Suspension Plasma Spraying: Process Characteristics and Applications

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Robert Vaßen, Holger Kaßner, Georg Mauer, and Detlev Sto¨ver (Submitted April 25, 2009; in revised form September 24, 2009) Suspension plasma spraying (SPS) offers the manufacture of unique microstructures which are not possible with conventional powdery feedstock. Due to the considerably smaller size of the droplets and also the further fragmentation of these in the plasma jet, the attainable microstructural features like splat and pore sizes can be downsized to the nanometer range. Our present understanding of the deposition process including injection, suspension plasma plume interaction, and deposition will be outlined. The drawn conclusions are based on analysis of the coating microstructures in combination with particle temperature and velocity measurements as well as enthalpy probe investigations. The last measurements with the water cooled stagnation probe gives valuable information on the interaction of the carrier fluid with the plasma plume. Meanwhile, different areas of application of SPS coatings are known. In this paper, the focus will be on coatings for energy systems. Thermal barrier coatings (TBCs) for modern gas turbines are one important application field. SPS coatings offer the manufacture of strain-tolerant, segmented TBCs with low thermal conductivity. In addition, highly reflective coatings, which reduce the thermal load of the parts from radiation, can be produced. Further applications of SPS coatings as cathode layers in solid oxide fuel cells (SOFC) and for photovoltaic (PV) applications will be presented.

Keywords

photovoltaic, solid oxide fuel cells, suspension plasma spraying, thermal barrier coatings

1. Introduction In the field of surface coating, the atmospheric plasma spraying (APS) is since several decades a well-established technology with many improvements especially with respect to plasma gun technology. Although a rather wide flexibility of coating morphologies can be obtained with this process, within the coatings typically the size of microstructural features is dictated by the used feedstock. This is for conventional plasma spraying a well flowable powder in the size range of about 10 to 100 lm. Also, the minimum thickness of the coatings is limited to about 10 lm, as at least several piled up splats should form the coating. Here, the use of liquid feedstock as solutions or

This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. Robert Vaßen, Holger Kaßner, Georg Mauer, and Detlev Sto¨ver, Forschungszentrum Ju¨lich GmbH, Institut fu¨r Energieforschung (IEF-1), 52425 Ju¨lich, Germany. Contact e-mail: r.vassen@fz

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