Review of recent progress in the supersonic cold-spraying technique with solid particles and liquid suspensions

Supersonic cold-spraying involves the use of a converging–diverging de Laval nozzle to convert an upstream flow of pressurized gas at high temperature into a high-speed downstream flow in which particles are entrained, accelerated, and deposited on a substrate at supersonic speed. A chamber pressure of ≤ 10 bar enables the successful deposition of particles as large as a few micrometers in size. Particles of various types of materials, including metals, ceramics, nanowires, and graphene sheets, can be flattened and deposited onto substrates to produce thin films for energy and environmental applications. A liquid precursor comprising suspended particles of submicrometer dimensions can be atomized into micrometer-sized droplets, which are entrained and accelerated for film deposition. The dissolution of salt-based substances in the liquid precursor allows the liquid to be atomized into droplets and supplied to the supersonic stream. As a result, the droplets undergo evaporation and eventually yield salt residues during their flight. These salt residues are accelerated and deposited, permitting the construction of various nanostructures. Supersonic spraying is a versatile technique for constructing multilayer nanostructures with various functionalities for specific applications. In addition, supersonic spraying facilitates strong adhesion, which is necessary for the durable and reliable operation of the intended functions. Herein, we introduce the basic mechanisms of the supersonic spraying technique and its use in producing functional films for transparent flexible electronics, heat transfer enhancement, thermal and electrical insulation, and energy storage and conversion device applications.