Investigation of the deposition mechanism for the aerosol deposition of ceramics by evaluating of the processes that occur when micrometer-sized particles impact on surfaces

• Applicants: Professor Dr.-Ing. Ralf Moos; Privatdozent Dr.-Ing. Martin Seipenbusch
• Subject Area: Mechanical Process Engineering ; Chemical and Thermal Process Engineering ; Synthesis and Properties of Functional Materials
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434829389

In recent years, a new process has emerged to produce dense ceramic coatings, which has some advantages over the well-established high-temperature processes. In order to manufacture ceramic components and coatings, sintering temperatures of over 1000 °C are usually required. As a result, ceramic layers can hardly be applied to low-melting metals, glasses or polymers. With the new process, the so-called Aerosol Deposition Method (ADM), the ceramic layers can be deposited directly from the corresponding powder. It is a completely cold process, in which neither carrier gases nor powders or substrates need to be heated. For this purpose, the powder is aerosolized and deposited onto the surface to be coated in a jet flow directed towards it.However, the exact mechanism of layer formation remains unclear. So far, it has been known that the high kinetic energy of the particles, which ideally have diameters in the range from a few hundred nm to a few micrometers, leads to fragmentation into nanometer-sized fragments upon impact with the substrate. The formation of an anchoring layer on the substrate leads to a continuous build-up and densification of the layer. This process is known as Room Temperature Impact Consolidation (RTIC).Similar phenomena can be observed during the investigation of the strength of particle agglomerates by impact fragmentation. They are separated at high speeds in a so-called impactor from a jet flow onto a surface. Here, too, the impact of the particles on the carrier surface obviously leads to processes that have so far been inadequately understood. In particular, the phenomenon of particle bounce during impaction has not yet been fully understood. The yield pressure of the particles and the impaction plate play a role here. In addition, electrostatic charging of particles can occur due to the phenomenon of contact charging, which can also influence the deposition efficiency via Coulomb interactions with the impaction plate However, predictions based on macroscopic material properties often do not explain the experimental observations.A comparison of the two processes, in which the two PIs conducted much preliminary work, reveals a large overlap both with regard to the experimental findings and to the problems. The overall aim of the proposed experimental project is therefore to understand the processes better that occur between the impact of the particles and their incorporation into a solid film. The results of the impact fragmentation of aerosol particles will be better interpreted and the formation of particle layers will be more precisely controlled by impaction and the quality of ceramic layers from the ADM will be improved.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Ulrich Nieken