In collaboration with colleagues at the Colorado School of Mines we are developing an aerosol based, additive manufacturing route for the production of thermoelectric materials. This process involves: (1) ball milling to obtain precursors suspensions, (2) spray drying of suspensions to generate particulate clusters in the gas phase, and (3) deposition of clusters at supersonic to hypersonic speeds (at reduced pressures).
Ball milling is a well-established method to obtain nanoparticles with a coarse size-distribution. In this project, we use similar comminution techniques to obtain kilogram quantities of nanoparticles. Further, wet-milling methods are also employed to obtain a colloidal dispersion of sub-300 nm nanoparticles in various solvents such as water and alcohols. This colloidal dispersion is aerosolized and injected into a high-vacuum chamber through a de Laval nozzle to accelerate them to supersonic speeds. On impact, the nanoparticles coalesce. When impacted on a surface that is mounted to a rastering stage inside the vacuum chamber, a thin film of the given material can be formed via additive deposition of the supersonic nanoparticles.
Our primary focus in this project is to manufacture thin films of thermo-electric materials on a large scale. However, unlike other additive manufacturing techniques such as inkjet printing this method is independent of precursor materials and solely relies on the nozzle design and vacuum gradient across the nozzle.