Project 5: High-temperature oxidation behavior of ceramic coatings based on polymer-derived ceramic nanocomposites
Polymer-derived ceramic nanocomposites (PDC-NCs) provide an attractive combination of high-temperature properties (e.g. high thermal stability, self-healing capability and low intrinsic thermal conductivity), which makes PDC-NCs a promising candidate for thermal barrier coatings (TBCs) for harsh operation conditions beyond 1300 °C. However, the oxidation behavior, which plays a crucial role for the assessment and selection of materials for TBCs, has not been investigated systematically. In general, silicon-based PDC-NCs rely on a thermally grown SiO2 layer, which provides protection against further oxidation at high temperatures. However, the presence of water vapor at high temperatures leads to evaporation of the protective SiO2 scale due to formation of volatile Si(OH)4. By variation of the chemical composition oxidation behavior of PDC-NCs can be further enhanced.
The major goal of sub-project 5 is to systematically examine the influence of the chemical composition of PDC-NCs on the high-temperature oxidation behavior (T ≥ 1300 °C). Therefore, the chemical composition of the polymeric precursor will be selectively modified in cooperation with Project 1 and Project 2, while measuring the effect on the oxidation kinetics and the microstructure of the resulting oxide scales. First, monolithic ceramic samples will be investigated in dry atmospheres. In addition, the reactions in wet atmospheres and the oxidation behavior of PDC-NC coatings will be evaluated including the interaction of the coatings with the underlying substrate.
The experimental results will be combined with thermodynamic modeling (Project 11) to get a deeper understanding of the underlying oxidation processes. Furthermore, the results will serve as a baseline for the assessment of the thermomechanical properties (Project 4), lifetime predictions (Project 6) and corrosion behavior (Project 7) of the thermal barrier coatings.