Marvin Chan, SURF IT Fellow Jesse Angle, Graduate Student Mentor Professor Mecartney, Faculty Mentor

 Introduction  Oxygen Sensors  Problem of Thermal Shock  Preparation and Test Methods  Results for Additives of SiO 2, Al 2 O 3 to ZrO 2  Theoretical Calculations  Experimental Results  OOF2: Finite Element Modeling (FEM)  Results  Conclusion

 Oxygen sensors ◦ Made of yttria-stabilized zirconia (YSZ) ceramic ◦ Used to determine correct fuel to air ratio in internal combustion engines  Problems ◦ Oxygen sensor operates most efficiently at 900°C ◦ System must be heated slowly from ambient to optimal operating temperature  fuel is wasted  carbon emissions are high

 YSZ will fracture if heated or cooled too quickly.  The property that measures resistance to fracture upon heating/cooling is called thermal shock resistance.  Research Question: How to improve and predict the thermal shock resistance of YSZ?

Sintering Bisque Firing Machining CIP’ing Testing YSZ Silica/ Alumina Milling Drying Sieving Packing into Molds SEM Imaging Polishing

 Samples analyzed via: ◦ SEM imaging of Microstructure ◦ Thermal shock quenching and 3-Point bend tests for strength ◦ Compare strength after quenching to unquenched samples

 Thermal Shock Parameter (R):  Improve thermal shock resistance by: ◦ Increasing fracture strength (σ) ◦ Decreasing Poisson’s ratio (ν) or elastic modulus (E) or thermal expansion coefficient (α) ◦ Idea: Make a composite! Use Rule of Mixtures νE (GPa)α (1/K) k (W/m*K) YSZ E-62 SiO E-61.4 Al 2 O E-635 σ=Strength E=Elastic Modulus α=Thermal Expansion Coefficient ν=Poisson’s Ratio

 Grain Size Analysis using ImageJ software YSZ YSZ with 10 vol. % SiO 2 Average Grain Size 2.4 µmAverage Grain Size 9.2 µm Smaller grain size for ceramics usually gives higher strength.

 Using ImageJ, we analyzed the grain size for all SEM Images..  Smaller grain sizes should yield higher Flexural Strength Specimen Avg. Grain Size (µm) YSZ9.2 YSZ+10 vol% Al 2 O YSZ+ 20 vol% Al 2 O YSZ+ 10 vol% SiO 2 2.4

YSZ+ 20 vol% Al 2 O 3 YSZ+ 10 vol% SiO 2

 Modeling of microstructures  Computes stresses, strain, and temperature gradients

 YSZ +10 vol. % Al 2 O 3 Altered colors for easier processing and viewing Zirconia—Yellow Alumina—Blue

 Microstructure of YSZ + 10 vol% Al 2 O 3 Creation of the Skeleton and FE Mesh

Enter Boundary Conditions and Material Parameters 10 vol. % Al 2 O 3 ; Strain Field Boundary Conditions: *Apply compressive stresses left, right and from below Max Stress Min Stress

 YSZ + 20 vol% Al 2 O 3 had the highest Flexural Strength and highest Thermal Shock Resistance  YSZ + 10 vol% SiO 2 and YSZ +10 vol% Al 2 O 3 had less than ideal results—led to negligible improvements  OOF2 models areas of stress, i.e. compression and tension for thermal shock- continuing work in the fall!

 Professor Martha Mecartney, Faculty Mentor  Jesse Angle, Graduate Student Mentor  Edward Su, Technical Support