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This paper considers the deposition of a commercial steel powder with a chemical composition that allows the coating to obtain an amorphous structure using thermal spray techniques. The processes used are characterized by high cooling speeds of the particles after the impact upon the substrate. The powders were sprayed with two different processes: cold gas spray (CGS) and high velocity oxyfuel (HVOF). A comparison between the samples obtained reveals that only the CGS coatings are completely amorphous; the HVOF samples exhibit nanocrystalline phases, detected with XRD analysis and SEM micrographs. Furthermore, the CGS coatings are more compact and show lower hardness with a comparable Young’s modulus. A hypothesis is that the formation of the amorphous structure is related to plastic deformation at impact (due to the high energy of the particles), rather than to the temperature; the mechanism could resemble that of a severe plastic deformation process. Additional thermal treatments and mechanical tests are in progress to investigate the toughness and other mechanical properties of the coatings.

Ein Multiskalen-Modellierungs-Ansatz basierend auf ab-initio Berechnungen für die heterogene Katalyse wird vorgestellt, der "first-principles" kinetische Monte-Carlo-Simulationen für die Oberflächenchemie in eine fluiddynanische Behandlung the makroskopischen Transports im Reaktor integriert. Exemplarisch wird die CO-Oxidation an RuO2(110) betrachtet. Die Relevanz von "first-principles" kinetische Monte-Carlo-Simulationen wird durch den Vergleich mit dem gemeinhin verwendeten, allerdings weniger genauen, ratengleichungsbasierten Zugang für die Oberflächenchemie demonstriert. Große Unterschiede bzgl. der berechneten Reaktivität und eine qualitativ falsche Vorhersage der tatsächlichen Oberflächendynamik machen den letzteren Ansatz untauglich für die Benutzung mit Elektronenstrukturinput. Es wird eine effiziente, allgemein anwendbare Methodik entwickelt, welche es erlaubt, makroskopische, katalytische Reaktoren mit der gleichen Geschwindigkeit wie mit empirischen Ansätzen zu simulieren, wobei allerdings die gut fundierte, elektronische Basis und die akkurat Behandlung der Oberflächenchemie durch kinetische Monte-Carlo-Verfahren beibehalten wird. Als einfaches Beispiel wird die entwickelte Methode auf eine Staupunktströmung gegen eine RuO2(110)-Einkristall-Oberfläche angewendet. Die Simulationsergebnisse zeigen, wie Wärme- und Massentransport die beobachtete katalytische Funktion für Gasphasenbedingungen beeinflussen, die typisch sind für moderne in situ Experimente. Desweiteren erhalten wir für einen Bereich von Gasphasenbedingungen mehrere stationäre Zustände, die nur durch die Kopplung von Gasphasentransport und Oberflächenchemie auftreten. Diese zusätzliche Komplexität muss in Betracht gezogen werden, wenn versucht wird durch dedizierte in situ Experimente ein atomares Verständnis der heterogenen Katalyse bei technologisch relevanten Gasphasenbedingungen zu etablieren. A first-principles based multiscale modeling approach to heterogeneous catal- ysis is presented, that integrates first-principles kinetic Monte Carlo simula- tions of the surface reaction chemistry into a fluid dynamical treatment of the macro-scale transport in the reactor. Using the CO oxidation at RuO2 (110) as representative example the relevance of first-principles kinetic Monte Carlo is demonstrated by the comparison with the commonly employed, but less accurate rate equation based approach to surface chemistry. Huge differences between both approaches in the predicted reactivity and qualitatively wrong predictions on the ongoing surface dynamics disqualify the latter approach for the use with first principles input. An efficient general purpose methodology is developed, which allows for simulations of macroscopic catalytic reactors with the same speed as mentioned empirical approaches, but retains the sound electronic basis and the accurate treatment of surface chemistry by kinetic Monte Carlo simu- lations. As a simple showcase the developed method is applied to stagnation flow fields in front of a RuO2 (110) single crystal surface. The simulation results show how heat and mass transfer effects can readily affect the observed catalytic function at gas-phase conditions typical for modern in situ experiments. For a range of gas-phase conditions we furthermore obtain multiple steady-states that arise solely from the coupling of gas-phase transport and surface kinetics. This additional complexity needs to be accounted for when aiming to use dedicated in situ experiments to establish an atomic-scale understanding of the function of heterogeneous catalysts at technologically relevant gas-phase conditions.

We present a first-principles based multiscale modeling approach to heterogeneous catalysis that integrates first-principles kinetic Monte Carlo simulations of the surface reaction chemistry into a fluid dynamical treatment of the macroscale flow structures in the reactor. The approach is applied to a stagnation flow field in front of a single-crystal model catalyst using the CO oxidation at RuO2(110) as representative example. Our simulations show how heat and mass transfer effects can readily mask the intrinsic reactivity at gas-phase conditions typical for modern in situ experiments. For a range of gas-phase conditions we furthermore obtain multiple steady states that arise solely from the coupling of gas-phase transport and surface kinetics. This additional complexity needs to be accounted for when aiming to use dedicated in situ experiments to establish an atomic-scale understanding of the function of heterogeneous catalysts at technologically relevant gas-phase conditions.