Suspension and precursor solution plasma spraying by means of synchronous injection in a pulsed arc plasma

Abstract

Research has led to the development of nanostructured coatings by suspension plasma spraying (SPS) or solution precursor plasma spraying (SPPS). Both techniques open a new way to applications in the field of microelectronic devices. However, a better control of plasma/material interactions is necessary. Mono-electrode DC plasma torches indeed generate strongly fluctuating plasma that modifies the thermal and dynamic transfers to the injected suspension droplet, resulting in an inhomogeneous treatment of the latter. This directly influences the texture and microstructure of deposits and subsequently their properties. Efforts to understand the origins of these instabilities have been made and have led to propose a new approach, i.e. an alternative to instabilities attenuations: the reinforcement and modulation of the instabilities. The adjustment of process parameters has allowed obtaining a pulsed laminar plasma and a modulation of its properties. This device is synchronized with an ink-jet print head to reproduce the same conditions of plasma/material interaction for each injected droplet. A home-made DC torch was made. His power of 1kW is well below the standard torches (~30kW for commercial torches) but is well adapted to the flow rate that can be delivered by the print head. This low powered home-made DC torch is used and operates with pure nitrogen as plasma forming gas. Aluminum nitrate aqueous solutions and TiO2 suspensions are injected. The objectives of this work are firstly to characterize this pulsed plasma and its interactions with droplets to facilitate the understanding of heat and dynamics transfers. They are analyzed by time-resolved imaging and optical emission spectroscopy. Secondly, coatings are characterized by SEM, TEM and DRX analysis.