Science des Procédés Céramiques et de Traitements de Surface (SPCTS)

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Centre National de la Recherche Scientifique (CNRS)
Université de Limoges
Ecole Nationale Supérieure de Céramique Industrielle (ENSCI)


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Accueil du site > Axes de recherche > Axe 2 "Procédés de traitements de surface" > Thèmes de recherche > Procédés arc et projection thermique, dépôts nano- ou micro-structurés > Etudes des arcs électriques en courant continu : instabilités générées > Origin and limitation of plasma instabilities

Origin and limitation of plasma instabilities

Dynamics of interactions in plasma processes.
Application : Suspension plasma spraying


Contacts

Jean-François COUDERT jean-francois.coudert@unilim.fr
Vincent RAT vincent.rat@unilim.fr


Context/Objectives

Realizing finely structured deposits by the use of suspension plasma spraying implies the understanding of interaction mechanisms which occur between the plasma and the suspension. They are largely dependent on the electric arc instabilities generated by the plasma torch. The impact of operating parameters on the plasma source and particularly the origin of electric arc instabilities have to be understood in order to control their effects on vaporization and fragmentation phenomena. Physical models are developed and experimentally confirmed. Arc voltage variations, responsible for the lack of reproducibility in coating properties, are mostly due to compressibility effects of the plasma gas that create a mechanical resonance inside the cathode cavity of the plasma torch. The latter operates as an Helmholtz-like acoustic resonator, in which elongation-breakdown-rearcing phenomena of the electric arc into the nozzle along with associated pressure effects, stimulate the resonator. These oscillations are repeated by the resonator, according to a positive feedback effect, creating thus quasi – periodic variations of the arc voltage amplitude and torch power. With the implementation of relevant diagnostic techniques (synchronous time-resolved imaging, acoustics), suspensions/plasma interaction mechanisms are highlighted. A new method for controlling arc instabilities resulted from these works and was granted by a CNRS patent registered in 2009.

 

Time-resolved imaging and synchronized with arc  voltage (Opening time 10µs)
 
Oscillation modes illustration of a plasma arc spraying torch
Oscillation modes illustration of a plasma arc spraying torch
Time-resolved imaging and synchronized with arc voltage (Opening time 10µs)   Oscillation modes illustration of a plasma arc spraying torch


Activities

The laboratory focuses its activity on these points :

  • Dynamics of plasma processes and discharges
  • Non-transferred plasma torch and Suspension Plasma Spraying
  • Metrology of process
  • Physical modeling of phenomena


Specific equipments

  • Suspension plasma spraying set-up
  • Metrology (data acquisition systems using the Labview software, acoustic and pressure measurements, signal processing, time-resolved imaging)


Selected publications

  1. V. RAT, J.F. COUDERT
    Pressure and arc voltage coupling in dc plasma torches : Identification and extraction of oscillation modes
    J. Appl. Phys. sous presse
  1. V. RAT, J.F. COUDERT
    Acoustic stabilization of electric arc instabilities in non-transferred plasma torches
    Appl. Phys. Lett. 96, 2010, 101503

  2. V. RAT, J.F. COUDERT
    Acoustic signature analysis of the interaction between a dc plasma jet and a suspension liquid jet
    J. Phys. D : Appl. Phys. 42, 2009, 195202

  3. J.F. COUDERT, V. RAT
    Influence of configuration and operating conditions on the electric arc instabilities of a plasma spray torch : role of acoustic resonance
    J. Phys. D : Appl. Phys. 41, 2008, 205208

  4. J.F. COUDERT, V. RAT, D. RIGOT
    Influence of Helmholtz oscillations on arc voltage fluctuations in a dc plasma spraying torch
    J. Phys. D : Appl. Phys. 40, 2007, 7357

Updated February 23, 2010

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