Key Challenges and Opportunities in Suspension and Solution Plasma Spraying

Over the last 15 years many research papers have presented the potential of suspension and solution plasma spraying to achieve coatings, essentially ceramic coating, with a nanometric or sub-micrometric microstructures. Such coatings exhibit improved properties (e.g. lower thermal diffusivity, higher hardness and toughness) in comparison with coatings with a micrometric microstructure. This paper presents first the techniques that are now used to characterize these plasma spray processes and the resulting coatings; it, then, examines, the main plasma torches and their limits, the preparation of suspensions and solutions, the interactions between the liquid feedstock and plasma jet, the processing of droplets and particles and the coating formation. Finally, the key issues for the transfer of these technologies from the laboratories to industry will be discussed.