Materials Design for Thermal Radiation Blocking Thermal Barrier Coatings
Abstract
A new class of functional coatings -- thermal radiation barrier coatings -- is proposed to block radiative heating and protect components in a variety of high-temperature applications, such as turbine blades in aero-engines. The objective is to modify existing and candidate thermal barrier coating materials to minimize radiative heat transport through them while maintaining their low thermal conductivity at high temperatures. The proposed research is based on using selective atomic-level doping of existing low thermal conductivity oxides (and silicates) to absorb the thermal radiation emitted by hot gases. Two classes of dopant ions, rare-earth ions and transition elements ions, based on their electronic structures for non-radiatively, down- converting photons from the radiative flux to lattice phonons at high tempeflux at high temperatures will be quantified with complementary heat transfer simulations as well as using associated research being proposed by Prasanna Balachandran, Patrick Hopkins and Haydn Wadley, all of University of Virginia. Thermal radiation barrier coatings are needed as the demands on thermal management cooling systems in propulsion systems are increasing with increasing gas temperatures. Until now, radiative heating through coatings in Navy aerospace turbines has been neglected but as gas temperatures are increased to enable even higher engine performance the radiative contribution to the heat flux through a coating will increase. At the same time, the traditional approach to handling higher temperatures and higher heat fluxes by using lower thermal conductivity materials is reaching a physical limit as the theoretical minimum thermal conductivity is being reached. Complicating materials selection for thermal protection in future aerospace engines is that all low thermal conductivity oxides and silicates are transparent to radiative heat transfer as they are intrinsically large band-gap materials. Furthermore, radiative heat transfer through transparent coatings leads to a new form of thermal shock, hitherto not considered -- instantaneous radiative thermal shock. At Harvard, three interent thermal barrier coating oxides and candidate environmental barrier coating silicates. The objective of this task is to identify combinations, and concentrations, of different dopants that can absorb the thermal radiative spectrum from 0.5 to 5 microns, characteristic of emission from gases up to ~ 2000 oC, as well as their effect on their high-temperature thermal conductivity; (ii) combined radiative and conductive heat transport calculations and simulations through coatings that include finite thickness effects and microstructural effects common in thermal protection coatings; (iii) measurements, with supporting modeling activities, of the thermal radiative and thermal conductive contributions to the heat fluxes through coatings operating under conditions representative of engine conditions. Possible radiative thermal shock effects and the development of transient stresses will also be investigated.When completed, the results of our collaborative investigations will provide engine designers, the Navy and DoD, physically based guidelines for the compositional design of coatings to block radiative heating and thermal shock in current and future high-performance engines. It is anticipated that these will significantly reduce the heat flux through coatings, decreasing engine cooling requirements,and reduce the severity of thermal shock when pilots need to abruptly increase power. A 50% reduction in radiative heating through coatings is our objective.*Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 09, 2021
- Source ID
- N000142112478
Entities
People
- David B. Clarke
Organizations
- Office of Naval Research
- President and Fellows of Harvard College
- United States Navy