Powder aerosol deposition of ceramic coatings: optically induced thermal post-treatment to restore the functional properties

• Applicant: Dr.-Ing. Jaroslaw Kita
• Subject Area: Coating and Surface Technology ; Synthesis and Properties of Functional Materials
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504114273

Powder aerosol deposition (PAD) can be used to produce dense ceramic coatings at room temperature. In addition to the low process engineering effort and the high deposition rates, the advantage is that temperature-sensitive materials, such as flexible polymers, can be coated without material degradation. However, process-related stresses in the crystal lattice are often responsible for a deterioration of the functional properties of PAD coatings, e.g. the reduced charge carrier mobility leads to lower electrical or ionic conductivity. The project aims at the mild restoration of the functional properties of PAD ceramics by energy input using optical radiation.Specifically, we are investigating how laser and LED radiation can significantly reduce lattice deformations on the exposed layer surface without damaging temperature-sensitive substrates through delamination, interdiffusion or material degradation as in classical heat treatment. While laser radiation enables spot processing, high-power LEDs with high beam angles allow a uniform area irradiation. The maximum approximation to the bulk properties at minimum temperature stress requires knowledge about the energy absorption of the coating as well as about the heat distribution within the material composite. Therefore, a simulation model of the spatially and temporally resolved temperature gradients of irradiated coatings of different thicknesses on substrates is established in an understanding-oriented manner. Depending on the emitted radiation spectrum and the material-specific parameters, such as the wavelength-dependent absorption and the thermal conductivity, it shows generally valid critical post-treatment parameters of the time-dependent irradiation.Experimentally, crucial variables for a model-based increase of the functional properties are determined on layers of different thickness of two model ceramics. Specifically, the influence of wavelength, irradiance and duration of action of the optical radiation on the mechanical and electrical properties is investigated in comparison to the bulk properties of sintered reference samples. In turn, predictions of the simulations on target process parameters are experimentally verified.Thermoelectric copper-iron delafossites and lithium ion-conducting lithium garnets are chosen as model ceramics with a high application potential for energy conversion. They are well known, can be characterized at room temperature, and have already been reproducibly deposited via PAD. Since their absorption coefficients differ greatly, different post-treatment successes are expected for the same irradiation parameters. If the project progresses rapidly, the generally valid model will be validated with further functional ceramics and substrates.

• DFG Programme: Research Grants