This article presents what is our present knowledge in plasma spraying of suspension, sol, and solution in order to achieve finely or nano-structured coatings. First, it describes the different plasma torches used, the way liquid jet is injected, and the different measurements techniques. Then, drops or jet fragmentation is discussed with especially the influence of arc root fluctuations for direct current plasma jets. The heat treatment of drops and droplets is described successively for suspensions, sols, and solutions both in direct current or radio-frequency plasmas, with a special emphasize on the heat treatment, during spraying, of beads and passes deposited. The resulting coating morphologies are commented and finally examples of applications presented: Solid Oxide Fuel Cells, Thermal Barrier coatings, photocatalytic titania, hydroxyapatite, WC-Co, complex oxides or metastable phases, and functional materials coatings.

Suspension Plasma Spraying (SPS) is a relatively new deposition process which enables to spray micron and submicron particles. It offers the possibility to form finely structured coatings with intermediate thicknesses of a few tens of microns. In order to have a better understanding in SPS, the two parts of this paper are devoted to the description of the phenomena involved in this spray process. The first part focuses on the suspension injection within a d.c. plasma jet. Simplified models, backed by plasma and suspension diagnostics, allow describing the interaction plasma-suspension. It is shown that the suspension is atomized by the plasma jet before the starting of the droplets vaporization. The plasma jet recovers its flow symmetry about 15 mm downstream of the nozzle exit. The strong influence of plasma instabilities on suspension injection is also highlighted. The second part is devoted to solid particle treatments and the coating formation.