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THERMAL PROPERTIES
OF NOVEL THERMAL BARRIER COATINGS
The focus of the research is to select oxides with low thermal conductivity.
Currently 7-weight percent yttria stabilized zirconia is the thermal
barrier coating (TBC) in use. At high temperatures 7YSZ partitions
into a mixture of tetragonal and cubic zirconia. As 7YSZ cools a
transformation occurs. The tetragonal phase changes to a monoclinic
phase resulting in the delamination of the coating. We are exploring
material systems with a lower thermal conductivity as a potential
TBC. We substituted hafnia for zirconia using a mass substitution
technique. We did ten comparisons of ranging Zr and Hf ratios with
two levels of yttria concentrations, one at 7 weight percent yttria
and the other at 14 weight percent yttria in two groups of five.
A thermal flash technique is used to measure thermal diffusivity
and heat capacity of the sample from which thermal conductivity
can be calculated. Applications include the use of TBCs in gas powered
turbine engines and other applications where protection against
high temperatures is required. This increases the engine efficiency
and life of the components coated by the oxide. The research will
explore oxides that are capable of operating at temperatures required
for the next generation of gas powered turbine engines.
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