Wet powder spraying—a process for the production of coatings

Abstract Coatings of different materials with controlled varied porosity and thickness have been produced by the wet powder spraying process. In this process, a fluid mixture or suspension is applied onto a substrate by means of an air or a manual brush. The starting mixtures or suspensions consist of three main components: powder, binder and a volatile carrier, where the latter also acts as binder solvent. During or shortly after application (at ambient conditions), the carrier is removed by evaporation, while the binder precipitates mainly on the powder particles adhering them one to another and to the substrate; thus a “green coating” is obtained. Following a thermal step where the binder is removed (debinding), the coating-substrate combination is subjected to a controlled sintering step in which interdiffusion bonding (particle-particle, particle-substrate) is enhanced. Since relatively small volume fractions of binder are employed (2–5 vol.%) the debinding step is very short and the debinding and sintering cycles are performed continuously in a single furnace. This paper reports the preliminary results obtained from a feasibility study aimed at the production of nickel, as well as some selected ceramic coatings or deposits, on compatible substrates.