Synthesis and Characterization of Mixed Rare Earth Zirconia, Zirconate and Silicate Radiative Barrier Coatings
Abstract
The components used to make the high-pressure turbine of gas turbine engines must be protected from the increasingly high combustion gas temperature by thermal and environmental barrier coatings (T-EBCs). These coatings provide thermal protection by impeding the conduction of heat that is convectively transferred from the gas to the surface of coated engine components. Engine efficiency is progressively increasing as a result of increases in the combustion gas pressure and temperature. However, this accompanied by a radiant mode of heating that has now become important to control. This radiation arises from the black body emissions of carbonaceous materials in the combustion system and by the decay of excited hydrocarbon reaction products (principally H2O and CO2) which increase in the former case as gas temperature T4 and in the latter with gas pressure. This radiative form of heating is efficiently transmitted by the coating materials currently in use, and gives rise to undesirable component heating, reducing the life of expensive engine components, shortening inspection intervals and raising the cost of engine maintenance. This proposed program, conducted in close collaboration with parallel ONR funded efforts by David Clarke (Harvard University), and Patrick Hopkins and Prasanna Balachandron (UVA), explores emerging opportunities to develop environmental and thermal barrier coatings (EBC and TBC) materials that better reflect, absorb and re-emit the radiant thermal flux now present in gas turbine engines. The EBC material will be designed using beyond DFT methods with Balachandron and will be based upon transition metal doped multi-rare earth disilicate systems. The TBC will be based upon ZrO2-YTaO4 system in which the yttrium is replaced by combinations of lanthanide elements, and again selectively doped with transition metals. The program will develop solution-based methods to efficiently synthesize chemically homogeneous, nanoscopic oxide and silicate ceramic powder forms of both the tantalates and disilicates. Furthermore, by refining these approaches, particle diameters can potentially be decreased into the region where cold pressing and conventional or flash sintering can be used to create theoretical density samples enabling measurement of optical constants and thermo-physical properties such as thermal conductivity and the coefficient of thermal expansion. X-ray diffraction (XRD) will be used to identify the phases that are formed by these synthesis approaches. Both diffuse reflectance and ellipsometry-based techniques will be used to measure the short (0.4 # 3.3 micrometer) wavelength absorbance and emittance, and Fourier transform infrared methods to determine absorbance at wavelengths beyond this. The bulk (effective) thermal expansion coefficient will be measured together with the three thermal expansion coefficient tensor components for the non-cubic materials using hot stage XRD. The thermal conductivity will be measured in collaborations with the Hopkins group using their thermoreflectance techniques including time domain thermoreflectance, frequency domain thermoreflectance, and steady statethermoreflectance. These approaches use either pulsed or periodic laser heating of the sample to generate temperature variations in the sample that are measured based on the temperature dependent reflectance. The measured reflectance, absorbance and emittance of the most promising coating systems will used with thermal transport models developed by Clarke to demonstrate the temperature reductions achievable by this new approach to coating design and gas turbine thermal management.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 10, 2025
- Source ID
- N000142512210
Entities
People
- H.N.G. Wadley
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia