombic ordering/distortion variant of the perovskite type structure (space group Cmcm) and are isotypic to the border phases (x = 0 or 1) reported previously. A minimum water content was observed for the composition with x = 0.5, which increases steadily for Co or Fe richer compositions. Impedance studies show that the conductivity increases with increasing Co-content, with BaCo0.5Fe0.5O2.07(OH)0.74 showing a total electrical conductivity of 10−7 S cm−1 at 298 K, an order of magnitude higher than found for BaFeO2.33(OH)0.33. Further, bifunctional catalytic activity for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was found for the compounds of the series as investigated in 0.1 M KOH, with BaFe0.8Co0.2O3−y−δ(OH)y possessing the best bifunctional performance parameter of ΔU = 1.10 V, which is comparable to that of other non-precious metal catalysts.