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3873 |
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Friday, May 23, 2014, Hall A 11:20 AM Process Diagnostics, Sensors & Controls |
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Laser diagnostic techniques for suspension and solution plasma spraying |
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Armelle Vardelle / University of Limoges-CNRS, France Simon Goutier* / University of Limoges CNRS, France William Duarte/ Centre National dEtudes Spatiales, France Aurélien Joulia/ Centre National dEtudes Spatiales, France Michel Vardelle/ University of Limoges CNRS, France |
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Plasma spraying of suspensions and solutions makes it possible to elaborate coatings with a finer microstructure and/or lower thickness than the conventional plasma spray process and is now emerging in industrial applications. However, the need for a higher deposition rate and better reproducibility of the final product as well as for longer spray distances requires that the design and control strategy of liquid feedstock plasma spray processes be based on a broad understanding of the phenomena which occur when the liquid jet interacts with the plasma jet and during the further residence of droplets and particles within the plasma jet. In particular, a key point for particle/droplet deposition onto the substrate is their impact velocity as it should be high enough so that the particle/droplet's inertia dominates and they continue along their trajectory and not follow the plasma fluid streamlines close to the substrate. The experimental and projected data on droplets and submicronic particles within the plasma jet are still scare and difficult to interpret. Therefore the development or adaptation of dedicated measurements techniques would be useful. Laser-based techniques which are non-intrusive and may have excellent spatial and temporal resolution could be useful diagnostic tools for liquid plasma spray processes. This study is concerned (i) with the behavior of liquid jet and droplets in the liquid fragmentation area (ii) with the particle/droplet velocity distribution in the vicinity of the substrate. It makes use of shadowgraphy and Particle Image Velocimetry techniques. Different liquid feedstock (suspensions and solutions) and solvent are investigated. The radial and axial profiles of droplet diameters within the plasma jet and fields of droplet/particle velocities are presented for various plasma operating conditions. |