Plasma Spraying of Solution Precursor in Pulsed Mode: In-Flight Phenomena and Coating Deposition

In the field of plasma spray technologies, new processes were developed in order to obtain coatings with nanostructured architectures. Among them, solution precursor plasma spraying is a promising technique. However, to be industrially viable, efforts must be made to understand and control the steps of the process. In alternative to instabilities attenuations, the time-modulation of current–voltage characteristics of a low-powered arc plasma jet was proposed, resulting in time-modulation of plasma properties. This modulation was synchronized with a drop-on-demand printhead for injection to improve the control of plasma/material interaction. An aluminum nitrate ink was formulated to be compatible with a drop-on-demand printhead dispenser. Plasma composition was calculated by the Gibbs free energy minimization method. Moreover, in-flight diagnostics coupled with coating characterization were carried out. Results showed that the controlled injection system leads to the formation of vapors of aluminum oxide that leaded to the deposition of nanostructured cauliflowers-like structures. Amorphous alumina coatings with inclusions of γ-alumina micro-sized particles were obtained and a description of main in-flight mechanisms was proposed.