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Intern: Wesley Francillon Mentor: Rafael Leckie Faculty Supervisor: Professor Carlos G. Levi Department: Materials

THE STUDY OF NEW THERMAL BARRIER COATING MATERIALS BY THE SYNTHESIS OF RARE EARTH OXIDE-ZrO₂-Al₂O₃

Thermal Barrier Coatings (TBCs) are a critical component in today?s jet engines. By insulating the turbine blades and other hot zone components from the hot combustion gases TBC?s increase the operating temperature of the engine and extend the life of the components. This improves both the efficiency and reliability of the engines. Key parameters for TBC materials are low thermal conductivity and the ability to operate at high temperatures. The coatings provide an increase in fuel efficiency of the engines of approximately 1% resulting in savings that can extend to the 100s of million dollars.

However, the durability of the coatings is an issue under increasing operating temperatures and extended exposure times. One of the crucial parameters for the design and life-prediction of TBCs is the thermal conductivity. Exposure to the high combustion gas temperatures leads to a decrease in the insulation value of current TBC materials (7 wt. % yttria stabilized zirconia) because of a process called sintering. This increases the oxidation of the metal on the surface of the blade, leading to TBC failure and shorter blade life.

The purpose of this research is to study a class of potential new TBC materials, Rare Earth Oxide-Zirconia ceramics, that show lower thermal conductivity and possibly greater sintering resistance than yttria stabilized zirconia. Specifically I will be doing phase diagram studies looking at lanthanum oxide-zirconia mixtures and their interaction with aluminum oxide. Aluminum oxide is grown as an oxygen barrier on the surface of the turbine blade, underneath the TBC. Any reactions between the TBC and this protective coating are considered undesirable. Virtually no data is available in the literature regarding these ternary systems. Following the synthesis of La₂O₃-ZrO₂-Al₂O₃ compositions, the crystal phases present after different heat treatments will be established using primarily X-Ray Diffraction.

The second portion of this research project involves a kinetic study of two different stabilizers including yittra for comparison at seven weight percent. These stabilizers are Lanthanum and Gadolinium. The kinetic study will give an understanding of the temperature at which phase segregation occurs that in general unwanted due to ceramic structural changes.

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