Aerogel-based thermally sprayed coatings for aero-propulsion systems

Abstract Despite being considered as the world's best thermal insulator, silica aerogel cannot be often applied in aero-propulsion systems due to weight and space constraints. This study proposes an innovative route to achieve a single-layered micro-thick thermally sprayed coating by firstly identifying the suitable aerogel powders for atmospheric plasma spraying (APS) and suspension plasma spraying (SPS) and secondly by deducing the spraying conditions. The aerogels were characterized to evaluate their physical properties and hence their appropriateness for APS and SPS. Technical installations and plasma spraying design parameters such as nozzle diameter, electric power, plasma gas flow rate, carrier gas flow rate, and concentration of aerogel and dispersant were varied methodically until a coating could be possibly achieved. Characterization of the developed coatings using scanning electron microscopy was performed. Out of six aerogel powders, only GEA 0.125 and Enova IC3100 were used for plasma spraying. A coating was achieved using APS using as-received GEA 0.125 with a nozzle diameter of 4 mm powered at 25 kW, a plasma gas rate of 45 + 5 slpm, and carrier gas flow rate of 8.1 slpm. The coating had a bimodal microstructure with a thickness ranging from 77.9 to 132.0 μm. SPS was not successful with GEA 0.125 due to blockage. Enova IC3100 could nevertheless be propelled onto the substrate but no melting of particles occurred, which was thought because of insufficient power supplied by the SPS gun. It can be concluded that a single-layered aerogel-based thermally sprayed coating with a bimodal microstructure can be achieved using pure aerogel particles without any further treatment such as spray-drying. SPS of submicron aerogel powders seems to be promising and is foreseen to be achievable using a gun with a power higher than 40 kW.