Interaction dynamics of Pulsed Laminar Arc-plasma with Synchronous injection for the elaboration of finely structured ceramic MATerials – PLASMAT

Following previous work developed at the SPCTS laboratory (CNRS, University of Limoges, France) showing that the electric arc motion can be controlled by acoustic resonance phenomena, a new oscillation mode of an electric arc confined within a direct current plasma torch was highlighted. The resulting arc jet has self-sustained pulsed features around one kilo Hertz frequency and produces thermal balls emitted at the resonance frequency. A piezo-electric printing head is used to inject inside the arc jet droplets of ceramic ink or solution precursors. The latter contain the elements plasma treated in-flight which forms the coating.
The reproducibility of plasma treatments must be ensured by the periodic feature of the plasma and the synchronous injection. Time-resolved diagnostic of plasma by means of imaging and optical emission spectroscopy permits to study the plasma properties and coatings are obtained following the injection timing.

A laminar pulsed arc jet was developed and generates thermal plasma balls in which droplets of 50 micrometers in diameter are injected. Each droplet contains either ceramic nanoparticles or the elements to deposit dissolved within a solvent. The interaction dynamics between the plasma and the materials are analyzed by optical emission spectroscopy demonstrating the prime importance of the injection timing. Moreover, the efficiency of droplet synchronization affects the as-sprayed coatings properties.

The project PLASMAT has allowed a better understanding of the generation of the self-sustained pulsed mode and its association with a piezoelectric printing head of liquids. Synchronous and time-resolved diagnostics were implemented to highlight the influence of the injection delay upon the plasma treatment of materials. Titanium dioxide and aluminum nitride coatings were elaborated which the properties are dependent on the injection delay.
PLASMAT has opened original perspectives in plasma spraying field such as the use of a pulsed power supply to control the arc instabilities. However, many research efforts still remain to understand the effect of pulsed current on arc motion confined within a plasma torch.
At last, if the plasma oscillations can be stabilized by means of pulsed power supply, robust and flexible liquid injection systems with high feeding rates must be developed to cope with industrial constraints.

The PLASMAT project has given rise to 8 publications in peer-reviewed international journals, 4 invited conferences and 9 communications in international and national conferences.

F. Mavier, V. Rat, M. Bienia, M. Lejeune, and J.F. Coudert, Suspension and precursor solution plasma spraying by means of synchronous injection in a pulsed arc plasma, Surface and Coating Technol. soumise
V. Rat and J.F. Coudert, Analytical interpretation of arc instabilities in a dc plasma spray torch: the role of pressure, J. Phys. D: Appl. Phys. 49 235202 (2016)
V. Rat and J.F. Coudert, Theoretical and experimental investigations of the coupling of time-dependent parameters in a blown arc plasma torch, J. Phys. D: Appl. Phys. 49 065203 (2016)
V. Rat, J. Krowka, and J.F. Coudert, Modulation of the specific enthalpy of a pulsed arc plasma jet, Plasma Sources Sci. Technol. 24 045009 (2015)
V. Rat, F. Mavier, M. Bienia, M. Lejeune, J.F. Coudert, Pulsed Plasma Spraying of Liquid Feedstock for Coating Elaboration, Plasma Physics and Technology 2 251-260 (2015)
J. Krowka, V. Rat, S. Goutier and J.F. Coudert, Suspension phased injection in pulsed arc jet for coating elaboration, J. Thermal Spray Technol. , J. Thermal Spray Technol. 23 786-794 (2014)
J. Krowka, V. Rat and J.F. Coudert, Investigation and control of dc arc jet instabilities to obtain a self-sustained pulsed laminar arc jet, J. Phys. D: Appl. Phys. 46 505206 (2013)
J. Krowka, V. Rat and J.F. Coudert, Resonant mode for a dc plasma spray torch by means of pressure–voltage coupling: application to synchronized liquid injection, J. Phys. D: Appl. Phys. 46 224018 (2013)

The reduction of natural energy resources, ecological concerns and the tendency of a better energy management give rise to the development of more and more complex integrated devices associating finely structured metallic and ceramic layered materials. The elaboration of ceramic coatings with finely structured architecture and graded properties requires new advanced elaboration processes such as Suspension or Solution Precursor Plasma Spraying which were recently shown to be promising. However, these processes hardly struggle to efficiently deposit advanced materials due to poorly controlled heat and mass transfers between plasma and materials, plasma instabilities, and irrelevant material injection method which make very difficult, for example, to maintain the appropriate material crystallographic structure in plasma when material melting temperature is close to that of decomposition. Uncontrolled plasma instabilities relatively to the injection method also results in non-homogeneous treatment of in-flight materials. The objective of this project is to address the above mentioned drawbacks of plasma spraying by developing a tunable resonant arc plasma source associated with a synchronous material injection. This new plasma source will permit not only to produce laminar pulsed arc jet but also to control heat and mass transfers by appropriate material injection timing. This project will intend to tackle the problem of reactive plasma spraying which is quite unaffordable for conventional plasma spraying process, and even remains unstudied in suspension plasma spraying. First, plasma resonance phenomena will be studied and plasma properties determined without and with material injection by optical emission spectroscopy. Second, the elaboration of coatings will allow correlating material properties with plasma characteristics.