This study examines the fundamental reactions that occur in-flight during the solution precursor plasma\ud spraying (SPPS) of solutions containing Zr- and Y-based salts in water or ethanol solvent. The effect of\ud plasma jet composition (pure Ar, Ar-H 2 and Ar-He-H 2 mixtures) on the mechanical break-up and\ud thermal treatment of the solution, mechanically injected in the form of a liquid stream, was investigated.\ud Observation of the size evolution of the solution droplets in the plasma flow by means of a laser\ud shadowgraphy technique, showed that droplet break-up was more effective and solvent evaporation was\ud faster when the ethanol-based solution was injected into binary or ternary plasma gas mixtures. In\ud contrast with water-based solutions, residual liquid droplets were always detected at the substrate\ud location. The morphology and structure of the material deposited onto stainless steel substrates during\ud single-scan experiments were characterised by SEM, XRD and micro-Raman spectroscopy and were\ud shown to be closely related to in-flight droplet behaviour. In-flight pyrolysis and melting of the precursor\ud led to well-flattened splats, whereas residual liquid droplets at the substrate location turned into non\ud pyrolysed inclusions. The latter, although subsequently pyrolysed by the plasma heat during the depo-\ud sition of entire coatings, resulted in porous ‘‘sponge-like’’ structures in the deposit

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